PALEOCENE-EOCENE BOUNDARY

SEDIMEI\JTA-rION II\J THE

POTOMAC RIVER VALLEY,

VIRGINIA Af\lD MARYLAND

I.G.C.P. PROJECT 308

FIELD TRIP GUIDEBOOK

THOMAS G. GIBSON AND LAUREL M. BYBELL, LEADERS

OCTOBER 31, 1991

TABLE OF CONTENTS

Page

Paleocene and Eocene strata of the central Atlantic Coastal Plain by Thomas G. Gibson. Laurel M. Bybell. and David L. Govoni ... . ......... . ........... 1

Calcareous nannofossils and foraminifers from Paleocene and Eocene strata in Maryland and Virginia by Laurel M. Bybell and Thomas G. Gibson . . . . . . . .. 15

Lower Ternary (Pamunkey Group) dinoflagellate biostratigraphy. Potomac River area, Virginia and Maryland by Lucy E. Edwards, David K Goodman, and Roger J. Witmer ........ .... ......... .. ... . .......... . . . ... .. ........ .. 31

Dinoflagellate biostratigraphy of the Nanjemoy Formation at Popes Creek, southeastern Maryland by David K Goodman ............... .. ..... .. . 47

Lower Tertiary pollen biostratigraphy. Maryland and Virginia by Norman O. Frederiksen . .... . ....... . ......... . .. . .......... . .......... . . . 57

Composition and biogeographic significance of the gastropod mollusk fauna of the Brightseat Formation (Paleocene: Danian) of Maryland by David L. Govoni .. .. . ....... . .... . ......... .. .... . ..... . . . .... . ... . .......... 63

Potomac River Paleocene and Eocene Stop Descriptions by Thomas G. Gibson and Laurel M. Bybell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85

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Paleocene and Eocene strata of the central Atlantic Coastal Plain

By Thomas G. Gibson, Laurel M. Bybell, and David L. Govoru U.S. Geological Survey, Reston, VA 22092

REGIONAL SE'ITING

Sedimentary deposits of Paleocene and Eocene age crop out near the inner (western) margin of the Atlantic Coastal Plain from New Jersey to Georgia. In the Potomac River Valley in Maryland and Virginia, these deposits are exposed a short distance to the east of the ''Fall Line" (fig. 1). This line marks the inner margin of the preserved onlap of Cretaceous and Cenozoic sedimentary rocks of the Atlantic Coastal Plain Province onto the Precambrian and early Paleozoic crystalline rocks and early Mesozoic sedimentary and igneous rocks of the Piedmont Province that lie at the exposed edge of the continental craton.

In the Chesapeake Bay region, the basement complex upon which the Cretaceous and Cenozoic units rest is downwarped into a shallow, east­southeastward plunging, eastwardly open­ended basin known as the Salisbury Embayment (Richards, 1948) or the Chesapeake-Delaware Embayment (Murray, 1961). The Salisbury Embayment is bounded on the north and south by basement structural highs known respectively as the South Jersey High and the Norfolk Arch. Hansen (1978) postulated that the position and extent of downwarping within the Salisbury Embaymen t is con trolled by an underlying Triassic rift basin system that delimits a zone of crustal weakness. The Atlantic Coastal Plain contains a series of these down warped areas, usually termed

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embayments, and structural highs, termed highs or arches (fig. 2).

Willow Landing, the starting point for the field trip (fig. 1), is located a short distance east of the Fall Line in the west­central part of the Salisbury Embayment. The strata that we will see in detail on the field trip are representative of Paleocene and Eocene sediments in the southern and central parts of the Salisbury Embayment.

In addition to the Paleocene and Eocene sequences that crop out in the western part of the Coastal Plain (fig. 3), there are some sedimentary sequences that are preserved only in subsurface sections in coreholes in more downbasin areas to the east of the outcrop belt. The middle Eocene Piney Point Formation and the upper Eocene Chickahommy Formation do not crop out in the Potomac River Valley; they occur only in the subsurface of the lower Potomac River Valley. Originally, these units must have been present in the outcrop area that we will visit, but they were completely removed by an extensive period of erosion during the Oligocene.

The Paleocene and Eocene deposits in the Potomac River Valley are composed mainly of clayey and silty, very fine to fine­grained sand. The sediments contain abundant glauconite, which may exceed 50 percent of the sand-sized fraction. The total thickness of the outcropping glauconitic serumen ts in the Potomac River Valley is about 200 feet, and they represent all or parts of nine calcareous nannofossil zoneg (Bybell and Gibson, thiB guidebook). The long period of time represented by this relatively thin

a 40

SOUTH JERSEY HIG

PENNSYLVANIA ----""""'"

FIELD TRIP AREA

VIRGINIA

Western Limit of ---.. ... J

Coastal Plain

NOR-rH CAROLINA

Figure 1. Map of central Atlantic Coastal Plain, showing field trip area in west-central part of Salisbury Embayment. Continuous coreholes are 1) GL 913, 915, 916, and 917, 2) Clayton, 3) Solomon's Island, 4) Waldorf, 5) Oak Grove, 6) Putney Mill, 7) Dismal Swamp, 8) Gates County 163, and 9) Valhalla. Modified from Gibson (1983).

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I ,

I 1 80 160

KILOMETERS

sedimentary column of shallow marine deposits suggests that numerous diastems and/or thin sequences occur. The presence of thin columns of glauconitic sediments in the Paleocene, Eocene, and Oligocene of southern Maryland and Virginia also indicates that low sedimentation rates prevailed throughout this region during the Paleogene. The dominance of biogenic and biochemical sedimentation in the lower Miocene section in the Salisbury and Albemarle Embayroents (Gibson, 1983) suggests that this low sedimentation rate persisted into the early or early middle Miocene, and that it was due to low influx of clastic debriB. The renewed uplift of the Appalachians to the west in the early to middle Miocene resulted in a large influx of coarse clastic material eastward onto the Atlantic Coastal Plain (Gibson, 1970; McCartan, 1989).

Even including both surface and subsurface sequences, the Paleocene and Eocene sedimentary record that is preserved in the west-central Salisbury Embayment of Maryland and Virginia is far less complete than the sedimentary record that is preserved in New Jersey or in the Gulf Coastal Plain. Though most of the marine sedimentary sequences of the Gulf Coaatru Plain also are represented in Maryland and Virginia (see Bybell and Gibson, this guidebook, fig. 2), they are much thinner here. In contrast to the Gulf Coast, where thick, fluvial to marginal­marine sediments are present in some of the sedimentary sequences. such sequences are absent in Maryland and Virginia.

Large-scale erosion of sediments, particularly of the more upbasin faci-es, has occurred both in the Atlantic and Gulf Coastal Plain areas. However, a larger number of sedimentary sequences apparently has been largely or completely removed in the Atlantic Coastal Plain because the thinner units in the Atlantic Coastal Plain were more susceptible to removal by erosion than the thick Gulf

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Coastal Plain units, particularly if the erosion occurred during prolonged periods of low sea level.

In Virginia and New Jersey, some upper Paleocene and lower Eocene strata are found in the outcrop belt and/or shallow subsurface that are not present in the deeper subsurface near the coast or on the continental margin (Brown and others. 1972; Olsson and Wise, 1987; Poag and Low, 1987). Various erosional mechanisms, such as submarine canyon formation and headward erosion, channeling, and collapse slumping, have been proposed to explain the absence of these sediments offshore (Mountain, 1987).

Recent drilling by the U.S. Geological Survey in the northern part of the Salisbury Embayment reveals that a much more complete record of Paleocene and Eocene strata is present in New Jersey than was previously recognized. 1."'he completeness of the record is greater here than that found in more southerly parts of the Salisbury Embayment and other embayments to the south (Owens and others, 1988; Poore and Bybell, 1988; see Bybell and Gibson, this guidebook). Of particular note is the presence in New Jersey of continuous sedimentation from Martini's (1971) upper Zone NP 9 into lower Zone NP 10 (Gibson, Bybell, and Owens, 1991). The Zone NP 9-NP 10 boundary forms the most commonly recognized Paleocene-Eocene boundary (Berggren and others, 1985). Though the record is more complete here, many of the sequences found in New Jersey, including the Zone NP 9-NP 10 section, do not crop out and are only known from subsurface occurrences.

Continuous sedimentation across the Paleocene-Eocene boundary is known only in the Atlantic Coastal Plain from New Jersey. In the southern Atlantic Coastal Plain, a more fragmentary record of sediments near the Paleocene-Eocene boundary occurs in South Carolina (Gohn

,. /---,

/ I

/

N

t o 100 200 300 MILES

-I i' I I I ! I I I

o 100 200 )00 400 KILOMETERS

GULF OF MEXICO

Figure 2. Generalized tectonic map for the Atlantic continental margin (from Owens and Gohn.1985).

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and others, 1983; Van Nieuwenhuise and Colquhoun, 1982) and in the Albemarle Embayment in North Carolina (Brown and others, 1972). For example, lower Eocene sediments of Zone NP 10 age are missing in South Carolina (Bybell, unpubl. data; Wallace Fallaw, oral commun., 1990).

PALEOCENE AND EOCENE STRATIGRAPHY OF THE POTOMAC RIVER VALLEY

The outcropping Paleocene and Eocene sediments in the Potomac River Valley are subdivided into four lithostratigraphic units; in ascending order they are the Brightseat Formation (lower Paleocene), Aquia Formation (upper Paleocene), Marlboro Clay (upper Paleocene), and Nanjemoy Formation (lower Eocene). Two additional units are found only in the subsurface to the east of the field trip area; they are the Piney Point Formation (middle Eocene) and the Chickahominy Formation (upper Eocene). All of the above units are placed in the Pamunkey Group, and they form. a distinctive series of glauconitic, clastic sediments of middle neritic to marginal-marine origin in the outcrop and subcrop belt (Hazel, 1969; Gibson and others, 1980; Ward, 1985). The sediments are comprised predominantly of unconsolidated to poorly indurated., variably megafossiliferous. argillaceous sands, glauconitic sands, and clay. The biostratigraphic basis for the age placements of the formations is given in Bybell and Gibson (this guidebook).

Previous work

Early stratigraphic investigations of Paleogene strata of Maryland and Virginia consisted of high quality studies done by Darton (1891), Clark (1896), Clark and Martin (1901), and Clark and Miller

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(1912). Subsequent lithologic studies of the Paleogene strata in this area include those of Beauchamp (1984.), Brown and others (1972), Glaser (1971), McCartan (1989), Mixon and others (1989), Reinhardt and others (1980), Teifke (1973), Ward (1984, 1985), and Ward and Strickland (1985). References to additional lithologic studies of this region can be found in these works. References to primarily biostratigraphic studies are contained in Bybell and Gibson (this guidebook).

Paleocene strata

Lower Paleocene sediments of the outcrop belt in Maryland and Virginia represent considerably less Paleocene time than the strata occurring in Alabama. Only strata of NP 3 age are known from southern Maryland and Virginia (Gibson and others, 1980; Bybell, unpubL data)~ in comparison, sediments placed in Zones NP 1, NP 2, and NP 3 are present in Alabama (Gibson and others, 1982).

Younger Paleocene strata (uppermost Zone NP 9) occur in the Potomac River Valley than occur in Alabama (Frederiksen and others, 1982). Unfortunately, the youngest Paleocene deposit in Virginia., the­Marlboro Clay. is of marginal marine origin and does not contain calcareous microfossils except in a few cases where thin laminae of shallow marine origin are interbedded.

Brightseat Formation

The Brightseat Formation is the lowest stratigraphic unit of the Pamunkey Group, and was named for outcrops found just to the southeast of Washington, D.C. Bennett and Collins (1952) applied the name Brightseat Formation to beds of fossiliferous, dark-gray to olive-gray, micaceous, silty and clayey, fine-to-very-

fine quartz sand. Coarse sand grains and granules of quartz- are scattered throughout the unit; small quartz pebbles and phosphate grains and pebbles occur, especially near the base. The unit is variably, but usually sparsely, glauconitic. Fragments of lignitized wood, some quite large, are scattered throughout, but are most abundant toward the base. The beds have undergone intense bioturbation, which has obscured primary bedding structures. The Brightseat Formation disconformably overlies the Upper Cretaceous Severn Formation in the outcrop area; downdip in the Solomons Island corehole, the Brightseat has a dis conform able contact marked by burrowing into the underlying strata of the Lower and Upper(?) Cretaceous Potomac Group.

The formation is thin, with a maximum thickness of 10-12 feet in a few scattered outcrops found just east of Washington, D.C. in Maryland (fig. 1) and with a thickness of less than 20 feet in the subsurface. Exposures of the Brightseat continue in Maryland to the north and east of the type area in a narrow and highly discontinuous band that extends with an east-northeastern strike. The formation rapidly thins and disappears, because of erosional removal, approximately 10 miles south of the type area.

Several outcrops to the south of this known area have been placed in the Brightseat Formation, including those of Clark and Martin's (1901) bed 1 of the Aquia Formation along Aquia Creek (Hazel, 1969) and one outcrop along the Rappahannock. River (Ward, 1985). There also was a questionable placement into the Brightseat of beds similar to bed 1 that occur at the base of the Paleocene section in the Oak Grove corehole (Gibson and others, 1980). The main basis for the inclusion of these beds into the Brightseat was their dark-colored unfossiliferous character and the fact that they underlay

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the calcareous fossiliferous beds of the Aquia. However, examination of the grain size of these bedB shows them commonly to be coarser than those found in the type Brightseat; in addition. the age of these beds was shown by palynomorphs to be younger than the type Brightseat (Frederiksen, 1984, reprinted in this guidebook; Frederiksen, 1991). The formational designation of these beds is uncertain. Strata of Zone NP 3 age have been identified elsewhere in Virginia in a subsurface section of the Dismal Swamp corehole in southeastern Virginia (fig. 1). The bedB assigned to Zone NP 3 in the Dismal Swamp corehole and the Brightseat sediments of Zone NP 3 age that occur in the Solomons Island corehole (fig. 1) contain foraminiferal assemblages suggestive of middle to outer neritic environments of deposition (Gibson, unpubl. data). The outcropping beds of the Brightseat at the western edge of the coastal plain in Maryland contain foraminiferal faunas suggestive of middle neritic environments (Nogan, 1964; Gibson, unpubl. data); Drobnyk (1965) and Beauchamp (1984) present sedimentary evidence supporting a middle neritic depositional environment (about a 300 foot water depth). In Virginia, Maryland, and New Jersey, the Zone NP 3 sequence represents the deepest depositional environments of any Tertiary unit in each area (Gibson, unpubl. data). The high sea level present in this area during Zone NP 3 agrees with the Cenozoic cycle chart of Haq and others (1988) in which Zone NP 3 also is shown as the time of highest sea level and greatest coastal onlap.

The middle neritic environments present at the western (innermost) limits of coastal plain sediments in Maryland and the outer neritic environments present at the western limits in New Jersey show that this transgressive sequence originally extended a considerable distance to the west of the present limit of the Coastal

Plain. The presence today in the Coastal Plain of only isolated exposures of this deep water sequence, and its almost total absence in Virginia and other parts of the Coastal Plain, indicates large seale erosion of this unit starting early in the Paleocene before the deposition of the overlying Aquia Formation.

The contact between the Brightseat Formation and the overlying, upper Paleocene Aquia Formation is noticeably disconformable both in outcrop and in the subsurface. Hazel (1969) presented both lithologic and faunal evidence to confirm the existence of the disconformity and demonstrated that it represents a significant hiatua. He calculated the absolute duration of the break to be about 3.6 m.y. More recent published estimates for the duration range from about 3.5 m.y. (Bybell and Govoni, 1977) to about 2.9 m.y. (Hazel and others, 1984).

Aquia Formation

The Aquia Formation is a medium-to. dark olive-gray, very fine-to-medium­grained, massively-bedded sand, which usually is abundantly glauconitic. The glauconite content of the sand fraction ranges from a low of 5 to 10 percent to well over 50 percent. The unit is heavily bioturbated. and thalassinodian crustacean (?) burrows dominate the ichnofauna of the less shelly beds. Mollusk shells are abundant in many beds; sometimes they are randomly scattered, and sometimes they occur in lenses or as thick, laterally· persistent lag deposits. Several, indurated, shelly sand beds, 0.5 to 2.0 feet thick, are present in many areas and form prominent marker beds in outcrop exposures. In the upper parts of outcrops, the unit weathers to a buff-gray or orange color. The Aquia is approximately 80 feet thick in the type area at Aquia Creek., but the thickness increases to 150 feet to the east in the

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subsurface section in the Solomons Island corehole (fig. 1). The Aquia was divided by Clark (1896) into nine lithologic zones, which now are commonly called beds. The basis for the subdivision into beds was the lithologic nature and amount and variety of mollusk shells in the sediments. Although useful in the type area at Aquia Creek, the beds cannot be easily identified in other outcrop areas and in subswface sections. Clark and Martin (1901) divided the Aquia into two members, a lower Piscataway Member that was a more "poorly sorted" clayey sand, and an upper Paspotansa Member that was a "better sorted" sand. They placed the original member boundary between bed 7 and bed 8. A revision of the member boundary, which involved lowering it to the boundary between bed 5 and bed 6, was made by Ward (1985). A discussion of the member boundary is contained in the discussion of Stop 1 of our trip (Gibson and Bybell, this guidebook).

The Aquia Formation is placed in upper Zone NP 5 through much of Zone NP 9 (see Bybell and Gibson, this guidebook). Some of the nannofossil rones are represented here by a thin sedimentary deposit of inner-neritic origin (Zone NP 7 is recognized only in a two foot interval of bed 5 and uppermost bed 4, and Zone NP 8 is found only in the two feet of bed 6 at Aquia Creek), and the sediments may represent only short intervals of time within the zones.

The depositional environments of the Aquia Formation in the type area are of inner-neritic depths as interpreted from the foraminiferal assemblages (Nogan, 1964; Gibson. unpubl. data); inner-neritic environments are also suggested by sedimentological studies (Beauchamp, 1984). The contact between the Aquia Formation and Marlboro Clay, where seen in outcrop and in most subsurface exposures, is disconformable with a gently undulating surface as we will see at Stop

4 of the field trip. In the Oak Grove corehole, however, a rapid upward transition from glauconitic sand of the Aquia to interbedded thin laminae of glauconitic sand and clay to massive clay of the Marlboro occurs within a one foot zone and suggests a conformable relationship between the two units in this area (Reinhardt and others, 1980).

Marlboro Clay

The Marlboro Clay is a relatively thin but widespread unit that includes the uppermost Paleocene (uppermost Zone NP 9) strata in this area. The thickness ranges from 0.5 to 4.0 feet in the stops on the field trip, but it commonly is from 10 to 20 feet thick with a maximum thickness approaching 30 feet (Glaser, 1971). This clay unit is found through much of southern Maryland and Virginia, both in outcrops and in the subsurface. In most exposures, the clay is dominantly pink to red-brown in color, but it may contain a considerably lesser amount of silver-gray colored clay. The gray colored beds, if present, generally occur in the upper few feet of the formation. The clay of the Marlboro, which is typically 50 percent kaolinite with 40 percent illite (Reinhardt and others, 1980), contains varying amounts of fine silt. Most of the Marlboro is massively bedded and without structure, but cross laminations of clay to fine silt are sometimes visible (Reinhardt and others, 1980).

The lower contact with the Aquia Formation generally is disconformable as can be seen at Stop 4 of the field trip; in the Oak. Grove corehole, however, the glauconitic sand of the uppermost Aquia is finely interlaminated with the clay of the lowest Marlboro over a one-foot interval, and there appears to be a gradational transi tion between the two formations (Reinhardt and others, 1980).

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The upper contact with the Nanjemoy Formation always is marked by a burrowed surface, and sediments of the Nanjemoy commonly are burrowed several feet down into the Marlboro. The burrows may be straight-sided or open-spiral (Gyrolithes) crustacean burrows (Reinhardt and others, 1980, fig. 5). This disconformable contact will be seen at Stop 4 of the field trip.

The Marlboro Clay contains few calcareous fossils, but it has a low­diversity dinoflagellate assemblage that suggests deposition in an estuarine environment (Gibson and others, 1980).

Eocene strata

Lower Eocene strata are well represented in the Paleogene outcrop belt in Virginia and Maryland, and they compare favorably with the lower Eocene strata in Alabama in terms of thickness and possible number of sequences. Much. less of middle and late Eocene time is represented by strata in this part of the Salisbury Embayment in Virginia and Maryland than in Alabama, and even those units found in the Potomac River Valley are present only in subsurface exposures (Bybell and Gibson, this guidebook, fig. 2).

Nanjemoy Formation

The Nanjemoy Formation is an olive­gray, massively-bedded, very fine to fine­grained glauconitic sand that contains considerable but varying amounts of clay and silt. Bioturbation has obscured primary bedding structures. The clay fraction is composed mostly of illite with an increase in the amoun t of kaolinite near the lower contact with the Marlboro Clay (Reinhardt and others, 1980). Mollusk shells are found in most of the formation,

both in outcrop and in subsurface exposures, but they are cOIll!iderahly less numerous than in the outcropping Aquia Formation in the Aquia Creek area.

Clark (1896) proposed a sequence of numbered "zones" (beds), which he numbered from 11 to 17, for strata that subsequently was named the N~emoy Formation by Clark and Martin (1901). Clark and Martin (1901) divided the Nanjemoy Formation into two members, the lower Potapaco Member and the upper Woodstock Member. The beds and members of Clark and Martin (1901), which are difficult to recognize in the Potomac River Valley and surrounding areas, are not used in this guidebook.

The formation is named from Nanjemoy Creek., which enters into the north side of the Potomac River between Stops 6 and 7. The thickness of the formation along the Potomac River is estimated at 125 feet (Clark and Martin, 1901); the thickness is 124 feet in the Oak Grove corehole and thickens downbasin to 157 feet in the Solomons Island corehole. A relatively~ thin section of 55 feet is present in the Putney Mill corehole in south~central Virginia

The environments of deposition for the formation along the Potomac River and in much of the strata in the coreholes is inner neritic. The strata placed in Zone NP 11 in the Oak Grove, Putney Mill, and Solomons Island coreholes represent the deepest water found in the formation, reaching middle neritic environments in the Solomons Island core hole (Gibson, unpubl. data), In the field trip area the Nanjemoy is disconformably overlain by the Miocene Calvert Formation; we will see this contact at Stops 7 and 8. In the subsurface to the east, the Nanjemoy is disconformably overlain by the Piney Poin t Formation.

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Piney Point Formation

The name Piney Point Formation was applied by Otton (1955) to 30 feet of glauconitic sand with thin, interbedded, cemented shell beds penetrated in a drill hole along the lower reaches of the Potomac River, about 30 miles to the east of our final field trip stop (Stop 8). In the Solomons Island corehole, which is located 12 miles to the northeast of the type area, the Piney Point is 50 feet thick. The formation in the Solomons Island core appears to be similar to that found in the type area; it consists of thin, grayish-olive­green calcareous sandstones, which are fine~grained with some medium grains, moderately glauconitic, and with abundant thick shells, principally Cubitostrea sellaefarmis. and which are interbedded with glauconitic. clayey fine sand. Coarse sand and fine gravel occur at the base of the formation. The Piney Point Formation is found in outcrop along the Pamunkey and James Rivers in central and southern Virginia (Ward, 1985), where it consists of clayey, glauconitic sand that tends to be coarser grained than the underlying Nanjemoy.

The foraminiferal faunas in the Solomons Island corehole suggest deposition in inner to possibly inner middle~neritic environments (Gibson, unpubl. data). The age placement within the middle Eocene is discussed in Bybell and Gibson (this guidebook).

Chickahominy Formation

The Chickahominy Formation was described by Cushman and Cederstrom (1945) from drillholes a short distance to the southeast of the Putney Mill cOl-ehole. There are no known outcrops of the formation. It is present in the subsurface of the lower Potomac River Valley. but presumably was eroded from the area of

the Solomons Island core hole during a long Oligocene hiatus. The lithology is a slightly glauconitic, micaceous. slightly sandy clay.

The formation is placed in the late Eocene Zone NP 19/20 (see Bybell and Gibson, this guidebook). The depositional environment for this unit, interpreted from limited samples, appears to be of middle­neritic depths. This suggests that the unit once occurred across the field trip area but was subsequently eroded away.

ACKNOWLEDGMENTS

The illustrations in the guidebook were prepared by Jean Self-Trail and Thomas Servais. Preparation of numerous calcareous microfossil samples was done by Elizabeth Hill, Jean Self-Trail, and Thomas Servais. Helpful comments on the manuscripts were made by Norman Frederiksen and Robert Weems.

REFERENCES

Beauchamp, R.G., 1984, Stratigraphy and depositional environments of the Brightseat and Aquia Fonnations, Maryland and Virginia: In Frederiksen, N.O., and Krafft, Kathleen, eds., Cretaceous and Tertiary stratigraphy, paleontology, and structure, southwestern Mary land and northeastern Virginia, American Association of Stratigraphic Palynologists Field Trip Volume and Guidebook, p. 78-11l.

Bennett, R.R., and Collins, G.G., 1952, Brightseat Formation, a new name for sediments of Paleocene age in Maryland: Washington Academy of Science J oumal, v. 42, p. 114-116.

Berggren, W.A., Kent, D.V., Flynn, J.J., and Van Couvering, J.A. 1985, Cenozoic geochronology: Geological Society of America Bulletin, v. 96, p. 1407·1418.

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Brown, P.M., Miller, J.A., and Swain, F.M., 1972, Structural and stratigraphie framework, and spatial distribution of permeability of the Atlantic Coastal Plain, North Carolina to New York: U.S. Geological Survey Professional Paper 796, 79 p.

Bybell, L.M., and Govoni, D.L., 1977. Preliminary calcareous nannofossil zonation of Brightseat and Aquia Formations (Paleocene) of Maryland and Virginia - stratigraphic implications: American Association of Petroleum Geologists Bulletin, v. 61, p. 773-774.

Clark, W.B., 1896, The Eocene deposits of the middle Atlantic slope in Delaware. Maryland, and Virginia: U.S. Geological Survey Bulletin 141, 167 p.

Clark, W.B., and Martin, G.C., 1901, The Eocene deposits of Maryland: Maryland Geological Survey Eocene volume, p. 19-92.

Clark, W.B., and Miller. B.L., 1912, Physiography and geology of the coastal plain province of Virginia: Virginia Geological Survey Bulletin 4, p. 1·58, 88-222.

Cushman, J.A, and Cederstrom, D.J., 1945, An upper Eocene foraminiferal fauna from deep wells in York County, Virginia: Virginia Geological Survey Bulletin 67, p. 1-57.

Darton, N.H., 1891, Mesozoic and Cenozoic formations of eastern Virginia and Maryland: Geological Society of America Bulletin, v. 2, p. 431-450.

Drobnyk, J .W., 1965, Petrology of the Paleocene-Eocene A.quia Formation of Virginia, Maryland, and Delaware: Journal of Sedimentary Petrology, v. 35, p. 626-642.

Frederiksen. N.O., 1984, Lower Tertiary pollen biostratigraphy, Maryland and Virginia: In Frederiksen, N.O., and Kram, Kathleen, eds., Cretaceous and Tertiary stratigraphy, paleontology, and structure, southwestern Maryland and northeastern Virginia, American Association of Stratigraphie Palynologists Field Trip Volume and Guidebook, p. 163-168.

.... ----, 1991, Midwayan (Paleocene) pollen correlations in the eastern United States: Micropaleontology, v. 37, p. 101-123.

FTederiksen, N.O., Gibson, T.G., and Bybell, L.M., 1982, Paleocene-Eocene boundary in the eastern Gulf Coast: Gulf Coast Association of Geological Societies Transactions, v. 32, p. 289-294.

Gibson, T.G., 1970, Late Mesozoic-Cenozoic tectonic aspects of the Atlantic Coastal Margin: Geological Society of America Bulletin, v. 81, p. 1813~1822.

~--------, 1983, Stratigraphy of Miocene through Lower Pleistocene strata of the United States central Atlantic Coastal Plain: In Geology and Paleontology of the Lee Creek Mine, North Carolina, Ray, C.E., ed., Smithsonian Contributions to Paleobiology, Number 53, p. 35-80.

Gibson, T.G., Andrews, G.W., Bybell, L.M., Frederiksen, N.O., Hansen, Thor, Hazel, J.E., McLean, D.M., Witmer, R..J., and Van Nieuwenhuise, D.S., 1980, Biostratigraphy of the Tertiary strata of the core: In Geology of the Oak Grove Core, Part 2, Virginia Division of Mineral Resources, Publication 20, p. 14-30.

Gibson, T.G., Bybell, L.M., and Owens, J.P., 1991, Paleocene-Eocene boundary 10

southwestern New Jeysey: a rare continuous section: Geological Society of America Abstracts with Programs, v. 23, no. 1, p. 35.

Gibson, T.G., Mancini, KA, and Bybell, L.M., 1982, Paleocene to middle Eocene stratigraphy of Alabama: Gulf Coast Association of Geological Societies Transactions, v. 32, p. 449-458.

Glaser, J.D., 1971, Geology and mineral resources of southern Maryland: Maryland Geological Survey Report of Investigations Number 15, 84 p.

Gchn, G.S., Hazel, J.E., Bybell, L.M., and Edwards, hE., 1983, The Fishburne Formation (lower Eocene), 8 newly defined subsurface unit in the South Carolina Coastal Plain: U.S. Geological Survey Bulletin 1537-C, p. C1-C16.

Hansen, H.J., 1978, Upper Cretaceous (Senonian) and Paleocene (Danian) pinchouts on the south flank of the Salisbury Embayment, Maryland, and their relationship to antecedent basement

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structures: Maryland Geological SUTVey Report of Investigations 29, 36 p.

Haq, B.U., Hardenbol, Jan, and Vail, P.R., 1988, Mesozoic and Cenozoic chronostratigraphy and cycles of sea-level change: In Sea-level changes: an integrated approach, Wilgus, C.K, Hastings, B.S., Ross, C.A., Posamentier, Henry, Van Wagoner, John, and Kendall, C.G. St. C., eds., Society of Economic Paleontologists and Mineralogists Special Publication No. 42, p. 71-108.

Hazel, J .E., 1969, Faunal evidence for an unconfonnity between the Paleocene Brightseat and Aquia Formations (Maryland and Virginia): U.S. Geological Survey Professional Paper 650-C, p. C58~ C65.

Hazel, J.E., Edwards, hE., and Bybell, L.M., 1984, Significant unconformities and the hiatuses represented by them in the Paleocene of the Atlantic and Gulf Coastal Province: In Schlee, J.S., ed., Interregional unconformities and hydrocarbon accumulation, American Association of Petroleum Geologists Memoir 36, p. 59-66.

Martini, Erlend, 1971, Standard Tertiary and Quaternary calcareous nannoplankton zonation: Planktonic Conference, 2nd, Rome, 1969, Proceedings, p. 739-785.

McCartan, Lucy, 1989, Mineralogy of the Haynesville, Virginia, cores: U.S. Geologica.l Survey Professional Paper 1489-B, p. B1-B9.

Mixon, R.B., Po wars , D.S., Ward, L.W., and Andrews, G.W., 1989, Lithostratigraphy and molluscan and diatom biostratigraphy of the Haynesville cores - outer coastal plain of Virginia: U.S. Geological Survey Professional Paper 1489-A, p. AI-A48.

Mountain, Gregory, 1987, Cenozoic margin construction and destruction offshore New Jersey: Cushman Foundation fOT Foraminiferal Research, Special Publication 24, p. 57-83.

MWT8.Y, G.E., 1961, Geology of the Atlantic and Gulf Coastal Province of North America: Harper and Brothers, New York, 692 p.

Nogan, D.S., 1964, Foraminifera, stratigraphy, and paleoecology of the Aquia Formation of

Maryland and Virginia: Cushman Foundation for Foraminiferal Research Special Publication 7, 50 p.

Olsson, R.K, and Wise, S.W., Jr., Upper Paleocene to middle Eocene depositional sequences and hiatuses in the New Jersey Atlantic Margin: Cushman Foundation for Foraminiferal Research Special Publication 24, p. 99-112.

Otton, E.G., 1955, Ground-water resources of the southern Maryland Coastal Plain: Maryland Department of Geology, Mines, and Water Resources Bulletin 15,347 p.

Owens, J.P., Bybell, L.M., Paulachok, Gary, Ager, T.A, Crtlnzalez, V.M., and Sugarman, P.J., 1988, Stratigraphy of the Tertiary sediments in a 945-foot>-deep corehole near Mays Landing in the southeastern New Jersey Coastal Plain: U.S. Geological Survey Professional Paper 1484, 29 p.

Owens, J.P., and Gohn, G.S., 1986, Depositional history of the Cretaceous series in the U.S. Atlantic Coastal Plain: stratigraphy, paleoenvironments, and tectonic controls of sedimentation: In Geologic Evolution of the United States Atlantic Margin, Poag, C.W., ea, Van Nostrand Reinhold Co., New York, p. 25-86.

Poag, C.W., and Low, Doris, 1987, Regional unconformities cored on the New Jersey continental slope: Cushman Foundation for Foraminiferal Research Special Publication 24, p. 113-136.

POOTe, R.Z., and Bybell, L.M., 1988, Eocene to Miocene biostratigraphy of New Jersey core ACGS #4: implications for regional stratigraphy: U.S. Geological Survey Bulletin 1829, 22 p.

Reinhardt, Juergen, Newell, W.L., and Mixon, RB., 1980, Tertiary lithostratigraphy of the core: In Geology of the Oak Grove core, Virginia Division of Mineral Resources Publication 20, Part 1, p. 1-13.

Richards, H.G., 1948, Studies on the subsurface geology and paleontology of the Atlantic Coastal Plain: Philadelphia Academy ofN atural Science Proceedings, v. 100, p. 39-76.

Teitke, RH., 1973, Stratigraphic units of the Lower Cretaceous through Miocene series:

13

In. Geologic Studies, Coastal Plain of Virginia, Virginia Division of Mineral Resources, Bulletin 83, p . 1-78.

Van Nieuwenhuise, D.S., and Colquhoun, D.J., 1982, The Paleocene-lower Eocene Black Mingo Group of the east central coastal plain of South Carolina: South Carolina Geology, v. 26, p. 47-67.

Ward, 1.. W., 1984, Stratigraphy and mollusean assemblages of the Pamunkey and Chesapeake Groups, upper Potomac River: In Frederiksen, N.O., and Krafft, Kathleen, eds., Cretaceous and Tertiary stratigraphy, paleontology, and structure, southwestern Maryland and northeastern Virginia, American ABsociation of Stratigraphic Palynologlsts Field Trip Volume and Guidebook, p. 3-77.

--------, 1985, Stratigraphy and characteristic mollusks of the Pamunkey Group (lower Tertiary) and the Old Church Formation of the Chesapeake Group-Virginia Coastal Plain: U.S. Geological Survey Professional Paper 1346, 78 p.

Ward, L.W., and Strickland, G.1.., 1985, Outline of Tertiary stratigraphy and depositional history of the U.S. Atlantic Coastal Plain: In Geological Evolution of the United States Atlantic Margin, Poag, C.W., ed., Van Nostrand Reinhold Co., New York, p. 87-123.

14

Calcareous nannofossils and foraminifers from Paleocene and Eocene strata in Maryland and Virginia

By Laurel M. Bybell and Thomas G. Gibson U.S. Geological Survey, Reston, VA 22092

INTRODUCTION

Calcareous nannofossils and foraminifers are common constituents of the richly fossiliferous, marine to marginal marine, Paleocene and Eocene strata of Maryland and Virginia that occur both as outcrops and in the subsurface (fig. 1). These units also contain other fossil groups including mollusks, dinoflagellates, spores and pollen, and vertebrate remains. The strata are divided into six lithostratigraphic units: the Brightseat Formation (lower Paleocene), Aquia Formation (upper Paleocene), Marlboro Clay (upper Paleocene), Nanjemoy Formation (lower Eocene), Piney Point Formation (middle Eocene), and Chickahominy Formation (upper Eocene). See Gibson and Bybell (this guidebook) for a discussion of the various lithologic units and a list of previous lithologic investigations.

PREVIOUS WORK

There are limited published data on Paleocene and Eocene calcareous nannofossils from Maryland and Virginia. Bybell and Govoni (1977) studied assemblages from the outcropping Brightseat and Aquia Formations. Bybell (in Gibson and others, 1980) examined calcareous nannofossils from the Aquia Formation, Marlboro Clay, and Nanjemoy Formation from the Oak Grove corehole in northern Virginia, and Gibson and Bybell

15

(1984) discussed the calcareous nannofossils and foraminifers in the Brightseat, Aquia, and Nanjemoy Formations.

Paleocene and Eocene foraminiferal studies, which are more numerous than those concerning calcareous nannofossils, began with Bagg's early studies (1898, 1901). Subsequent important papers by Cushman (1944), Shiffiett (1948), and Nogan (1964) examined the foraminiferal assemblages of the Aquia Formation. Cushman and Cederstrom (1945) studied the foraminifers of the Chickahominy Formation, a unit known only from the subsurface of eastern Virginia (Gibson, 1970). Cushman (1948) examined Paleogene foraminifers from the Hammond well on the Eastern Shore of Maryland. Page (1959) studied the Brightseat foraminifers, as did Shifflett (1948), who unknowingly included the foraminifers of some Brightseat strata (then still unrecognized as Danian in age) in her study of Aquia assemblages. More recen tly, Gibson and others ( 1980) reported on assemblages from the Aquia and Nanjemoy Formations in the Oak Grove corehole in northern Virginia, as did Poag (1989) from a corehole in northeastern Vil'ginia.

Most of the early foraminiferal studies concentrated on the benthonic assemblages. Planktonic foraminifers, which are uncommon in most of the Paleocene or Eocene lithologic units in this region, were not regarded in the past as being as important for biostratigraphy as

VIRGINIA

FIGURE 1. Localities in Maryland and Virginia. Dots indicate coreholes, and striped pattem indicates outcrops.

16

•

they are today. However, Loeblich and Tappan (1957) conducted a pioneering study on planktonic foraminifers of the Atlantic and Gulf Coastal Plains that included assemblages from the Brightseat and Aquia Formations. Subsequent studies, such as those of Page (1959), Nogan (1964), and Poag (1989), placed increasing emphasis on the planktonic component of the foraminiferal assemblages.

FOSSn.. ZONATIONS AND DATUMS

Calcareous nannofossils and planktonic foraminifers are the two fossil groups that are most commonly used for worldwide, Paleogene biostratigraphic correlation. Calcareous nannofossil assemblages are sufficiently diverse and abundant in the Paleocene and Eocene units of the Salisbury Embayment to serve as a useful tool in dating these coastal plain sediments. In contrast, age-diagnostic, planktonic foraminiferal species are not common in most samples from these shallow-marine strata or are them common downbasin and to the east in samples from slightly deeper-water deposits that are found in the subsurface.

Calcareous nannofossils and benthonic foraminifers occur in fair abundance in most of the outcropping Paleocene strata and in lesser numbers in the outcropping Eocene strata of Maryland and Virginia. The abundance, diversity, and preservation of both groups generally increase in core hole samples. The increase in these two groups is a result of the fact that the subsurface samples generally are from more offshore, deeper-water environments, which also are finer-grained than coeval sediments in surface exposures; these finer-grained sediments have less ground water movement through them and thus there is less dissolution of the fossils. Where possible, corehole samples were

17

used to determine biostratigraphic relationships because all the samples in a core hole have a known vertical position. This contrasts with the necessity for piecing together a composite section from the thin, isolated sections found in surface exposures. The difficulty in piecing together separated outcrop sections will be demonstrated on the field trip.

In addition to the calcareous nannofossil and foraminiferal studies, there have been numerous studies on other fossil groups preserved in the Brightseat and Aquia Formations, the Marlboro Clay, and the Nanjemoy Formation in the Potomac River valley and adjacent area.s. Dinoflagellate studies include those of Whitney (1976), Goodman (1979; 1984, reprinted in this guidebook), Witmer (in Gibson and others, 1980), EdwardB and others (1984, reprinted in this guidebook), and Edwards (1989). Frederiksen (1979; 1984, reprinted in this guidebook; 1991) and Frederiksen and others (1982) examined the spore and pollen assemblages from the Brightseat and Aquia Formations, the Marlboro Clay, and the Nanjemoy Formation in the current field trip area. Weems (1984, 1988) and Weems and Horman (1983) are studies of the vertebrate remains in the Brightseat, Aquia, and Nanjemoy Formations. Hazel (1968) studied the ostracodes of the Brightseat Formation.

Calcareous nannofossils

There are two commonly-used calcareous nannofossil zonations. The zonation of. Martini (1971) is based primarily upon studies in hemipelagic sediments, while the zonation of Bukry (1973, 1978; Okada and Bukry, 1980) is based primarily upon studies of samples collected by the Deep Sea Drilling Project. Both of these zonations were considered for the current study, but the zonation of

Martini (1971) proved to be much more useful because the diagnostic species in this zonation occur in the study area.

The following list enumerates the calcareous nannofossil horizons that are used to date Paleocene and Eocene sediments from Maryland and Virginia. These horizons are based on data in Martini (1971), Bukry (1973, 1978), Okada and Bukry (1980), and Perch-Nielsen (1985), as well as from BybeU's calcareous nannofossil studies. An asterisk (*) indicates a species used to define a horizon in the zonation of Martini (1971), and a pound sign (#) indicates a species used to define a horizon in the zonation of Bukry (1973, 1978). FAD indicates a first appearance datum. and LAD indicates a last appearance datum. Figure 2 shows the placement of Martini's NP Zones relative to Blow's (1969) planktonic foraminiferal zones and to geologic time (modified from Berggren and others, 1985).

Eocene Markers

LAD *ChiasmolithuB bUkns / solitus - top of Zone NP 16

FAD Daktylethra punctulata - in Zone NP 15 LAD *IWiscoaster sublodoensis - base of Zone

NP 14 LAD *Tribrachiatus orthostylus - top of Zone

NP 12 FAD Helicospluura lophtJta - near top of Zone

NP 12; can be used to approximate the Zone NP 12113 boundary

LAD Ellipsolithus macellus - near the top of Zone NP 12

FAD Helicosphaera seminulum - mid Zone NP 12

FAD *#DiscOO8ter lodoensis - base of Zone NP 12

FAD Chiphragmalithus calathus - in Zone NP 11

LAD *#Tribrachiatus contortus - top of Zone NP 10

LAD Discoaster multiradiatus . near top of Zone NP 10

18

LAD Tribrachiatus bramlettei - near top of Zone NP 10

FAD Tribrachiatus orthtJstylus - upper part of Zone NP 10

FAD #Discooster diastypus - mid Zone NP 10 FAD #Tribrachiatus contortus - mid Zone

NP 10 LAD Placozygus sigmoides - lower Zone NP 10 LAD Fasciculithus spp. - lower Zone NP 10 LAD Hornibrookina sp. - lower Zone NP 10 FAD *Tribrachiatus bramkttei - base Zone

NP 10

Paleocene Markers

FAD Transuersopontis pulcher - uppermost Zone NP 9

LAD Scapholithus apertus - upper Zone NP 9 LAD Biantholithus astralis . upper Zone NP 9 FAD Toweius occultatus - in Zone NP 9 FAD Toweius callos us - in Zone NP 9 FAD Lophodolithus nascens - upper Zone

NP 9 FAD #Campylosphaera ecxkla / dela - mid Zone

NP9 FAD *#Discoaster multiradiatus - base of Zone

NP9 FAD *Heliolithus riedelii - base of Zone NP 8 FAD #Discoaster mohleri - base of Bukry'8

Zone CP6·; approximately equivalent to base of Martini's Zone NP 7

FAD *tlHeliolithus kleinpellii - base of Zone NP6

FAD Helwlithus cantabria.e - mid Zone NP 5 FAD &aphtJlithus apertus - in Zone NP 5 FAD Toweius touae - in Zone NP 5 FAD Chiasmolithus bidens - in Zone NP 5 FAD *#Fasciculithus tympaniformis - base of

Zone NP 5 FAD Toweius pertuslLS - in Zone NP 4 FAD Ellipsolithus distichus - near base of

Zone NP 4 FAD *Ellipsolithus macellus - base of Zone

NP 4 FAD *Chiasmolithus danicu8 - base of Zone

NP3 FAD *#Cruciplacolithus tenuis - base of Zone

NP2

-CI1 C/) C/) :?! w w "-'" z Z LL LL LL CI) (J) (J) 0 CJ)O~ 0 0>- 0 0:: ()N_ :IN''''' CJ)O « I W Z...Jm O...J cn zZ <t C/)w CJ)« w 0«0) w-T""

O~ClZ ZC/) z~ >- <.) CJ ~O::T"" 0:: C/) -- 00:: 0« w - «C/)z f->-Z- -w LL

«0::<0 f- . f-OO 0 0 « ZLL~ O°f- «""""l «~ ...JLL.0:: ~ « cr: ::E~ (J) a... I-- :5 Z 9 «0« cr: ~ > o::w ~« Z a...:::Ero OZ~ 0 Oz 0 0 w en «- Z-....- LL LL LL ...J 0:: « ...J

~ z :::E

NP 21 PIT

NP 19120 ~ W P16 r ~

~~

:5 PRIABONIAN NP18 t-40 P15 ....... ~-

NP17 BARTONIAN P14 PINEY POINT -~

I-' :'l FORMATION NP16 SHARK

W W P12 RIVER t- 45 ......J .-. --- FORMATION

Z Q LISBON

W 0 FORMATION

0 ~ LUTETIAN P 11 NP15

-so 0 W P10 ~

NP14 ~.-.. .....

P9 TALLAHATTA NP13 FORMATION >-

-I P8 NP12 MANASQUAN t-55 a: YPRESIAN NANJEMOY FORMATION ----« P7 NP 11 FORMATION BASHIANOL W HATCHETIGBEE

P6 b NP10 F2.R~ATIONS .... JMARLBORO I.. lJruSCAHQ~

P5 NP9 ~ CLAY ..... //.7L~ V'I FORMATION" ill

W ---Z r SELANDIAN P4 NP8 AQUIA VINCENTOWN NANAFALIA 1-60 ill « NP7 FORMATION FORMATION FORMAnON

0 ......J NP6 IJ NAHEOLA'" 0 P3 b

• ~~ ~ FORMATIONr.

P2 NP4 ~/ -L' L/ ~ u,; w >- HORNERS. ~~K ---J ......J c TOWN

<! (( DANIAN P1 - NP 3 FOl=lflAA I N FORMATION 1-65 « ~ ~~ YTON a.. UJ b NP2 FORMATION

hr- NP -yy"

FIGURE 2. Correlation chart of Paleocene and Eocene strata that are present in Alabama, Maryland, New Jersey. and Virginia. Time scale from Berggren and others, 1985.

19

Foraminjfers

AI though they are less common than the calcareous nannofossils, there are sufficien tly diverse, planktonic foraminiferal assem blages to allow placement within a specific zone for a limited number of samples from Paleocene and Eocene intervals in the outcropping strata, and a slightly greater number of samples from the more downbasin coreholes. However, there are relatively thick intervals throughout all these shallow-water strata that contain only a few non-diagnostic specimens, and these sediments could not be dated with planktonic foraminifers.

Both Loeblich and Tappan (1957) and Nogan (1964) applied an early planktonic foraminiferal zonation to the outcropping Aquia Formation strata in the Aquia Creek area. Loeblich and Tappan placed the Aquia in the uppermost subzone of their three planktonic subdivisions of the Paleocene (the Globorotalia velascoensis­Globorotalia acuta-Globigerina spirolis subzone of the Globorotalia angulata zone); they probably were the first to recognize that the Aquia is late Paleocene in age rather than the previollsly postulated early Eocene age_ Nogan (1964) also used the Loeblich and Tappan zonation, but incoITectly assigned their uppermost subzone, and thus much of the Aquia, to the lower Eocene. Because of extensive downward mixing of Aquia sediments into the underlying Brightseat Formation due to bUITowing, Nogao also inconectly identified the uppermost part of the Brightseat Formation and considered it to be part of the overlying Aquia Formation. At the same time, the presence of Globoconusa daubjergensis in rus mixed sample led him to erroneously consider that the lowermost part of the Aquia was of Danian age (Hazel, 1969).

Poag (1989) applied a modified planktonic zonation of Blow (1969, 1979)

20

with some mixed success to the Paleocene and Eocene strata from a corehole near Haynesville, Virginia. Poag was unable to date some relatively thick intervals in the upper Paleocene and lower Eocene strata because they lacked diagnostic planktonic assemblages. On the basis of the very limited planktonic assemblages available, he did assign ages to some intervals in this core. However, some of these ages are in conflict with those derived from palynomorphs from the same intervals in this corehole (Edwards, 1989).

Some benthonic foraminiferal species have ranges restricted to parts of the upper Paleocene and lower Eocene in the study area. These species may prove useful fol' local correlation within similar, inner-neritic depositional environments that occur in the more upbasin areas (fig. 3). Gibson currently is conducting a study that compares the biostratigraphic distribution of benthonic species found in outcrop samples of the Brightseat, Aquia, and Nanjemoy Formations with those found in subsurface sections, for example at the Oak Grove, Solomons Island, Waldorf, and Putney Mill coreholes (fig. 1).

Other benthonic species in this region have local extinction horizons that are identical to or similar to those reported far outside the study area. The most prominent example of this is Tappanina selmensis. Van Morkhoven and others (1986) recorded that this species becomes extinct in deeper water deposits in the world oceans at the end of planktonic Zone P6b (equivalent to the middle part of Zone NP 11). This species becomes extinct in Virginia and Maryland in the lower part of Zone NP 10 - within the lowest 10 feet of the Nanjemoy Formation in several core holes (Gibson and others, 19BO). In Alabama, this species also disappears in the lower part of Zone NP 10 in the lower part of the Bashi Formation (Gibson, unpubl. data).

s:- :c ~ <.)

o a.. UJ

UJ z UJ

8 UJ

w z w <.)

0 W .-J < a..

~ >--I (i) a: Lfi w

a: a.. >-

FORMATIONS OF VIRGINIA AND MARYLAND

NANJEMOY FORMATION

MARLBORO CLAY

AQUIA FORMATION

I III1 I I I I

I

I I I I I I I I I

I I

I' I .11 I I .1 , I I I

I I I I

11II I I I I

I I I I I I I I I I I

II I I I I FIGURE 3. Range chart of important species Of benthonic and planktonic foraminifers in Paleocene to lower Eocene strata of Maryland and Virginia; species ranges modified from Gibson and others, ~ 980.

21

I

I

BIOSTRATIGRAPHY

Brightseat Formation - early Paleocene Zone NP 3

The Brightseat Formation occurs m scattered exposures that are east of Washington, D.C. in Prince Georges County, Maryland and northeast to Anne Arundel County in central Maryland. Subsurface samples of this formation were obtained from the Solomons Island and Waldorf coreholes in southern Maryland (fig. 1). No Brightseat strata are known from northern and central Virginia. Gibson and others (1980) originally identified Brightseat strata in the Oak Grove core hole in northern Virginia. Subsequent pollen studies by Frederiksen (1991), which placed these strata in the upper Paleocene, make it highly unlikely that these sediments are in the Brightseat Formation. The Brightseat is early Paleocene in age in every other sample where it can be dated. Calcareous nannofossils placed this entire formation within Zone NP 3, based on the presence of Chiasmolithus danicus (FAD at the base of Zone NP 3) and the absence of members of the genus Ellipsolithus (first occurs at base of Zone NP 4).

The occurrence of the planktonic foraminifers Globoconusa daubjergensis, Planorotalites compressa, and Subbotina pseudobulloides places these strata in the middle to upper part of Zone PI, which supports an early Paleocene, Zone NP 3, age. Numerous benthonic foraminiferal species that occur in the Brightseat are not present in sediments overlying this formation (Page, 1959; Gibson, unpubl. data).

The Brightseat Formation can be correlated with the lower part of the Hornerstown Formation of New Jersey, which contains sediments assigned to both Zone NP 3 and Zone NP 4 (fig. 2). In the Gulf Coastal Plain, sediments of Zone NP

22

3 age occur in the Clayton Formation and the Porters Creek Formation of Alabama and western Georgia (Gibson and others, 1982).

Aquia Formation - late Paleocene Zones NP 5-NP 9

The Aquia Formation is exposed in numerous outcrops in southern Maryland near Washington, D.C., in northeastern Virginia near Aquia Creek., and along river systems further to the south in Virginia. The Waldorf and Solomons Island core holes in Maryland and the Oak Grove corehole in Virginia (fig. 1) penetrated the entire Aquia Formation. The Putney Mill corehole was not drilled deeply enough to penetrate Aquia strata.

The Aquia Formation spans much of late Paleocene time. At least some portions of Zones NP 5, NP 6, NP 7, NP 8, and NP 9 are present at the type section of the Aquia Formation along Aquia Creek. Although all of the late Paleocene calcareous nannofossil zones are represented here, many of these zones are represented by a very thin sedimentary record; disconformities of a greater or lesser time interval are assumed to separate many of the zones. The oldest calcareous nannofossil-bearing Aquia strata, which are exposed at Aquia Creek and at numerous exposures in Prince Georges County in southern Maryland, are assigned to the upper part of Zone NP 5, based on the presence of FCUlciculithus tympaniformis and Heliolithu8 cantabriae. Strata that are in Zone NP 5, but which do not contain the upper Zone NP 5 indicator Heliolithus cantabriae, are present in the Solomons Island., Oak Grove, and Waldorf coreholes. Strata belonging to Zone NP 6 and/or NP 7 are well represented in the Aquia Formation outcrops near Washington, D.C., along the Potomac River in the vicinity of Aquia Creek, and at the

Oak Grove corehole in northern Virginia. HelwUthus kkinpellii, the FAD of which marks the base of Zone NP 6, is present in these samples. At the Aquia type locality along Aquia Creek, it is possible to distinguish Zone NP 7 from Zone NP 6 based on the presence of Discoaster mohleri (FAD can be used to appro:rim.ate the base of Zone NP 7). This species, however, has not been identified in the Aquia Formation at any other localities. Zones NP 8 (recognized by the presence of Heliolithus riedelii) and NP 9 (recognized by the first occurrence of Discoaster multiradiatus) occur throughout the study area.

Evidence for several disconformities of varying duration within the shallow­marine sequence can be seen both in outcrop and in subsurface sections. For example, a significant unconformity occurs in the Solomons Island and Waldorf coreholes; here strata placed in Zone NP 5 are overlain by strata placed in Zone NP 8. There also is a shoaling upward sequence at the top of the Aquia that is separated from the overlying marginal marine sediments of the Marlboro Clay by a disconformity of apparently short duration within Zone NP 9 in the Aquia Creek area; this disconformity is found throughout much of the area where these two formations occur.

A limited amount of supporting biostratigraphic data for Aquia strata is provided by the planktonic foraminifers. The planktonic foraminifer Morozovella angulata, which occurs in low frequency in some samples from the lower and middle part of the Aquia, has a range from the base of the M. angulata Zone (Zone P3 of Blow, 1969) to the upper middle part of the Planorotalites pseudomenardii Zone (Zone P4) (Toumarkine and Luterbacher, 1985). This level is approximately equal to the upper part of Zone NP 8 according to Berggren and others (1985). The highest occurrence of M. angulata in the Aquia

23

Creek section is in the middle part of bed 6 of Clark and Martin (1901) in the same sample that contains calcareous nannofossils characteristic of Zone NP 8.

Loeblich and Tappan (1957) recordedP. pseudomenardii from their Aquia Creek section at 15 to 17 feet above beach level; this height is most likely within bed 6. Zone P4 is the total range zone of Planorotalites pseudomenardii, and this occurrence substantiates a Zone NP 8 placement. The listing of this species by Loeblich and Tappan in probable bed 6 sediments is the only recorded occurrence that can be tied reasonably closely to the middle part of the outcropping Aquia. Although Nogan (1964) reported P. pseudomenardii from the Aquia Creek section, no detailed locality data were given with which individual beds can be determined. N ogan also recorded this species from outcrops along Cabin Branch in Prince Georges County, where only the lower Aquia is exposed, and from Piscataway Creek, where lower and middle Aquia are exposed. In the Oak Grove corehole (Gibson and others, 1980), P. pseudomenardii was found in a six-foot interval that was placed in Zone NP 8 on the basis of calcareous nannofossils. Planorotalites pseudomenardii is one of the more abundant late Paleocene marker species found in the somewhat deeper­water strata of the coreholes.

There is a significant change in the benthonic foraminiferal assemblages between the lower and upper parts of the Aquia Formation. An extinction horizon, which occurs in the Oak Grove Corehole at 372 ft (Gibson and others, 1980), corresponds to the calcareous nannofossil Zone NP 8·NP 9 boundary and suggests that there is a hiatus at this depth in the Oak Grove corehole. Cibicides neelyli, C. howelli, Cibicidoides marylandicus, Pararotalia perclara, and Marssonella conica are benthonic species that are only present in the lower part of the Aquia

below this depth. A few species, however, such as Anomalinoidespseudowelleri, have their first appearance in the upper strata. Currently, we are examining assemblages from the Aquia Creek outcrop sections tD see if there are corresponding benthonic foraminiferal changes across the Zone NP 8-Zone NP 9 boundary at this location.

A large-scale extinction of deep-sea foraminiferal species and the presence of low-oxygen species occurs near the Paleocene-Eocene boundary in oceanic sections (Miller and others. 1987; Thomas, 1989; Kennett and StDtt, 1991). In Maryland and Virginia, only a limited number of species become extinct near the end of the Paleocene at the top of the Aquia Formation. However, a significant number of benthonic species do have their first appearance in the basal Eocene strata. of the Nanjemoy Formation. Some of the species from the Nanjemoy Formation suggest low-oxygen environments (Gibson and others, 1980; Gibson, unpubl. data). Low-oxygen foraminiferal faunas, which were deposited in middle-to-outer neritic environments, occur in the upper Paleocene and lower Eocene sediments of the Manasquan Formation of New Jersey (Gibson and others, 1991). The possible low-oxygen sediments of the Nanjemoy probably correlate with the Zone NP 10 low-oxygen sediments of the Manasquan. The late Paleocene foraminifers of the Aquia Formation do not contain low­oxygen faunas; the sediments of the Aquia were deposited in very shallow-marine environments under high-energy, agitated, and oxygenated conditions. The uppermost Paleocene Marlboro Clay may be equivalent in time to the Zone NP 9 low­oxygen deposits of New Jersey, but these sediments were deposited in water too shallow and too brackish to support calcareous foraminiferal assemblages.

The Aquia Formation correlates with the Vincentown Formation of New Jersey, which has strata also spanning Zones NP

24

5-NP 9. In the Gulf Coastal Plain, the Nanafalia Formation (upper Zones NP 5 through lower NP 9) and the Tuscahoma Formation (Zone NP 9) correlates with the Aquia Formation.

Marlboro Clay - late Paleocene upper Zone NP 9

The Marlboro Clay is a marginal marine unit that occurs in varying thicknesses of less than a foot to 20 feet throughout the study area. Although the generally massively~bedde~ brick red and gray clays of the Marlboro appear to be an unlikely source of calcareous microfossils, we routinely sample and examine some intervals for calcareous nannofossils and foraminifers. In the Waldorf and Putney Mill coreholes, more coarsely-grained, glauconitic, thin laminae of presumed shallow-marine origin are interlaminated with relatively pure clay beds; these glauconitic laminae contain calcareous nannofossils that indicate placement within Zone NP 9. These laminae in the Waldorf corehole occur near the top of a thick, continuous, section of the Marlboro, which suggests that in this corehole, and probably in most of the other coreholes, the entire Marlboro is of late Paleocene age. Frederiksen and others (1982) postulated that the Marlboro Clay spanned the Paleocene-Eocene boundary on the basis of a change in the pollen assemblage wi thin the Marlboro. The calcareous nannofossil data, however, indicate that the Marlboro Clay is more likely entirely Paleocene in age.

Only five, agglutinated foraminiferal species were recovered from the Marlboro Clay, and they do not have any known age significance.

On the basis of its stratigraphic position near the tDp of the Paleocene (uppermost Zone NP 9), the Marlboro correlates with lithologically-similar clay

beds from the lower part of the Manasquan Formation of New Jersey.

Nanjemoy Formation - early Eocene Zones NP 10-NP 13

The Nanjemoy Formation is well exposed along the Potomac River and along river systems in southern Maryland and in northern and central Virginia. The Waldorf, Solomons Island, Oak Grove, and Putney Mill coreholes penetrated the entire Nanjemoy. The Nanjemoy contains sediments that can be placed in the lower Eocene calcareous nannofossil Zones NP 10, NP 11, NP 12, and NP 13. The first appearance datum (FAD) of Tribrachiatus bramlettei marks the base of Zone NP 10, which according to Berggren and others (1985) is the base of the Eocene. T. bramlettei is present in basal Nanjemoy samples from the Waldorf and Solomons Island coreholes and along the Potomac River. Thus, the Paleocene-Eocene boundary (Zone NP 9-NP 10 boundary) probably occurs at the Marlboro-Nanjemoy contact. The lowest Nanjemoy sample examined in the Oak Grove corehole, however, does not contain Tribrachiatus bramlettei, and there is a possibility that these sediments are still Paleocene in age (Zone NP 9) and that the Zone NP 9-NP 10 boundary occurs wi thin the lower part of the Nanjemoy. This would be similar to the situation in New Jersey where the Paleocene-Eocene boundary occurs within the lower part of the Manasquan Formation. The U.S. Geological Survey recently drilled the Loretto corehole near the Oak Grove corehole, and samples from the lower Nanjemoy will be examined in this new corehole in order to determine an accurate age for the basal Nanjemoy in this part of Virginia

Significant post-Nanjemoy stripping of sediments in the study area determined what portions of the Nanjemoy Formation

25

are presently preserved. Although stripping occurred on a regional basis, local variations in the presence and thickness of calcareous nannofossil zones from corehole to corehole and outcrop to outcrop may be controlled in part by faulting (Mixon and Powars, 1984). The higher, and thus younger, portions of the Nanjemoy in the more upbasin areas are missing, and in the Waldorf corehole only Zones NP 10 and NP 11 are present. In the Oak Grove corehole, Zones NP 10 and NP 11 also are well represente~ but there is only one sample from Zone NP 12, and Zone NP 13 is missing entirely. This may reflect local faulting or deeper erosion because in the nearby field trip area along the Potomac River, Zones NP 10, NP 11, NP 12, and possibly Zone NP 13 are well represented. In the Putney Mill corehole to the south, Zones NP 10 through NP 13 are present. In more downbasin sections, such as in the Solomons Island corehole, the Nanjemoy contains thick sections of Zones NP 10, NP 11, NP 12, and NP 13.

The LAD of Tribrachiatus contortus is used to mark the top of Zone NP 10, and the FAD of Discoaster lodoensis marks the base of Zone NP 12. The LAD of Tribrachiatus orthostylus is the marker for the top of Zone NP 12.

Planktonic foraminiferal assemblages in the Nanjemoy are scarce and have low diversity. Most species of Morozovella, a planktonic foraminiferal genus that is used to zone the early Eocene, are conspicuously abs.ent from the Nanjemoy. The few age­diagnostic forms that are found agree with the calcareous nannofossil zonation. Some samples from the lower part of the Nanjemoy contain Morozovella 8ubbotinae, which ranges from the uppermost Morozovella. velascoensis Zone (P6a = uppermost Zone NP 9) to the middle of the Morozovella aragonensis Zone (P8 = parts of Zones NP 12 and NP 13), and Acarinina wilcoxensis, which ranges from the middle of the M. velascoensis Zone (P5 = Zone 9)

to the top of the Morozovella formosa formosa Zone (P7 = part of Zones NP 11 and NP 12). Pseudohastigerina wiicoxensis, which has its FAD near the base of the Eocene (Berggren, 1971) and ranges up into the middle Eocene, occurs throughout much of the Nanjemoy.

The FAD's of numerous benthonic species occur either at the base or in the lower part of the Nanjemoy (fig. 3). Some of these species have relatively short stratigraphic ranges in the study area and become extinct in the lower and middle part of the Nanjemoy, whereas other species continue up through much or all of the formation. The extinction of Tappanina selmensis in the lower beds of the Nanjemoy, which were deposited in shallow-water environments, is discussed above in the Fossil Zonations and Datums section. This species has a cosmopolitan distribution throughout Upper Cretaceous into lowermost Eocene strata (Zone P6b = Zone NP 10 and part of Zone NP 11), according to Van Morkhoven and others (1986). In the Nanjemoy, T. selmensis has its LAD in the lower part of Zone NP 10. According to Berggren and others (1985) the base of Zone NP 10 correlates with the base of Zone P6b. This may reflect a more precise placement for the extinction level of this species, or it may represent an earlier disappearance in the shallow-water environments of the Nanjemoy in comparison to deeper-water environments.

The Nanjemoy Formation correlates with the middle part of the Manasquan Formation of New Jersey, which contains Zones NP 9-NP 14. In the Gulf Coastal Plain, the Bashi and Hatchetigbee Formations (Zones NP 10-NP 11) and the lower part of the Tallahatta Formation (Zones NP 12-14) of Alabama correlate with the Nanjemoy Formation.

26

Piney Point Formation - middle Eocene Zone NP 16 and possible Zone 17

The Piney Point Formation is absent in the Waldorf and Oak Grove coreholes, presumably because of subsequent erosion of these strata. In the Solomons Island corehole, sediments of the Piney Point are assigned to either Zone NP 15 or NP 16 of the middle Eocene. These two zones could not be separated easily in this corehole because no calcareous nannofossil species are present that are diagnostic of Zone NP 15 or Zone NP 16. However, large specimens of Reticulofenestra umbiUco. indicate that these sediments most likely belong to Zone NP 16. The Putney Mill corehole also contains sediments that provisionally are assigned to Zone NP 16 and one sample that may be in Zone NP 17 because it does not contain Chiasrnolithus SOlitU8, which has its LAD at top of Zone NP 16. DiMarzio (1984) examined strata of the Piney Point Formation that are exposed along the Pamunkey River, and he assigned these sediments to Subzone CP 14a of Bukry (1973; Okada and Bukry, 1980), based on the presence of Reticulofenestra umbilica and Chiasrnolithus solitus. This subzone is approximately equivalent to Martini's (1971) upper Zone NP 15 and Zone NP 16.

Age diagnostic planktonic foraminifers are not found in these relatively shallow­water sediments. Numerous first appearances of benthonic species in the Maryland Eocene occur in this formation. Many of these species were previously reported from the middle Eocene Castle Hayne Formation in North Carolina (Jones, 1983).

In New Jersey, portions of the Shark River Formation (Zones NP 14-NP 18) correlate with the Piney Point Formation. In Alabama, much of the Lisbon Formation (Zones NP 15-17) correlates with the Piney Point Formation.

Chickahominy Formation - late Eocene Zone NP 19/20

The Chickahominy Formation was described by Cushman and Cederstrom (1945) from subsurface sections in eastern Virginia. This formation is known only from subsurface sediments in eastern Virginia and far eastern Maryland, Delaware, and New Jersey (Gibson, 1970). Calcareous nannofossils were examined from two Chickahominy samples collected from a corehole 20 miles southeast of the Putney Mill corehole. The samples indicate placement in the late Eocene Zone NP 19/20. There are no other calcareous nannofossil data for this formation.

Cushman and Cederstrom (1945) in their original study of the Chickahominy described a distinctive benthonic foraminiferal assemblage. Gibson examined planktonic foraminifers from the type wells. Although the original material was from drillhole cuttings, they appear to have been sampled very carefully and exhibit little obvious contamination. Planktonic marker species from the type interval of the Chickahominy include Globigerina a ngiporo ides, Hantkenina alabamens is I and Turborotalia cerroazulensis cerroazulensis; these species indicate a late Eocene age (Zone PIS-PIB).

REFERENCES

Bagg, RM., Jr., 1898, The Tertiary and Pleistocene Foraminifera of the middle Atlantic slope: Bulletins of American Paleontology, v. 2, no. 10, p. 1-54.

---------, 1901, Protozoa: In Maryland Geological Survey, Eocene, p. 233-258.

Berggren, W.A, 1971, Tertiary boundaries and correlations: In Funnell, B.M. and Riedel, W.R., eds., Micropaleontology of the Oceans, Cambridge University Press, p. 693-809.

Berggren, WA, Kent, D.V., Flynn, J.J., and Van Couvering, J.A, 1985, Cenozoic

27

geochronology: Geological Society of America Bulletin, v. 96, p. 1407-1418.

Blow, W.H., 1969, Late middle Eocene to Recent planktonic foraminiferal biostratigraphy: In Proceedings of the First International Conference on Planktonic Microfossils, Geneva, 1967, E.J, Brill, Leiden, p. 199-422.

-----, 1979, The Cainozoic Globigerirrida: Leiden, The Netherlands, E.J. Brill, 1413 p.

Bukry, David, 1973, Low-latitude coccolith biostratigraphic zonation: In Edgar, N.T., and others, Initial reports of the Deep Sea Drilling Project, v. 15: Washington, D.C., U.S. Government Printing Office, p. 685-703.

------1978. Biostratigraphy of Cenozoic marine sediments by calcareous nannofossils: Micropaleontology, v. 24, p. 44-60.

Bybell, L.M., and Govoni, D.L., 1977, Preliminary calcareous nannofossil zonation of Brightseat and Aquia Formations (Paleocene) of Maryland and Virginia -stratigraphic implications: Abstract, American Association of Petroleum GeolOgists Bulletin, v. 61, p. 773·774.

Clark, W.B., and Martin, G.C., 1901, The Eocene deposits of Maryland: Maryland Geological Survey, vot1l-331, p. 21-92.

Cushman, J.A, 1944, Foraminifera from the Aquia Formation of Virginia: Contributions, Cushman Laboratory for Foraminiferal Research, v. 20, pt. 1, p. 17-28.

----------, 1948, Foraminifera from the Hammond well: Maryland Department of Geology, Mines, and Water Resources, Bulletin, v. 2, p. 213·267.

Cushman, J.A, and Cederstrom, D.J., 1945, An upper Eocene fOTarniniferal fauna from deep wells in York County, Virginia: Virginia Geological Survey Bulletin 67, p. 1-57.

DiMarzio, J.A, 1984, Calcareous nannofossils from the Piney Point Formation, PamWlkey River, Virginia: In Ward, L.W., and Kra.fit, Kathleen, eds., Stratigyaphy and paleontology of outcropping Tertiary beds in the PamWlkey River region, central Virginia Coastal Plain - Guidebook for

Atlantic Coastal Plain Geological Association 1984, p. 111-116.

Edwards, LE., 1989, Dinoflagellate cysts from the lower Tertiary formations, Haynesville cores, Richmond County, Virginia: U.S. Geological Survey Professional Paper 1489-C, p. CI-C12.

Edwards, L.E., Goodman, D.K., and Witmer, R.J., 1984, Lower Tertiary (Pamunkey Group) dinoflagellate biostratigraphy, Potomac River area, Virginia and Maryland: In Frederiksen, N.D., and Krafft, Kathleen, eds., Cretaceous and Tertiary stratigraphy, paleontology, and structure, southwestern Maryland and northeastern Virginia, American Association of Stratigraphic Palynologists Field Trip Volume and Guidebook, p. 137-152.

Frederiksen, N.O., 1979, Paleogene sporomorph biostratigraphy, northeastern Virginia: Palynology, v. 3, p. 129-167.

.-.-----., 1984, Lower Tertiary pollen biostTatigraphy, Maryland and Virginia: In Frederiksen, N.D., and Krafft, Kathleen, eds., Cretaceous and Tertiary stratigraphy, paleontology, and structure, southwestern Maryland and northeastern Virginia, American Association of Stratigraphic Palynologists Field Trip Volume and Guidebook, p. 163-168.

------, 1991, Midwayan (Paleocene) pollen correlations in the eastern United States: Micropaleontology, v. 37, no. 2, p. 101-123.

Frederiksen, N.O., Gibson, T.G., and Bybell, L.M., 1982, Paleocene-Eocene boundary in the eastern Gulf Coast: Gulf Coast Association of Geological Societies Transactions,v. 32,p. 289-294.

Gibson, T.G., 1970, Late Mesozoic·Cenozoic tectonic aspects of the Atlantic Coastal Margin: ~ological Society of America Bulletin, v. 81, p. 1813-1822.

Gibson, T.G., Andrews, G.W., Bybell, L.M., Frederiksen, N.O., Hansen, ThOI', Hazel, J.E., McLean, D.M., Witmer, R.J., and van Nieuwenhuise, D.S., 1980, Biostratigraphy of the Tertiary strata of the core: In Geology of the Oak Grove core, Virginia. Division of Mineral Resources Publication 20, p. 14-40.

28

Gibson, T.G., Bybel1, L.M., and Owens, J.P., 1991, Paleocene-Eocene boundary in southwestern New Jersey: a rare continuous section: Geological Society of America Abstracts with programs, v. 23, no. 1, p. 35.

Gibson, T.G., Mancini, E.A, and Bybell, L.M., 1982, Paleocene to middle Eocene stratigraphy of Alabama: Gulf Coast Association of Geological Societies Transactions, v. 32, p. 449-458.

Goodman, O.K., 1979, Dinoflagellate "communities" from the Lower Eocene Nanjemoy Formation of Maryland, U.S.A: Palynology, v. 3, p. 169-190 .

. --•. _ .. , 1984, Dinoflagellate biostratigraphy of the Nanjemoy Formation at Popes Creek, southeastern Maryland: In Frederiksen, N.O., and Krafft, Kathleen, eds., Cretaceous and Tertiary stratigraphy, paleontology, and structure, southwestern Maryland and northeastern Virginia, American Association of Stratigraphic Palynologists Field Trip Volume and Guidebook, p. 153-161.

Hazel, J .E., 1968, Ostracodes from the Brightseat Formation (Danian) of Maryland: Journal ofPs.leontology, v. 42, p. 100-142.

_ ..... _._-, 1969, Faunal evidence for an unconformity between the Paleocene Brightseat and Aquia Formations (Maryland and Virginia): U.S. Geological Survey Professional Paper 650-C, p. C58-C65.

Jones, G.D., 1983, Foraminiferal biostratigraphy and depositional history of the middle Eocene rocks of the coastal plain of North Carolina: North Carolina Geological Survey Special Publication 8, 4S p.

Kennett, J.P., and Stott, L.D., 1991, Abrupt deep-sea wanning, palaeoceanographic changes and benthic extinctions at the end of the Palaeocene: Nat.ure, v. 353, p. 225-229.

Loeblich, AR., Jr., and Tappan, Helen, 1957, Planktonic Foraminifera of Paleocene and early Eocene age from the Gulf and Atlantic coastal plains: U.S. National Museum Bulletin 215, p. 173-198.

Martini, Erlend, 1971, Standard Tertiary and Quaternary calcareous nann ()plankton zonation: Planktonic Conference, 2nd, Rome, 1969, Proceedings, p. 739-785.

Miller, KG., Janecek, T.R, Katz, M.E., and Keil, D.J., 1987, Abyssal circulation and benthic foraminiferal changes near the Paleocene/Eocene boundary: Paleoceanography, v. 2, p. 741-761.

Mixon, R.B., and P()warS, D.S., 1984, Folds and faults in the inner coastal plain of Virginia and Maryland: their effect on distribution and thickness of Tertiary rock units and local geomorphic history: In Frederiksen, N.O., and Krafft, Kathleen, eds., Cretaceous and Tertiary stratigraphy, paleontology, and structure, southwestern Maryland and northeastern Virginia, American Association of Stratigraphic Palynologists Field Trip Volume and Guidebook, p. 112-122.

Nogan, D.S., 1964, Foraminifera, stratigraphy, and paleoecology of the Aquia Formation of Maryland and Virginia: Cushman Foundation for Foraminiferal Research Special Publication 7, p. 1-50.

Okada, Hisatake, and BUKry, David, 1980, Supplementary modification and introduction of code numbers to the low­latitude coccolith biostratigraphic zonation (Bukry, 1973; 1975): Marine Micropaleontology, v. 5, no. 3, p. 321-325.

Page, R.A, 1959, Micropaleontology and stratigraphy of the Brightseat Formation: Unpublished PhD dissertation, Rutgers University, 166 p.

Perch-Nielsen, Katerina, 1985, Cenozoic calcareous nannofossils: In Bolli, H.M., Saunders, J.B., and Perch-Nielsen, Katerina, eds., Plankton stratigraphy: Cambridge, Cambridge University Press, p. 427-554.

Poag, C.W., 1989, Foraminiferal stratigraphy and paleoenvironments of Cenozoic strata cored near Haynesville, Virginia: U.S. Geological Survey Professional Paper 1489-D, p. Dl·D20.

Shifflett, Elaine, 1948, Eocene stratigraphy and Foraminifera of the Aquia Fonnation: Maryland Department of Geology, Mines and Water Resources Bulletin 3, p. 1-93.

29

Thomas, Ellen, 1989, Development of Cenozoic deep-sea benthic foraminiferal faunas in Antarctic waters: In Crame, J.A, ed., Origins and evolution of the Antarctic Biota, Geological Society Special Publication 47, p. 283-296.

Toumarkine, Monique, and Luterbacher, Hanspeter, 1985, Paleocene and Eocene planktic foraminifera: In Bolli, HM., Saunders, J.B., and Perch-Nielsen, Katerina, eds., Plankton stratigraphy: Cambridge, Cambridge University Press, p. 87·154.

Van Morkhoven, F.P.C.M., BerggTen, W.A, and Edwards, AS., 1986, Cenozoic cosmopolitan deep-water benthic foraminifera: Bulletin des Centres de Recherches Exploration­Production Elf-Aquitaine, Memoire 11, 421 p.

Weems, R.E., 1984, Vertebrate biozones of the Pamunkey Group (Paleocene and Eocene, Maryland and Virginia): In Ward, L.W., and Krafft, Kathleen, eds., Stratigraphy and paleontology of the outcropping Tertiary beds in the Pamunkey River Region, central Virginia Coastal Plain, p. 198-204.

.-------, 1988, Paleocene turtles from the Aquia and Brightseat Formation, with a discussion of their bearing on sea turtle evolution and phylogeny: Proceedings of the Biological Society of Washington, v. 101, no. I, p. 109-145.

Weems, R.E., and Honnan, S.R., 1983. Teleost fish remains (Osteoglossidae, Blochiidae, Scornbridae, Triodontidae, Diodontidae) from the lower Eocene Nanjemoy Fonnation of Maryland: Proceedings of the Biological Society of Washington, v. 96, no. 1, p. 38-49.

Whitney, B.L., 1984, Dinoflagellate biostratigraphy of the Maestrichtian­Danian section in southern Maryland: 1n Frederiksen, N.O., and Krafft, Kathleen, eds., Cretaceous and Tertiary stratigraphy, paleontology, and structure, southwestern Maryland and northeastern Virginia, American Association of Stratigraphic Palynologists Field Trip Volume and Guidebook, p. 123-136.

30

Reprinted from Frederiksen. N.O., IlDd Krafll, K., eds., 1984 , Cretaceous and Tertiary stratigraphy, paleontology, II.lid structure, southwestern Maryland Ilud northwellStern Virginia. American Association of SLrllligraphic Palyno\ogillts Field Trip VollJme and Guidebook.

LOWER TERTIARY (PAMUNKEY GROUP) DINOFLAGELLATE BIOSTRATIGRAPHY, POTOMAC RlVER AREA, VIRGINIA AND MARYLAND

Lucy E. Edwards l , David K. Goodman 2 and Roger J. Witmer3

lU.S. Geological Survey, 970 National Center, Reston, VA 22092 2AROO Oil and Gas Company, P.O. Box 2819, Dallas, TX 75221 3union Oil Company of California, P.O. Box 76. Brea, CA 92621

INTRODUCTION

The pamunkey Group in Virginia and Maryland consists of glauconitic sands and silts, often with abundant shells, and clays and silty clays. Dinoflagellate cysts in these sediments typically are abundant and well preserved. Some of the dinocyst floras are quite diverse (as many as 70 species per sample), suggesting normal marine conditions. Other floras are of low diversity, dominated by a single species. and may suggest estuarine, nearshore, or brackish conditions. The lowest Paleocene is absent in the Potomac River basin! the Brightseat Formation in Maryland represents the upper part of the lower Paleocene (Hazel ~ ~., in press) • The Brightseat (?) Formation in Virginia may represent the upper part of the lower Paleocene or the lower part of the upper Paleocene. 1'he remainder of the Paleocene and the lower Eocene is represented by nearly continuous deposition in the Aquia Formation, the Marlboro Clay, and the Nanjemoy Formation. The dinocysts in these sediments record a distinctive succession of species and have considerable potential for biostratigraphic analysis.

McLean (197la), Goodman (1975), and Witmer (1975) have detailed the dinoflagellates of the Pamunkey Group in unpublished theses. Published works of a taxonomic or descriptive nature include McLean (1971b, 1972, 1973a, 1973b, 1974, 1976), Goodman (1979), and Edwards (19B2). Goodman (1979) provided a detailed account of the quantitative distribution of cyst species in the upper part of the N.anjemoy near Popes Creek, Maryland. Dinoflagellate biostratigraphy of the Pamunkey Group in the Oak Grove core in northern Virginia (Text - Figure 1) was given in Gibson !:!.~. (1980). Additional preliminary biostratigraphic data were also discussed in abstracts by Witmer and Goodman (1980) and Edwards and Witmer (19B3) .

The poorly exposed nature of Coastal Plain outcrops makes detailed biostratigraphy difficult. Recently, however, more than a dozen coreholes have been dr illed by or for the U.S. Geological Survey in the Virginia Coastal Plain. These coreS allow much refinement of the dinoflagellate succession. The purpose of this chapter is to summar ize br iefly the important occurrences of selected dinocysts in cores taken near the field trip stops and at several outcrops near the field trip stops (Text-Figure 1). Text-Figure 2 shows the ranges as assembled using graphic correlation (technique modified from Shaw, 1964) from four cores in northern Virginia at Oak Grove, Ashton, Lake Jefferson, and ForI: McLean. Ranges from the Popes Creek sections in southern Maryland (field trip Stop 8) have been incorporated by inspection. A brief discussion of the formations and the significant dinocyst ranges follows.

31

N

Fort

o 5

I I I o 5 10

Virginia

10 Miles I

I 15 Kilometers

• Lake Jefferson core

Maryland

Popes Creek

core

Text-Figure 1. Index map showing the location of principal cores and outcrop sections used to compile the ranges in the present study.

32

BRIGHTSEAT (7) FORMATION

As noted in Gibson ~ al. (1980), the lower 41 feet of the Paleocene in the Oak Grove core lacks calcareous mater ial and contains a dinocyst flora that is noticeably older than the overlying shelly beds of the Aquia Formation. This noncalcareous unit is also present at field trip Stop 4, where it is a very micaceous sand, and in the Ashton and Fort McLean cores. It is apparently absent in the Lake Jefferson core, possibly owing to the Skinkers Neck structure of Mixon and Powars (this volume) . This unit is questionably referred to the Brightseat Formation in the present chapter. The dinocyst flora of the Brightseat in Maryland is treated" in Whitney (this volume).

Palaeoperidinium pyrophorum (Plate 1, fig. 4) is found in the Brightseat(7) but not in younger material. Glaphrocysta exuberans­complex (Plate 2, fig. 1) is relatively abundant. Fibradinium annetorpense is common and ?Danea californica (Plate 1, fig. 3) is often present.

AQtJIA FORMATION

The Aquia Formation is a massive-bedded, fine, glauconitic quartz sand, locally calcareous, containing horizons of abundant shell (typically Turritella mortoni). The formation has been divided into a lower member, the Piscataway, and an upper member r the Pa"spotansa (Clark and Martin, 1901), recently revised by ward (in press) .

The lower Aquia (Piscataway Member, as revised and restricted by Ward, in press) bears a relatively low-diversity dinoflagellate flora dominated by the Glaphrocysta exuberans-complex and locally by Deflandrea cf. ~ dartmooria (Plate 1, fig. 7). The lowest occurrence of Deflandrea phosphoritica is found in the lower Aquia. The lower Aquia can be subdivided by means of dinoflagellates into a lower zone containing Fibradinium annetorpense and an upper zone above the last appearance of this species. Xenikoon australis is present in the lower Aquia; its last appearance is at the top or perhaps just below the top of the Piscataway. Adnatosphaeridium robustum, an unnamed species of Cassidium (Plate 2, fig. 6), and, less consistently, Eocladopyxis peniculata, first occur in the upper Piscataway.

The upper Aquia (Paspotansa Member, as revised by Ward, in press) is marked by an influx of species including Kallosphaeridium brevibarbatum and an unnamed spec ies of Impag id inium (Plate 3 r fig. 7). Apectod inium homomorphum has its lowest occurrence at the base of the upper Aquia in some cores and slightly above the base in others; it becomes increasingly dominant upwards in the Aquia.

On the basis of Foraminifera, Gibson ~ a1. (1980) suggested a shallow marine environment for the lower Aquia, with the formation representing gradually deepening and then shoaling conditions. The abrupt termination of foraminifer and dinoflagellate species and the influx of new species suggest a possible diastem at the Piscataway­Paspotansa boundary. Nogan (1964), McLean (197la) and Gibson et al. (1980) suggest a gradual shoaling within the upper Aquia to the brackish

33

.. ::i <I)

ILl .., a:: t,;) W c( I/)

r- - r---S3

54 W Z

55 w (.)

0 W

- 56

-57 -

..

58 ·

w 59 Z

UJ U 0 60 UJ ...J c(

? a.

z 0 ~ « ::i a:: 0 u.

z 2 I-« ::I II: 0 ... ~

0 ::Ii 11/ ., z '" z

m 0

'" 0

}I :z: 0

:!; =>. 0;( "'a:

0

~ ~ 'r::li 0"-Ii ..

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Z :;)

700"

2'50

300

3S0

400

450

. ~

1111

.. u

" N _..., ...

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I I

Text-Figure 2. Ranges of selected dinoflagellates in the Pamunkey Group in the Potomac River area. Vertical scale units are derived from the actual measured footage at Oak Grove, but the ranges are composites based on the sections and outcrops shown in Text-Figure 1. Ages in mega-anni (Ma) are from Hazel et al. (in press). Dashed ranges indicate that the range of a given taxon is known to extend up or down based on personal observations from other sections in the Virginia Coastal Plain.

34

conditions of the overlying Marlboro C~?y.

According to Gibson et~. (1980), the Aquia Formation spans most of the late Paleocene, from nannofossil zones NP 5 to NP 9 (Martini, 1971) . The first occurrence of Apectodinium homomorphum is an important biostratigraph ic datum and roughly approximates the base of NP 9 (Costa and Downie, 1976; Jan du Chene, 1977). Many of the dinoflagellate species found in the Aquia Formation are also known from the Gulf Coast of the united States (Edwards, 1980). The succession of first and last occurrences varies somewhat in the two areas, and more details need to be clarified.

MARLBORO CLAY

The Mar Iboro Clay is a ligh t-grey to redd ish-brown, compact clay that at some localities lies between the Aquia and Nanjemoy Formations. The lower boundary of the Marlboro consists of layers of clay interbedded with or burrowed into typical Aquia lithology. The upper part of the Marlboro Clay bears sand-filled burrows from the overlying Nanjemoy Formation.

Dinoflagellate diversity is low in the Marlboro. Seneqalinium? dilwynense is the only abundant species. Phelodinium rnagnificum-complex (Plate 1, fig. 9) and Fromea fragilis have their highest appearances within the Marlboro. Muratodinium fimbriatum has been found in the upper Marlboro Clay.

Sporomorph data (Freder iksen, 1979; Gibson ~ ~., 1980) indicate that at least the lower part of the Marlboro Clay is of late Paleocene age. Brenner ~ a1. (1979) and Frederiksen (l979) suggested that the Paleocene-Eocene boundary lies within or at the top of the Marlboro. The Marlboro Clay contains sporomorphs, dinoflagellates, Pseudoschizaea, and agglutinated Foraminifera (Gibson ~ ~., 1980), suggesting a brackish­water environment of deposition.

NANJEMOY FORMATION

The Nanjemoy Formation is a variably clayey, fine, glauconitic quartz sand, with horizons of abundant shell (typically Venericardia). The formation has been divided into a oore clayey lower member, the Potapaco, and a typically sandier upper member, the Woodstock (Clark and Martin, 1901; see also Ward, in press).

The Potapaco Member of the Nanjemoy Formation is character ized by the abundant Ot consistent occurrence of Senegalinium? dilwynense, Deflandtea phosphoritica, Muratodinium fimbriatum, species of Areoligera and Adnatosphaeridium, and species of the Wetzeiiella-complex including Apectodinium homomocphu~, Wilsonidium tabula tum, Wetzeliella hampdenensis, and Wetzeliella varielongituda/samlandica. First occurrences of probable age significance are, in ascending order, Ascostomocystis hydria (base of the member), Wilsonidium tabulatum, Wetzeliella hampdenensis, Biconidinium longissimum, Emmetrocysta sp., Homotryblium tasmaniense, Achilleodinium bifotrnoides and Wetzeliella varielongituda/samlandica. Foraminiferal species diversities and

35

percentages of planktic species suggest deposited under inner to middle shelf transgressive phase (Gibson ~ al., 1980).

that the Potapaco str-ata were conditions dUring a general

The dinoflagellate flora in the Potapaco Member indicates correlation with the sequence from the base of the Eatonicysta ursulae (LC-2) Assemblage Zone (Bujak ~~., 1980) to the top of the Dracodinium similis Zone (Costa and Downie, 1976) of the Isle of Wight, England (see Goodman, this volume, for a more detailed discussion). These correlations suggest that the Potapaco corresponds to a late early Ypresian Age. The horizon marked by the massive appearance of Wilsoriidium tabulatum may represent the same hor izon noted by Jan du Ch~ne (1977) in the Schlieren Flysch of Switzerland.

The Woodstock Member of the Nanjemoy is characterized by the consistent occurrence of Wetzeliella varielongituda/samlandica, W. hampdenensis, Kisselovia coleothrypta, Spinidinium SPa of Goodman, 1979, and Eiconidinium longissimum (see Goodman, 1979, and this volume). Range bases with probable age significance are, in ascending order, Kisselovia coleothrypta, Homotryblium caliculum, B. tenuispinosum/pallidum, Hafniasphaera 9oodmanii, Spinidinium Spa of Goodman, 1979, and Wetzeliella SPa of Goodman, 1979. The Woodstock strata were deposited in inner to middle shelf environments (Gibson ~ al., 1980), which may have been punctuated by local transgressive-regressive pulses (Goodman, 1979).

Goodman (1979) noted the first OCCUrrence of ~ coleothrypta in the lower third of the Woodstock Member in the Popes Creek sections. This species has its lowest occurrence in the Oak Grove core a few feet above a lithologic change at 246 ft depth. We use these observations to suggest that the Potapaco-Woodstock boundary in the Oak Grove core should be placed at the lithologic change at 246 ft, rather than at 276 ft as suggested by Gibson ~~. (1980). (See also, Ward, in press.)

Dinoflagellate stratigraphy indicates that the Woodstock Member is correlative with the upper part of the Eatonicysta ursulae (LC-2) Assemblage Zone, the Kisselov ia reticulata (LC-3) Assemblage Zone, and part of the Homotryblium abbreviatum (B-1) Assemblage Zone (Bujak ~ al., 1980) on the Isle of Wight (equivalent to the Wetzeliella varielongituda Zone and the lower part of the Kisselovia coleothryPta Zone of Costa and Downie, 1976). These correlations suggest a middle to late Ypresian Age for these strata (see Goodman, this volume, for more discussion).

ACKNOWLEDGMENTS

The authors thank those who helped make this study possible including D. M. McLean, R. E. Mixon. and L. W. Ward. Helpful suggestions were made by N. O. Frederiksen and T. G. Gibson. Publication authorized by the Director, U.S. Geological Survey on September 20, 1984. Published wi th permission of Arco Oil and Gas Company and Union Oil Company of California.

36

References

BRENNER, G. J., PATRICELLI, JUDITH, and RACHELE, LINDA 1979 Palynology of the Paleocene-Eocene sediments from PGDf-35

well, Prince Georges County, Maryland (U.S.A.) (abs.). Palynology, 3:280.

BUJAK, J. P., DOWNIE, C., EATON, G. L., and WILLIAMS, G. L. 1980 Dinoflagellate cyst zonation of the Eocene, southern

England. In: Bujak, J. P., Downie, C., Eaton, G. L, and Williams, G. L., Dinoflagellate cysts and acritarchs from the Eocene of southern England. Palaeontolog ieal Association of London, Special Papers in Palaeontology No. 24:15-26.

CLARK, W. B., and MARTIN, G. C. 1901 The Eocene deposits of Maryland. Maryland Geoloq ical

COSTA, L. I., 1976

EDWARDS, L. E. 1980

1982

Survey, Eocene Volume, 331 p. and DOWNIE, C. The distribution of the dinoflagellate Wetzeliella in the Palaeogene of northwest Europe. Palaeontology, 19:591-614.

Dinoflagellate stratigraphy: a first look. ~: Reinhardt, J., and Gibson, T. G., upper Cretaceous and lower Tertiary geology of the Chattahoochee River Valley, western Georgia and eastern Alabama • ..!.r!.: Frey, R. W. (ed.), Excursions in southeastern geology, v. 2. Geological Society of America, Annual Meeting (93rd) Atlanta 1980, Field Trip Guidebooks, p. 424-427. Biostratigraphically important species of Pentadinium Gerlach, 1961, and a likely ancestor, Hafniasphaera goodmanii n. sp., from the Eocene of the Atlantic and Gulf Coastal Plains. Palynology, 6:105-117.

EDWARDS, L. 1983

E., and WITMER, R. J. Paleocene and early Eocene dinOflagellate zonation, Virginia Coastal Plain (abs.). American Association of Stratigraphic Palynologists, Inc., 16th Annual Meeting San Francisco, Program and Abstracts, p. 13-14.

FREDERIKSEN, 1979

N. O. Paleogene sporomorph biostratigraphy, northeastern Virginia. Palynology, 3:129-167.

GIBSON, T. G., ANDREWS, G. W., BYBELL, L. M., FREDERIKSEN, N. 0., HANSEN, T., HAZEL, J. E., MCLEAN, D. M., WITMER, R. J., and VAN NIEUWENHUISE, D. S.

1980

GOODMAN, D. 1975

1979

K.

HAZEL, J. E., In press

Part 2: Biostratigraphy of the Tertiary strata of the core. In: Geology of the Oak Grove Core. Virg inla Division of Mineral Resources Publication 20:14-30.

Lower Eocene Dinoflagellate Assemblages from :the Maryland Coastal Plain South £!. Washington, D.C. Unpu.blished M.S. thesis, Virginia Polytechnic Institute and State University, 298 p. Dinoflagellate "communities" from the lower Eocene Nanjemoy Formation of Maryland, U.S.A. Palynology, 3:169-190. EDWARDS, L. E., and BYBELL, L. M. Significant unconformities and the hiatuses represented by

37

Figure 1

PLATE 1

Cyclopsie11a? sp. R 3020 A (I), Office Ball core, King George County, Va., Brightseat(?) Formation, orientation unknown, 62SX.

2 Cannosphaeropsis sp. R 3020 B (3), Office Hall core, King George County, Va., Brightseat{?) Formation, right lateral view, 600X.

3 ?Danea californica (Drugg) Stover & Evitt VPISUPL-307 (AL-15), Oak Grove core, Westmoreland County, Va., Brightseat(?) Formation, dorsal view, 475X.

4 Palaeoperidinium pyrophorum (Ehrenberg) Sarjeant VPISUPL-303 (AD-2), Oak Grove core, Westmoreland County, Va., Brightseat(?) Formation, dorsal view of ventral surface, 325X.

5 Fibradinium annetorpense Morgenroth VPISUPL-308 (A0-17), Oak Grove core, Westmoreland County, Va., Aquia Formation, ventral view of dorsal surface, 7S0X.

6 Xenikoon australis Cookson & Eisenack VPIStJPL-309 (A0-19), Oak Grove core, Westmoreland County, Va., Aquia Formation, orientation unknown, SOOX.

7 Deflandrea cf. D. da·rtmoor 1a Cookson & Eisenack R 2868 Bt Ashton core, King George County, Va., Brightseat(?) Formation, dorsal view, SEM, 600X.

8 Caligodinium amiculum Drugg VPIStJPL-306 (A0-10), Oak Grove core, Westmoreland County, Va., Aquia Formation, orientation unknown, 4S0X.

9 Phe10dinium magnificum-comp1ex R 3020 K (2), Office Hall core, King George County, Va., Aquia Formation, dorsal view of dorsal surface, 600X.

10 Fromea fragilis (Cookson & Eisenack) Stover & Evitt R 3107 J (2), Carters Corner core, Caroline County, Va., Aquia Formation, orientation unknown, 400X.

38

PLATE 1

1

2

3

5

4

6

8

7 9

10

39

Figure 1

PLATE 2

Glaphrocysta exuberans-complex VPISUPL-309 (~o-l9), Oak Grove core, westmoreland County, Va., ~quia Formation, ventral view of ventral surface, 400X.

2 Diphyes colligerum (Deflandre & Cookson) Cookson VPISUPL-264 (AL-55) Popes Creek sections, Char les County, Md., Nanjemoy Formation, dorsal view of ventral surface, 650X.

3 Seneqalinium? dilwynense (Cookson & Eisenack) Stover & Evitt VPISUPL-323 (Ao-47), Oak Grove core, Westmoreland County, Va., Marlboro Clay, ventral view of ventral surface, 57SX.

4 Turbiosphaera filosa (Wilson) Archangelsky VPISUPL-3l2 (A0-24) I Oak Grove core, Westmoreland County, Va., Aquia Formation, dorsal view of dorsal surface, 400X.

5 ?~ndalusiella rhombohedra (Benson) Stover & Evitt R 3020 J (2), Office Hall core, King George County, Va., Aquia Formation, dorsal view of dorsal surface, pericyst missing, 375X.

6 Cassidium sp. VPISUPL-361 (A0-35), Oak Grove core, Westmoreland County, Va., Aquia Formation, orientation unknown, 400X.

7 Deflandrea phosphor i tica EisenacK R 3020 J (2), Office Hall core, King George County, Va., Aquia Formation, dorsal view of dorsal surface, 375X. '

8 Protoperidinium? sp. VPISUPL-330 (A0-68), Oak Grove core, Westmoreland County, Va., Nanjemoy Formation, ?dorsal view, 450X.

9 Adnatosphaeridium robustum (Morgenroth) De Coninck VPISUPL-316 (A0-35), Oak Grove core, westmoreland County, Va., Aquia Formation, orientation unknown, SOOX.

10 Eocladopyxis peniculata Morgenroth VPISOPL-3l6 (A0-35) I Oak Grove core, Westmoreland County, Va., Aquia Formation, orientation uncertain, 450X.

11 Turbiosphaera magnifica-cornplex R 3020 \J (2), Office Hall core, King George County, Va., Aquia Formation, right-lateral view, 400X.

>

-- ~--- - ------ -",

40

PLATE 2

1 2 3

41

Figure 1

PLATE 3

Muratodinium fimbriatum (Cookson &-Eisenack) Drugg R 2668 J, Wilcox Camp core, Caroline County, Va., Nanjemoy Formation, dorsal view, SEM, 540x.

2 Apectodinium homomorphum-complex R 2868 I (2), Ashton core, King George County, Va., Aquia Formation, dorsal view of dorsal surface, 375X.

3 Kallosphaeridium brevibarbatum De Coninck VPISUPL-245 (AK-42), Popes Creek sections, Charles County, Md., Nanjemoy Formation, ventral view of ventral surface, SOOX.

4 Catillopsis abdita Drugg R 3020 0 (2), Office Hall core, King George County, Va., Marlboro Clay, orientation unknown, 600X.

5 Lingulodinium machaerophorum (Deflandre & Cookson) Wall R 2664 AA (2), Lake Madison core, King George County, Va., Aquia Formation, apical view, 720X.

6 Ascostomocystis hydria Orugg & Loeblich R 2668 J, Wilcox Camp core, Caroline County, Va., or ientation unknown, SEM, 660X.

7 Impagidinium sp. R 2386 E, WF-2 core, Caroline County, Va., dorsal view, SEM, 600X.

8 Wetzeliella hampdenensis Wilson VPISUPL-266 (AL-68), Popes Creek sections, Charles County, Md., Nanjemoy Formation, dorsal view of dorsal surface, 320X.

9 Wilsonidium tabulatum-complex R 2668 K, Wilcox Camp core, Caroline County, Va., Nanjemoy Formation, dorsal view, SEM, 600X.

10 Biconidinium lonqissimum Islam VPISUPL-241 (AK-l3), Popes Creek sections, Charles County, Md., Nanjemoy Formation, ventral view at mid-focus, 360X.

11 Ermnetrocysta Spa R 2664 H (2), Lak~ Madison core, King George County, Va., Nanjemoy Formation, antapical view of antapex, 600X.

42

PLATE 3

: \

2

4

7

\ '

0,..,.

I,,~ f t - ,

~;~.~ 'W l -(

H /1

, , 10

43

3

5

8

1 1

Figure 1

PLATE 4

Rhombodinium SPa i~.

R 2669 G (2), Lake Jefferson core, King George County, Va.,· Nanjemoy Formation, dorsal view of dorsal surface, 430X.

2 ~chilleodinium biformoides (Eisenack) Eaton VPISUPL-264 (At-51), Popes Creek sections, Charles County, Md., Nanjemoy Formation, ventral view at mid-focus, 320X.

3 Romotryblium tasmaniense Cookson & Eisenack VPISUPL-27l (AL-93). Popes Creek sections, Charles County, Ma., Nanjemoy Formation, antapical view of antapex, 375X.

4 Wetzeliella varielongituda/samlandica R 2285 W, Putneys Mill core, New Kent County, Va., Nanjemoy Formation, dorsal view, SEM, 600X.

5 Kisselovia coleothrypta (Williams & Downie) Lentin & Williams R 3020 AS (2), Office Rall core, King George County, Va., Nanjemoy Formation, dorsal view of dorsal surface, 400X.

6 Homotryblium caliculum Bujak VPISUPL-264 (At-54), Popes Creek sections, Charles County, Md., Nanjemoy Formation, antapical view of antapex, 420X.

7 Homotryblium tenu iseinosum/pallidum VPISUPL-264 (At-52), Popes Creek sections, Charles County, Md., Nanjemoy Formation, or ientation uncertain, 400X.

8 Hafniasphaera goodmanii Edwards R 1895 H, Popes Creek sections, Char les County, Md., Nanjemoy Formation, dorsal view, SEM, 600X.

9 Spinidinium SPa of Goodman, 1979 VPISUPL-337 (AG-84), Oak Grove core, Wesbnoreland County, Va., Nanjemoy Formation, dorsal view of ventral surface, 7S0X.

10 Wetzeliella sp. of Goodman, 1979 VPISUPL-264 (AL-52), Popes Creek sections, Cha.rles County, Md., ;-lanjemoy Formation, ventral view at mid-focus, 350X.

44

PLATE -4

3

1 2

6

4 5

9

.~- .

7 8

10

45

" JAN DU CHENE, 1977

MARTINI, E. 1971

A.

MCLEAN, D. M. 1971a

1971b

1972

1973a

1973b

1974

1976

NOGAN , D. S. 1964

SHAW, A. B. 1964

WARD, L. W. In press

WITMER, R. J. 1975

them in the Paleogene of the Atlantic and Gulf Coastal Province. In: Schlee, J-. S. (ed.), Interregional unconformities and hydrocarbon accumulations. American Association £f Petroleum Geologists Memoir 36. R. E. Palynostratigraphie (Maastrichtien-Eocene inferieur) des Flyschs du Schlieren (Canton d 'Obwald, Sllisse centrale). Revue de Micropaleontologie, 20(3):147-156.

Standard Tertiary and Quaternary calcareous nannoplankton zonation. In: Farinacci, A. (ed.), Proceedings, Second Planktonic Conference. Rome, Edizioni Tecnosciencza 2:739-785.

Organic-walled Phytoplankton from the Lower Tertiary Pamunkey Group £f Virginia and Maryland. Unpublished PhD. dissertation, Stanford University, 165 p. Transfer of Baltisphaeridium septatum Cookson & Eisenack, 1967, from the Acr i tarcha to the Dinophyceae. Journal of Paleontology, 45(4) :729-730. Cladopyxidium septatum, n. gen., n. sp., possible Tertiary ancestor of the modern dinoflagellate Cladopyxis hemibrachiata Balech, 1964. Journal of Paleontology, 46 (6) : 861-863. Emendation and transfer of Eisenackia (Pyrrhophyta) from the Microdiniaceae to the Gonyaulacaceae. Geologiska Foreningens i. Stockholm Forhandlingar, 95: 261-265. A problematical dinoflagellate from the Tertiary of Virginia and Maryland. Palaeontology, 16 (4) :729-732. Two new Paleocene dinoflagellates from Virg inia and Maryland. Palaeontology, 17(1) :65-70. Eocladopyxis peniculatum Morgenroth, 1966, Early Tertiary ancestor of the modern dinoflagellate pyrodinium bahamense Plate, 1906. Micropaleontology, 22(3) :347-351.

Foraminifera, stratigraphy and paleoecology of the Aquia Formation of Maryland and Virginia. Cushman Foundation for Foraminiferal Research Special Publication 7, 50 p.

Time in stratigraphy. McGraw-Hill, New York, 365 p.

Stratigraphy and character is tic mollusks Group (lower Tertiary) and the Old Church Chesapeake Group, Virginia Coastal Plain. Survey Professional Paper 1346.

of the Pamunkey Formation of the

U.S. Geological

Taxonomy and biostratigraphy of; lower Tertiary dinoflagellate assemblages from the At!antic Coastal Plain near Richmond, Virginia. Unpublished M.S. thesis, Virginia Polytechnic Institute and State University, 168 p.

WITMER, R. 1980

J., and GOODMAN, D. K. Early Tertiary Wetzeliella assemblages Maryland (U.S.A.) Coastal Plain (abs.).

46

from the Virg inia­Palynology, 4:254.

Reprinted from Frederiksen, N,Q., and Kraffi. K .. cds., 1984, Cretaceous and TCl'litiry stratigruphy, paleontology, and structure, southweBtern Maryland and northeastern Virginia. American Association or StrAtigraphic PlI.lynologists Field Trip Volume and Guidebook.

DINOFLAGELLATE BIOSTRATIGRAPHY OF THE NANJEMOY FORMATION AT POPES CREEK, SOUTHF.ASTERN MARYLAND

D. K. Goodman

ARCO Oil and Gas Company, Exploration/production Research Center, P.O. Box 2R19, Dallas, Texas ~5221

ABSTRACT

The Lower Eocene Woodstock Hember of the Nanjemoy Formation at Popes Creek, Charles County, Maryland, contains a well preserved, species-rich dinoflagellate cyst assemblage. Approximately one hundred fifteen species occur in two stratigraphically sequential sections exposed along the eastern bank of the Potomac River; the strata also contain moderate­ly diverse assemblages of terrestrial palynomorphs and acritarchs. The Woodstock Member is moet likely correlative with the upper Eatonicysta u-rsulae (LC-2) and the Kisselovia reticulata (LC-3) Assemblage Zones (Bujak et 81., 1980) of the upper London Clay on the Isle of Wight (equivalent--to the Wetzeliella varielongituda and lower Kisselovia coleothrypta Zones of Costa and Downie, 1976), suggesting a middle to late Ypresian age for these beds.

TIiTRODUCTION

The purposes of this paper are to summarize the significant aspects of the upper Nanjemoy dinoflagellate flot'8 i..'1 tbe vicinity of the town of Popes Creek, Maryland, located approximately 35 miles south of Washington, D. C., to briefly document correlation of the Nanjemoy to British sec tions using standard dinoflage lla te zones, and to es timate probable age limits of the Nanjemoy based on dinoflagellate strati­graphy. The two outcrop localities discussed herein are the sections descri bed by Cla.rk and 11artin (1901) R.S Local Sections IX and X. Section n: is located 2.0 miles north of Popes Creek; 40 feet of Woorl­stock and 40 feet of Miocene bens a.re exposed in a vertical cliff sec­tion here. Section X is located about 0.25 mile south of the town a.nd contains 14 feet of upper Woodstock and 10 feet of Miocene strata. A nearly complete Woodstock section (Section X overlies IX) can be compo8-ited from the two localities, with a small interval of less than six feet of unexposed and therefore ullsampled strata separating the t-II"O

sections.

A fairly comprehensive analysis of the dinoflagellates i~ the sections has been made (Goodman, 1975), as has a detailed account of the quantitative distribution of cyst species (Goodman, 1979). Nanjemoy dinoflage lla tea are also reported in Virginia from ou tc rops along the Pamunkey River, Hanover County (Witmer, 1975), and along Aquia Creek, Stafford County (McLean, 1971), and in the U.S.G.S. Oak Grove Corehole, Westmoreland County (Gibson ~ a1., 1980).

47

GEOLOG Ie AND STRATIGillHIC SETTING

The Nanjemoy Formation crops out in a discontinuous, arcuate band from north of Petersburg, Prince Georges County, Virginia, north­northeastward to the area just south of Annapolis, Anne Arundel County, Maryland (Text-Figure 1). It is exposeo. along the major rivers and streams of the area, anrl the thickest and best exposed sections are located in the bluffs along the Po toroac River. It is composed of glauconi tic, fine-grained quartz sands that are locally calcareous and argillaceous. Formational strike is approximately north-south, with dip to the east at 12-15 feet per roile. The formation is 125 feet thick (Clark and Martin, 1901) at the type locality along Nanjemoy Creek, Charles County, Maryland; it thickens to the east to a maximum recorded (Teifke, 1973a) thickness of 250 feet in the Emmet Taylor Well #1 loca ted on the De lmarva Peninsula, Accomack Coun ty, Vi rginia (Tex t­Figure 1). The most recent and complete 11 tho logic (Reinhardt et a1., 1980) and biostratigraphic (Gibson et aL, 1980) analyses Orthe Nanjemoy Fonnation are based on Oak GroveCore samples. Nogan (1964) and Weems (1974) postulate that there is no depositional break between the nanjemoy Form~tion and the underlying Marlboro Clay, although paly­nological evidence (Witmer, 1975) suggests that the contact might be, at least locally, disconformable. R'owever, the formational contact is gradational, due in part to biogenic reworking, and therefore difficult to interpret lithologically pas t eener~l agreement with the biological argument of either absence of, or presence of only a small-scalp., uncon­formity. The upper boundary of the Nanjemoy is a major erosional sur­face wit~ variable relief developed; the Nanjemoy is unconformably over­lain by the middle Eocene Piney ~oint Formation, Mio~ene deposits, or by Plio-Pleistocene sands And gravels throug~out the outcrop area.

Clark anrl Martin (1 Q01) divided the ~anjemoy ~ormation into the Potopaco and Woodstock members, and each member was further subdivided into a number of "zones." They are:

~anjemoy Formation Woodstock Member ("Zones" 16-17)

Potopaco Member ("Zones" 10-15)

"Zones" through g comprise the underlying Paleocene Brightseat ann Aquia Fonnations. The "zones" of Clark and Martin were vllriably defined on the basis of litho logy and/or paleonto logy, and as such have little or no biostratigraphic utility. The members are valid lithostrati­graphic units and c.an be recognized using molluscan assemblages (Gibson ~ a1., 1980).

Teifke (1973b) indicated that the Nanjemoy was deposited on a rather uniform, eastward sloping surface with 8 major break in slope at the present longitudinal position of Chesapeake Bay. The formation appears to have been deposited during the early stages of a transgres­sive marine sequence, during which time the regional tectonic framework of the area changed to produce a gradually expanding basin whose deepest part shifted progressively sout~ward, and with deposition accompanied by a rather uniform basement subsidence estimated to be from about 50 to 150 feet. Owens and Sohl (1969) indicated that the Manasquan Formation,

48

40'

79" 77"

PENNSYLVANIA

., J I ", I

I

VIRGINIA

NORTH CAROLINA

o I

..... ....

50 75 100 . . ,

MILES

Text-~igure 1. Index map of central Atlantic Coastal ?lai~ states showing locations of Popes Creek, Maryland (star), along the Potomac River. ~eavily shaded area indicates limits of Nanjemoy Formation outcrop belt.

49

38'

36

a correlative unit in New Jersey, was deposited under nearshore gulf to ou ter she If conditions during a generally transgressive phase; this agrees in general terms ri th Teifke' s (f973b) determinations, based on his distributional map of the Nanjemoy. Gibson et al. (1980) suggest' that the Nanjemoy was deposited in middle to innar shelf water depths. These authors indicate an initial transgressive sequence followed by a shallowing (coarsening) upwards trend through the formation in the well.

DllOFLAGELLA TE PLORA

Dinoflagellate cysts are the most abundant organic-walled micro­fossil group in the Popes Creek sections. Occurrence data for 36 selected age significant species in the composite section a.re shown in Text- Figure 2. Occurrence charts i llustra ting the stratigraphic d is­tribution of over 100 species are illustrated in Goodman (1975). Corre­lation and age determination of the Woodstock Member based on dinoflag­ellate cysts are discussed in the following section.

Goodman (1979) recognized six sequential species associations in the Woodstock l~ember based on major changes in species composition and relative abundances, and suggested the a.ssociations might be related to broadly defined fluctuations in local paleoenvironment along an offshore-inshore gradient. Associations characterized by moderate to high relative diversity and low to moderate relative dominance by a few species were postulated to reflect a more offshore paleoenvironmental trend. Associations characterized by low to moderate relative diversity and moderate to high relative dominance were postulated to t'eflect a more inshore trend. The general characteristics of each association through the ~ection (see Text-Figure 2) are listed below:

Suggested Paleoenvironmental

Association Trend --------------------F More inshore

E More offshore

D t10re inshore

C More inshore

B Hore offshore

Abundant ann/or Characteris tic Species

Areoligera senonensis, Ho~otI7blium

tasmaniense, Thalassiphora pela~ica,

Wetzeliella hempdenensis, ~. lunaris

Cleistosphaeridium diversispinosum. ?Millioudodinium giuseppei. Spinifer­ites supparus, Homotrybliurn tenuisuin­osum. Spinidinium sp- of Goodman 1979

Deflandres phost)hori tica, Wetzeliella lunaris

Areoligera senonensis, Hystrichokol­porna Spa cf. ~. torquata, Phthanoperi­dinium resistente, Thalessiphora pelagica, Wetzeliella lunaris

Cleistosphaeridium diversispinosum. Diphyes colligerum, Kisselovia co leo­th?Yfta, Lingulodinium machaerophorum. Sp~n~dinium IDacmurdoense

50

A More offshore Biconidinium 10ngiss1mum" Lingulodin­ium machaerophorum, Spiniferites supparus, Wetzeliella samlandica

AGE OF THE lWIJEJlOT JORJIIA'rIOB

Dinoflagellates from the basal Nanjemoy Formation in the Oak Grove corehole (Witmer, 1984) indicate correlation with the lowermost Estonicysta ursulae (LC-2) Assemblage Zone (Bujak ~ al., 1980) of the middle London Clay on the Isle of Wight, England. Although the zonal nominate species is not present in the well, correlation is based on the lowest occurrences of Adnatosphaeridium multispinoawn (at the base of Nanjemoy) and Spiniferi tea monilia (3 ft above the base). Bujak et al. (1980) report the lowest occurrence Homotryblium tenuispinosum just below the base of the zone, (as~. pallidum; at the base of the zone if ~. pallidum and ~. tenuispinosum are retained separately) which is significantly lower (older) than its lowest occurrence both at Popes Creek and Oak Grove (a bove the base of the Woods tock Member). Tbe lowest occurrence of Thalassiphora pelagica is wi thin the ~. ursulae Zone on the Isle of Wight (Bujak et a1., 1980); Witmer (1984) records its base of consistent occurrenceatthe base of the Nanjemoy at Oak Grove, but also reports two specimens in the Danian Brightseat Formation about 100 ft lower in the core, in agreement with a previous report (Whitney, 1975) of abundant !. pelagica from the Brightseat in Marylano, east of Washington, D.C.

The boundary between the Potopaco and overlying Woodstock Members at Oak Grove is placed at 276 feet (Gibson et a1., 1980). The lowest occurrence of 'w'etzeliella varielongituda in thecore is in the sample immediately above this boundary (273 feet) suggesting correlation of the lower Woodstock strata with the Wetzeliella varielongi tuda Zone (Costa and Downie, 1976), which is equivalent to the upper part of the Eatonicysta ursulae Zone.

The basal Woodstock strata exposed at Popes Creek appear to be somewhat higher (younger) than the base of the Woodstock identified at Oak Grove. "Zone" 16 at Oak Grove is therefore represented by the interval between 226 and 273 feet, and "Zone" 17 by the interval between 201 and ?20 feet. The intervals between sample 1 0 and sample A 14 at Popes Creek, and between 201 and 241 ft. at Oak Grove, are correlative wi th the Kisselovia reticulata (LC-3) Assemblage Zone (Bujak et 81., 1980) of the upper London Clay, based on the lowest occurrence-of Kisselovia coleothrypta. This datum is easily recognized at Popes Creek and Oak Grove by the nearly simultaneous lowest occurrences of le. coleothrypta, Spinidinium macmurdoense, ?Senegalinium asymmetricum, Wetzeliella lunaria. and Cleistosphaeridium diversispinoaUID. The!. reticulate Zone is equivalent to the lowermost part of the Kiaselovia coleothrypta Zone of Costa and Downie (1976).

Based on these correlations, the ba~e of ?Millioudodinium giuse ei in Maryland-Virginia is older (base of LC-2) than in England base of LC-3; Costa and Downie, 1979, report its base in the Late Paleocene); the base of Achilleodinium biformoidea in M-V is younger (upper LC-2) than in England ( uppermost LC-1); the base of Biconidinium longissimum

51

LOWER EOCENE SERIES EATONICYSTA KISSELOVIA RETICULATA - DINOFLAGELLATE ZONE

URSULAE (LC-3) (BUJAK ET AL.. 1980) (LC-2J

NANJEMOY (WOODSTOCK MEMBER) FORMATION \

~ .

~ SECTION

\ (CLARK & MARTIN. 19(1)

.... ..... "ZONE" OJ , ...... (CLARK & MARTIN . J90')

, }> »» DISTRIBUTION (FT) .... .... - .... ...... N to.,) to.,) N to.,) » » » > > ... .......... SAMPLE

· 0 ~ ~ f~ .cr 'f t cr IX) 0 ~ t f 'f ~ 'ft'r'r c;' ~t I I I

• • • • • Rottn.alla boruu/c$

• • • • • • • • • Blconldlnlum long/lOs/mum

• • • • • • • • • I W./ullella sam/andice

• • • • • • • • • Apleodlnlum .us/rellens.

• • I • • • • • · ... ?Cordosphn"dlum tlll/Olum

I • • • I • • I I • J(a/losphuridlum br.vlbllrbarum

• I I • • • • • • • • • • Ph/hlnoparldlnlum resislenl.

I • • • • • • • I • • !.Iura/od/nium /imbrielum

• • • I • • • • I • • • • Senttgal/nlum dl/wynens.

• • • • • • • • • I • • • • Imp/ll/osphtl8fldlum rugosum

• I I • • • • • • • Ps/l~cystodlnium gollowense

I • I • • • • • • • I • • • • I • • Achill.odinium bilormoides

• • I • • • I • • I • • • • • Adn8tosphe8fidlum mul/lsplnosum

I • • I • • • • • • • • • • • • • • • C.f1JrJop$ls wardenensls

• • • • I • • • • • • • • • • • • Diphyes collig~m

I • • • • • • I • • • ?Mlllloudodlnium gluseppel

• • • • • • • • • • • • • • • • • The/us/phora p&/eglcJl

• • • • • • • W"lellelle varle/ong/luds

• • • • • • • Psucisphuridium Inw1fsibucc/num

• • • • • • • • • • EocllJdopy;ltIs pen/cula la

• • • • • • • Splfliferlles pSfiudolurC8lus

• • • • • • • • • DellandfIJs phosphoflllCil

, • • • • • • • • • Acl1omosphaera crassipellls

• • • • • • • • • • • • • • • CI./s/osph88ridlum dNerslspinolum

• • • • • • • ?SeneglJlnlum //.symmelr/cil

• • • • • • • • Systems/ophof//. p/sCllcef)/hlJ

• • • • • • • Xlsse/ovis co/eolhrypllJ

• • • • • I Fibrocyst. IIJPpeCOII

• • • • • • • • • • • • • • • W,Hztliellfl lunalls

• • • • • • • • • • • • • • Wetzell,lIa nlmpdenens/s

• • • • Homo/rybllutn csliculum

• • • • • Homo/rybllum ,enuispinosum

-. We/laliell//. sp. 01 Goodman 1979

• • • • • • • Homotrybllum tasmanl.nsa

• • • • • • • Splnidlnlum sp. 01 Goodman 1979

l> I CD I () I 0 I . ..,) I m I " I~ CYST ASSOCIATION (GOOOMAN. 1979)

Text-Figure 2. Occurrence chart for selected dinoflagellate species in the Nanjemoy section (Woodstock Member) composited from two outcrop localities near Popes Creek.

52

is somewhat older (uppermost LC-2) than in England (base of LC-3): the base of Impletosphaeridium rugoswn is considerably older (uppermost LC-2) than in England (within HomotrybliUJll abbreviatum (B-1) Assemblage Zone in the lower Bracklesham. Beds); and the base of Homot:rwbliwn caliculum is considerably older (base of LC-3) than in En-gland ~i thin Heteraulacacysta porosa. (BAR-1) Assemblage Zone _ in the Middle Eocene lower Barton Beds in southern England). IslBlll. (1983a,b) considers the base of the Homotryblium abbreviatum (B-1) Zone to be older than estimated by Bujak et a1. (1980) and to coincide with the base of the LC-3 Zone in the upper part of the London Clay Division 1) on the Isle of Sheppey. Costa and Downie (1979) report H. 'lbbreviatum in their lower Kisse lovis coleothrypta Zone on the "Rockall Plateau. thus providing apparent parti'll support for Islam's interpretation.

The dinoflagellate data therefore indicate the Nanjemoy Formation in this area is no older than the base of the Eatonicysta ursulae Zone and no younger than t'l1.e uppermost Homotryblium abbreviatum (B-1) Zone (the upper limit of the Nanjemoy is difficult to determine reliably due to lack of index forms within the interval equivalent to the middle and upper B-1 Zone; palynologically barren and therefore undatable Bagshot sands above the London Clay which may correspond to upper Nanjemoy; and difficulties in detennining the oldest probable age of the basal B-1 Zone and its relationship to the underlying LC-3 Zone (Islam, 1983a). The correlative London Clay to Lower Bracklesham sequence represented by this interval belongs to NP11-NP13 (Berggren et a1.. in press, and J. Hardenbol, pers. comm.). The Potopaco Member is-equivalent to the basal Eatonicysta ursulae (LC-2) Zone to the top of the Dracodinium similis Zone (Costa and Downie, 1976), and thus belongs to NF11. The Woodstock Member is equivalent to the basal Wetzeliella varielongituda Zone (uppermost LC-2), the Kisselovia reticulata (LC-3) Zone, and a part ( perhaps all?) of the Homotryblium abbreviatum (B-1) Zone (contingent upon accurate definition of the base of (B-1)), and thus belongs to NP12 and to an unknown part (or perhaps all given current uncertabties) of NP1'3. Hazel et a1. (in press) indicated the top of the Nanjemoy as corresponding to the top of Chronozone 23. which suggests a mid-NP13 upper limi t for the Woodstock. This may represent a more precise determination than is possible using dinoflagellate correlations alone; rgsults r.aseri on riinoflagellates herein would comfortably agree with that upper limit. Summarizing, these da.ta suggest an e):].rly (but not earliest as suggested by Hazel et 81., in press) to late (but not latest) Ypresian age for the Nanjemoy-rQrmation.

53

BERGGREN, W. A •• KENT. D. V., and FLYNN, J. J. in press Paleogene geochronology and chronostratigraphy.

BUJAK, J. P., DOWNIE, C .• EATON, G.L., and WILLIAMS. G.L. 1980 Dinoflagellate cysts and acritarchs from the Eocene of

southern England. Special Papera in Palaeontology 24:1-100.

CLARK 1 W. B., and MARTIN. G. C. '1901 The Eocene deposits of Maryland. Maryland Geological Survey,

Eocene Volume: 331 pp.

COSTA. L. I. and DOWNIE, C. 1976 The distribution of the dinoflagellate Weheliella in the

Paleogene of north-west Europe. Palaeo:ntology • 19:591-614.

1979 Cenozoic dinocyst stratigraphy of Sites 403 to 406 (Rockall Plateau). !POD. Leg 48. Initial Reports of the ~ Sea Drilling Project 48:513-529.

GIBSON, T. G., at al. Biostratigraphy of the Tertiary strata of the ~ore, in Geology of the Oak Grove Core. Virginia Division of Mi:ner81 Resources Publication 20:14-30.

r,OODMAN. D. K. 1975 Lower Eocene rtinoflagellate assemblages from the Maryland

coastal pl~in south of Washington, D. C., unpubL M.S. thesis, Virginia Polytechnic Institute and State University: 298 pp.

1979 Dinoflagellate "communities" from the Lower Eocene Nanjemoy Formation of Maryland, U.S.A. Palynology 3:169-190.

HAZEL, J. E., EDWARDS, L. E • • and BYBELL. L. M. in press Significant unconformities and the hiatuses represented by

them in the Paleogene of the Atlantic and Gulf Coastal Province.

ISLAM, M. A. 1983a Dinoflagellate cysts from the Eocene cliff sections of the

Isle of Sheppey, southeast Sngland. Revue de Micropaleon­tologie 25:231-250.

, 983b Dinoflagella.te cysts from the Eocene of the London and the Hampshire Basins, southern England. Palynology 7:71-92

McL8AN. D. M. 1971 Organic-walled phytoplankton from the Lower Tertiary Pamunkey

Group of Virginia and Maryland, unpubl. ~.D. dissert., Stanforn University: 165 pp.

54

NOGAN, D. S. 1964 Foraminifera, stratigraphy and paleocology of the Aquia Forma­

tion of Maryland and Virginia. Cushman Foundation for Fora­miniferal Research Special Publication Number 7:50 pp-.--

OWENS, J. 1969

P., AND SOHL, N. F. Shelf and deltaic paleoenvironments in the Cretaeous-Tertiary formations of the New Jersey Coastal Plain, in S. Sibutsky (ed.), Geology of selected areas in New Jersey and eastern Pennsylvania, Rutgers University Press: 235-278.

REINHARDT, J., NEWELL, '1/. L., AUD MIXON, R. B. 1980 Tertiary lithostratigraphy of the core, in Geology of the Oak

Grove Core. Virginia Division of MineraI Resources Publica­tion 20:1-13.

T13IFKE, R. !-t. 1973a Stratigraphic units of the Lower Cretaceous through Miocene

series, in Geologic Studies, Coastal Plain of Virginia. Virginia DiviSion of Mineral Research Bulletin 83 pt. 1:1-7~.

1973b Paleogeology 0 f F.arly Cretaceous through Miocene time, in Geologic Studies, Coastal Plain of Virginia. Virginia Divi­sion of Mineral Resources Bulletin 83, pt. 2:79-98.

WEEMS, R. :So 1975 Geology of :-!anover Academy and Ashland Quadrangles, Virginia,

unpub. M.S. thesiS, Virginia Polytechnic Institute and State University: 98 pp.

1.>lITMER. !L J. 1975 ~ayonomy and biostratigraphy of Lo~er ~ertiary dinoflagellate

assemblages fror.J the Atlantic Coastal Plain Near Richmond, Virginia, unpubl. M.S. theSis, Virginia Polytechnic Institute and State Uni'/ersity: 176 pp.

55

56

Reprinted from Frederiksen, N.D ., and !{ram, K.. eds., 1984. Cretaceous and Tertiary stratigra.phy, paleontology, and structure, southwestern Maryland a.nd no)"thwe8.lltern Virginia, American Association of Stratigraphic Palynologist.s Field Trip Volume and Guidebook .

. LOWER TERTIA·RY POLLEN BIOSTRATIGRAPHY, M1.RYLAND AND VIRGINIA

N. O. Frederiksen

U.S. Geological Survey, 970 National Center, Reston, Virginia 22092

Lower Tertiary strata in Maryland and Virginia are rich in palynomorphs as well as in calcareous mega- and microfossils. In this paper, I present the known ranges of 52 pollen taxa in the Br ightseat Formation (lower Paleocene), Aquia Formation (upper Paleocene), Marlboro Clay ( upper Pal eocene and ? lowermost Eocene), and Nanjemoy Forma t ion (lower Eocene) in the Potomac River region.

Previous studies on early Tertiary spores and pollen grains from Maryland and Virginia include abstracts by Brenner and Patricelli (1977) on the Marlboro Clay of Maryland, and by Brenner et~. (1979) on the upper part of the Aquia Formation, the Marlboro Clay, and the lower part of the Nanjemoy Formation of Maryland; and papers by Groot and Groot (1962) on the Brightseat Formation of Maryland and by Frederiksen (1979, and in Gibson et a1., 1980) on the Aquia Formation, Marlboro Clay, and NanjelTOY Formationof northern Virginia. In the present paper, I have summarized data from Frederiksen (1979) and have included some previously unpublished data of mine on G,e Brightseat Formation of Maryland.

Text-Figure 1 shows observed ranges of significant pollen taxa in Paleocene and lower Eocene strata of southern Maryland and northern Virginia. Data on the Brightseat Formation are from study of t~ree

samples from Cabin Branch, Prince Georges County, Md. (locality 1 of Text-Figure 2; locality HL 34 of Razel, 1968). This locality is 2.2 miles southwest of the stratotype locality of t.'le Brightseat (locality 2 of Text-Figure 2). The Brightseat samples of Groot and Groot (1962) came from Addison Road (locality HL 33 of Hazel, 1968), O.S mile sout~west of the Cabin Branch site. My samples were collected by L. M. Bybell and D. L. Govoni and are from the middle part of the Brightseat, from 2.5,5.5, and 6.6 ft, respectively, below the top of the formation. I avoided samples from the lower part of the formation that conta in reworked Cretaceous material (Razel, 1968; palynomorphs from the Brightseat Formation illustrated by Groot and Groot (1962) include several reworked from the Cretaceous), and I also did not examine samples from the upper part of the formation, which has burrows filled with Aquia material (Hazel, 1968, 1969).

Data on the Aquia Formation, Marlboro Clay, and Nanjemoy Formation in Text-Figure 1 are from the U.S. Geological Survey Oak Grove core in Westmoreland County, Va. (locality 10 of Text-Figure 2). Pollen data on th is core were published by Freder i~sen (1979, and in Gibson et al" 1980) • The Oak Grove borehole was cored from a depth of 80 ft to 13S0 ft, including strata of Barremian?, Aptian, Albian, Paleocene, Eocene, and Miocene ages (Gibson et a1., 1980; Reinhardt et a1., 1980). The lowest 41 ft of Paleocene section in the core, from 454to 413 ft depth I

is of uncertain age because it lacks calcareous fossils. This interval contains some palynomorphs of Brightseat (early Paleocene) age, for example Danea mutabilis Morgenroth 1968, Palaeoperidinium pyrophorum (Ehrenberg 1838) Sarjeant 1967, Pseudoplicapollis cf. P. endocuspis

57

Tschudy 1975, Choanopollenites cf. C. consanquineus Tschudy 1973, Choanopo llen i tes? sp., and Choanopo llen i tee conspicuus (Groot & Groot 1962) Tschudy 1973. However, the early Paleocene pollen grains, at least, are rare in these samples, and they occur in this interval of the core together with abundant carya pollen grains that are not found below the upper Paleocene in the Gulf Coast or in South carolina. Because Carya pollen has not been observed in the Br ightseat Formation in its stratotype area, it is clear that the lowest part of the Paleocene section in the oak Grove core is younger than the stratotype Brightseat, and appears to be late Paleocene (Aquia) in age but containing reworked early Paleocene palynomorphs. Although I am sure that rocks correlative with the stratotype Brightseat are missing from the oak Grove core section, the lowermost preserved Tertiary in the core could possibly represent rocks missing by unconformity between the Brightseat and the overlying Aquia in the stratotype area of the Brightseat.

Except for the rare early Paleocene specimens in the lowest part of the Paleocene section of the core, the rest of the pollen taxa in this interval are the same as those occurring higher, in definite Aquia Formation. To avoid confusion because of the probable reworking, I have not shown the lowest part of the cored Paleocene section in Text-Figure 1.

Text-Figure 1 shows that the Brightseat, Aquia, Marlboro, and Nanjemoy formations all have distinctive pollen assemblages. Differences between the Brightseat and the Aquia are not surprising because, at least in the stratotype area of the Brightseat, these formations are separated by a disconformity in which calcareous nannofossil zones NP 4 and the upper half of NP 3 are missing (Bybell and Govoni, 1977 i Bybell, oral commun., 1984). Neither the Brightseat nor the Aquia can be subdivided biostratigraphically using pollen on the basis of present knowledge, except that the uppermost sample of the Aquia has many pollen taxa in common with the Marlboro. The lower and upper parts of the Marlboro are different because the lower part of the formation contains Paleocene species not known elsewhere to range into the Eocene, such as Retitrescolpites angulo1uminosus (Anderson 1960) Frederiksen 1979 (Text­Figure 1, no. 7), Momipites strictus Frederiksen & Christopher 1978 (8), Choanopollenites alabamicus (Srivastava 1972) Frederiksen 1979 (20), and Piolencipollis endocuspoides Freder iksen 1979 (21). The upper part of the Marlboro contains sparse pollen of Platycarya platycaryoides (Roche 1969) Frederiksen & Christopher 1978 (44), which is basically an Eocene species although it may possibly range (as rare specimens) down into the uppermost Paleocene in the Gulf Coast. The upper part of the Marlboro also contains the Paleocene species Momipites flexus Frederiksen 1979 (25) and Kyandopollenites anneratus Stover in Stover et a1. 1966 (26), which are known elsewhere only from the Paleocene. The Nanjemoy Formation, on the other hand, contains a rich Eocene pollen assemblage.

Litholcq ically, the greensand of the Aquia grades up in to the gray to red clay of the Marlboro, and the Marlboro clay grades up into the greensand of the NanjeTOCly. calcareous microfossils are absent from the Marlboro, and mollusks are rare, but the overlap within this formation of pollen spec ies restr icted elsewhere to the Paleocene or Eocene, and the physical stratigraphic evidence, indicate that deposition was more or

58

'" .., ; ~

... z

~

'" S ~ i: ~

~

~ ~

~ ~ It'

C) ~ ~ ,:

t; C

~ .? "< %

~

0 Q ;?;

:% ~ :z: g ~

1;::

&' I!t

I ~

I · ·

'1° yOlltSIAN NANJEMOY

·

II rIll I

:r

Text-Figure 1. Observed ranges of significant pollen taxa in Paleocene and lower Eocene s tea ta of sou the rn Mary land and nor the rn V irg in i a . "Depth

D

for the Aguia, Marlboro, and Nanjeroc>y Formations is depth in the Oak Grove core, Virginia; "depth" for the Brightseat Formation is distance below the top of the formation in outcrop at Cabin Branch, Maryland. Ab901u te ages are from Hazel et ala (in press). MPP complex ~ Momipites-Plicatopollis-Platycaryapollenites complex of Freder iksen (1979). Several taxonomic names used here are different from those of Frederiksen (1979): see Table 1.

59

Text-Figure 2. Sampling localities of this paper, stratotype or lectostratotype localities of lower Tertiary Formations, and Tertiary stops of this field trip. 1. cabin Branch sampling locality (Brightseat Formation) • 2. Stratotype locality of the Brightseat Formation (no longer

accessible) . 3. Town of Upper Mar Iboro. The stratotype locali ty of the Mar Thoro

Clay was described by Clark and Martin (1901) as being in this vicinity.

4. Field tr ip stop 4. 5.- Field trip stop 5; lectostratotype locality of the Aquia

Formation. 6. Field trip stop 6. 7. Pield trip stop 7. 8. Field trip stop 8. 9. Lectostra to type locality of the NanjeIOOY Formation.

10. Location of the Oak Grove corehole.

less continuous from the Paleocene Aquia Formation across the Marlboro Clay and into the Eocene Nanjemoy Formation. In contrast, a small unconformity occurs between Paleocene and Eocene formations in the eastern Gulf Coast (Frederiksen et al., 1982) and in South carolina (Gohn eta 1., 1983). In nor thern Virg in 1a, pollen grains ind ica te that the PalecK:ene-Eocene boundary is either within the upper part of the Marlboro or within the Marlboro-Nanjemoy gradational contact zone. Whether the Nanjemoy can be subdivided biostratigraphically using pollen remains to be determined by examining other sections of this formation.

Table 1. Names used in this paper that are different from those in Frederiksen 1979, Text-Figure 2.

This paper

Bombacacidites reticulatus Krutzsch 1961

Insulapo11enites sp. Plicatoeollis triradiata type

(Nichols 1973) Frederiksen & Christopher 1978

Porocolpopollenites ollivierae (Gruas-Cavagnetto 1976) Frederiksen 1983

Taxon number, Text-Figure 1,

this paper

16

9 14

11

60

Freder iksen 1979

Intratriporopollenites reticulatus (Groot & Groot 1962) Frederiksen

Cupan Ie id i tes? Plicatopollis

1979 sp.

lunata

Riestedtipollis? sp.

0

I [

0 5

/ , WASHINGTON '\. ,

D. C. , f,;\

" 0

/ /

/

(@

5 10 !

I I I

1°61 15

/

/ / CD /

15 MILES I

I 20 KILOMETERS

References Cited

BRE:ilNER, 1977

BRDllNER, 1979

G.J., and PATRICELLI, J. palynology of the Marlboro Clay (Eocene) from Pr ince Georges County, Maryland (abs.). Palynology, 1: 171-172.

G.J., PATRICELLI, J., and RACHELE, L. Palynology of the Paleocene-Eocene sediments from PGOf-35 well, Prince Georges County, Maryland (U.S.A.) (abs.) Palynology, 3: 280.

BYRELL, L.M., and GOVONI, D.L. 1977 Preliminary calcareous nannofossil zonation of Br ightseat and

Aquia Formations (Paleocene) of Maryland and Virginia-­stratigraphic implications (abs.). AIDer ican Association of Petroleum Geologists Bulletin, 61: 773-774.

CLARK, W.B., and MARTIN. G.C. 1901 The Eocene deposits of Maryland. Maryland Geolog ieal Survey,

Eocene Volume, p. 1-92, 122-204. FREDERIKSEN, N.O.

1979 Paleogene sporomorph biostratigraphy, northeastern Virginia. PalynologY, 3: 129-167.

FREDERIKSEN, N.O., GIBSON, T.G., and BYBELL, L.M. 1982 Paleocene-Eocene boundary in the eastern Gulf Coast: Gulf

Coast Assoc iation ~ Geolog ical Soc ieties, Transactions, 32: 289-294.

GIBSON, T.G., ANDREWS, G.W., BYBELL, L.M., FREDERIKSEN, N.O., HANSEN, T., RAZEL, J.E., MCLEAN, D.M., WITMER, R.J., and vm NIEUWENHUISE, D.S.

1980 Biostratigraphy of the Tertiary strata of the core. In: Geology of the Oak Grove core. Virginia Div i5ion of Mineral Resources Publication, 20: 14-30.

GOHN, G.S., HAZEL, J.E., BYBELL, L.M., and EDWARDS, L.E. 1983 The Fishburne Formation (lower Eocene), a newly defined

subsurface unit in the South Carolina Coastal Plain. U.S. Geological Survey Bulletin, 1537-C: CI-C16.

GROOT, J.J., and GROOT, C.R. 1962 Some plant microfossils from the Brightseat Formation

(Paleocene) of Maryland. Palaeontographica, Abteilung ~ ill: 161-171.

HAZEL, J.E. 1968 Ostracodes from the Brightseat Formation (Danian) of

Maryland. Journal of Paleontology, 42: 100-142. 1969 Faunal evidence for an unconformity between the Paleocene

Brightseat and Aquia Formations (Maryland and Virginia). u.s. Geological Survey Professional Paper, 650-C: C58-C65.

HAZEL, J.E., EDWARDS, L.E., and BYBELL, L.M. In press Significant unconformities and the hiatuses represented by

them in the Paleogene of the Atlantic and Gulf Coastal Province. American Association of Petroleum Geologists Memoir.

REINHARDT, J., NEWELL, W.L., and MIXON, R.B. 1980 Tertiary lithostratigraphy of the core. In: Geology of the

Oak Grove core. Virginia Division of Mineral Resources Publication, 20: 1-13.

62

;.

"

r

Composition and biogeographic significance of the gastropod mollusk fauna of the Brightseat Formation (Paleocene: Danian) of Maryland

By David L. Govoni U.s. Geological Survey. Reston, VA 22092

INTRODUCTION

Bennett and Collins (1952) first recognized the presence or a discrete. marine sedimentary unit between the Upper Cretaceous Severn Formation and the upper Paleocene Aquia Formation in the lower Potomac River Valle, near Washington, D.C. They named this deposit the Brightseat Formation. Calcareous nannofossils place the Brightseat Formation in the early Paleocene (Danian) Zone NP 3 of Martini (1971). There is very Jittle published data on either the composition or significance or the molluscan macrofauna of the Brightseat, whieh constitutes the only diverse and reasonably well-preserved, early Paleocene molluac.an assemblage in the Atlantic Coastal Plain. ThOle studies that did focus upon the mollusb (for example, Kauffman and Beauchmnp, 1989; Bretsky, 1974; Bretsky and Kauffman, 1977) dealt primarily with the Bivalvia.. Govoni (1983) provided an extensive treatment of the taxODomy and biogeography or the Brightseat gastropod fauna.

This paper presents a summary of the Brightseat gastropod fauna and provide& a prelimjnAry comparison with several gastropod assemblages of similar age in the Gulf Coastal Plain of North America, West Greenland, and the Northwest European Tertiary Basin. For a more

63

complete treatment of these topics see Govoni (1983). See Gibson and others (this guidebook) for a discussion of the distribution. oomposition, and lithostratigraphy of the Brightseat Formation and Bybell and Gibson (this guidebook) for a discussion of the age of the Brightseat Formation.

CORREl"ATION OF THE BRIGHTSEAT FORMATION

Due to ita location on the western margin of the NOrth Atl&ntic Ocean Basin. the Brigl1tseat FOrmation occupies a by position far transatlantic correlation and biogeographic comparison with macrofossiUferoua, lOwer Paleocene deposita around the periphery of the basin. Fieure 1 is a pneralized . correlation chart, based on a synthesis of nUIDerous paleontologic:a1 and stratigraphical studies (see, for example, Cats.. 1982; Frederiksen .and others, 1982; Gibson and others, 1982; Hazel and othen, 1984; Toulmin, 1977), that summarizes the age and relative stratigraphic relationships between the Brightseat Formation and other Paleocene-age units that are exposed in the Gulf and Atlantic Coastal Plains of North America. Texas and Alabama were selected as broadly charac:teriBtic of the stratigraphic sequence of the western and eastern halves, respectively, of the

CALCAREOUS GUlF COASTAL PLAIN

(MAli EPOCHS I STAGES I FORAM""'F!AAl I NANNOF088IL (EASTERN) (WESTERN)

7rA11:411 ZONES MARYlAND AlABAMA TEXAS (MARllNI,1911)

MARLBORO

W . '". '" ClAY TUSCAHOMA

W FORMAT~ ;1;

601 Z SEGUIN

~ SELANDIAN P4 AOUIA NANAFAliA

W ~ NP6 FORMATION FORMAn ON

() p~ b

0 NP4 W >- c .....J --' ['~ a: DANIAN P1 NP3 MEMBER o~

651 « « b - -- ~~ Cl. NP2 CLAYTON PISGAH

ill MEMBER -Ir FORMATION litO

a NP 1 - - - - - ~-- - - II..

FIGURE 1. Generalized oonelstlon chart showing aeleded Paleocene "ratlgraphle units prne~ In the autr and Allantlc Coastal PlaIns of North America. Data complied from numerous SOUrt:89.

Gulf Coastal Plain and because gastropod assemblages from the Paleocene portions of these sections are better documented than those from elsewhere in the region. Figure 2 is a generalized correlation chart that compares the Brightseat Formation to selected Paleocene units around the northern and eastern periphery of the North Atlantic Ocean Basin that contain diverse and well­known gastropod assemblages. The correlationa presented are compiled from numerous sources (for example. Anderson. 1982; Berggren, 1964, 1971; Hooybergha, 1980; International Geological Correlation Programme, 1980, 1988; Kollmann and Peel, 1983, Marliere, 1977; Rasmussen, 1965; Robaszynski, 1979).

The Brightseat Formation is correlated with the Tehuacana Member of the upper Kincaid Formation in the Gulf Coastal Plain of Texas (fig I). Farther east in Alabama. the Brightseat is equivalent to the MeBryde Limestone Member of the Clayton Formation and. in western Alabama, to the 10wer member" of the Portera Creek Formation. Across the Atlantic Ocean, the Brightseat Formation COtTelates with the !llaCrOfossiliferous marine beds of the Agatdal and upper Kangilia Formations in West Greenland (fig. 2). In the Northwest European Tertiary Basin. the Tuft'eau de Ciply in the lower part of the Mons Formation in Belgium and the middle and upper parts of the Danian limestone Formation (Coral and Bryozoan Limestone to Crania Limestone) of Denmark are equivalent in age to the Brightseat Formation.

GASTROPOD FAUNA OF THE BRIGHTSEAT FORMATION

Diverse and well-preserved molluscan faunas of Danian age are scalce and

65

widely scattered around the margin of the North Atlantic Basin. By virtue of its moderately high diversity and its geographic position relative to assemblages of similar age, the gastropod fauna of the Brightseat Formation is well suited for transatlantic faunal comparison and biogeographic analysis. Its position in the Atlantic Coastal Plain Province places it in an intel'm.ediate geographic position with respect to penecontemporaneous faunas in the Gulf Coastal Plain, West. Greenland, and northwestern Europe (fig. 3).

CompoaitioD of the gaatropod fauna

The gastropod fauna ofthfl Brightseat. Formation consists of 52 species or forms that represent 44 genera and subgenera and 22 families (table 1). Half of these tau are new species (Govoni, 1983). Mesogastropods, which are represented by 35 species or forms, dominate the fauna. Cephalaspida follow with seven species. while the neogastropoda and entomotaeniates are represented by four species each. The archaeogastropoda and notaspida. are both represented by a single species. Mesogast.ropods also dominate the fauna at the generic level and comprise nearly two-thirds of the total gastropod genera in the Brightseat.

Mesogastropod dominance is comparable to similar patterns seen in other early PaJeocene faunas (for example, Rosenkrantz, 1970 and KoUmann and Peel. 1983 far the Agatdal Formation; Glibert, 1973 for the Calcaire de Mona; and Toulmin, 1977 for the Clayton Formation). Meeogastropods in these faunas account for between 40% (Agatdal) and 62% (Clayton) of the total genera preserved in these faunas.

CI) rJ)

~ ~J NORTH ATLANTIC OCEAN MARGIN LLO CJ) 0 N m C/)Nr::. ~~ :r: ffi zO;J Q) 5=~1 WESTERN I NORTH-CENTRAL I EASTERN z 41( () C!) ~ .... w~~ Q~ 0 c( ~~~ ~O~ ~~ 0.. ~ 5~g ~~~I U.S.A. WEST :t> W c.. ~m O;~ MARYLAND GREENLAND BELGIUM DENMARK

ft Z

~I ~ 62~ 1:5 ~ P lElliNGE ~ a GREENSAND

P2 NP4 C CAl D

~ I 63-f W 'r-r----1 -~~-----

Zw ~ CALCAIRE DE 41( GHUN

o c ~ M~ 0 ~

W z (f) ~ ~ ~ < NP 3 BRIGHTSEAT ~ TUFFEAU DE ~ '"'" a: Z FORMATION :t CIPL Y ~ a.. < <" P1 KANGILIA I- CORAL AND

65~ W C FORMATION f:3 BRYOZOAN ~ LIMESTONE

b I ~""""""'~"~ . ~""''''''''''''''\I ~ 41(

~ -----------. . Q CERITl1lUt./I LS

I 66j I I bdNP1 ~~~~; FlGURE2 .

800 600

-It

•

30Q 0° 30° FIGURE 3. Paleogeographic reconstruction of the region surrounding the North Atlantic Ocean BarNo c:turtng the ealty Paleocene showing distrbJUoo of land (sUppled) and water masses, and locations 0' Danian to early Selandlan faunas ,,888d In text (TX -Texas; Al. - Alabama; MD. Marytand; WG - West Greenmnd; B • BeAg!um; D - Oenmartt). ReJattve poaIUons pt continental masses and paleolatitudes and longitudes OU1l1necJ on map are based upon the Paleocene map 01 SmIIh and Briden (1~77). PaJeogeographlc dala compiled 'rom numerous sources. i .

TABLE 1 SYSTEMATIC LIST AND RELATIVE ABUNDANCE OF GASTROPODS

FOUND IN THE BRIGHTSEAT FORMATION

Total Spec:Iea Abundance n.ta Agrept.ed by 0e1DlA&b!iv1l1Ul: R. Rare (1-9 IndMclDat.>; C • Common (lG-99l.!ldMduals); A • AbDDdaD& (100 or DIOn! inclividuat.)

Number ot Spede8 Rel&dw

~ p.mO, Genu I ~SubllVDUl Or'Ot'ID8~ AbllDdaace

~ AtaphrtdM AlopoVw,, ____ ._------ 1 II '----- . ~ __ _ . __ __ 0_--

Meqaatn>poda I.acuJUd •• lAt:un4(P~ 1 II MtJdoriDpBU ~ 1 II

VitriJleWdae T~ 1 C \fUrIJwUa (VitrWHDpc) 1 II ~ 2 II aC£rc::ul»a- 1 II ~ 1 II ~ 1 II

An:hit.ectoniddu Psc~ 1 II An:AUc1Dlllm (G~) 1 II Al'o\Uelonim (SWJ.o.zJ..p) 1 R

1'IlnitelUdae R~ 1 A RlUUII4I.orl :I A Torquaao 1 A q. TOI"C'Ul4 1 R Slp&aGlI4 1 C

Mathildidaa Mo.thi.ldtJ (MctJallda) " C Mt1i.hild4 ('lib.6ri4U.lW 2 C ~III 1 II Tubo1 1 II

Epftonildae Cin0tnJfa4 ~ 1 C ClnIolrvrt.a (CDroraU1cGJ.a) 1 C

EuHmidae EulUruJ 2 C Eulimldae7· PaAtlwJUJ 1 R Aporrhaidu Aporrhaid. avn.. IUld .p. lndet.. 1 R Strombtda.e CalyplraphlInu 1 C Calyptraeid&e Calypt:rtuo 1 A Nattddae NI!rJD'UG. (Ner>UiJ4j 1 A

Neogastropoda Buacl.nl.dae Lod1li4 1 C SlpMlvJJa 1 C

Ollvldae PanuIollDa 1 II Vuldae Pyropm,., 1 R

EntolDDUeniata PyramidaUidae M,naiM (EvaJ.m) 1 R ~ (Bra.elay.tomio) 1 It SyrrwUJ (Pu.~ 1 C CnoMll4 1 C

Cepbalupidea Acteoniw k~ 1 II T0TnI1U1Uu4 (TOnl4J,tUaeQJ 1 A CmUl4bWm 1 R

Rlngiculidaa Gilbuti.ruJ 1 C ActeocinidM ZiUurnliA 1 C Scapbandrida.e ScapNuuJ.u (Pri.sctJpluutdD-) 1 A Retusidae /Ulluto (CylkluWuJ) 1 C

Nota 8pi dea UmbracuUdae UmbracuhJm1 1 R

68

Abundance of the gastropod fauna

Most genera in the Brightseat fauna are represented by only a few individuals of single species or forms (table 1). Only six genera or subgenera. occur abundantly in the fauna; another fifteen genera are common; the rema;nin, majority of the taxa are rare in occurrence.

Of the most abundant genera, two _ belong to the mesogastropod family Tun-itellidae. The mOlt commonly represented genua (including two species ranked individually u abundant) is Haustator; the second moat common is Torquesia. Two other mesogastropods, Neverita and Calyptraea. also rank amonr the dominant farms. The remaining two moat abundant genera include the cephalaspida TomatelUu4 and ScapluvuUr.

Among the common genera is a second turritellid genua (Sipaesalill). Other common mesogastropod genera include TeinostDmtJ, Mo.tJa-ilda, EuUma, CalyptrtJphDnu, and CirsotremtJ. Two neogaatropod re~ Lacinia and Siphonalia, are also rather common, as are two entomotaeniatea" SYrM/4 and Creon.ella. Three cephalaspids. Gilbertina, ZikkW'Otio., and Retusa are also common.

The numerical dominance or the turritellida in the Brightseat gastropod fauna suggesta an ec:ological similarity to other Turrltella·rlch assemblaps in both modern (Thorson, 1957; Allmon, 1988) and ancient environments (Merriam. 19(1). Similar assemblages occur in the Upper CretaceoU8 of the Atlantic Coastal Plain (Sohl, 1977), the lower Paleocene Kincaid Formation (Gardner, 1935) and Clayton Formation (Lowe, 1933; Toulmin. 1977) in the Gulf Coastal Plain, and in the late Paleocene Aquia Formation of Maryland and Vu-ginia (Clark and Martin. 1901). Similarly. in Europe, Anderson (1975; 1976) reported that one

69

species of Haustator is the most abundant and two other turritellids rank amonl the most common pstropods in the late Danian to early Selandian age H(lckelhoven Member in the Lower Rhine Embayment of Germany.

It is interesting to note that these turritellid.dominated uaemblagea are generally, though not always, associated with inner-shelf(upper neritic), marine soft.iubatrate deposita (Merriam, i941;-­Allmon, 1988). The Brightseat, however, probably was deposited in deeper, possibly middle neritic, depths (Gibson and others, this guidebook), near the lower limit of the turritellid's typical depth range. Al1mon (1988) noted that several modern turritellida live at depths greater than 100 meters. The presence or abundant turritellids in the Brightseat cannot be used. as evidence or a shallOw· water origin for the formation.

Faunaiaftinjties otthe pstropoda

Two factors hamper a detailed regional comparison and precise biogeographic analysis-or the fauna. First, the large proportion of new species recognized in the Brightseat fauna gives it a highly endemic character. Second, most of the available monograpm.: studies of contemporaneous faunas are out of date and in need of extensive taxonomic revision, particularly at the species level These two problema make compariSon of the faunas at the species level highly unreliable. In order to ovel'a)me these problems in the present study, comparisons of gastropod faunas were undertaken at the generic (and subgenaric) level The generic level is amenable to fast and accurate taxonomic revision and is less susceptible to sampling bias than are studies based upon species·level OCCUlTence data. ~neric·level comparison provides

information about faunal affinities that allows meaningful comparisons among gastropod assemblages.

For the present study, three primary and six secondary geographic divisions of the North Atlantic Ocean Basin margin are recognized (table 2). These subdivisions provide a convenient and meaningful geographU: Cramework within wbich to compare Paleocene gastropod faunas. Within the six secondary divisions, there are ten lithologic units ranging in age from early Danian to early Selandian that contain sufficiently diverse and adequately described gastropod faunas to allow valid generic­level oomparison with the Brightseat as.sem bIage,

As an additional means of simplifying the analysis, occunence data from some of the geologic units in each region were combined and composite regional faunal units were established. (table 2). This waa done far units oC very similar age or lithology (for example, the Kangilia and Agatdal Formations; Tufi"eau de Ciply and Calcaire de Mona within the Mons Formation: and the Cerithium Limestone and Coral and Bryozoan Limestone of the Danian limestone Formation) or where the published occurrence data did not allow more precise stratigraphic differentiation (for example, the Kincaid Formation and lower Wills Point Formation and the upper and lower Clayton Formation). Table 3 summarizes the occurrence data for these composite regional faunal units.

Each gastropod assemblage lived under a unique set of local ecological conmtimu(fur~p~:~p~~d substrate type) that exerted a strong influence on the occurrence and relative abundance of individual taxa. These local ecological conditions acted independently of regional factors (such as physical barriers to migration, currents for larva dispersal, and regional

70

temperature gradients) that controlled regional, or provincial· level , molluscan distribution patterns. In evaluating the extent that local ecological conditions might have inOuenced the distribution of some generaltaxa in the pstropod assemblages, the faunal units were classified in terms of two primary aapecta of their phJBical environment: lithofacies (substrate) type and general environment of ~position (table 4), lithofacies are broadly defined 88 being either carbonate-dominated or clastic (non-carbonate>-dominated. Environment of deposition is keyed to water depth and shelt position. This classification empbasizea fundamental differencea between depositional (and hence ecological) regimes of the faunas.

Differential preservs.Uon of the gastropod Cauna in the individual sedimentary units may also affect the observed composition c:i the assemblages. For exam~ in carbonata-dominated units, aragonitic sheIla may be selectively destroyed or greatly altered. This can re8ult in gaatropod ahella that are too poorly preserved to identify at even the generic level Dissolution significantly affected the gastropod assemblages of the Clayton Formation in the eastern Gulf' Coastal Plain (Tou1min, 1977) 8Ild the Danian limestone Formation of Denmark (Rosenkrantz, 1960), and these two units have the least taxonomic aftinity with the Brightseat (seven and tan shared genera, respectively), Thus, preservational bias can artificially accentuate the role of litbotaciea oontrol on distribution at the expense of the more subtle regional environmental patterns. However, the use of composite, generic-level distribution data compiled from monographic studies appears to mitigate preservation bias sufficiently to allow worthwhile faunal comparisons.

This study indicates that the Brightseat fauna. which occura in clastic

TABLE.2

AGE, LOCATlON, AND GEOGRAPHIC POSmON OF SELECTED PALEOCENE GASTROPOD FAUNAS AROUND THE MARGIN OF THE NORTH ATLANTlC OCEAN BASIN

COMPOSITE GEOGRAPHIC REGIONS GEOLOGIC UNITS AGE REGIONAL

FAUNAL UNITS

z KINCAID FM. EARLY-MIDDLE

=s WESTERN DANIAN WESTERN GULF

tl.. GCP COASTAL PLAIN () ...J (TEXAS) - LOWER------- - -

DANtAN--i= ~- WILLS POINT FM.

LATE DANlAN Z (1)tl..

=s <U EARLY-MIDDLE

EASTERN GUlF

~~ OQ. CLAYTON FM. COASTAL Pl.A1N U EASTERN DANIAN DANIAN

zC) u.. GCP MATIHEWS lANDING a: a: ...J EASTERN GULF :::> (ALABAMA) EARLY w< C) MARlMBR. COASTAl PLAIN .... :E (PORTI:AS CREEK FM.l S El.AN DIAN SElANDIAN. en w ~ ......

'IIORTHERN ACP NORTHERN ATlANTIC ~ ~~~~ ~~~~ BRIGHTSEAT FM. MIDDLE DANIAN COAST AI.. PLAIN

(MARYLAND) DANIAN

!i~i KANGILIA FM. EARLY-MIDDLE

DANIAN WEST GREENlAND WEST GREENlAND

AGATDAL FM. MIDDLE DANIAN DANIAN

0"",

z z TUFFEAU DE CIPL Y MIDDLE DANIAN (!) (j) (MONS FM.) a: < BELGIUM BELGUIM

c( It!

:i >- CALCAJRE DE MONS DANIAN a::: LATE DANIAN U c( (MONS FM.) ~ ~

a: CERITHIUM LS. Z UJ

~ I- (DANIAN EARL Y DANIAN z UMESTONE FM.) DENMARK .... ~ < qg,RALANO Q. DANIAN Z a DENMARK BR~OZOAN LS. EARL V-MIDDLE a:- lI: II~~~~FU\ DANIAN W :J I- UJ en 3: LEllINGE EARLY DENMARK c( w z

GREENSAND SElANOIAN SELANDIAN

71

TABLE 3

OCCURRENCE OF SELECTED GENERA AND SUBGENERA OF GASTFi IN DEPOSITS OF DANIAN TO EARLY SELANDIAN AGE

AROUND THE MARGIN OF THE NORTH ATLANTlC OCEAN BASI

- --,. - -- .-COMPOSITE REGIONAL FAUNAl. UNITS

DANIAN SELANDIAN DANIAN DANIAN NORTHERN DANIAN DANIAN DANIAN SEL.A

GENUSJSUBGENUS EASTERN WESTERN EASTERN A n.ANl1C CP ~LANDBElGlUM DENMARK DEN~ GULFCP GULF CP GULF CP (BRIGHTSEA 1)

Ataphtu. • • ~ (1Wud«;j1Cf»J • • • 1Mdot"~) • • • • T ........ '. • • • V1riw18~) • • ~ • • CJtaU • • • ? C»docI.,4<:14 , Artti2tnu PsIIUdanaI&rit .. • • • AidJlt«»lictl (~) • • • ~»ctJ(~ ? • • Haw,..". • • • • • • T~ • • • • • Torr:Ua • • sr,m...'iI ? MaNda (MaIIIIdI) • • • • • 1.WJIt»~) • • • • ~ • • • • TuM ? • • • ChunmI~J : • ChOo1ImI~ ~ • • • PuiIh«JM • ~ • • • • • ~ • • • • • • ~~ • • I..acM • • ~ • • • PNut/c:IIM • • • , • • • ~(&MNI • 0drasaamII (&wIrpaa.a.) ? • S)'m:IIa(~ • • • Cr8aneII - • • • • ActIGn • • • Tama11111N8 (T CItMIifIIIItM) • • I • ·Crrftr.blwrt • • GiNrIN • • • • • ZJdua. ~(~) • I ? RMuu (Cyfd;ttIna) ? • ~ 1

explanation of (X)~site regional faunal units listed given In Table 2. A -00.- denotes a confirmed OCCL a -1- denotes a questionable occurrence. Aportnalds are omitted from consideraUon due to the inability assign the Brtghtseat matertaJ to a specifk: gerus. Where a partIcUlar subg&nUS is represented In the Bri fauna, occurrences In other units of the geoos 10 which. belongs Is not Indicated unless the same subg' also represented in those units. Occurrence data derived from numerous sources.

72

TABLE"

LITHOLOGICAL AND ENVIRONMENTAL CLASSIFICATION OF COMPOSITE REGIONAL FAUNAL UNITS OF DANIAN TO EARLY SELANDIAN AGE AROUND THE MARGIN OF THE

NORTH ATLANTIC OCEAN BABIN

COMPOSITE REGIONAL DOMINANT ENVIRONMENT OF FAUNAL UNITS LITHOFACIES DEPOSITION

WESTERN GULF COASrAL PLAIN CLASTIC Middle shelf marine DANIAN (approx. 90 m.)

EASTERN GULF COASTAL PLAIN CARBONATE Inner shelf marine DANIAN (20-90 m.)

EASTERN GULF COASTAL PLAIN CLASTIC Inner shelf marine SELANDIAN (20-90 m.>

NORTHERN ATLANTIC COASTAL PLAIN CLASTIC Middle shelf marine DANIAN (BRIGHTSEAT) (90-100 m.)

WEST GREENLAND DANIAN CLASTIC Mixed, vet)' sh.l1ow to midd1e shelf marine

BELGIUM DANIAN CARBONATE Very shallow shelf marine to estuarine

DENMARK DANIAN CARBONATE Middle shelf marine (80-150 m.)

DENMARK SELANDIAN CLAST1C Middle shelf marine

Explanation of composite regional faunal units given in tabJe 3. Lithofacies classified as being dominantly CARBONATE OT dominantly CLASTIC (non-carbonate). Data on lithofacies and environment of deposition derived from numerous aourtU. .

•

73

sediments of moderately deep (middle­neritic) origin (table 4») is generally more closely related to faunas from other clastic units than to those from carbonate-dominated lithofacies) regardless of water depth. The greatest affinity is with the fauna of the West Greenland Danian, with which the Brightseat assemblage shares twenfy; or . nearly half, of ita genera and subgenera (table 3). The fauna of the carbonate­dominated Belgium Danian follows closely, with 16 shared genera. While no strictly contemporaneous assemblages from claatic-dominated units are known in either Belgium or Denmark, the slightly younger (early Selandian) Lellinge Greensand in Denmark shares fourteen genera with the Brightseat. In contrast, the fauna of the early Selandian clastic deposits of the upper member of the Porters Creek Formation in the eastern Gull Coast shares seven genera with the Brightseat. In the Danian of the Gulf region, the clastic units of the western Gulf Danian share nearly twice the number of genera (thirteen) with the Brightseat as does the . carbonate-dominated Clayton Formation of the eastern Gulf Danian (seven genera).

These data indicate that local differences in ecological conditions (as reflected in substrate type) do indeed exert a strong influence on gastropod distribution. However, t.b.is ecological influence does not completely obscure broader regional patterns and relationships.

BIOGEOGRAPmC IMPLICATIONS OF THE BRIGHTSEAT FAUNA

Available data suggest that there were two broadly-overlappmg, more-or­less latitudinally defined, amphiatlantic faunal realms in the North Atlantic

74

Basin during the early Paleocene. The more northerly province is commonly referred to 88 the "Boreal" Province; the southerly province has generally been regarded as a warm-water extension of the sub-tropical to tropical "Tethyan" Realm (Davies. 1929, 1975; Gardner. 1931, 1935).

. - . -,- -~---------- - .. -~

The "Boreal" or Northern Mild­Temperate Biogeographic Province

In the early Paleocene, the so-alled "Boreal" Provinee occupied the northern tier of the North Atlantic Ocean Basin (fig. 4). On its northern and eastern periphery, it encompassed an area that extended from the Labrador Sea and the straits between Greenland and northwest Europe through the region of the Northwest European Tertiary Basin at least as far south sa the Mona and northern Paris Basins, and possibly as far south as the vicinity of the modem Pyren.ee8 (Anderson, 1976; Davies, 1975; Kollmann, 1979).

On the western margin oC the North Atlantic Ocean, the smlthern limit of the "Boreal" Province is less clearly defined. The mixed, but predominsntly eastern and northern Atlantic, affinities of the Brightseat fauna suggest that the "Boreal" Province probably extended, with dim;njahing intluence, at least 88

far south along the AtJ8.Iltic Coastal Plain as the Salisbury Embayment.

Use of the term "Boreal n connotes a faunal (or floral) province characterized by co1d·temperate biotas (Berggren and Hollister, 1974). However, there is ample evidence to suggest that early Paleocene marine and atmospheric paleotemperatures in the Northern Hemisphere remained substantially higher than those recorded at present, so that temperate to warm·temperate conditions existed well into the subarctic

"'I Of

6

3 SWT

80° 600 30° 0° 30° FIGURE 4. ZOOgeographIc dMsAons 01 the marine molluscan ahen faunas and inlelT8d lUlface amant cIrcuIalion In the North AtlantIC Ocean cUIng the early PaIe(Jcene. Paleogeographic reconatRJdions In FJgure 3. NMT - Nofthem Mild--l"If11*a&e ProYlnce; 8WT • Southem Warm-Temperate Provtnce; T - Telhyarl ProvInce: Shaded areas indicate transbionaI zones Of over1appUlg lnfkJence between adJacent provinces. Arrows Indicale Inferred patterns of flow of the doninant surface currents. Data U88d for estabIistung the provtncial zoNdlon and current panem derived from numerous sources.

and even arctic latitudes (Berggren and Hollister, 1974; Frakes, 1979; Krassilov. 1975; OberbAnsli and Hsu, 1986, Savin, 1977; Savin and others, 1975).

A temperate terrestrial climate prevailed at least sa far north as central West Greenland durina the Danian, as demonstrated by the composition of the flora associated with the marine beds of the Agatdal Formation (Rosenkrantz, 1970). Siuillarly, the general composition of the marine macrofauna! assemblages preserved in the West Greenland Danian (including ecbinoids, c:ruataceans, corals, and ~ in addition to the mollusks) is indicative or mild-temperate water conditions (Berggren and Hollister, 1974; Kollmann, 1979; Roaenkrants, 1970). Among the West Greenland patropods are several genera characteriatic of warmer conditions, including Calliosto11UJ, HautltlJtor. the Cypraeidae. Calyptrnea, Pseudoliva, Harpa, and Acteon (Kollmann., 1979; Kollmann and Peel, 1983; Rosenkrantz, 1970). The gastropod faunas from the Danian of Denmark contain a similar component of warm-water genera. The diverse molluscan fauna of the late Danian Calcai.re de Mons in Belgium is also known to contain a substantial number of thermophilic taxa, including among the gastropods Ha.u.stalm-, Torqrusia. and Sigmesalia, Calyptl'aphorus, CiJlyptrcua. Pseutioliva., Drupa, 8Ild Acuon (Davies, 19715; Villatte, 1977).

Though climatic conditions in the northern part of the North Atlantic Basin were clearJy quite mild during Danian time. the occurrence of some taxa with cooler-water affinities (for example. gastropod {smiliea like the Lacunidae and Aporrhaipae and pnera such as Vanikoropsu 8Ild ~rithiella.. particularly in the West Greenland Danian, indicates that the marine climate in the northern part of the basin was at least somewhat cooler than that which prevailed further south.

76

For this study. use of the term "Boreal" to describe the early Paleocene northern North Atlanti,c Ocean marine fauna] province is abandoned in favor oC Northern Mild-Temperate (NMT).

The Southern Warm.Temper.a~ . Biogeographic Province

South of the North.em Mild­Temperate (NMT) Province, a seoond broad early Paleocene Atlantic Ocean faunal province, the Southern Warm-Temperate (SWT) Province, stretched acrose the North Atlantic Basin (fig. 4). The SWT Province was bounded on the south by the circ:um-equatorial "Tethyan" Province. The Tethyan Province is c:haracterized by a rather cosmopolitan biota of clearly subtropical to tropical affinities that occupied the remnants oC the "Tethyan SeaW8J-. which once uten.ded in a broad east-west belt that ccmnect.ed the Atlantic and Paci6c Oceana <Bemren and Holliater, 1974).

There is little paleontological evidence to locate the latitudinal boundaries of the swr Province on the eastern side of the North Atlantic Basin. It probably occupied a relatively narrow zone. extending perhaps from the position or the present-day Pyrenees to the southwaetem tip or the Iberian Peninsula at the Atlantic opening of the Mediterranean Tethys. The SWT Province broadened to the west to encompass the entire Gull of Mexico and Caribbean regiODS. To the north, the deposita of the Gull Coastal Plain contain the northernmost occurrences of typical SWT faunas. To the south. the province merged very gradually with the Tethyan Province. For emmple, the Danian molluscan faunas of Colombia and Trinidad maintain their strongest affinities for those of the Gulf Coastal

Plain and yet exhibit a subtle but definitA! Tethyan influence (Etayo-Serna, 1979; Gardner, 1931, 1935; Rutsch, 1940, 1948).

In contrast to the early Paleocene gastropod faunas of the NMT Province, those of the SWT Province are characterized by a significant increase in the diversity of thermophilic but not, as Kollmann (1979) has pointed out, strictly tropical tam. Conversely, there is a general absence in the SWT Province of cooler-water forma such as CerithielltJ and the Lacunidae. Among the more prominent of the NMT cryophilic gastropods, only the aporrhaids appear to have extended their range southward into the northern (Gulf) half of the 8WT Province. Many of the warmer-water taxa range throughout the entire north-south length of the 8WT Province, and some are known to extend eastward across the Atlantic into the southw.est Asian Tethyan region (Adegoke, 1972; Davies, 1929, 1971, 1975). The consistent southerly increase in the Tethyan component of the SWT fauna, along with the close taxonomic relationships between seyera1species pairs in the Gulf and Caribbean halves of the province (for eumple, between species of HaustatDr, Mesalia, Pseudoliua, and Torquesia), lend a distinctive and internally homogeneous aspect to the province on the we.tem side of the Atlantic Ocean Basin (Harris, 1~96i Maury, 1912; Ru~ 1943; Woodring, 1971).

BiogeolP'aphic Position of the Brightseat Fauna

The gastropod fauna of the Brightseat Formation shares elements in common with those of both the NMT Province and the 8WT Province. This suggests that the Brightseat gastropods flourished

77

within a transition zone between the two provinces. As demonstrated earlier, the Brightseat fauna displays a greater affinity with the Atlantic Danian and early Selandian NMT faunas to the north and east than with oontemporaneoua SWT faUIL88 in the Gulf Coastal Plain­Of particular signjficance ia the appearance in the Brightseat or the Lacunidae and the Aporrhaidae, which are both indicative or somewhat cooler water conditions. No Brightseat lacunida are known from Paleot.ene deposits south of the Salisbury Embayment. To the north, the 1acunids become increasingly diverse and are particularly well represented in the West Greenland Danian The aporrhaida do occur, but only rarely, in the Gull Coastal Plain duriDg the Danian. Like the laCUDida, however, their diversity and abundance also increase northward, and they too ant best represented in the West Greenland deposits. Other Brightseat tau with affinities' for NMT Atlantic forms include an ArchiUctonica (GrtJ1I08Olarium) thai ia closely allied to certain early Paleocene western European and Ukranian species; a very small HaustatDrl that resembles a species from the early Selandian of Denmark and Poland; a Sigmesalia that closely approaches a species compiez widely distributed in the late Danian and early Selandian(?) of Belgium, France, Germany, and Poland; a MtJthildD. (MatAUda) and a CreoMllD. that appear to be closely related to West GreenJand species; and a small Crenilabium that ia very close to a species found in the Danish Selandian.

There is a corresponding SWT influence on then Brightseat fauna. For example, a small number of Brightseat species, including a Tomatellaea, a Gilbertina, and a ZikltU1TJtia. are conspeci.fic with taxa described from the Danian of the western Gulf. Three Brightseat forms from the genera

Teinostoma, OdDstomia., and Retusa strongly resemble Gulf Coastal Plain species.

The Brightseat fauna also includes several forms that appear to be early representatives of species complexes that

lower· latitude waters of the Gulf, Caribbean, and P9Dsmjc regions (Davies, 1971; Marwirk, 1957; Palmer, 1974; Pilsbry and Olsson, 1950).

evolved within the Western Hemisphere ImpHcatioDS tor early Paleocene during the Paleogene. These forms are paleobiopographic recon.truetion generally well represented in the and interpretation Paleogene of the northern Atlantic---------.. ·-·-- ···· . Coastal Plain (for example, in the The distinctive mmure olNMT and Brightseat and Aquia Formations), but 8WT faunal elements that cl1aracterizea have their greatest diversity and the Brightseat fauna suggests that the georraphic distribution in the northern Danian sediments of the SaHsbury half of the SWT Province (the Gulf Embayment accumulated within a zone Coastal Plain). Most important among of transition or overlap between the two these taxa are two turritellids. The first, provinces. The importance of ambient Haustatar, belongs to the "TurritelhJ thermal conditions in controlling the mortoni Subgroup" (seMU Bowles. 1939). distribution of mollusu (as well 88 other The second, TOrqueBiaj is closely related marine organjsms). and hence in defining to members of Bowles' "TurriUlla marine biogeographic units, is well hUTnerosa Subgroup." Both groups are known (Hutchins, 1947; ~ 1964). The well represented in the Gulf and Atlantic boundaries between thermally-controlled Coastal Plain regions durin&, ~e biogeographic provinces are marked by Paleocene, and the widespread gradual thermal gradienta rather than by occurrence of one member of the sharp discontinuities. In the relatively-humerosa group in the Danian of mild and weakiy-differentiated, early Colombia, Trinidad, and Brazil further Paleocene. North Atlantic Ocean, the reinforces the apparent preference of the thermal boundary between the NMT and humerosa complex for the warmer waters SWT Provinces was broad and gradual. of the SWT Province. Additional A gastropod mollusk. assemblage of mixed . Brightseat taD that have affinities with thermal affinities could develop in the Gulf-based species complexes in(:lude the this region, which included the Salisbury bucci.nid Laeinia and possibly the retusid Embayment. lUtusa (Cylichnina). It is postulated that the transitional

Four genera have their earliest zone, in which the Brightseat gastropods known occurrence in the Paleocene lived. developed. at the northwestern. edge sediments of the Brightseat. This group of a thermal ecological barrier. This includes three vitrinellids (Vitrinella barrier, which is analogous 10 that (Vitrinellops), Cyclostremiscua, and presently developed at Cape Hatteras Anticlimax) and a turritellid referred to that de.t1ects the modem Gulf Stream the genua Torcula. Bemuse this is the northeastward away from North America, only known record of these genera in the existed along the Atlantic coast south of Paleocene, their actual distribution at the Salisbury Embayment (fig. 4). This this time is unknown. However, the barrier prevented the southward distribution of these taxa in younger migration of diagnostic NMT Caunal Tertiary sediments reveals a distinct and elements into the Gulf of Mexico and consistent preference for the warmer, Caribbean regioIl5 and at the same time

78

greatly retarded the successful northward migration along the continental shelf of swr elements from the Gulf.

Surface-water circulation within the North Atlantic Ocean Basin during early Paleocene time was dominated by a large anticyclonic gyre of warm water situated in the southern half oC the basin (Fell, 1967; Luyendyk and others, 1972; Bartlett, 1973; Berggren and Hollister, 1974, 1977; Haq, 1981; OberhAnsli and }{sft, 1988). This gyre, which is analogous tD the modern North Atlantic Gyre, enclosed the large warm-water mass that formed the core of the SWT Province. The northern margin of the gyre marked the boundary between the NMT and SWT Provinces. The gyre probably was fed from the east by flow out of the Mediterranean Tethys. Some of this warm Tethyan water flowed westward across the Atlantic and into the Pacific Ocean via the Strai ta of panama as part of a circum-global Tethyan current system. The rest of the water was deflected into the North and South Atlantic Basins.

Much oftha northward-detlected flow proceeded northeastwerq through the Caribbean and into the Gulf of Mexico where it turned eastward across the shallow shelf of the Gulf Coastal Plain Province. The entire Florida Peninsula and Bahamian Platform was submerged at this time (Chen, 1965), and the Gulf water may have re-entered the central Atlantic Basin through the Suwannee Channel across northern Florida.. where it merged with water deflected off the Florida and the Bahamian Platform and gave rise to the early Paleocene equivalent of the Gulf.stream. The configuration of the continental masses around the North Atlantic Basin in Danian time probably deflected the flow of this Paleo-Gulf Stream toward the center of the Atlantic in a more easterly direction than the northeastward

79

direction it baa today. This deflected eastward flow, and thus the position of the ecological barrier between the NMT and swr Provinces~ was probably well south of ita present position at Cape Hatteras. A possible location for the deflection point and hamer was in the vicinity or the so-called ·Charleston Bump", a prominent bathymetric high compaaed of a progradational wedge of Late Cretaceous clastic sedimenta. which was developed on the northern side of the Blake Plateau off the southern coast of South Carolina. Pinet and others (1981) have shown that since at least the late Paleocene, this feature has periodically deflected to the east and 80uth the normally northeastward flow of the Gulf Stream system.

As the Paleo-Gulf Stream moved eastward across the Atlantie, it became the North Atlantic Boundary Current, the northern margin of the SWT gyre. As it approached Europe, some oftha warm water spread out to the north and south as the current system was deflected by the continental mass, and some water continued eastward into the Paris and Mona Basins. The warming influence of this flow may aocount in part for the substantial thermophilic component developed within the NMT Province molluscan Caun.u of the Belgian Danian. This component is most pronounced in the fauna of the Calcaire de Mons, lending it a distinctly transi tiona! aspect, similar to that of the Brightseat. Some of the flow was deflected south toward the Bay of Biscay and the Iberian Peninsula to complete the gyre. The remainder of tha flow was deflected to the north along both coasts of Greenland, extending ita warming influence well into the northern reaches of the ocean basin that included the site West Greenland Danian deposits.

To summari%e, the thermal regime of the early Paleocene North Atlantic Ocean

was dominated by the persistent northward distribution of Tethys-derived warm water from the swr gyre. Consequently, the latitudinal thermal contrast within the basin was much lower than it is today, and a temperate marine climate existed throu(hout the ocean. AI, a result, the latitudinal environmental contrast that existed at

continental margin: paleogeography, paleoclimatology and seafloor spreading: In Hood. P .J., ed.. Earth science symposium on offshore eastern Canada: Geological Society of Canada. Paper 71-23, p. ~72.

Bennett. R.1l, and Collinl, a.c., 1952, Brightseat Formation, a new name for aedimenta 01 Paleocene age in Maryland.:

this time allowed the development of Dnly- - - ,- --Jo~~_~f the Washington Academy of Scieneea, v.-~ p. 114-118. --- -

two broad, cloaely related, molluscan biogeop:aphic provinces. The fauna of the Brightseat representa a transitional assemblage developed in the zone of overlap in the vicinity of the Salisbury Embayment.

REFERENCES

Adegoke, 0.8., 1.972, Tethyan affinities of West Afriean Paleogene Mollusca: Section 7, Paleontology, Twenty-fourth International Geoloaical Congt'eB8, Canada, 1972, p. 441-449.

Allmon, w.n., 1988, Ecology of Recent turritelline Gastropoda (Proaobranchia. Turritellidae): Current knowledge and paleontologieal implications: Palaios, v. 3, p. 259-284.

Anderson, H . ..J., 19715. Die Fauna dar paltloclnen HllckeIhovener Schichten sus dem Schacht Sophia Jacoba 6 CErk.elenzer Hont, Niederrheinieche Bucht). Tell 3: Scaphopoda. Gastropoda. Ceph8Jopoda: Geologica et Palaeontological v. 9, p. 141-171-

--, 1976, Stratigraphie and paleogeographic significance of mollusk faunu from the Paleoeena of the NW-German Tertiary Basin.; IGCP Project 1.24, The Northwest European Tertiary Buin, Report No. I, p. 92-95.

---, 1982, Daa Pall&:An in Nordwestdelltschland Obenicht Uber den gegenwirtigen Stand der Kenntnia: Geologica et Palaeontologica, v. 15, p. 161-166.

Bartlett, GA, 1973, The Canadian Atlantie

80

Berggren, W A. 1964, 'nle Maestrichtian, DaniaQ and Montia Stage. and the Cretaeeous-Tertiary boundary: Stockholm Contributions to Geology, Y. 11, no. 6, p. 10;),176.

--, 1971. Tertiary boundarie. and correlations: In Funnell, B.M.. and Riedel. W.R., eel. The micropaleontology of oceana: Cambridge Univenrity Pres., Cambridge. p. 693-809.

Berggren, WA, and HolliJter. c.n., 1974. Paleogeography, paleobiogeography and the history of dreulation in the Atlantic Ocean: 17& Hay, W.W., eel., Studiea in palecHC:eallOl"lphy: Society of Economic Paleontologilta and MIneralogists. Special Pub~tiOD No. 20, p. 126-188.

---, 1977, Plate tectoniea and paleocircula.tion • commotion in the ocean: Tectooophysiea, v. 38~ nOl. 1·2, p. 11-48.

Blow, W.R., 1969, Late middJe Eocene to Recent planktonic foraminifera1 biostratigraphy: In Proceedings of the First In temational Conference on Planktonic Microfossils, Geneva, 1967, E.J. Brill, Leiden, p. 199-422.

Bowles, Edgar. 1939, Eocene and Paleocene Turritellidae of the Atlantic and Gul( Coastal Plain of North America: Journal of Paleontology, v. 13, p. 267-336.

Bretsky, Sara., 1974, A powle ease of phyletic gradualism in Paleocene Bivalvia (Monusca): Geological Society oC America, Abstracts with Programs. v. 6, p. 666.

Breuky, Sara, and Ka~ E.G., 1971, Morphological variability and temporal change in a Paleocene lu.cinid bivalve moUusk: Bulletin of the Geological Society of Denmark, v. 26, p. 161·174.

Cate, AS., 1982, Biostratigraphie framework

of the Cretaceou.atrertiary boundary: I" Maddocks, R.F., eel, Texas Ostracoda: Guidebook of excursions and related papers for the Eighth Intemational Symposium on Ostracoda., Houston, 1982, p. 211-222.

Chen, C.S., 1966, The recional lithostratigraphic analysis of Paleocene and Eocene roek.s of Florida: Florida Geological Survey Bulletin 45, 105 p.

Clark, W.B., and Martin, G.C., 1901, TIte Eccane deposita of MaJylanck Maryland Geological Survey, p. 11-33L

Davies. AM., 1929, Faunal migrations since the Cretaceous Period: Proceedings a( the Geologists' Association, v. 40, no. 4, p. 307-327.

---, 1971, Tertiary (aunas, 2nd ed. (1971, 1975) (revised by Eames, F.E.); Vol. 1 (1971), The composition of Tertiary faunaa: George Allen" Unwin, London, p.7-571.

--, 1975, Tertiary f'au.nas, 2nd ed. (1971, 1975) (revised by Eames, F.E.); Vol. 2 (1975), The sequence of Tertiary faunas: George Allen" Unwin., London, p. 7-447.

Etayo-Sema, Fernando, 1979, La fauna de Moluacos del Paleoceno de Colombia. Moluacos de una capa del Paleoceno de Manantial (G~ira): Baletin de Geologia de la Univenidad Induatrial de Santander, Bucaramanga (Colombia), v. 13, no. 27. p. 5-56.

Fell, RB., 1967, Cretaceous and Tertiary surface CUrTentB of the oceana: In Bames, H., ed., Oceanography and marine biology, Anona! Review, v. 5, p. 317·341.

Frakes, L.A., 1979. Climatel throughout geologie time: Elsevier, Amsterdam, p. 1-310.

Freden1taen, N.O., Gibson, T.G., and Bybell, L.M., 1982, Paleocene-Eocene boundary in the eastern Gulf Coast: Gulf Coast Association of Geological Societies, Transactions, v. 32, p. 289-294.

Gardner. Julia, 1931, Relation of certain foreign faunas to Midway fauna olTuas: Bulletin of the American Association of Petroleum Geologists, v. 15, no. 2. p. 149·160.

81

----, 1935, The Midway Group of Teua. Ineluding a chapter on the coral fauna by T. Wayland Vaughan and Willis Parkison PopenOe: University of Texas Bulletin No. 3301 (1933), p. 5-403.

Gibson, T.G .. Mancini, EA. and Bybell. L.M., 1982, Paleocene to middle Eocene stratigraphy of Alabama: Gulf Coast Association or Geological Societies, Tran-.etiona, no. 32, p. 449-458.

Glibett, Muime. 1973, Revision dee gaatropoda du Danien et du Montien de 1& &Igique, L Lea patropoda du CaIcaire de Mona: Institut Royal des Seiencea Naturelles de Belgique. M4moire No. 173. p. 1-118.

Govoni, 0.1.., 1983, Gastropod mollu5ea from the Bright&eat Formation (paleocene: Danian) of Maryland! Unpubliahed MS Thesis. TIte George Washington University, Washington, D.C., p. 1-270.

Hall, C.A, Jr., 19M, Shallow-water marine climates and moDU8C8Jl provinces: Ecology, v. 46, no. 2, p. 228-234.

Haq, B.U., 1981, PaJeogene paleoceanography: early Cenozoic oceana revisited; Colloque C4. Geologie des Oceans, Twenty-linh International Geological Congress, Paria, 1980: Oceanologica Aeta., v. 4 (Supplement), p. 71-82.

Hanis, G.D., 1896, The Midway Stage: Bulletins of American PaJeontology, v. I, no. 4, p. 1-167.

Hazel, J.B .• Edwards. L.E.. and Byben, L.M., 198-', Significant unconformities and the hiatu.aes represented by them in the Paleogene of the Atlantic and Gulf Coastal Province: 1,. Schlee, J.B .• ed., Interregional unconfonnities and hydrocarbon Accumulation: American Association of Petroleum GeoJogists Memoir 36, p. 59-66.

Hooyberghs, H.J.F., 1980. Present status in the biostratigraphy by means of nannoplankton and planktonic foraminifera in the Tertiary of Belgium: IGCP Project No. l24, The Northwest. European Tertiary Basin, Report No.6, p. 106-118.

Hutchins, L.W., 1947, The bases for

umperature zonation in geographical distribution: Ecological Monognlphs, v. 17, no. 3, p. 325-335.

International Geological Correlation Programme, 1980, A lithostratigraphic scheme for the NW·European Tertiary Basin: Kockel. F .. compHer, IGCP Project. No. l.24, Newaletters on Stratigraphy, v. 8, no. 3, p. 236-237.

--, 1988, The Northwest European Tertiary Baain: Result. of the International Geolociw Correlation Programme, Project No. 124. Vinken, a, compiler: Geoloeiaches Jahrbuch. Seriel ~ no. 100, 508 p.

Kauffman, E.G., and Beauchamp, R.G" 1969, Sediments of faunas of Paleocene marine cycles., Potomac River Valley. Geological Society of America. Abstracta with Programs, Part 7, p. ll9-12O.

Kollmann, HA, 1979, Distribution patterns and evolution of gastropods around the CretaeeouaiTertiary boundary: In. Christensen, W.K., and Birkelund, T., eds., Cretaceouafl'ertiary boundary events symposium, D. Proceedings, Copenhagen, p.83-87.

Kollmann, H.A., and Peel, J.8 .. 1983. Paleocene gastropods "from Ndgssuaq, West Greenland: Gntnlanda Geologiske Undersegels8, Bulletin 146, 115 p.

Krusilov, V.A., 1975, Climatic changes in eastern Asia as indicated by fossil floras. U. Late Cretaceous and Danian: Palaeogeography. Palaeoclimatology, Palaeoecology, v. 17, no. 2. p. 157·172.

Lowe, E.N., 1933, Midway and Wilcox Groups: Miasissippi State Geological Survey. BulletiD No. 25, p. 1-125".

Luyendyk, B.P., Fonyth, D., and Phillips, J.D., 1972, Experimental approach to the paleocirculation of the oceAnic surface waters: Geological Society of America Bulletin. v. 83, no. 9, p. 2649-2664.

Marliere, R., 1977, Historique; Ie 80ndage de Mona; Ven une delimitation du stratotype: III Sur Ie stratotype du Montien a Mons: M~moirel pOUT Servir a l'Explication des Cartes Geologiques et Minieres de 18 Belgique, Memoire No. 17, p. 3-25.

82

Martini, Erlend, 1971, Standard Tertiary and Quaternary calcareous nannoplankton zonation: III Farinacci, A. ed., ProceedingJ of the II plankronic conference, Rome, 1970, v. 2. p. 739-785.

Marwick, J., 1957, Generic revision of the Turritellidae: Proceedings of the Ma.lacologica1 Society of London, v. 32, pt. 4, p. 144-168.

Maury, C.J., 1912, A contribution to the paleontology of Trinidad: Journal of the Academy of Natural Sciences of Philadelphia, 2nd sar., Y. lli; no. 3, p. 25-112.

Merri~ C.W .. 1941, Fossil turritellu from. the Pacific Coast region of North America: Univenity of California PuhUeation, Bulletin of the Department of Geological Science .. v. 26, p. 1-214.

Oberh4nsli, Hedi, and Hsu, K.J., 1986, Paleocene - Eocene Paleoceanography: In. Had. K.J., ed., Mesozoic and Cenozoic Oceans: American Geophysieal Union, Geodynamies Series, v. 15, p. 85-100.

Palmer, It V.W., 1974, Composition with reJationahip. of Paleocene and Eocene mol1wscan fauna of the East Americas: Verhandhmgen der Naturfonehenden GeseI1schaft in Basel, Y. 84, p. 1, p. 468-482.

Pilsbry, H.A, and Olsson, A.A, 1950, Review , of Antklinuu, with new Tertiary species (Gastropoda, Vitrinellidae): Bulletins of American Paleontology, v. 33, no. 135, p. 1-22.

Pinet, P.R., Popenoe, Peter, and Nelligan, D.F., 1981, Gulf Stream: reeonstruetion of Cenozoic now patterns over the Blake P14teau: Geoloe,y, v. 9, no. 6, p. 266-270.

Rasmussen, H. W., 1965, The Danian affinities of the Tuff"eau de Ciply in Belgium and the "Post-Maastrichtian" in the Netherlands: Mededelingen van de Geologische Stichting, New Series, no. 17, p.33-38.

Robaszynski, Francis, 1979, Cret.aceousll'ertiary boundary events in the Mons Basin with remarks on the Danian and the Montian of this area: Ira Christensen, W.K, and Birkelund, T., ed., CretaceoustTertiary boundary events

sympoaium, II, Proceedings, Copenhagen, p. 143.150.

Rosenkrantz, Alfred, 1960, Danian Mollusca from Denmark: In Rosenkrantz, A., and Brotun, F., eds., Part V, the Cretaceous-Tertiary boundary: In Sorgenfrei, T., eci., Report of the Twenty·first International Geological Congre1ls, Norway. 1960, p. 193-198.

---, 1970, Marine Upper Cretaceous and lowermost Tertiary deposits in West Greenland: Meddelelaer fra Dansk Geologisk Forenin •• v. 19, p. 406-453.

Rutsch, Rolf, 1940, Evolution of tropical Ameriean Tertiary faunas and theory of continental drift: Proceedings of the Sixth Pacific Science Congress of the Pacific Science Association, v. 2, p. 619·626.

---, 1943, Die PaJeocaen . Mollusken der Inseln Trinidad und Soldado Rock (Britisch Weatinruen): Eelogae Geologicae Hetvetiae, v. 36, p. 139-192.

Savin, S.M., 1977, The history of the earth's surface temperature during the past 100 million yean: In Donath, F.A, StehH, F.G., and Wetherill, G.W., eds .• Annual Review of Earth and Ftanetary Sciences, v. 5, p. 319-aM.

Savin, S.M., Douglas, R.G., and Stehli, F.G., 1975, Tertiary marine paleotemperatures: Geologiea.l Society of America Bulletin, v. 86, no. 11, p. 1499-1610.

"'---, 1977, Benthic marine molluscan associations from the Upper Cretaceous of New Jersey and Delaware: In Owens, J.P., Soh). N.F., and Minard, J .P., A field guide to Cretaceous and lower Tertiary beds of the Raritan and Saliabury Embayments, New Jersey, Delaware, and Maryland: American Association of Petroleum GeologisWSociety of Economic Paleontologista and Mineralogists, Annual Meeting, Washington, D.C., 1977, Field Trip Guidebook, p. 7o-9L

Thorson. Gunnar, 1957. Bottom communities {!lublittoral 01' shallow shelO: Ira Hedgpeth, J. W., ed., Treatise on marine ecology and paleoecology, Vol. 1. Ecology: Geological Society of America, Memoir 67, p.461-534.

Toulmin, LD., 1977, Stratigraphic

83

distribution of Paleocene and Eocene fossils in the Eastern Gulf Coast region: Geological Swvey of Alabam~ Monograph 13, v. 1 and 2, p. 1-602-

Villatte, J ., 1977. Lei Mollusques du sondage de Mons: In Sur Ie stratotype du Montien a Mons: Memoires pour SemI' a l'Explication des Cartes GeologiQues at Minieres de Ia Belgique, Memoire No. 17: p. 27-219.

Woodring, W.P., 1971, Zoogeographic affinities of the Tertiary marine molluscan faunas of northeastern Brazil: Simposio Brasileiro de Paleontologia, Anais d.a Academia BTB.Sileira de Ciencias, v. 43 (Supplement), p. 119-124.

84

Potomac River Paleocene and Eocene Stop Descriptions

By Thomas G. Gibson and Laurel M. BybeU

INTRODUcrION

There will be eight stops along the shores of the Potomac River where we will see Paleocene and Eocene strata (fig. 1). The strata generally have a gentle eastward dip in this area, and we will encounter progressively younger beds as we proceed eastward down the river. Stop 1 will be in lower upper Paleocene beds, and Stop B will be in upper lower Eocene beds. These eight localities contain all nine calcareous nannofossil zones from upper Zone NP 5 through probable Zone NP 13.

As we leave the Willow Landing Marina and proceed southeastward down Aquia Creek, we will pass sediments that bracket the CretaceoWl-Tertiary boundary. The boundary section in this area consists of nonmarine and marginaJ-marine, Lower Cretaceous strata of the Potomac Group that are overlain by non-calcareous, marine, lower upper Paleocene deposits of the Aquia Formation. These deposits are found in small sections that are exposed in most instances along the southern bank of Aquia Creek; our limited time precludes stopping to see these beds.

The lithologic sections for each of the eight field trip stops (figs. 2-9) are accompanied by a brief discussion of the stratigraphic position of the strata, other geologic aspects of the stop, and by a partial listing of the calcareous nannofossils, and where possible, the foraminifers that occur at each locality.

85

~

38·20'

.-0 o

,)..

o ~ -y o

77·'5' 77"10'

MARYLAND

VIRGINIA

77"15' 77·10'

N

l' o 1 2 3 4 5

I I I I 1- I SCALE IN MILES

Figure 1. Map of Potomac River area showing the location of field ~rip stops.

38"20'

•

LITHOLOGY LEGEND

111--------------------_ ... -

II ------------------

~ ~

~

CONGLOMERATE

SAND

INDURATED SAND

CLAYEY SAND

SILlY CLAY

CLAY

GLAUCONITE

SHEll

~ TURRII'EUA

~ G CALCAREOUS MICROFOSSIL SAMPLE

87

STOPl

Right (southwest) bank of the Potomac River, 1.5 miles below (southeast) of Youbedamn Landing at the mouth of Aquia Creek, Stafford County, Virginia, Passapatanzy 7 1/2-min. quadrangle. This is the type locality for the Aquia Formation.

........................................................... Thickness (ft)

Aquia Formation Sand, buff-tcHlrange, fine-grained, glauconitic, massively- bedded;

contains scattered mollusks; interspersed shelly sandstone beds 0.5-2.0 ft thick occur in lower part (bed 9 of Clark and Martin, 1901) .................................................. 12.0

Sand., buff-to-olive, fine-grained, glauconitic; contains abundant Turritella (bed 8) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 17.0

--- undulating and burrowed surface -----

Sand. olive-gray (5Y 312), very 5ne-grained, slightly clayey, glauconitic, micaceous; more sandy than below; contains some scattered mollusks (bed 7) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 10.0

.------ undulating surface --------

Sand, olive-gray (5Y 312), very fine-grained, slightly clayey, very glauconitic, with abundant mollusk shells, especially Turrilella (bed 6) ..................................... . . . . . . . . . . . . . 2.5

Sandstone, olive-gray (5Y 411), glauconitic, with abundant mollusk shells (bed 5) .. "......................................... 1.5

Sand, olive-gray (5Y 312), very fine-grained, clayey, massively-bedded, bioturbated, locally indurated, very glauconitic. with abundant oyster and other mollusk shells (bed 4) ......................... 5.0

Sandstone, olive-gray (5Y 4/1), fine to very fine-grained, glauconitic, with abundant mollusk shellB; laterally grades into three, separate, indurated beds (bed 3) .............................. 1.0

Sand, olive-gray (5Y 312) in upper part and greenish black (5G 211) in lower plfrt, fine to very fine-grained, clayey to slightly clayey, bioturbated, with green-stained quartz, abundant glauconite; is locally indurated, with abundant mollusk shells, oyster lenses, and shell lags; some lignite in lower, less shelly part (bed 2) ........ 10.0

-----------beach level ---------- ... -

88

-STOP 1 - 1.5 MILES BELOW AGUJA CREEK

SERIES FORMATION

w Z w o o w -' « a...

z o ~

« ~ a:: o

a: w CO ~ LU ~

« C/) Z

~ o a.. CI) e::( a..

LL r---

a: UJ CO ~ W

« ~

::J >-a «

~ « « l-e::( 0 C/)

a..

NAN NO. BED LITHOLOGY ZONE

NP 9 8

NP 8 6

NP 7

NP 6

4 \t~;~>.;~i~-+-~~1~ 3 . ' .. ~ .rr-:;. .. : '~ -~~-- -<::J

NP5

FEET

50-

40-

30-

20-

10 -

.' .... . ~--~----~~----~~-~-'~-'~' ~,,~,,~.~ .. ~.~. ~'~'~~'~-'~-~~------O-

89

Ward (1985) designated this locality as the lectostratotype of the Aquia Formation. This locality is probably the same sampling site that Cushman (1944), Shifflett (1948), and Nogan (1964) used for their foraminiferal studies, and it is also the same locality from which Loeblich and Tappan (1957) obtained the holotypes and paratypes of several planktonic species. The sandy upper part of the Aquia Formation typically exhibits considerable weathering when it is at the tops of exposures, such as at Stop 1. The condition of the upper part of this exposure has deteriorated over the past 10 years. At the next two stops, the upper beds of the Aquia are exposed closer to water level and are in a less-weathered condition.

Clark and Martin (1901) subdivided the Aquia Formation into a series of numbered lithologic "zones" that currently are called "beds." These bed numbers can be applied to the Aquia Formation in its exposures along Aquia and Potomac Creeks. However, these numbers can be applied only partially to adjacent exposures in Maryland and Virginia (Bybell and Govoni, 1977), and in most cases the beds cannot be recognized in the subsurface.

The Aquia Formation was divided by Clark and Martin (1901) into two members, the lower Piscataway Member and the upper Paspotansa Member; they separated the members at the contact between beds 7 and 8, and later workers (for example Beauchamp, 1984) also used this same level to distinguish the two members. Ward (1985) considered that the m~or sedimentary change in the formation at this locality (Stop 1) was from a clayey sand in beds 2 through 5 to a very well-sorted, fine sand in beds 6 through 9, and he proposed a placement of the member boundary at the bed 5 - bed 6 contact. Ward noted that floral and faunal changes also had been reported at this level; bed 5 is placed in calcareous nannofossil Zone NP 7, and bed 6 is placed in Zone NP 8.

The first author's work shows, however, that both at this locality and at other localities in this area, bed 6 and even part of bed 7 are as clayey as many intervals in beds 2 and 4; although beds 6 and 7 are somewhat transitional in the amount of clay that they contain, overall they appear more similar lithologically to the lower Piscataway Member than to the upper Paspotansa Member where Ward placed them. An undulating and highly burrowed surface occurs between bed 7 and 8; this surface divides what we consider to be the major lithologies in the section: a lower, more or less clayey sandy section overlain by a more purely sandy section. This swiace between beds 7 and 8, the one upon which the original member separation was based, is scoured and burrowed. It probably represents an unconformity contained within Zone NP 9; the amount of time the diastem represents within this rather long microfossil zone is uncertain.

In addition to the disconfonnity identified by Ward at the bed 5-6 contact, there also are surfaces higher in the Aquia Formation than the bed 5-bed 6 contact that also exhibit physical, biological, and zonal changes. Within bed 6 occurs the calcareous nannofossil zonal change from Zone NP 8 to Zone NP 9. Also, an undulating surface of uncertain significance occurs at the top of bed 6.

The lowermost Aquia strata at Stop 1 are placed in the upper part of Zone NP 5 (early late Paleocene). Zones NP 6, NP 7, NP 8, and NP 9 (late Paleocene) also are present in the formation. It is uncertain how much calcareous fossiliferous Aquia is present below beach level at this location, but it could be from 5 to 20 feet. Underlying these sediments would be the non-calcareous bed 1 strata that are exposed along the south bank. of Aquia Creek.

90

Calcareous Nannofossils

Over the past 15 years, approximately 75 samples have been collected from this locality. Calcareous nannofossils are fairly abundant at Stop 1, provided that the samples are taken six inches to one foot below the weathered surficial zone. However, the preservation and abundance of the calcareous nannofossils can vary significantly from year to year; this appears to be dependent upon how long the sediments are exposed to weathering processes. These cliffs are subject to slumping, and when this occurs. the resulting fresh exposures contain better-preserved calcareous nannofossils. Unfortunately, this outcrop currently has a significant amount of overgrowth, which has impeded slumping in recent years.

The most commonly-occurring species are listed below for each of Clark and Martin's (1901) beds. Asterisks (*) indicate stratigraphically diagnostic species.

Lower bed 2 samples - Zone NP 5 - fair-to-good preservation, one specimen per 1-10 fields of view at 500X magnification.

Chiasmolithus bickns Coccolith us pelagicus Cruciplacolithus sp. Cyciagelosphaera sp. Ericsonia subpertusa Fasciculithus inuolutus *Heliolithus cantabriae Hornibrookina sp.

Markalius inversus Neochiastozygus concinnus Placozygus sigmoides Toweius eminens Toweius pertusus Toweius touae

Upper bed 2 samples - Zone NP 6 - fair preservation, 1-5 specimens per field of view at 500X magnification.

Chiasmolithus bidens Coccolith us pelagicus Cyclagelosphaera sp. Ericsonia subpertusa Fasciculithus involutus Heliolithus cantabriae "'Heliolithu8 kleinpellii Hornibrookina sp.

Markalius inversus Neochiastozygus concinnus Placozygus sigmoides Scapholithus apertu8 Toweius eminens Toweius pert usus Toweius touae

Bed 3 sample - Zone NP 6 - poor preservation, one specimen per 1-10 fields of view at 500X magnification.

Chiasmolithus bidens Coccolith us pelagicus Hornibrookina 8p. Neochiastozygus concinnus Toweius pert usus

91

Lower and middle bed 4 samples ~ Zone NP 6 - fair preservation, 1-10 specimens per field of view at 500X magnification.

Braarudosphaera bigelowii ChiasmoZithu8 biLUns CoccolUhus pelagicus Cyclagelosphaera sp. Ericsonia subpertusa Fasciculithus involutus Goniolithus {luckigeri Heliolithus cantabriae *Heliolithus kleinpellii

Hornibrookina sp. M arkalius apertus Markalius inversus Neochiastozygus concinnus Placozygus sigmoUks Toweius eminens Toweius pertusus Toweius tovae

Uppermost bed 4 and bed 5 samples - Zone NP 7 - fair preservation, one specimen per 1-10 fields of view at 500X magnification. The sample from the upper few inches of bed four, which contains Discooster mohkri, may represent a mixed assemblage as a result of downward burrowing from the overlying bed.

Braarudosphaera bigelowii Chiasmolithus bidens Coccolithus pelagicu8 *Discoaster mohleri Fasciculithus inuolutus Heliolithus kleinpellii Hornibrookina sp. Markalius apertus

Markalius inversu8 Micrantholithus sp. Neochiastozygus concinnus Placozygus sigmoides Scapholithus apertus Toweius eminens Toweius pertusus Toweius tovae

Lower bed 6 samples - Zone NP 8 - fair preservation, 1-10 specimens per field of view at 500X magnification.

Biantholithus astralis Braarudosphaera bigelowii Chiasmolithus biLUns Coccolith us pelagicus Cruciplacolithus sp. Cyclagelosphaera sp. Discooster saZisburgensis Ellipsolithus distichus Ericsonia 8ubpertusa Fasciculithus involutus *Heliolithus riedelii

92

Hornibrookina sp. Markalius apertus Markalius inversus Micrantholithus sp. Neochiastozygus concinnus Placozygus sigmoides Toweius eminens Toweius pertusus Toweius tovae Zygodiscus herlyni

Upper bed 6 samples - Zone NP 9 - fair preservation. 1-5 specimens per field of view at 500X magnification.

Biantholithus astralis Braarudosphaera bigelowii Chiasmolithus bidens Coccolith us pelagicus Cyclagelosphaera sp. *Discoaster multiradiatus Discoaster salisburgensis Ellipsolithus distichus Ericsonia subp€rtusa Fasciculithus involutus GoniDlithus /Zuckigeri

Heliolithus riedelii Hornihrookina sp. Markalius apertus Markalius inversus Neochiastozygus concinnus Placozygus sigmoides Scapholithus apertus Toweius eminens Toweius pe1'tusus Toweius tovae Zygodiscus herlyni

Bed 7 samples - Zone NP 9 - fair-to-poor preservation, one specimen per 1-5 fields of view at 500X magnification. The upper part of this bed is barren of calcareous nannofossils.

Biantholithus astralis Chiasmolithus bidens Coccolithus pelagicus Cruciplacolithus sp. Cyclagelosphaera sp. *Discoaster multiradiatus Discoaster salisburgensis Ellipsolithus distichus Ericsonia subpertusa Fasciculithus involutus

Fasciculithus schaubii M arkaliu8 apertus Markalius inversus Neochiastozygus concinnus Placozygus sigmoides Toweius eminens Toweius pert usus Toweius tovae Zygodiscus herlyni

Bed 8 samples - Zone NP 9 - fair-ta-good preservation, 1-10 specimens per field of view at 500X magnification. The lower part oftrus bed is barren of calcareous nannofossils, and the upper part has interspersed barren samples and samples containing calcareous nannofossils with fair-to-good preservation and 1-10 specimens per field of view at 500X magnification.

Biantholithus astralis Braarudosphaero bigelowii Chiasmolithus bidens Coccolith us pelagic us Cruciplacolithus sp. Cyclagelosphaera sp. *Discooster multiradiatus Discooster salisburgensis Ellipsolithus distichus Ericsonia subpertusa Fasciculithus involutus

93

Fasciculithus schaubii Goniolithus {luckigeri Lophodolithus nascens Markalius apertus Markalius inversus Placozygus sigmoides Scapholithu8 apertus To wei us eminens Toweius pertusus Toweius tovae Zygodiscus herlyni

Bed 9 samples - probable Zone NP 9 - poor preservation, one specimen per 1-10 fields of view at 500Xmagnification. Only two sample were collected from this bed at this locality, and the upper sample was barren of calcareous nannofossils.

Ericsonia subpertusa Scapholithus apertus Toweius pert usus Zygodiscus herlyni

Foramjnifers

Foraminiferal assemblages from beds 2 and 4 have relatively low benthonic species diversities of 10-17 species. The assemblages are heavily dominated by Anomalinoides umboniferus, but they also contain significant numbers of polymorphinids (particularly Globulina gibba), Nonion cf. N. graniferum, andPararotalia perclara. Planktonic specimens range from totally absent in some aliquot assemblages of 300 foraminiferal specimens to a few rare Subbotina specimens in other assemblages. The depositional environments vary from inner inner-neritic water depths to middle inner-neritic depths (30-200 feet).

The benthonic diversity in the bed 6 assemblages increases to approximately 20 species. Although Anomalinoides umboniferus is still an important component of the benthonic assemblage, many of the specimens have a plano-convex test and prominent umbilical flaps, and they grade into morphologic characteristics suggestive of Hanzawaia. Adult specimens of Subbotina occur in low frequencies in this bed. The assemblages suggest deposition in middle inner-neritic environments.

Planktonic foraminifers are relatively rare in all samples from beds 2-7 at this locality, and they usually compose only one or two percent of the assemblage. Most planktonic specimens belong to Subbotina, but Acarinina specimens are found in some intervals along with lesser numbers of Morozovella. Although planktonic specimens compose a small percentage of the aliquots from the samples, the relatively large numbers of foraminiferal specimens in many of the samples indicates that fair numbers of planktonic specimens can be obtained if a large volume of sediment is processed, and the specimens are concentrated by flotation. Bed 6 yields the largest planktonic assemblage in the Aquia in the field trip area A sample from bed 6 at a locality 200 yards down river from this stop contains Acarinina aquiensis, Morozovella acuta, M. angulata, Planorotalites chapmani, and P. imitata; this suggests probable placement in Zone P4. Loeblich and Tappan (1957) obtained specimens of Planorotalites pseudomenardii from 15 to 17 feet above the beach in this area, which probably corresponds to bed 6. Nogan (1964) also reportedP.pseudomenardii from his Aquia Creek section, but gave no detailed locality information.

This stop should be the same location as, or at least very near to, the locality sampled for Loeblich and Tappan's (1957) classic paper on planktonic foraminifers of the Gulf and Atlantic Coastal Plains. Either the holotypes or the paratypes of the species listed below were obtained from these Aquia beds. The footage following the species name is the height above beach level where the type sample was collectecL The sample heights above beach were listed in three-to~four foot segments, and it appears likely that channel samples were taken for these intervals.

94

Globigerina aquiensis L&T, holotype 10-13 ft, paratype 6-9 ft Globorotalia apanthesma L&T, holotype 10-13 ft Globorotalia hispidicidaris L&T, holotype 15-17 ft Globorotalia reissi L&T, holotype 0-3 ft Globorotalia trichotrocha L&T, holotype 3-6 ft Globorotalia tribulosa L&T, paratype 14-16 it Globorotalia perclara L&T, paratype 6-9 ft

The Aquia Formation above bed 7 is difficult to reach at this locality; in addition, foraminiferal assemblages in these upper beds are weathered because they are near the top of the exposure. Less-weathered examples of these beds, which are closer to beach level, are present at the next two stops.

95

STOP 2

Right (south) bank ofPot(jmac Creek, at the western end of an unnamed bluff just to the west of Bull Bluff, King George County, Virginia, Passapatanzy 7 IJ2-minute quadrangle .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Thickn.ess (ft)

Aquia Formation

Sandstone, light-olive-gray, glauconitic (bed 9 of Clark and Martin, 1901) ...... . . . ...... .. ................................ .. 6.0

Covered interval . . .. . .... . ......... . .......................... . 24.0

Sand, medium-dark-gray-green, fine-grained, clayey, glauconitic, massively-bedded, bioturbated; sandier than below; contains scattered molluscan shells (bed 7) .. . .... . ........... . . ... .. . .. 2.0

-------- undulating surface with 0.5-1.0 it relief ---------

Sand, medium-dark-gray-green, fine-grained, clayey. glauconitic, massively-bedded; contains very abundant and diverse molluscan shells, common corals, vertebrates, and lignite (bed 6) ........... . .. ..... . . . . . .. ............. . .. . ...... . .... 2.0

---------------------- beach level ---- --------------.-----

96

STOP 2 - POTOMAC CREEK, WEST END OF BULL BLUFF

SERIES FORMATION NANNO. BED ZONE

w z w o o W --.J

« a...

Z

0

r-« ~ a: 0 LL

« :::J a «

a: w III ~ 9 w ~

« en Z « r-a 0-en « 0-

1----

L- __

a::: w co ~ w ~

>-« 3:

NP 9 ~ « 0 U)

NP8 a..

LITHOLOGY FEET

~" : S"' ,' , '" ' , t. ,

7s;):;T' i' : "':''; .::': ";:.:' -'., . '. ,,' .. ",' : :

" , . : . . ".. . . ... 30-~''', , '' ': 'G ,' t. ': , ';;"·

o

o \

20-

m

m

CJ 10-

This locality is not mentioned in most modern studies of this area; it either has been overlooked in the past or is an exposure of recent origin. The outcrop is valuable because it contains relatively unweathered sediments of beds 6 and 7 and because the contact between the two beds is well exposed. The calcareous nannofossil Zone NP 8 - Zone NP 9 contact occurs within the upper part of bed 6; this change is marked by the first appearance of Discooster multiradiatus. The lowermost sediments of bed 6 at this locality are in calcareous nannofossil Zone NP 8 (i.e .. contain Heliolithus riedelii). while the upper sediments of bed 6 contain Discooster multiradiatus and are placed in Zone NP 9.

Calcareous Nannofossils

Ten samples were collected from this locality. The most commonly occurring species are listed below. Asterisks (*) indicate stratigraphically diagnostic species.

Zone NP 9 samples - fair-to-poor preservation, one specimen per 1-10 fields of view at 500X magnification.

Biantholithus astralis Chiasmolithus bidens Coccolithus pelagicus *Discoaster multiradiatus Discoaster salisburgensis Ericsonia subpertusa Fasc ic ul ithus tympaniformis

Hornibrookina sp. Markalius apertus Placozygus sigmoides Toweius emirnms Toweius pert usus Toweius tovae Zygodiscus herlyni

Zone NP 8 samples - poor preservation, one specimen per 1-10 fields of view at 500x..

ChiCUlmolithus bidens Coccolith us pelagic us Ericsonia subpertusa Fasciculithus tympaniformis *Heliolithus riedelii

Foramjnifers

Markalius sp. Thoracosphaera spp. Toweius pertusus Toweius tovae

The lower part of bed 6 contains a fairly low diversity assemblage of about 15 benthonic species. Dominant forms include Spiroplectammina wilcoxensis, Hanzawaia, Epistominella. A nomalino ides , and Nonion cf. graniferum. The planktonic component includes only a few juvenile specimens of Subbotina.

The upper part of bed 6 contains a more diverse benthonic assemblage, comprising around 25 species. The dominant species include Spiroplectammina wilcoxensis. Hanzawaia (possibly an ecophenotypically flattened form of Anomalinoides umboniferus). Buliminella cf. B. elegantissima, and Bulimina virginiana. The very sparse planktonic assemblage consists of some juvenile and some adult specimens of Subbotina andAcarinina. Although all of bed

98

6 appears to be uniform sedimentologicaily, there probably is some slight deepening upward of the depositional environment from the inner-neritic environments characteristic of the lower part. A possibly higher organic content in the sediments during the deposition of the upper part of bed 6 is suggested by the relative abundance of specimens of Buliminella and Bulimina.

The lower part of bed 7 has a low diversity benthonic fauna of 17 species; the dominant taxa are Robulus, Hanzawaia, Cibici.des alieni, and Bulimina cr. B. ovata. No plankwnie specimens were found. Deposition occurred in inner-neritic environments. The benthonic species diversity increases upward in bed 6 from about 15 species in the lower part of the bed to 25-30 species in the upper part. The benthonic assemblage in the lower part of the bed is dominated by Spiropiectammina wilcoxensis, Epistominella, Hanzawaia. Anomalinoides, and Nonion d. N. graniferum. Assemblages in the upper part of the bed are dominated by Spiroplectammina wiicoxensis, Hanzawaia (probably is a flattened form of Anomalinoides umboniferus), Buliminella cf. B. elegantissima, Bulimina v irgin iana , and polymorphinid taxa. The planktonic component is small in ail samples, but it increases upward; adult specimens of Subbotina and Acarinina are found only in the upper part of bed 6. Although all of bed 6 was deposited in inner-neritic environments, the depth increased w the outer part of this depth zone during deposition of the upper part of the bed..

99

STOP 3

Right (south) bank of the Potomac River, 0.2 miles upriver from Belvedere Beach, King George County, Virginia, Passapatanzy 7 1J2-minute quadrangle .

. . . . . . . . . . . . . . . . . . . . , ..................... . ....... . ....... . Thickness (ft)

Aquia Formation

Sandstone, light-olive-gray (bed 9) 2.0

Sand, buff-orange, fine-grained, silty, glauconitic; contain.s abundant Tumtella; weathered upper part of bed 8 . . . . . . . . . . . . . . . . . . . . . . . . 6.0

Sand, dark-greenish-gray, fine-grained, silty, glauconitic, locally indurated; contains abundant Turritella, commonly in lenses; many shell fragments (bed 8) ...... . ............ . . . .......... 12.5

----------------- beach level ---.-.---------------

100

STOP 3 - BELVEDERE BEACH

SERIES FORMATION NANNa. BED ZONE LITHOLOGY

. . ~': .::1· .. ,.'.:-'

9 '. -_. . ----r;: _.. . =r: .~ .......... ~.: .

. , .. ..,.,..,.... ... . . .'. . . .

; .. >:~: .. : ::'~'.:~.'::: ~:.: .... :. ~.,::~.:::-:;.::.::. ::.~ .. ,~ . z 0

c: I- w

en « ::2!

. :. :.: ":' .... '." ..

;:;g:i)1~~.<;

w ~ w ::2!

Z a: w 0 0 u... 0 NP9

W 8

--.J « « CJ)

z a... <t r-« 0

a.. (J)

::::) « a a...

:: ', .. ::' :: .. '.::: .,.: .)~t:· ";.:. ::'. ~::.: .:: >: .:. . . '"':. -; .... ' - -. ;,." . . ". ;:... .. . .

• ~ .•• "!~' •.• G\/~;~G; •. ~ ::.~i/i;';i.iii •.......

:. '. ..". - ... '. ..-

«

101

FEET

20 -

15-

10-

5-

At Stop 3, relatively unweathered sediments from bed 8 of the Aquia Formation are exposed at beach level. Abundant specimens of Tumtella, both scattered through the sediments and concentrated in lenses, characterize bed 8 in this area. The entire exposure belongs in Zone NP 9; the section exposed here contains the youngest Aquia strata in the type area that have a well~preserved calcareous microfauna and microflora. Most exposures oibed 9 at Bull Bluff and at Aquia Creek are barren of calcareous microfauna! assemblages or conta:in poorly presenred assemblages.

Calcareous Nannofossils

Five samples were collected from this locality. The most commonly occurring species are listed below. Asterisks (*) indicate stratigraphically diagnostic species.

Zone NP 9 samples - fair-t~good preservation, 1-10 specimens per field of view at 500X magnification.

Biantholithus astrolis Braarudosphaera bigeiowii Chiasmolithus bidens Coccolithus peiagicus Cruciplacolithus sp. CyclageZospluura sp. *Discoaster muUiradiatus Discoaster salisburgensis Ellipsolithus distichus Ellipsolithus macellus

Foraminifers

Fasciculithus tympaniformis Goniolithus fiuckigeri Markalius inversus Placozygus sigmoides Scapholithus apenus Thorac.osphaera spp. Toweius eminens Toweius pert usus Toweius tovae Zygodiscus herlyni

Foraminifera are common in these beds, but the species diversity usually is less than 15. Most assemblages are heavily dominated by Anomalinoides umboniferus. Spiroplectammina wilcoxensis and Cibicides alieni also are important components of most samples. Planktonic specimens are absent from some of the samples at this locality; if present, they consist of only a few immature individuals of Subbotina. These strata were deposited in inner inner-neritic environments.

102

NOTES

103

STOP 4

Right (south) bank of the Potomac River, 0.7 miles downriver from the Fairview Beach wharf, King George County, Virginia, King George 7 112~minute quadrangle .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Thicmess (ft)

Nanjemoy Formation

Sand, light-olive~gray (SY 512), very fine~grained, clayey, silty, micaceous, glauconitic, massively~bedded. bioturbated; contains no visible shells; carbonaceous debris present ................... 10.0

----undulating contact, 0.5 ft relief, burrows 1.5 ft deep--~~~~

Marlboro Clay

Clay, medium~gray (N5), slightly silty in some levels, massively~bedded; contains no visible shells .................................... 4.0

~-~-~-~~~-~- ---~---~~- und ula ting contact --- ---------- -~-~~-~~~

Aquia Formation

Sand, olive~gray (5Y 3/2), very fine-grained, clayey, silty, glauconitic, massively~bedded, bioturbated; contains molds of bivalves and Turritella . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 3.5

~~-------------------- beach level -------------------

104

STOP 4 - 0.7 MILE BELOW FAIRVIEW BEACH

SERIES FORMATION NANNO. ZONE LITHOLOGY

w z w o o w

w z w o o W .....J <3:: a..

>- z oQ ~I­W<3:: J~ Zc: ~o Z LL

o a: 0>­CD <3:: -I...J a: O <3:: ~

z<! O(J'J «-zo: - t- <!UJ :::> « I- CD

a ~ ~~ « a: CI) ~ O~ LL

105

FEET

15 -

10-

5-

The strata exposed here span the Paleocene-Eocene boundary (Zone NP 9-NP 10 boundary according to Berggren and others, 1985). The upper part of the Aquia Formation, the Marlboro Clay, and the Nanjemoy Formation are non-calcareous at this stop, but several coreholes in northern Virginia and southern Maryland have penetrated these boundary strata where good calcareous microfossil assemblages are present. At Stop 4, the Marlboro Clay is bounded both above and below by unconformities. A burrowed unconformity is present at the top of the Marlboro in all known localities, but the upward change from the Aquia to the Marlboro is transitional in the Oak Grove and Putney Mill coreholes in Virginia

Calcareous Nannofossils

There are no calcareous nannofossil specimens preserved at this locality.

Foraminifers

No specimens were obtained from these becla at this exposure.

106

NOTES

107

STOP 5

Right (south) bank of the Potomac River, 1.4 miles downriver from the Fairview Beach wharf, King George County, Virginia, King George 7 112-minute quadrangle .

. . . . . , ..................................................... Thickness (ft)

Pleistocene

Conglomerate, orange; contains sand to cobble-sized material . . . . . . . . . . . .. 10.0

Nanjemoy Formation

Sand, olive-gray (5Y 312), very fine-grained, clayey, silty. slightly micaceous and glauconitic, massively-bedded, bioturbated; contains scattered small shells and shell fragments . . . . . . . . . . . . . .. 15.0

-------.------------ beach level ---------------------

108

STOP 5 - 1.4 MILES BELOW FAIRVIEW BEACH

SERIES FORMATION NANNO. ZONE

w z w o o t­en W ---1 a..

w z w o o w

z o -t-« ~ a: o LL

>­o ~ W J Z « Z NP10

LITHOLOGY

",' . :,' ... . ~. . . .

,' " , . ' ...

• ' .....•...• t <:,·,···.··.O.· •. · ••.•...• • .• ··'.· .. i·.·· ~ .• ; .••.•....• .-; .•...•...•... , . ',:." .. . '. 0' : . , '., _ .". -': _ :.: : " _ .. ". '., ' .. _, . ' :.: -.: :. . .. . '. - ':.: " :.-

109

FEET

20-

15-

10 -

5-

This exposure contains the oldest calcareous fossiliferous beds of the Nanjemoy Formation exposed along the Potomac River. The sample at beach level contains Tribrochiatus bramlettei, which places these strata in the lower part of Zone NP 10. It is unknown how far the basal Nanjemoy beds at this location are above the top of the Marlboro Clay, but the contact with the Marlboro could be from a few feet to possibly as much as 10 feet below beach level. This thickness estimate is based upon biostratigraphic information from the Virginia and Maryland coreholes where Zone NP 10 strata usually are less than 20 feet thick, and also by the close proximity of this stop to Stop 4 in an area where gentle dips of 10 to 20 feet per mile prevail.

Calcareous Nannofossils

Two samples were collected from this locality. The most commonly occurring species are listed below. AsteriBks (*) indicate stratigraphically diagnostic species.

Zone NP 10 samples - fair preservation, 1-10 specimens per field of view at 500X magnifica tion.

Braarudosphaera bigelowii Chiasmolithus bidens Coccolithus pelagicus Cyclagelosphaera sp. Discooster multiradiatus Ellipsolithus distichus Fasciculithus aubertae? Goniolithus fluckigeri Hornibrookina sp.

Foraminifers

Micrantholithus sp. Necx:hiastozygus concinnus Neococcolithes dub ius Thoracosphaera spp. Toweius callosus Toweius occultatus Toweius pertusus Transversopontis pulcher *Tribrachiatus bramlettei

Few specimens were recovered from these beds. Many of the species exhibit a fair amount aftest corrosion. Benthonic species diversity is less than 15; the most abundant taxa include Eponides lotus, Anomalinoides sp., and Robulus sp. Planktonic specimens are rare; they consist mostly of juvenile specimens of Subbotina. These strata were deposited in inner­neritic conditions.

110

NOTES

111

STOP 6

Right (south) bank of the Potomac River, 0.9 miles downriver of Somerset Beach, King George County, Virginia, King George 7 II2-minute quadrangle .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Thickness (ft)

Pleistocene

Conglomerate, orange; containing sand to cobble-sized material

------------------------ unconformity ----------------------

Nanjemoy Formation

Sand, olive-gray (5Y 3/2), very fine-grained, clayey, silty, slightly micaceous, moderately glauconitic, massively-bedded; contains a moderate number of shells that occur both scattered and in

25.0

bands; bands of Venericardia potapacoensis are present . . . . . . . . . . . . . 8.0

----------------------------})each level ------------------------

112

STOP 6 - 0.9 MILE BELOW SOMERSET BEACH

SERIES FORMATION

w z w o o I­CJ)

W --1 a...

w z w o o w

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z o -I-« ~ a: o LL

NANNO. ZONE LITHOLOGY FEET

30-

20

10-

----0

113

This exposure is the only one along the south bank of the Potomac River that contains strata that at least provisionally can be placed in Zone NP 11. Strata belonging to the upper part of Zone NP 10 (i.e., containing Tribrachiatus contortus) are unknown from these discontinuous exposures along the Potomac River, although they do occur in coreholes in nearby Virginia and Maryland.

Calcareous Nannofossils

One sample was collected from this locality. The most commonly occurring species are listed below. Asterisks (*) indicate stratigraphically diagnostic species. Neither Tribrachiatus conrortus, Tribrachiatus bramlettei, nor Discooster multiradiatus are present in this sample. Specimens of Toweius callosus and Transversopontis pulcher (which increase in size in the lower Eocene) are larger than at the previous stop. These data indicate a most probable placement is within Zone NP 11.

Probable Zone NP 11 - fair preservation, one specimen per 1-10 fields of view at 500X magnifica tion.

Campylosphaera dela Cepekiella lumina Coccolith us pelagic us Discooster sp. cf. D. kuepperi Discoaster limbatus / binodosus Discoas~r salisburgensis Ellipsolithus macellus Markalius inversus

Foraminifers

Neococcolithes dubius Sphenolithus 8p. Toweius callosus Toweius occultatus Toweius pertusus Transversopontis pulcher Transversopontis pulcheroides?? *Tribrachiatus orthostylus

The benthonic assemblage from a sample at beach level at this locality contains 18 species. The common taxa are Cibicides alieni, Elphidium sp., Siphonina wiZconensis, Bolivina sp., and Turrilina robertsi. The planktonic foraminiferal component, which includes adult specimens of Subbotina, composes less than five percent of the total assemblage. These beds were deposited in a middle inner-neritic environment. The presence of Elphidium sp. supports an age placement in Zone NP 11 or younger.

114

NOTES

115

STOP 7

Right (south) bank of the Potomac River, 2.1 miles upriver from Mathias Point, King George County, Virginia, Mathi.as Point 7 1/2-minute quadrangle .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Thickness (ft.)

Pleistocene

Conglomerate, orange; sand to boulder-sized material . . . . . . . . . . . . . . . . . . . . 5.0

-------------------- ----- unconformity -- -----------------------

Calvert Formation

Clay, yellow-gray, silty, sandy toward base; contains phosphate pebbles and bone along the base .................................... 25.0

-------------- ---- ----- unconformity -------------------

Nanjemoy Formation

Sand, olive-gray (5Y 3/2), very fine-grained. clayey, silty, slightly micaceous, moderately glauconitic; contains shell molds in upper strata and scattered molluscan shells in lower 14 ft . . . . . . . . . . . . . .. 40.0

------------------------- beach level ------.------------------

116

STOP 7 - 2.1 MILES ABOVE MATHIAS POINT

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w Z w ()

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NP12

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50-

40-

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117

This exposure is at or near the lectostratotype locality ofthe upper Woodstock Member of the Nanjemoy Formation (Ward, 1985). The lowest beds in this exposure are placed in Zone NP 12 because of the co-occurrence of Tribrachiatus orthostyius and Discooster lodoensis.

Calcareous Nannofossils

Three samples were collected from this locality. The most commonly occurring species are listed below. Asterisks (*) indicate stratigraphically diagnostic species.

Zone NP 12 samples - fair-to-poor preservation, 1-10 specimens per field of view at 500X magnification.

Braarudosphaera bigelowii Campylosphaern dela Cepekiella lumina Chiasmolithus bidens Coccolithus pelagicus Discoaster distinctus / deflandrei Discoaster kuepperi *Discoaster lodoensis Ericsonia formosa? Goniolithus fluckigeri Helicosphaera??

Foramjnifers

Lophodolithus reniformis? M arkalius inversus Neococcolithes dub ius Rhabdosphai!-ra sp. Sphenolithus sp. Thoracosphaera spp. Toweius occultatus Transversopontis pulcher Transversopontis pulcheroides *Tribrachiatus orthostylus Zygrhablithus bijugatus

Specimens are moderately common in the lower beds at this locality. Species diversity is slightly greater than 20. The dominant taxa include Siphonina wilcoxensis. Elphidium 8p., Eponides lotus, Hanzawaia, Anomalinoides, Spiroplectammina wilcoxensis, and Turrilina robertsi. Planktonic specimens compose about four percent of the assemblage; most specimens are juvenile forms of Subbotina. but some adult specimens of Subbotina and Acarinina are present. These strata were deposited in a middle inner-neritic environment.

118

NOTES

119

STOPS

Left (northeast) bank of the Potomac River, 1.8 miles upstream from the mouth of Popes Creek, Charles County, Maryland, Mathias Point 7 1l2-minute quadrangle .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Thickness (ft)

Calvert Formation

Sand, brown in lower part; grades upward into yellow-gray diatomaceous clay ................................. unmeasured

-------------.----------- un~ILfoI1Ility ---------------------- --

Nanjemoy Formation

Sand., olive-gray (5Y 3/2), very fine-grained, clayey, silty, massively­bedded, bioturbated; contains some intervals with considerable clay; abundant glauconite and fairly abundant, scattered molluscan shells "in lower part; shells sometimes in lenses; beds become oxidized upward and only contain shell molds ............. 26.5

-------- burrowed surface; burrows extend 1.5 ft downward --------

Sand, grayish-olive-green (5 GY 3/2), very fine-grained, clayey, silty, slightly micaceous, moderately glauconitic; contains scattered molluscan shells ........................................... 1.5

--------------------------- beach level -----------------.---------

120

SERIES

W z W 0 a -~

w z w o a w

STOP 8 - 1.8 MILES ABOVE POPES CREEK

FORMATION NANNO. LITHOLOGY ZONE

Z f- a a: -

f-W « > ---1 ~ « a::: 0 a

LL

z a -r-« ~ a:: a LL

>­o ~ W J Z « z

----

------------------------------._---- --- - -"--- -__ • __ .....L.-.

NP12

121

FEET

30

20

10

---0

The lower two samples, examined at one foot above beach level (below the bUlTOwed surface) and at three feet above beach level (above the bUlTOwed surface), contain calcareous nannofossil assemblages characteristic of Zone NP 12. The highest sample, examined at 5.5 feet above beach level, contains a nannofossil assemblage probably referable to Zone 13.

Calcareous Nannofossils

Three samples were collected from this locality. The lower two samples are in Zone NP 12, and the upper sample probably belongs in Zone NP 13. This sample contains Discoaster lodoensis (occurs in Zones NP 12-NP 14) and does not have Tribrachiatu.s orthostylus (does not extend above Zone NP 12). The genus Reticulofenestra, which first appears in Zone NP 13. is present in this sample. The most commonly occurring species are listed below. Asterisks (*) indicate stratigraphically diagnostic species.

Zone NP 12 samples - fair-to-poor preservation, one specimen per 1-10 fields of view at 500X magnification.

Cepekiella lumina Chiasmolithus bidens Coccolithus pelagic us Discoaster kuepperi *Discoaster lodoensis Markalius inversus Neococcolithes dubius

Thoracosphaera spp. Toweius callosus Toweius occultatus Transversopontis pulcher *Tribrachiatus orthostylus Zygrhablithus bijugatus

Possible Zone NP 13 - fair preservation, one specimen per 1-10 fields of view at 500X magnification.

Braarudosphaera bigelowi Chiasmolithus bidens Coccolithus pelagic us Discoaster kuepperi *Discoaster lodoensis Markalius inversus Microntholithus vesper

Foraminifers

Neococcolithes dub ius "'Reticulofenestra spp. ThoracosphCU!7a spp. Toweius occultatus Transve,.sopontis pulcher Transversopontis pulcheroides Zygrhablithus bijugatus

Specimens are moderately common in the lower strata at this locality. The benthonic component consists of slightly greater than 20 species. Siphcnina wilcoxensis, Eponides lotus, Elphidium sp., and Spiroplectammina wilcoxensis are the dominant taxa. Planktonic specimens, all belonging to Subbotina. compose about four percent of the assemblage. Deposition of these strata occurred in middle inner-neritic environments.

122

COMPLETE SCIENTIFIC NAMES FOR CALCAREOUS NANNOFOSSIL SPECIES DISCUSSED IN GUIDEBOOK

Biantholithus astraLis Steinmetz & Stradner, 1984 Braarudosphaera bigelowi (Gran & Braarud, 1935) Deflandre, 1947 Campylosphaera ckla (Bramlette & Sullivan, 1961) Hay & Mohler, 1967 Cepekiella lumina (Sullivan, 1965) Bybell, 1975 Chia.smolithus bi.lkns (Bramlette & Sullivan, 1961) Hay & Mohler, 1967 Chiasmolithus danicus (Brotzen, 1959) Hay & Mohler, 1967 Chiasmolithus solitus (Bramlette & Sullivan, 1961) Hay, Mohler, & Wade, 1966 Chiphragmalithus calathus Bramlette & Sullivan, 1961 Coccolith us pelagicus CWallich, 1877) Schiller, 1930 CrucipU:u:olithus tenuis (Straciner, 1961) Hay & Mohler in Hay et a1., 1967 Daktylethra punctulata Gartner in Gartner & Bukry, 1969 Discooster deflandrei Bramlette & Riedel, 1954 Discoo.ster diastypus Bramlette & Sullivan, 1961 Discoaster distinctus Martini, 1958 Discoaster kuepperi Stradner, 1959 Discoaster lodoensi8 Bramlette & Riedel, 1954 DiscOtUter mohleri Bukry & Percival, 1971 Discoaster multiradiatus Bramlette & Riedel, 1954 Discoaster salisburgensis Stradner, 1961 Discooster sublodoensis Bramlette & Sullivan, 1961 Ellip80lithus distichus (Bramlette & Sullivan, 1961) Sullivan, 1964 Ellipsolithus macellus (Bramlette & Sullivan, 1961) Sullivan, 1964 Cyclococcolithu8 formosus Kamptner, 1963 Ericsonia subpertusa Hay & Mohler, 1967 Fasciculithus aubertae Haq & Aubry, 1981 Fasciculithus involutus Bramlette & Sullivan, 1961 Fasciculithus schaubii Hay & Mohler, 1967 Fasciculithus tympaniformis Hay & Mohler in Hay et a1., 1967 Goniolithus fluckigeri Deflandre, 1957 Helicosphaero lophota (Bramlette & Sullivan, 1961) Locker, 1972 Helico8phaero seminulum Bramlette & Sullivan, 1961 Heliolithus cantabriae Perch-Nielsen, 1971 Heliolithus kleinpellii Sullivan, 1964 Heliolithus riedelii Bramlette & Sullivan, 1961 LopJuxiolithus nascens Bramlette & Sullivan, 1961 Lophodolithus reniformis Bramlette & Sullivan, 1961 Mo.rkalius apertus Perch-Nielsen, 1979b Marko.lius inversus <Deflandre in Deflandre & Fert, 1954) Micrantholithus vesper Deflandre, 1954 Neochiastozygus concinnus (Martini, 1961) Perch-Nielsen, 1971c Neococcolithes dubius <Deflandre in Deflandre & Fert, 1954) Black, 1967 plactJzygus sigmoides (Bramlette & Sullivan, 1961) Romein, 1979b Scapholithus apertus Hay & Mohler, 1967 Toweius callos us Perch-Nielsen, 1971b Toweius eminens (Bramlette & Sullivan, 1961) Gartner, 1971a Toweius occultatus (lAlcker, 1967) Perch-Nielsen, 1971 Toweius pertusus (Sullivan, 1965) Romein, 1979b Toweius tovae Perch-Nielsen, 1971b

123

Transuersopontis pulcher (Deflandre in Deflandre & Fen, 1954) Perch-Nielsen, 1967 Transuersopontis pulcheroides (Sullivan, 1964) Baldi-Beke, 1971 Tribrachiatus bramlettei (Bronnirnann & Stradner, 1960) Proto Decima et a1., 1975 Tribrachiatus contort us (Stradner, 1959) Bukry, 1972 Tribrachiatus orthostylus Shamrru, 1963 Zygodiscus herlyni Sullivan, 1964 Zygrhablithus biJugatus (Deflandre in Deflandre & Fen, 1954) Deflandre, 1959

124