1. cenozoic and mesozoic sediments from the … · the mesozoic magnetic anomaly sequence) and the...

Larson, R. L., Lancelot, Y., et al., 1992Proceedings of the Ocean Drilling Program, Scientific Results, Vol. 129

1. CENOZOIC AND MESOZOIC SEDIMENTS FROM THE PIGAFETTA BASIN, LEG 129,SITES 800 AND 801: MINERALOGICAL AND GEOCHEMICAL TRENDS OF

THE DEPOSITS OVERLYING THE OLDEST OCEANIC CRUST1

Anne Marie Karpoff2

ABSTRACT

Sites 800 and 801 in the Pigafetta Basin allow the sedimentary history over the oldest remaining Pacific oceanic crust to beestablished. Six major deposition stages and events are defined by the main lithologic units from both sites. Mineralogical andchemical investigations were run on a large set of samples from these units. The data enable the evolution of the sediments andtheir depositional environments to be characterized in relation to the paleolatitudinal motion of the sites. The upper part of thebasaltic crust at Site 801 displays a complex hydrothermal and alteration evolution expressed particularly by an ochre siliceousdeposit comparable to that found in the Cyprus ophiolite. The oldest sedimentary cover at Site 801 was formed during theCallovian-Bathonian (stage 1) with red basal siliceous and metalliferous sediments similar to those found in supraophiolitesequences, and formed near an active ridge axis in an open ocean. Biosiliceous sedimentation prevailed throughout the Oxfordianto Campanian, with rare incursions of calcareous input during the middle Cretaceous (stages 2, 4, and 5).

The biosiliceous sedimentation was drastically interrupted during the Aptian-Albian by thick volcaniclastic turbidite deposits(stage 3). The volcanogenic phases are pervasively altered and the successive secondary mineral parageneses (with smectites,celadonite, clinoptilolite, phillipsite, analcime, calcite, and quartz) define a "mineral stratigraphy" within these deposits. Fromthis mineral stratigraphy, a similar lithologic layer is defined at the top of the Site 800 turbidite unit and the bottom of the Site 801turbidite unit. Then, the two sites appear to have been located at the same distal distance from a volcanic source (hotspot). Theycrossed this locality, at about 10°S, at different times (latest Aptian for Site 800, middle Albian for Site 801).

The Cretaceous siliceous sedimentation stopped during the late Campanian and was followed by deposition of Cenozoicpelagic red clay (stage 6). This deep-sea facies, which formed below the carbonate compensation depth, contains variable zeoliteauthigenesis in relation to the age of deposition, and records the global middle Cenozoic hiatus events. At the surface, the red clayfrom this part of the Pacific shows a greater detrital component than its equivalents from the central Pacific deep basins.

INTRODUCTION

The Pigafetta Basin in the western Pacific Ocean is an elongated,deep oceanic basin within the Jurassic quiet zone, surrounded bySeamount chains: the Magellan to the west-southwest and the Marcus-Wake to the north-northeast. The main objective of Leg 129 was torecover the oldest oceanic crust (predicted to be Middle Jurassic fromthe Mesozoic magnetic anomaly sequence) and the overlying deep-sea pelagic sediments (Lancelot, Larson, et al., 1990). These depositschronicle the paleoenvironment of the "superocean" at that time. Twosites were drilled: Site 800,40 miles northeast of Himu Seamount onmagnetic lineation M33 (21°55.38'N, 152°19.37'E, 5686 m waterdepth) and Site 801, in the central part of the basin (18°38.57'N,156°21.57'E, 5673 m water depth), on a magnetic quiet zone south-east of the M25-M37 magnetic lineation sequence (Fig. 1). Site 801,with three drill holes, is the first site ever to recover Callovian-Bathonian sediments and crust from the Pacific plate. Before drillingat Site 801, the previous attempts to recover Jurassic sediments in thisarea have failed in chert, thick volcaniclastic deposits of Cretaceousage (Deep Sea Drilling Project, or DSDP, Sites 461 and 585), andthick lavas flows, such as the volcanic sills of Early Cretaceous ageat Site 800.

The sedimentary facies at both Sites 800 and 801 resulted fromtwo main types of input: predominantly biosiliceous oozes and asso-ciated pelagic clays, which experienced different degrees of diagene-sis, and volcaniclastics related to the middle Cretaceous volcanicevent. The mixture of these phases, in variable proportions, forms

' Larson, R. L., Lancelot, Y., et al , 1992. Proc. ODP, Sci. Results, 129: CollegeStation, TX (Ocean Drilling Program).

2 Centre de Géochimie de la Surface—C.N.R.S., 1 rue Blessig, 67084 StrasbourgCedex, France.

several sedimentary units which can be correlated between sites,although these units are sometimes diachronous.

Thus, a synthetic and composite sequence has been established forthis area of the Pacific Ocean, with several deposition episodes orevents since the Middle Jurassic. The purp°se of the present study isto establish the main mineralogical and chemical characteristics ofthe successive deposits, and to characterize the dissimilarity betweenthe two sites and the possible influence of the volcaniclastic input andunderlying basaltic crust on the diagenetic evolution and chemicalcomposition of the biogenic sediments. The mineralogical and geo-chemical characterization of the sedimentary sequence over the oldestremaining Pacific crust can be used as a reference section, as isnecessary for any further comparison with the equivalent sectionsfrom the Jurassic superocean and Mesozoic oceanic realm, such asTethyan supraophiolite sequences. The Cenozoic condensed sedi-ments are compared to the equivalent red clays from central Pacificdeep basins.

SEDIMENTARY SEQUENCES FROM SITES800 AND 801

The sedimentary sequences penetrated at Site 800 and Site 801consist predominantly of pelagic clay, chert and porcellanite, lime-stone, volcaniclastic deposits, and siliceous red claystone as basalsediments. The stratigraphic sequences, ages, petrographic and majormineralogical compositions of the facies and their physical properties,sedimentation rates curves, and seismic stratigraphy are detailed inLancelot, Larson, et al. (1990).

Site 800

The sedimentary column has been divided into five units, from topto bottom, above a massive dolerite unit (498.1-544.5 mbsf) (Fig. 2):

160° 162°

18

16° -

14

Figure 1. Location map of Sites 800 and 801, Pigafetta Basin, western Pacific Ocean. Bathymetry in meters of the central western Pacific Ocean; main magneticanomalies and location of DSDP and ODP drill sites (from Lancelot, Larson, et al., 1990).

Unit I: 0-38.0 mbsf, Tertiary (Pliocene) to upper Campanianzeolitic pelagic brown clay.

Unit II: 38.0-78.2 mbsf, upper Campanian to Turonian brownchert and porcellanite.

Unit III: 78.2-228.6 mbsf, Cenomanian to lower Albian gray chertand silicified limestone, grading into nannofossil chalk at the base ofthe sequence.

Unit IV: 228.6-449.6 mbsf, Aptian redeposited volcaniclasticswith spectacular turbidite and debris-flow features.

Unit V: 449.6-498.1 mbsf, Hauterivian to Berriasian laminatedred claystone with hard chert at the base.

Site 801

The stratigraphic sequence at Site 801 is subdivided into six units,from top to bottom (Fig. 2):

Unit I: 8.0-64.0 mbsf, Tertiary (Pliocene) to upper Campanianzeolitic pelagic brown clay, with a thin interval of calcareous ooze.

Unit II: 64.0-126.5 mbsf, Campanian to Turonian brown chert andporcellanite.

Unit III: 126.5-318.3 mbsf, Cenomanian and Albian volcaniclas-tic turbidites with minor radiolarite near the base.

Unit IV: 318.3-442.9 mbsf, Lower Cretaceous to Upper Jurassicbrown radiolarite and manganiferous dark brown chert. Two subunitswere distinguished on the basis of the relative abundance of chertand clay: Subunit IVA is clay-poor radiolarite with abundant chert(Valanginian-upper Tithonian) and Subunit IVB is clay-rich radio-larite (upper Tithonian-Oxfordian).

Unit V: 442.9-461.6 mbsf, Callovian-Bathonian umber-coloredradiolarite and siliceous claystone.

Unit VI: 461.6-590.9 mbsf, Middle Jurassic basement, lava flowsand pillows basalt (alkalic and tholeiitic basalt) with interbeddedsilicified claystone and a hydrothermal deposit.

STAGES OF THE SEDIMENTARY HISTORY OF THEWESTERN PACIFIC

Sedimentary history begins during the Middle Jurassic at Site 801.Sites 800 and 801 show comparable successions of pelagic faciesthrough time since the Early Cretaceous. Biogenic sedimentation,dominantly siliceous, was masked during the Cretaceous by theabundant input of volcaniclastic material from the building of numer-ous volcanic edifices.

Six main deposition stages and events above the basaltic basement(sampled at Site 801) are defined here, and have been establishedfrom the sedimentary record, physical properties, and compiled petro-graphic, macroscopic, and microscopic descriptions, and from thepreliminary mineralogical investigations of the facies (ShipboardScientific Party, 1990a, 1990b); these stages are confirmed by themineralogical and geochemical data acquired for this study (Fig. 2).

The Jurassic Basement

The cored crustal sequence at Site 801, from 461.6 to 590.9 mbsf,consists of alkalic basalt overlying tholeiitic basalt. Pillow basalt isfirst identified at 495.0 mbsf. Several thin sedimentary layers wererecovered in the upper part of the sequence interbedded with thinbasalt flows. These deposits are mainly silicified claystone, chert, andrecrystallized limestone. At 521.7 mbsf, 60 m below the top of thebasement, a remarkable chrome yellow siliceous hydrothermal layer

SEDIMENTS FROM THE PIGAFETTA BASIN

S i t e 8 0 0 (5686 mbsl)

Age Unit Facies

DepositionStage

and Event Facies

Cenozoic

100 H

200 -

300 -

400 -

500 -

Q.<

early

Haut.-Bar.

Valanginian

Berriasian

l l l • l l l

NWW^

I38.0

II78.2

III

228.6

IV

449.6

V

498.1

VI544.5

Limestoneand

RadiolarianChert

VolcaniclasticTurbidite

with minorPelagic

Intervals

DoleriteSillsand

Chert

PelagicRed Clay

Brown Chertand

Porcellanitθ

VolcaniclasticTurbidite

with minorPelagic

Intervals

Chert,Radiolarite,

ClayeyRadiolarite,

andClaystone

Red Claystone

S i t e 8 0 1 (5674 mbsl)

Age Unit

Altered Pillows

HydrothermalDeposit

MORB Lava flows

Cenozoic

Paleocene late

Camp. - ?Maββtr.

CampanianConiac. - Saπton.

Coniacian

Cenomanian

Valanginian

Berriasian

late

early——_

Kimmeridgian

Callovian

Bathonian

S S S f

\ \ \ \

S N \ \f f f .

\ \ \ \

A

IJB

63.8

126.5

IV

442.9

V461:6

VI

590.9

Figure 2. Composite lithologic units described at Sites 800 and 801 (from Lancelot, Larson, et al., 1990) and equivalent deposition episodes (stages 1 to 6) establishedin this paper.

A. M. KARPOFF

(of which 2.64 m were recovered) overlies extremely altered pillowbasalt. The textural description of this interval established a possiblesequence of formation events: deposition of colloids as sphericalbodies, evolution of this primary material by recrystallization, andrapid invasion of silica-rich fluids with the crystallization of quartz(Shipboard Scientific Party, 1990b). Aphyric tholeiitic basalt flowsbecome less altered downhole (Alt et al., this volume).

Samples from the basalt interval are used as mineralogical andchemical references; they are metasediment lenses, hydrothermaldeposits, and interpillows and alteration materials.

Stage 1: Callovian-Bathonian Basal Sedimentation

The oldest sediments overlying the Jurassic basaltic crust are vividred radiolarite and hematitic claystone, with common manganesecoatings along silica-filled fractures. This 18-m-thick facies wasrecovered only at Site 801 (Unit V). The age given by the siliceousfauna is Callovian-Bathonian to basal Oxfordian (Matsuoka, thisvolume). The more or less rhythmic interbedding between Si-rich andclayey end-members is tentatively interpreted by Molinie and Ogg(this volume) to result from Milankovitch cycles; the contrast can alsobe related to bottom-current winnowing, episodic high iron input,differential silica dissolution, or diagenetic evolution. A characteristicof these deposits, buried below 442 m of sediments, is their relativelylow compaction, with a porosity of 46%. Another peculiarity is anapparent dip of about 30°. The estimated sedimentation rate for thesedeposits is about 3 m/m.y., relatively low compared to the rate ofpelagic clays and siliceous oozes (1—10 m/m.y.; references in Kennett,1982; Karpoff, 1989).

Stage 2: Oxfordian-Tithonian and Berriasian-BarremianBiosiliceous Sedimentation

A probable hiatus marks the lithologic boundary between Cal-lovian red radiolarite and Oxfordian-Tithonian brown clayey radio-larite (Subunit IVB at Site 801). The sediments grade upward to amore homogeneous siliceous deposit. The facies is characterized bymottling, burrows, and laminations. Millimetric manganese micro-nodules occur scattered or along the laminated stratification. Vari-colored dark brown chert occurs as lenses. The transition betweenlower Tithonian clayey radiolarite with abundant manganese micro-nodules to upper Tithonian cherty radiolarite appears to be sharp-Intensively brecciated radiolarian chert with numerous quartz-filledfractures occurs in the poorly recovered upper Tithonian section.

The Berriasian-Hauterivian deposits show small-scale variationsin the relative radiolarian concentration and in the development of thediagenetic silicification to porcellanite and chert (Behl and Smith, thisvolume). Partially coeval deposits occur at Sites 800 and 801 (basalUnit V at Site 800 and Subunit VIA at Site 801) with some dissimi-larities. At Site 800, the facies is microlaminated clayey radiolarite—aregular alternation of light-colored radiolarian-rich layers and darkred claystone layers, with an apparent cyclicity. At Site 801, theradiolarite displays an irregular, fine lamination, and vague rhythmicbanding. Within both sections, fine silica-filled fractures are commonand thin manganese coatings occur over the laminations.

The clayey radiolarite from the Oxfordian-Kimmeridgian andBerriasian-Valanginian sections have an average porosity about 42%,in contrast to that of the Tithonian chert (< 5%), and this value isslightly lower than that from the underlying basal red radiolarite. Theestimated average sedimentation rate is low, about 2-5 m/m.y., forOxfordian to early Barremian deposition as a whole (Site 801). Theupper Tithonian section corresponds to the more siliceous sedimentswith the apparently higher sedimentation rate of about 10 m/m.y.

Stage 3: Middle Cretaceous Volcanic Event andSedimentation

The deposition of the thick volcaniclastic turbidites occurred atSite 800 (Aptian, Unit IV) before that at Site 801 (Albian-Cenomanian,Unit III), with a slight overlap, indicating that most of the volcani-clastic deposition was diachronous (Fig. 3). This diachronism couldresult from different volcanic sources, from successive pulses fromthe same source, or even from the deferred migration of both sitesover the same location with respect to a fixed source (hotspot).The later possibility is suggested from the mineralogical facies (asdescribed below). The massive redeposition of volcanogenic materialmasked the biogenic sedimentation background, often making the agediagnosis difficult. Further, possible hiatuses could have occurredduring the Hauterivian-Barremian and at the Aptian/Albian boundary(Site 800) or during the Barremian-Aptian (Sites 800 and 801). Thescarce biogenic input is mainly siliceous and calcareous. The occur-rence of shallow-water fossils in some intervals indicates the proxim-ity to the source, possibly a volcanic edifice. Facies are mainly debrisflows, thick turbidites with upward-fining beds (over 4 m thick in theAlbian section at Site 801), and debrites; ripple and cross laminations,breccia horizons, redox fronts, bioturbation features, clay-filled frac-tures, or calcite veins are common (Shipboard Scientific Party, 1990a,1990b; Salimulah and Stow, this volume). In places, the degree ofalteration of the volcaniclastic phases, both in sandstone as well asclaystone, is relatively high, expressed by the occurrence of palago-nite and zeolites in a green clay matrix. The measured porosities varyfrom 65% to 32%. The sedimentation rate is estimated to be 5 m/m.y.(minimum for the section at Site 801) and 35 m/m.y. (maximum forthe section at Site 800), with an average rate of about 12 m/m.y.

Stage 4: Albian-Cenomanian Pelagic Sedimentation

At Site 800 Albian-Cenomanian deposits coeval with the volcani-clastic sequence from Site 801 are radiolarian chert and limestone(Unit III). The calcareous and siliceous contributions become pro-gressively more abundant over the latest volcanogenic input stillpresent at the base of the unit. The biogenic facies, with the associationof radiolarians, foraminifers, and nannofossils, reveals the high fer-tility of the surface water masses. Diagenesis created a full range ofvarious lithologies between chalk and chert (Shipboard ScientificParty, 1990a; Behl and Smith, this volume). The locally well-compactedsediments (38% to 7% porosity) were deposited with an averagesedimentation rate of 6 m/m.y.

Stage 5: Late Cretaceous Siliceous Sedimentation

At both sites, during the Turonian to late Campanian, depositswere predominantly biosiliceous and iron-rich, with a relatively lowsedimentation rate (3 m/m.y. in Unit II at Sites 800 and 801). Diage-netic transformation has lead to formation of porcellanite and chertwith low porosity (25%). These Upper Cretaceous facies are wide-spread in the northwestern Pacific (Pisciotto, 1981); the same strati-graphic sequence, with overlying red clay, was recovered at northernDSDP Site 198 (Heezen and MacGregor, 1973).

Stage 6: Latest Cretaceous to Quaternary Red ClayDeposition

The pelagic dark brown clay lying over both sedimentary sequencesat Sites 800 and 801 (Unit I) is similar to that recovered elsewhere in theabyssal basins (Karpoff, 1989, and references therein). This muddy facies(water content 50% to 84%) is composed of clay minerals, zeolites, and


Age

Ma

100-

1 5 0 -

176

Ter

tiary

c

Cre

tace

ous

Jura

ssic

late

Miocene middle

early

lateOligocene

early

late

_ middleEocene

early

Paleocene l a t e

eàTTy

Maestrichtian

Campanian

Santonian -Turonian

Cenomanian

Albian

Aptian

Barremian

Hauterivian

Valanginian

Berriasian

Tithonian

Kimmeridgian

Oxfordian

Callovian

Bathonian

0 Ma

5.3

23.7

36.6

57.8

66.5

74.5

84.0

91.0

97.5

113

119

124

131

138

144

152156

163

169

176

Site 800

Hiatus

II*

H i a t u s

Site 801 Paleolatitudes

20° S 10° N

Hiatus

?

Hiatus

•CT I Λ I V rCrOd

s s s V I ' × ×

Figure 3. Age correlation for Sites 800 and 801 (lithologic symbols same as in Fig. 2) and paleolatitudes vs. time at both sites (data from Lancelot, Larson, et al.1990). Time scale from Palmer (1983) and Kent and Gradstein (1985).

iron oxyhydroxides and manganese micro-nodules, resulting from earlydiagenesis; it is related to very slow sedimentation (0.5 m/m.y.) belowthe carbonate compensation depth (CCD). At Site 801 the red clay unitis interrupted by 45 cm of a nannofossil ooze layer with a mixed faunagiving a latest Cretaceous to late Paleocene age. In the red clay facies, therare, poorly preserved, and often mixed fauna tentatively corroborates

the existence of several successive hiatuses during these times. Themain and widespread Cenozoic hiatuses observed in the Pacific realmare at the Eocene-Oligocene boundary, in the middle Miocene, and atthe base of the lower Pliocene; these events are related to tectonicevents and motion of the Pacific plate and subsequent oceanic responses,including the dynamics of water masses and productivity (Karpoff, 1989).

A. M. KARPOFF

The age correlation diagram for Sites 800 and 801 also illustratesthe diachronism of the deposition of the equivalent facies and thesimilarity of the sedimentary histories (Fig. 3). For both sites, thecurves of the recorded paleolatitudes vs. time (from shipboard datain Lancelot, Larson, et al., 1990) also show that the periods of morebiosiliceous sedimentation correlate to the subequatorial position ofthe sites (1) during late Oxfordian to Tithonian, stage 2, Site 801—Unit IV, and (2) during the Cenomanian to Campanian, late stage 4and stage 5, Site 800—Units II and III, and Site 801—Unit II. Theseepisodes also correspond to the highest average sedimentation rates(estimated for compacted sediments), such as the Tithonian section atSite 801, or with the highest primary productivity (siliceous andcalcareous), such as the Cenomanian section at Site 800.

Following identification of the sequence of deposition stagespresented above, mineralogical and geochemical investigations onthe deposits were conducted for both sites. These analyses allow thespecific features of the deposits at each site and the trends of thesedimentary evolution (deposition and subsequent diagenesis) of thePigafetta Basin to be defined. The studied samples are representativeof the whole set of recovered lithologies. Although recovery was poor,some dense facies (i.e., chert and silicified limestone) and the missingmaterial in these units were probably softer clayey or chalky facies(Fisher et al., this volume). The samples taken may represent thevariety present in the complete section. The main lithological charac-teristics of the samples are given in Tables 1 and 2.

ANALYTICAL PROCEDURES

Mineralogical Investigations

Routine X-ray diffraction (XRD) analyses were made on bulkpowdered samples and on individual fragments using a PhillipsPW1710 diffractometer. Samples were run between 3° and 65° 2θ at40 kV/ 20 mA, using CuKα radiation, Ni filter, and a scan speed ofl°/min. For some samples, the clay fraction (< 2 µm) was separated andan XRD analysis was run on four types of oriented aggregates:(1) untreated, (2) ethylene-glycol treated, (3) hydrazine treated, and(4) heated (4 hr at 490° C). The following diffractometer conditions wereused for clay extractions: CoKα radiation, Fe filter, 40 kV/20 mA,0.2°-l° slits, and 1° 2θ/min scan speed. A few unoriented clay fractionswere also run under the powdered XRD conditions in order to confirmthe {060} diffraction peak position, allowing discrimination of dioctahe-dral and trioctahedral smectites. The untreated clay fraction was alsostudied under a Phillips EM300 transmission electron microscope (TEM).Mineralogical controls are also made from observations of thin sectionsand of coarse (> 63 µm) fractions separated on the same set of samplestreated for clay extractions; "Tracor" microprobe investigations (energydispersive X-ray analysis) were made on bulk fragments of samples orseparated grains, and observed under a JEOL JSM840 scanning electronmicroscope (SEM). Quantitative XRD analysis is difficult and aleatoryin such polyphased heterogeneous facies (Eberhart, 1989), and therelative abundances of minerals, with an average precision of about10%, were estimated from the height of the main refection and com-parisons with preceding and following samples. Results are given inTables 3 to 7.

Geochemical Analyses

Bulk chemical analyses were run on the same set of samples—bulk rocks or individual fragments. Prior to the elemental analysis,the samples were dried at 110° C and melted in a mixture of lithiumtetraborate and introduced into a glycolated solvent. Major ele-ment analyses were performed following the method described byBesnus and Rouault (1973), using arc spectrometry and an ARLquantimeter. Na and K contents were determined by emissionspectrometry. Major elements are expressed in percentage of ox-ides, the weight loss on ignition (LOI, at 1000°C) in percentage,for 100 g of dried sample and with a relative precision of ± 2%.

Trace elements were determined using an inductively coupled plasmatechnique (ICP-35OOO-ARL) (Samuel et al, 1985). The relative precisionfor minor elements (in parts per million, or ppm) is ± 10%. Results aregiven in Tables 8 to 11.

MINERAL ASSOCIATIONS: EXPRESSION OF THEORIGIN AND EVOLUTION OF THE SEDIMENTARY

SEQUENCE

Mineralogical Phases from the Alteration of the UpperPart of the Jurassic Crust

The few samples analyzed as references for alteration products ofbasaltic basement are (Tables 2 and 4): (1) a calcareous silicified tuffand a radiolarian metasiltstone interbedded with basalt, (2) the yellowhydrothermal deposit with botryoidal structures and a thin milli-metric, white layer at its base, (3) the clayey and siliceous materialbetween pillows and within veins and a breccia zone, and (4) slightlyaltered basalt pillow and flow.

The mineral composition of slightly altered basalt is feldspar,pyroxene, and olivine. Clay minerals show very broad diffractionpeaks. The green interpülow material comprises prevalent, very well-crystallized lathy celadonite with automorphic calcite and goethite(SEM observations). Celadonite also occurs within altered pillowmargins, associated with smectites. The formula of the green diocta-hedral mica is (Si, Al)4 K(Mg, Fe, Al)2O10(OH)2. Further microprobeanalyses will provide more information on the chemistry of the Site801 celadonite. Celadonite is a frequent secondary product of thelow-temperature hydrothermal alteration of basalt (Alt et al., 1986).The yellow breccia zone between lava flows (igneous unit 23from Shipboard Scientific Party, 1990b) is made of quartz, hematite,goethite, and calcite.

The remarkable hydrothermal ochre interval is quartz with goe-thite. The microscopic arrangement of the two phases is very imbri-cated, the goethite forms small (10 µm) aggregates within joinedquartz grains (Pl. 1, Fig. 1). The intergranular porosity is near zero. Atthe base of this massive hydrothermal deposit a small piece, 1.5 cmthick, has two thin layers: the lower laminae is white, the upper is paleyellow (Sample 129-801C-4R-1, 101-102 cm). XRD analysis estab-lishes prevalent quartz and traces of a phosphatic phase. In SEMobservation, the spectacular occurrence of apatite is revealed, moreabundant in the white part of the sample: apatite forms 20-µm crystalsmixed with very small (5-10 µm) automorphic bipyramidal quartzcrystals (Pl. 1, Fig. 2). The apparent porosity of this small interval isgreater than that of the massive ochre.

Hydrothermal authigenesis of apatite is rarely described. Similarautomorphic quartz and texture was found within hydrothermal met-alliferous deposits within upper lava sequences of the Oman ophiolite,and an occurrence of phosphate-enriched zones was also found insuch lenses (Karpoff et al., 1988). In the present case the formationof apatite may have resulted from the fast interaction betweenlava, scarce biogenic phases, and hydrothermal fluids. The supplyof phosphorous to oceanic deposits from ridge axes is evoked byFroelich et al. (1977) and Kolodny (1981). The temperature of for-mation of the ochre hydrothermal deposit is about 40°C (Alt et al.,this volume).

The interbedded sedimentary lense analyzed within the upper partof the crustal sequence (41m below the basement-sediment interface)is made of prevalent carbonates as ankerite (Ca(Fe,Mg,Mn)(CO3)2)and calcite associated with quartz. Hydrothermal recrystallization ofbiogenic carbonate at low temperature (about 70°C), forming dolo-mite, has been described in basal metalliferous sediments elsewhere(McKenzie et al., 1990, and references therein). Carbonates also formduring low temperature, reducing alteration processes of oceanic basalts(Alt et al., 1986).

The various secondary minerals found in these few sites of theuppermost crustal sequence (celadonite, smectites, quartz, goethite,


Table 1. Samples from Hole 800A and their main macroscopic characteristics.

Sample(cm, top)

Depth(mbsf) Unit

129-800A-

1R-CC, 13R-1, 1364R-1, 974R-2, 674R-2, 1164R-3, 804R-4, 17

6R-1.76R-1, 37 Clear6R-1, 38 Dark7R-1,668R-1, 18R-1, 229R-1, 1

10R-1, 1311R-1, 90 ClearHR-l,91Dark12R-1, 3713R-1, 4614R-1, 10117R-1,2518R-l,7018R-1, 12119R-1, 119R-1,3721R-l,54Gray21R-1, 56 White21R-2, 822R-1, 1924R-l,30

26R-1.426R-1, 10626R-2, 1227R-1, 3028R-1, 8228R-2, 4828R-4, 229R-3, 7230R-2, 2533R-2, 14633R-7, 6335R-2, 9836R-2, 3936R-3, 2837R-CC, 138R-1, 1238R-1.2438R-1, 29 Nodule39R-2, 11141R-1,9350R-1.59

51R-1,8851R-1, 135 Clear51R-1, 136 Dark52R-1, 14152R-2, 8652R-2, 86 Fissure53R-1, 11753R-2, 25 Pink53R-2, 27 Brown55R-1, 126

0.2811.9621.2722.3722.8624.0024.87

39.6739.9739.9849.8658.9159.1268.51

78.3388.7088.7197.67

107.26117.21144.45154.40154.91162.91163.27181.84181.86182.88191.19210.20

228.64229.66230.22238.30248.02249.18251.72260.22267.65290.46296.33308.88317.79319.18328.02334.62334.74334.79337.15363.43440.79

450.48450.95450.96460.21461.16461.20466.07466.65466.67480.36

I—Pelagic brown clay—Tertiary to upper Campanian (0-38 mbsf)Relatively homogeneous dark brown (5YR 3/2-2.5/2) soft clayRelatively homogeneous dark brown (5YR 3/2-2.5/2) soft clayRelatively homogeneous dark brown (5YR 3/2-2.5/2) soft clayRelatively homogeneous dark brown (5YR 3/2-2.5/2) soft clayRelatively homogeneous dark brown (5YR 3/2-2.5/2) soft clayRelatively homogeneous dark brown (5YR 3/2-2.5/2) soft clayRelatively homogeneous dark brown (5YR 3/2-2.5/2) soft clay

[ Very close layers

II—Brown cherts and porcellanites—Campanian to Turonian (38-78.2 mbsf)Brown (7.5YR 4/2)Reddish yellow (7.5YR 6/6)Dark brown (7.5YR 3/2)Dark reddish brown (5YR 3/3)Reddish brown and pink (5YR 4/3 and 8/4) fine laminaeLight reddish brown (5YR 6/4)Opalescent fragment (5YR 6/4) with small fissure

III—Gray siliceous limestones and cherts—Albian to Cenomanian (78.2-228.6 mbsf)Gray (5Y 5/1), with small spots of pyriteVery light gray (5 Y 8/1-7/1) iOlive gray (5Y 5/2) } Sharp contactLight olive gray (5Y 6/2)White (5Y 8/2)Light greenish gray (5Y 7/2)Light gray (5Y 7/1)Light gray (2.5Y 7/2)Light gray (5Y 7/1)Pale greenish grayOlive gray (5Y 4/2), sandyLight gray (5 Y 7/1) i u

White (5Y 8/2) JShaΦ contactWhite (5Y 8/1)Light gray (5Y 7/2); soft, clayeyPale brown (10YR 6/3)

IV—Redeposited volcaniclastic sandstones to claystones—Aptian (228.6^49.6 mbsf)Apple green, clayey, softGreen, siltyBlack (5Y 2.5/1), sandyOlive gray (5Y 5/2)Olive gray (5Y 5/2)Gray (5Y 6/1) silty, thin laminaeGrayish brown (2.5Y 5/2) clayey, thin laminaeLight gray (5Y 6/2), thin laminaeLight gray (10YR 6/2), clayeyPale green, sandyDark reddish gray (5YR 4/2), clayeyLight grayish green (5Y 7/1), clayeyDark brown (7.5YR 3/2), clayeyGreenish gray (5Y 5/1), clayey (with a sharp contact with sand)Olive gray (5Y 5/2-5/3), sandyGreenish, clayey with an apple green laminaReddish brown (5YR 5/4) with Mn dendritesBlack manganese micronodule extracted from bulk depositOlive gray (5Y 4/2)Green, silty sandBrown, clayey

} Sharp contact

V—Clayey radiolarites to siliceous claystones—Valanginian-Barremian (449.6^98.1 mbsf)Red (2.5YR 5/6) with darker patches (10R 3/4)Pinkish gray (5YR 6/2), softDark reddish gray (5YR 4/2), hardPinkish gray (7.5YR 6/2) with black laminae, siltyPinkish gray (7.5YR 7/2)Thin white fissure with dark coatings extracted from bulk depositPinkish gray (5YR 6/2) with black coatingsPinkish gray (7.5YR 6/2)Pinkish gray (7.5YR 6/2) with abundant black patchesPinkish gray (5YR 7/2) silty

A. M. KARPOFF

Table 2. Samples from Site 801 and their main macroscopic characteristics.

Sample(cm, top)

Depth(mbsf) Unit

I—Brown pelagic clay—Tertiary to Campanian (8-63.8 mbsf)IA Homogeneous dark reddish brown (5YR 2.5/2 to 7.5YR 3/4) soft clay

Homogeneous dark reddish brown (5YR 2.5/2 to 7.5YR 3/4) soft clayHomogeneous dark reddish brown (5YR 2.5/2 to 7.5YR 3/4) soft clayDark yellowish brown (10YR 3/4) clayLight yellowish brown (10YR 6/4) nannofossil oozeLight yellowish brown (10YR 6/4) nannofossil ooze

IB Dark yellowish brown (10YR 3/4) clayDark brown to brown (7.5 YR 4/4 to 5/6) clay

II—Brown cherts and porcellanites—Campanian-Cenomanian (63.8-126.5 mbsf)Pinkish gray (7.5YR 6/7) with pink laminaeLight reddish brown (5YR 6/3)

III—Volcaniclastic turbidites and Pelagic intervals—Cenomanian-Albian (126.5-318.3 mbsf)Gray (5Y 5/1) clayeyDark gray (5Y 4/1) sandyGreen, clayeyPale grayish green, clayey

129-801A-

1R-1,4O3R-1,633R-2, 1455R-1, 135R-1, 155R-1,625R-1,637R-1.67

7R-CC, 110R-1, 11

16R-1,416R-1, 14019R-1,5519R-1.70

129-801B-

2R-1.413R-1, 1005R-1, 50 Green5R-1, 52 Brown5R-2, 846R-4, 627R-1,348R-1, 1308R-5, 102

14R-l,24Gray14R-l,25Pink18R-1.2424R-1.5425R-1, 127R-1.30

33R-1.4333R-2,4835R-2, 12035R-2, 14035R-3, 1 Red35R-3, 3 Yellow35R-3, 19

44R-1, 125 Brown44R-1, 126 Green44R-1, 132

129-801C-

4R-1.734R-2, 1014R-2, 102 White

5R-2, 99 Green5R-5, 124 Green7R-3, 1208R-1,239R-2, 97

8.4021.0323.3539.7339.7540.2240.2359.67

63.9687.61

145.64147.00175.25175.35

203.91213.90232.20232.22234.04246.42251.34262.00267.72

318.54318.55356.04401.14405.21415.00

443.23444.78455.00455.20455.31455.33455.49

502.95502.96503.03

522.43524.08524.09

533.45537.93554.18559.73565.57

1 Sandy, thin laminae withi gradational color change

Olive gray (5Y 4/2), sandyGray (5Y 5/1), clayeyLight olive gray (5Y 6/2)Grayish brown (2.5Y 5/2)GreenPale green, clayeyPale green, clayeyGray (5Y 5/1), clayeyLight olive gray (5Y 6/2), clayey

IV—Brown radiolarites—Valanginian-Oxfordian (318.3-442.9 mbsf)IVA Pinkish gray (7.5YR 7/2), hard

Pink, with black small patchesVery pale brown (10YR 7/3) with Mn

IVB Light brownish gray (10YR 6/2) with Mn micronodulesPinkish gray (7.5YR 7/2) with Mn patchesChert, reddish brown and weak red (2.5YR 5/4-5/2)

V—Radiolarites and claystones—Callovian-Bathonian (442.9-461.6 mbsf)Strong brown (7.5YR 5/6)Yellowish red (5YR 5/8) softDark red (2.5YR 3/6)Dark red (2.5YR 3/6) with yellowish patchesDark red (2.5YR 3/6), soft, on external zone 1 Separated areas ofStrong brown (7.5YR 5/6), hard, as a nodular zone i the same sampleDark red (2.5YR 3/6)

VI—Interbedded basalt and silicified claystone—Callovian-BathonianReddish gray (5YR 5/2) 1 Fragments fromLight olive gray (5Y 6/2) / the same intervalLight reddish brown (5YR 6/4) and darker patches

| Two very thin layers

Hydrothermal ochreLight yellowish brown to olive yellow (2.5Y 6/4, 6-6)Yellow (2.5Y 7/6)White (2.5Y 8/2)

InterpiHow deposits and alteration productsGrass green fissure from grayish gray basaltGrass green fragmentBrownish yellow (10YR 6/8), alteration productDark reddish brown (5 YR 2.5/2), with few green fragments, margin of altered pillowBasalt

apatite, ankerite, and calcite) are those of low-temperature paragenesesresulting from the interactions between basalt, low sedimentary supply,and hydrothermal fluids. The fluid circulation is also demonstrated bythe textural features of the silicified facies and of the fracture network(see figures in Lancelot, Larson, et al., 1990). Redox conditions appearat the border between oxidizing and reducing environments, whichexist in the affected micro-sites (interpülow, sedimentary lenses).

Jurassic Basal Radiolarite and Claystone (Stage 1)

Callovian-Bathonian red radiolarite and claystone at Site 801(Unit V) comprise quartz, dioctahedral smectite (J{060} between1.48 and 1.50 Å), hematite, and some goethite. Volcanogenic minerals(mainly feldspars) are ubiquitous. In place, barite occurs in traceamounts. Barite is a common constituent of pelagic siliceous oozes

10


and cherts, where the mineral is often related to early biomineraliza-tion processes (Goldberg and Arrhenius, 1958; Church, 1979). Ahydrothermal origin is also suggested for deposits near spreading axes(Arrhenius and Bonatti, 1965; Church, 1979; McMurtry and Yeh,1981). It is often difficult to discriminate between both origins insiliceous deposits formed near volcanic edifices or ridge axes (Karpoff,1980; Karpoff et al., 1988). The preservation of barium within thesedeposits during the early diagenetic dissolution-recrystallization ofbiogenic compounds seems favored in such "active" environments.

The proportion of quartz is negatively correlated with that ofsmectites and oxides. The upper part of the unit (Core 129-801B-33R)appears richer in quartz and feldspar than the lower part close to thebasement (Core 129-801B-35R) where goethite occurs associatedwith hematite. The frequent fine white fillings of the fissures cross-cutting the laminations are made of cryptocrystalline quartz enclosingradiolarian tests, spheric aggregates of iron oxides, and thin manga-nese coatings (SEM observation). These fracture fillings are brokenas small slabs within the coarse fraction of the deposit which containsan abundant radiolarian fauna. The tests are often recrystallized, withmicrocrystalline quartz or chalcedony infillings.

The fine fraction (< 2 µm) is made of prevalent well-crystallizedsmectites with a rare 10 Å phase as illite, interlayered illite-smectite(I-S), goethite, and still-present quartz. Goethite and interlayered I Sare more abundant in the lower part; illite is better represented in themore quartzitic samples (Table 5). Smectites are mainly dioctahedral(large reflection between 1.50 and 1.51 Å). Under TEM (Pl. 1, Fig. 3),hematite displays clusters of very small rice-shaped grains (0 .1-0.2 µm), and the particles of smectite exhibit a flaky feature withdiffuse borders which is common for authigenic and diagenetic smectites.

The Callovian-Bathonian radiolarite and siliceous claystone arecomparable, by their composition and textural features, to basal metal-liferous sediments recovered either along ridges axes, or in asimilar stratigraphic position overlying ophiolite sequences, andwhose formation is related to the interaction between biogenic andhydrothermal phases (Bonatti et al., 1972; McMurtry and Yeh, 1981;Bonatti, 1981; Cole, 1985; Karpoff et al., 1988).

Oxfordian to Barremian Biosiliceous Sediments (Stage 2)

Clayey radiolarite, siliceous claystone, and brown radiolaritedeposited during the Late Jurassic and Early Cretaceous (Site 801—Unit IV, and Site 800—Unit V) contain prevalent quartz with smectite(Tables 3 and 4). The dissimilarity between coeval sediments ismainly the occurrence of abundant opal-CT (main peak at 4.05 Å) inthe Valanginian section at Site 801 (Core 129-801B-14R). The silicaphases consistently decrease upward at both sites. The accessoryminerals also emphasize small differences and heterogeneities: ironoxides and trace amounts of zeolites occur at Site 800, and illite andhalite are present at the Jurassic-Cretaceous transition (Cores 129-801B-18Rand-24R).

The numerous black patches and micronodules of manganeseoxides are not in evidence on the bulk XRD diagrams. Nevertheless,within the pinkish gray Valanginian radiolarite (Site 801), crystallitesof manganese oxide are easily identified on the borders of the opalinetests of radiolarians (Pl. 1, Fig. 4). The well-crystallized manganeseoccurs as rods, up to 40 µm long, closely mixed with very thin, curlyfibers of smectite.

The fine fraction of these deposits (Table 5) is composed ofdioctahedral smectite (d{060} = 1.50 Å), illite, and interlayered I-Sphases; clay-sized quartz is present as well. Palygorskite fibers arealso observed under TEM, associated with flaky particles of smectite,large illite particles with hairy outlines resulting from poor preserva-tion, and small spherules of opal.

This mineral association corresponds to the early diagenetic evo-lution of the biosiliceous sediment (formation of smectite, scarcepalygorskite, manganese oxide, and, in place of phillipsite, recrystal-lization of biogenic silica) which also contains primary detrital clays.

Volcaniclastic Turbidites from the Middle CretaceousEvent (Stage 3)

The middle Cretaceous redeposited volcaniclastic sand-, silt-, andclaystones overshadow the biosiliceous background sedimentation(Site 800—Unit IV; Site 801—Unit III). These deposits displayvarious secondary diagenetic minerals resulting from intense inter-actions between interstitial water and primary biogenic and volcano-genie phases (France-Lanord et al., this volume). Several distinctmineral associations including ubiquitous volcanogenic feldspar,pyroxene, and olivine have been defined and appear stratigraphicallyin ascending order; they may be time dependent (Tables 3 and 4).These associations, from bottom to top and with minerals in decreas-ing order of abundance, are (for Site 800):

a. Smectites, with trace amounts of quartz, phillipsite, clinop-tilolite, and well-crystallized manganite;

b. Smectites, calcite, phillipsite, and traces of quartz with clinop-tilolite;

c. Opal-CT, quartz, smectites, and traces of clinoptilolite;d. Smectites and celadonite (negatively correlated in abundance),

clinoptilolite, quartz, and sometimes smectites alone.

The associations (for Site 801) are:

e. Smectites and celadonite (negatively correlated in abundance),clinoptilolite, quartz, and sometimes smectites alone;

f. Smectites, analcime, and phillipsite; andg. Opal-CT, clinoptilolite, smectites, and trace amounts of celadonite.

From this set of data, clinoptilolite occurs in silica-rich intervalswhich are also pale brown to gray-colored, whereas rarer phillipsite isassociated with calcite. This discrimination is well established; thezeolite with the highest Si/Al ratio forms within silica-rich deposits(Kastner, 1979, 1981, and references therein). During basalt-seawaterinteractions, the formation of zeolite is favored when another non-basaltic source of silica, such as biogenic silica, is added (Crovisier etal., 1987). Local peculiarities include a high analcime content within adark olive siltstone (Sample 129-801B-2R-1, 41-46 cm), opal-CT-richlayers (reflection at 4.06 Å) at both sites, and very well-crystallizedmanganite as nodules or laminae at the base of the sequence fromSite 800. Analcime reflects a greater contribution of basaltic phases atpossibly slightly higher temperature than the clinoptilolite most fre-quently found in diagenetically altered biogenic sediments. The mangan-ite, MnOOH, forms small coalescent platelets (Pl. 2, Fig. 1). Thishydroxide is not commonly described in recent sediments. At Site 800,manganite could have resulted from aging of primarily less-orderedphases such as birnessite formed during early oxidizing diagenesis.

A frequently observed morphology of smectites is that of honey-comb nontronite found within altered hyaloclastites and bentonites(Khoury and Ebert, 1979; Karpoff et al, 1980; Konta, 1986). Never-theless, within the volcaniclastics from Sites 800 and 801, supplefibers and fibrilla, slightly curled, making "bridges" between aggre-gates (Pl. 2, Figs. 2 and 3), are more common. This feature is similarto that of the hydrothermal clay from the Galapagos hydrothermalmounds (Kurnosov et al., 1983; Karpoff, 1989) and that of fibrousillite formed by burial diagenesis (Keller et al, 1986). Calcite is arecrystallized phase mixed with clay minerals in fine fractures. Radio-larians trapped within the volcanogenic material are poorly preservedand the tests are often completely clay-replaced and quartz-filled; theclinoptilolite of such a clayey interval displays very small crystallites(Pl. 2, Fig. 4).

Clay minerals are smectites and celadonite (dioctahedral mica).From the double d{060) peak on XRD diagrams (1.50 and 1.53 Å),trioctahedral clay minerals appear associated with dioctahedral clayminerals. The clay from the analcime-rich interval is predominantlya trioctahedral smectite. The fine fraction extracted from some inter-

11

A. M. KARPOFF

Table 3. Bulk mineralogical composition of the sediments from Site 800, estimated by X-ray diffraction on powdered samples.

Sample(cm, top)

Depth(mbsf) Quartz Opal-CT Calcite Phillipsite Clinoptilolite Smectite 10Aa Halite Fe-oxides

Vole.minerals0

129-800A-

1R-CC, 13R-1, 1364R-1,974R-2, 674R-2, 1164R-3, 804R-4, 17

6R-1, 76R-1, 37 Clear6R-1, 37 Dark7R-1,668R-1, 18R-1,229R-1, 1

10R-1,11R-1,11R-1,12R-1,13R-1,14R-1,17R-1,18R-1,18R-1,19R-1,19R-1,21R-1,21R-1,21R-2,22R-1,24R-1,

1390 Clear90 Dark3746101257012113754 Gray54 White81930

26R-1, 426R-1, 10626R-2, 1227R-1.3028R-1, 8228R-2, 4828R-4, 2

29R-3, 723OR-2, 25

33R-2, 14633R-7, 6335R-2, 9836R-2, 39

36R-3, 2837R-CC, 138R-1, 1238R-1.2438R-1, 29 Nodule39R-2, 11141R-1.9350R-1, 59

51R-1.51R-1,51R-1,52R-1,52R-2,52R-2,53R-1,53R-2,53R-2,55R-1,

135 Clear135 Dark1418686 Fissure11725 Pink25 Brown126

0.2811.9621.2722.3722.8624.0024.87

39.6739.9739.9849.8658.9159.1268.51

78.3388.7088.7197.67107.26117.21144.45154.40154.91162.91163.27181.84181.86182.88191.19210.20

228.64229.66230.22238.30248.02249.18251.72

260.22267.65

290.46296.33308.88317.79

319.18328.02334.62334.74334.79337.15363.43440.79

450.48450.95450.96460.21461.16461.20466.07466.65466.67480.36

xxxxxxxxxxxxxxxxXXX

xxxxxxxxxxxxxxxxxxxxxxxxx

xxxxXXX

xxxxxXXX

xxxxx

xxxxx

o

oP

oP

XXX

xxxx

XX

XXX

XX

XXX

X

X

XX

xxxxXXX

xxxxXX

λXX

xx Cxx C

xC

XXX

xxxxxxxxXXX

xxxxxxxxxxxxxXXX

xxxxxxxxxXXX

XX

XX

oC

oC

oC

ΔΔΔΔΔΔΔΔΔ

ΔΔΔΔ

AΛΛ

Δ

ΔΛΛΛ

Notes: — = traces; o = present; x = relative abundance; Δ = mixture of volcanic minerals (with feldspars, pyroxenes, and olivine).a 10Å clay minerals at 10Å as illite; P = palygorskite; C = celadonite.b Volcanodetrital minerals, mainly feldspars.c See text for full discussion.

12


Table 3 (continued).

Sample(cm, top)

129-800A-

1R-CC, 13R-1, 1364R-1,974R-2, 674R-2, 1164R-3, 804R-4, 17

6R-1.76R-1, 37 Clear6R-7R-8R-8R-9R-

10R-11R-11R-

, 37 Dark,66, 1,22, 1

, 13, 90 Clear, 90 Dark

12R-1, 3713R-1.4614R-1, 10117R-1.2518R-1.7018R-1, 12119R-1, 119R-1.3721R-l,54Gray21R-1, 54 White21R-2, 822R-1, 1924R-1.30

26R-1,426R-1, 10626R-2, 1227R-1.3028R-1.8228R-2, 4828R-4, 2

29R-3, 7230R-2, 25

33R-2, 14633R-7, 6335R-2, 9836R-2, 39

36R-3, 2837R-CC, 138R-1, 1238R-1.2438R-1, 29 Nodule39R-2, 11141R-1.9350R-l,59

51R-1.8851R-1, 135 Clear51R-1, 135 Dark52R-1, 14152R-2, 8652R-2, 86 Fissure53R-1, 11753R-2, 25 Pink53R-2, 25 Brown55R-1, 126

Depth(mbsf)

0.2811.9621.2722.3722.8624.0024.87

39.6739.9739.9849.8658.9159.1268.51

78.3388.7088.7197.67

107.26117.21144.45154.40154.91162.91163.27181.84181.86182.88191.19210.20

228.64229.66230.22238.30248.02249.18251.72

260.22267.65

290.46296.33308.88317.79

319.18328.02334.62334.74334.79337.15363.43440.79

450.48450.95450.96460.21461.16461.20466.07466.65466.67480.36

Stages and mineralOther associations0

-

•

Pyrite

Pyrite

;

(d)

(c)

(b)

ManganiteManganite (a)

> 6

5

4

' 3

• 2

vals of the volcaniclastic sequences is composed of dominant smec-tites, celadonite, traces of interlayered I-S phases, and a possible 7-Åphase such as kaolinite or halloysite (Table 6). Under TEM, clayparticles exhibit various morphologies and some clay-sized zeolitefragments occur (Pl. 3, Figs. 1-3). Within the basal interval fromSite 800 (mineral association "a"), the smectites display two types ofparticles: (1) large flakes with curled edges, and (2) thin, small lathsforming a light felt. Within some samples, the rare squat cylinders canbe identified as halloysite. Celadonite, which is more abundant at thetop of the Site 800 sequence and the base of the Site 801 volcaniclasticsequence, exhibits very light platy particles. These mixed morpho-logical types are found in the green clays from the Galapagos mounds(Honnorez et al., 1983; Buatier et al., 1989). In oceanic volcanogenicrocks, celadonite is formed at higher temperature (> 25°C) thaniron-smectite (Bohkle et al., 1984; Duplay et al., 1989).

Peculiar and sometimes unusual mineral occurrences (calcite,analcime, and halloysite) illustrate the complexity of the diageneticreactions within these heterogeneous deposits (France-Lanord et al.,this volume). Part of the water-rock interaction could have occurredat higher temperatures than that of bottom seawater. Diageneticparagenesis is not primarily controlled by the grain size of the deposit;clay-, silt-, and sandstones from the same turbidite bed do not showdrastic differences. The variability of the paragenesis seems morerelated to the primary composition of the turbidite deposits, whichvaried stratigraphically.

The comparison between the two units (IV at Site 800 and IIIat Site 801) allows the mineral associations to be correlated (Tables3 and 4). In consequence, a "mineral stratigraphy" is establishedwithin these thick, redeposited sediments from the successive min-eral associations given above. The top of the upper Aptian unit atSite 800 (association "d") appears to be the lithologic equivalent ofthe base of the middle Albian section from Site 801 (association "e").Petrographical features corroborate this correspondence; at bothsites the turbidite facies, with fine-laminated thin beds, is similar.The correspondence is also recorded by the biogenic input charac-terized by the appearance of the radiolarian-nannofossil assem-blage (Erba, this volume). This interval (e-d) is bounded at topand bottom by silica-rich intervals (c, g), reflecting the dominantlysiliceous background biosedimentation.

The paleolatitude of Site 800 from late Aptian was the same as thatof Site 801 during the middle Albian (10°S, Fig. 3). Both sites appearto have been at the same distance from a distal fixed volcanic source(hotspot) at those times. Site 800 moved off from this source faster thanSite 801, back to a more subequatorial position in the high productivitybelt, allowing biogenic sedimentation to dominate its sequence.

Pelagic Sediments from Albian-Cenomanian Times(Stage 4)

This stage in the sedimentary evolution of the Pigafetta Basin isrepresented only by lithological Unit III at Site 800, consisting of lime-stone and gray chert. The mineralogical composition of the facies is inaccordance with its macroscopic features, and contains mainly silicaphases, opal-CT (reflection at 4.05 to 4.10 Å, increasing upward), andquartz of inversely varying proportions (Table 3). In places calciteis the prevalent mineral. Clay minerals are better represented withinsiliceous intervals, particularly at the base of the unit where clinoptilolitealso occurs (Core 129-800A-24Rto-18R). At this level the volcanogenicminerals, feldspar, and pyroxene are still present. Clay minerals aredioctahedral smectite (d{060} at 1.50 Å) and rare palygorskite. Acces-sory minerals are pyrite (around radiolarian tests) and oxides. The finefraction comprises smectite, palygorskite, and rare illite and inter-layered I-S phases (Table 5). The light particles of smectite havelath-shaped edges, with curled overgrowths. Palygorskite is long,lath-shaped. Aggregates of small granules of silica are very abundant(Pl. 4, Fig. 1).

13

A. M. KARPOFF

Table 4. Bulk mineralogical composition of the sediments and basement alteration products from Site 801, estimated by X-ray diffractionon powdered samples.

Sample(cm, top)

Depth(mbsf) Quartz Opal-CT Calcite Phillipsite Clinoptilolite Smectite 10Åa Halite Fe-oxides

Vole,minerals

129-801A-

1R-1,4O

3R-1.633R-2, 145

5R-1, 135R-1, 15

5R-1.625R-1,63

7R-1.67

7R-CC, 1

10R-1, 11

16R-1.4

16R-1, 14019R-1, 55

19R-1.70

129-801B-

8.4021.03

23.3539.73

39.7540.2240.23

59.67

63.96

87.61

145.64

147.00175.25

175.35

XX

X

X

X

ooX

X

X

X

o

0

xxxxxxxx

X

xxxx

oxxxxxxxxx

o

—

X

o

2R-1.41 203.91

XXX

oC

xC

3R-1, 100

5R-1, 50 Green5R-1, 50 Brown

5R-2, 846R-4, 62

7R-1.348R-1, 130

8R-5, 102

14R-l,24Gray14R-l,24Pink

18R-1.24

24R-1.5425R-1, 1

27R-1.30

33R-1.4333R-1, 14333R-2, 4835R-2, 120

35R-2, 14035R-3, 1 Red35R-3, 1 Yellow

35R-3, 19

44R-1, 125 Brown

44R-1, 125 Green44R-1, 132

129-801C-

4R-1.734R-2, 101

4R-2, 102 White

5R-2, 99 Green5R-5, 124 Green7R-3, 120

8R-1.239R-2, 97

213.90

232.20232.22234.04

246.42251.34

262.00267.72

318.54

318.55356.04401.14

405.21

415.00

443.23

444.23444.78455.00455.20455.31

455.33455.49

502.95

502.96503.03

522.43

524.08524.09

533.45537.93

554.18559.73565.57

0

XX

X

o

X

X

0XX

XX XXXXX XXX

xxxxxxxx

xxxxxxxxx

xxxx

xxxxxxxxX

XX

XX

XX

XX

XX—

xxxx

xxxxxxxxx

XXX

oXXX

o

xxxxxXXXX

XXX

XX

X

oC

xC

xx Cxxx C

xxxxxxxXXX

xxx

xxx Cxxxx C

xxx C

ΔΔ

ΔΔ

ΔΛΛΛΛΛ

Notes: — = traces; o = present; x = relative abundance; Δ = mixture of volcanic minerals (with feldspars, pyroxenes, and olivine).a10Å = clay minerals at 10Å as illite; C = celadonite.bVolcanodetrital minerals, mainly feldspars.cSee text for full discussion.

Within the basal section of this unit of early to late Albian age, theslight volcaniclastic input yielded similar secondary paragenesis tothat within the underlying deposit. Palygorskite, sometimes ascribedto volcanic phase alteration, is commonly found in silicified lime-stones and cherts and expresses the hypersilicic environment (Karpoffet al., 1981, and references therein).

Upper Cretaceous Chert (Stage 5)

As expected, the brown chert and porcellanite from both lithologicUnits II (Sites 800 and 801) are made of quartz and opal-CT (withvalues for the main peak ranging from 4.06 to 4.11 Å). For thediagenetic implications of the relative abundances and characteristics

14


Table 4 (continued).

Sample(cm, top)

129-801A-

1R-1,4O3R-1,633R-2, 1455R-1, 135R-1, 155R-1.625R-1,637R-1,67

7R-CC, 110R-1, 11

16R-1.416R-1, 14019R-1, 5519R-1, 70

129-801B-

2R-1.41

3R-1, 1005R-1, 50 Green5R-1, 50 Brown5R-2, 846R-4, 627R-1.348R-1, 1308R-5, 102

14R-l,24Gray14R-l,24Pink18R-1.2424R-1.5425R-1, 127R-1.30

33R-1.4333R-1, 14333R-2, 4835R-2, 12035R-2, 14035R-3, 1 Red35R-3, 1 Yellow35R-3, 19

44R-1, 125 Brown44R-1, 125 Green44R-1, 132

129-801C-

4R-1, 734R-2, 1014R-2, 102 White5R-2, 99 Green5R-5, 124 Green7R-3, 1208R-1.239R-2, 97

Depth(mbsf)

8.4021.0323.3539.7339.7540.2240.2359.67

63.9687.61

145.64147.00175.25175.35

203.91

213.90232.20232.22234.04246.42251.34262.00267.72

318.54318.55356.04401.14405.21415.00

443.23444.23444.78455.00455.20455.31455.33455.49

502.95502.96503.03

522.43524.08524.09533.45537.93554.18559.73565.57

Stages and mineralOther associations0

-

> 6

Λ

J 5

(g)

xx Analcime (f)

(e)

BariteBarite

BariteBarite

-

, 3

• 2

- 1

x Ankeritexxx Ankerite

Ankerite

x Apatite

of these silica phases, see Behl and Smith (this volume). Accessoryminerals are smectite and zeolites. The latter are prevalent clinop-tilolite in opal-rich facies and scarce phillipsite within the uppermostinterval of the unit at Site 800. Zeolites were not found in the fewsamples from this poorly recovered section at Site 801. Scarce detritalfeldspar also occurs at Site 800. This facies is similar to the underlyingsediments, with higher silica supply and strong diagenetic evolution.This facies is widespread in the northern Pacific (Larson, Moberly, etal., 1975; Thiede, Vallier, et al., 1981; Heath, Burckle, et al., 1985).

Uppermost Cretaceous and Cenozoic Pelagic Red Clay(Stage 6)

The latest episode consists of the slow deposition of deep-sea redclay below the CCD (Unit I—Sites 800 and 801). This facies containsthe phases commonly found within the equivalent facies from Pacificdeep basins: prevalent clay minerals, iron-oxides, and zeolites(Karpoff, 1989, and references therein). The manganese oxides thatform micronodules do not give diffraction peaks, as they are amor-phous phases. Halite is related to the high seawater content. Thespecificity to the red clays at Site 800 and 801 is the occurrence ofrelatively abundant detrital minerals (quartz, illite, scarce feldspar) inthe uppermost part of the unit, and the vertical repartition of zeolites(Tables 3 and 4).

Phillipsite and clinoptilolite contents are negatively correlated; thelatter is more abundant within the lower part of the unit. The relation-ship is progressive at Site 800 but emphasized at Site 801, where thenannofossil ooze interval is an effective border between the two levelsof different mineralogy. As established by Kastner (1979, 1981),clinoptilolite appears to be the representative zeolite of the oldestcondensed pelagic sediments (Upper Cretaceous), whereas phillipsiteis better developed within Cenozoic deposits.

The fine fraction of the red clay is heterogeneous, comprisingprevalent dioctahedral smectites, illite and interlayered minerals,kaolinite, chlorite, and quartz (Table 7). Palygorskite fibers areobserved within TEM preparations (Pl. 4, Fig. 2). The detrital inputfrom relatively close island sources is then obvious. The morphologi-cal segregation between detrital and authigenic smectites is some-times difficult to determine; the latter appears more abundant withinthe lowermost part of these red clay units.

Lithologically comparable to the widespread recent deep-sea redclays in the central Pacific, the Pigafetta Basin red clay is moreinfluenced by the detrital and eolian terrigenous input from nearbyislands and continents, such as the deposit from the most northwesternpart of the Pacific (Lenotre et al., 1985; Bryant and Bennett, 1988;Karpoff, 1989).

GEOCHEMICAL COMPOSITION OF THESEDIMENTS: THE MARK OF ENVIRONMENT

Chemical data (Tables 8-11) are considered for all samples fromSites 800 and 801. The major element compositions evidently reflectthe petrographical composition of each facies. Whole sequences aresilica-rich. The high silica contents relate both the biosedimentation,continuous during the long span of about 165 m.y., and the subsequentintense diagenetic silicification. The minor and trace elements reflectthe subtle differences of the deposits related to the variable inputs invarious environments. Several types of diagrams allow the facies tobe discriminated and related to the environments of deposition.

Biosiliceous Background: Relationship to Plate Motion

The variations in total silica content with depth are reflected assilica-rich chert, radiolarite, and silicified limestone. Pelagic input isdiluted within the volcanogenic deposits and claystone. Variations ofthe Si/Al ratio allow the main trend of biogenic input and diageneticsilicification to be specified (Figs. 4 and 5).

At Site 800 (Fig. 4), the curve for the maximum Si/Al ratio followsthe paleolatitude curve. The highly chertified layers give the highestratios; sites and episodes of intense silicification are near the basalticbasement (Early Cretaceous, stage 2) and during the early Campanian-Turonian (stage 5). Considering also the calcite-rich facies occurringwithin Unit III (stage 4), the highest biogenic sedimentation (Si andCa) correlates with the nearest equatorial position of the site, duringthe Cenomanian. In these deposits the volcanogenic input decreasesstrongly as well (see "Mineral Associations" section above). A drastic

15

A. M. KARPOFF

Table 5. Mineralogical composition of the fine fraction (<2 µm) of some samples of the Mesozoicsiliceous biogenic deposits (Stages 1, 2, and 4).

Sample(cm, top)

129-800A-

19R-L3722R-1, 1951R-1, 88

129-801B-

25R-1, 133R-1, 4335R-2, 12035R-2, 14035R-3, 1 Red35R-3, 19

Depth(mbsf)

163.27191.19450.48

405.21443.23455.00455.20455.31455.49

Stage

442

2

Smectites

xxxxxxxxxxxxx

xxxx

xxxxxxXXX

xxxxxxxxxxxxxxxxxxxx

Illite

XX

X

XX

XX

xxxxxX

X

X

X

I-S

XX

XXX

XX

XX

XXX

xxxxxxxxxxxxx

Palygorskite

XX

o

Other

Opal

x Quartz

QuartzQuartz; broad S peaks

Goethite, quartzGoethite, quartzGoethite, quartz

Notes: Relative abundance: x = 10%, o = trace. Smectites: main peak at 15Å. I-S = mixed-layer illite-smectite.

drop occurs at the chert-red clay boundary. The volcaniclastic de-posits exhibit a constant Si/Al ratio; the maxima are related toopal-rich intervals.

At Site 801 (Fig. 5), the Si/Al variations appears similar but lesssharp- For the sedimentary cover, the maximum curve also followsthe paleolatitude curve. Highly silicified intervals occur within theUpper Jurassic brown radiolarite (stage 2). The upper part of thecrustal sequence displays a wide range of Si variations; highly silici-fied zones include the metasediments, a hydrothermal deposit, and aninterlava flow breccia zone.

Diagenetic Markers

Strontium and barium are the trace elements commonly related tobiogenic silica and calcium carbonate. During early diagenesis involvingintense dissolution and recrystallization, these elements are releasedfrom the primary phases to secondary minerals or seawater. Someplanktonic species (e.g.,Acantharia, a radiolarian) exhibit a test madeof celestine. Sr is frequently reused by the authigenic silicates (clayminerals and zeolites) and oxides, and depleted within highly trans-Table 6. Mineralogical composition of the fine fraction (< 2 µm) of someintervals from Cretaceous volcaniclastic turbidites (Stage 3).

Sample(cm, top)

Depth(mbsf) Smectites I0Å I-S 7A

129-800A-

26R-I.426R-2, 1228R-I.8228R-4, 233R-2. 14633R-7, 6335R-2, 9836R-2, 3938R-1. 1238R-1.2441R-1.93

129-801B-

I6R-1.419R-1.55

129-801C-

3R-1. 1005R-2, 846R-4. 628R-5. 102

228.64230.22248.02251.72290.46296.33308.88317.79334.62334.74363.43

145.64175.25

213.90234.04246.42267.72

xxxxxxxxxxxxxxxxxxxxxxx

xxxxxxxxxxxxxxxxxxx

xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

xxxxxxxxxxxxxxx

xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

Clinoptilolite

Quartz

Smectite at I4Å

Clinoptilolite

Smectite at 13ÅSmectite at 14.5Å

Clinoptilolite; broader peaks

Note: Same legend as Table 5. Smectites: main peak at 15Å; 10Å = celadonite; 7Å = related to halloysite.

formed calcareous sediments (Veizer and Demovic, 1974; Karpoff,1980, 1989; Manghnani et al., 1980; Garrison, 1981). The sedimentsfrom Sites 800 and 801 are mostly Ca-poor (Fig. 6). The Sr/Ca ratioof the Paleocene nannofossil ooze (Site 801-Unit I, stage 6) is likethat of Cenozoic calcareous sediments. The calcitic beds from thesilicified sediments from Site 800-Unit III (stage 4) are Sr-depleted,as is the ankerite-rich metasediment (Site 801 basalt sequence),indicating intense carbonate recrystallization. Among the siliceousfacies with low Sr contents, the Jurassic basal red radiolarite (stage 1)has the higher Sr content. This facies is also barite-rich (Tables 4and 11). A hydrothermal origin could also be evoked for Sr andBa enrichments; nevertheless, the fairly preserved radiolarian fauna(Matsuoka, this volume), the medium compaction, and the relativelyhigh water content of the sediment are arguments for a biogenicsource and the preservation of Ba and Sr in this basal deposit.

The volcaniclastic sequence and the Cenozoic red clay are Sr-en-riched; both alterations of biogenic phases and volcanic detritussupply the Sr enrichment of the secondary zeolites and clay minerals.Further isotopic analyses would discriminate the Sr origins in thesefacies (Hoffert et al., 1978; Clauer et al., 1982).

Geochemical Expression of the Contribution of BasalticCrust and Volcanogenic Phases

In the pelagic realm, which is free of significant detrital input,major elements were derived from biogenic phases (Si, Ca, and minorFe and Mn), from halmyrolysis of basaltic and volcanic phases (Si,Fe, and to lesser extent Mn and Al), and from hydrothermal fluids (Fe,Mn, and Si). The relationships among these major elements, and therelated trace elements, define the various contributions of the primaryphases and the environment of deposition. Analog diagrams such asthose used by Boström (1970), Bonatti et al. (1972), Dymond et al.(1973), Toth (1980), and Bonatti (1981) are useful to discriminate thepelagic facies and enable the formation of hypotheses for similarorigins of comparable sediments (Karpoff, 1989; Karpoff et al., 1985,1988, and references therein).

The relationships between Fe/Ti and Al/Al + Fe + Mn ratiosdifferentiate detrital (as continental crust), basaltic (as mid-oceanridge basalt), and hydrothermal (as East Pacific Rise, or EPR, depos-its) contributions (Fig. 7). The value less than 0.4 for Al/Al + Fe +Mn ratio is indicative of metal enrichment of sediment (Boström,1970, 1983). The main facts are:

1. Siliceous ochre, metasediments, celadonite-rich interpillowdeposits, and breccia zones, all from the basaltic upper sequence, havea strong hydrothermal signature,

16


Table 7. Mineralogical composition of the fine fraction (<2 µm) of the Cenozoic pelagic redclay (Stage 1).

Sample(cm, top)

Depth(mbsf) Smectites Illite I-S Kaolinite Chlorite

128-800A-

1R-CC, 13R-1, 1364R-1.974R-3, 804R-4, 17

129-801A-

1R-1,4O3R-1,635R-1, 135R-l,62Ca-ooze5R-1.637R-1, 67

0.2811.9621.2724.0024.87

8.4021.0339.7340.2240.2359.67

xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

xxxxxxxxxx

xxxxxxxxxxxxxxxxxxxxxxxxxxxx

XXX

XXX

XX

XX

X

XX

XX

XX

XX

X

X

Other

QuartzQuartzQuartzQuartzQuartz

QuartzQuartz

Very broad peaks

Note: Same legend as Table 5.

100

2 0 0

CL

O

3 0 0

400 -

500 -

10Si/Al

100

20°S 10"

2.D Λ. 5.A Paleolatitude

Figure 4. Variation of Si/Al ratio vs. depth in sediments from Site 800. A. Curveof the maximum biogenic silica input. B. Possible curve of biogenic calcite inputand arrows showing the calcite-rich samples. C. Average line for volcaniclasticdeposits. D. Paleolatitude curve (from Lancelot, Larson, et al., 1990). Key tosymbols: (1) pelagic red clay (stage 6); (2) brown chert (stage 5); (3) chert andsilicified limestone (stage 4); (4) volcaniclastic turbidites (stage 3); and (5) clayeyradiolarite (stage 2).

100

200

300

400

500

600L

10 I / A l 100 IOOO-\ 1 I I I I I | 1 1 1—I I M I | 1 1 I I I I I I I

15"S 0° 10°N

#

6.Δ 7.× 8.X 9.-H

Figure 5. Variation of Si/Al ratio vs. depth in sediments and alteration productsof basaltic basement from Site 801. A-D. Same curves as in Figure 4.(Dashed line in (D) is error value). Key to symbols (1 to 5) same as inFigure 4; (6) Jurassic basal red radiolarite and claystone (stage 1); (7)metasediments; (8) hydrothermal deposit; and (9) interpillows material andbasalt (ß).

17

A. M. KARPOFF

1000 -re .

Sr (ppm)

800 —

600 -–

o

400 -–

200 -–

0 η

• ×

'P×H(9)

I I I I J I I I I I I L _ _ | I I i ' ' i J I I I I L

10 15 20 25

CaO (%)30 35 40 45 50

Figure 6. Relationship between CaO and Sr contents in lithologic facies from Sites 800 and 801. Key to symbols same as in Figures 4 and 5 (1 to 8), (9)white-cross squares for basement samples. A. Relation of Sr-Ca in the recent surface sediments, after Baker et al. (1982). B. Relation of Sr-Ca in Miocenecalcareous oozes, after Graham et al. (1982).

2. Jurassic basal red radiolarite and claystone (stage 1) show asignificant metal enrichment (and light trace metal enrichment, V, Zn,and Zr),

3. Brown radiolarite from stage 2 is intermediate between the Jurassicbasal red radiolarite and younger siliceous deposits (stages 4 to 5),

4. The volcanogenic supply (e.g., stage 3) to the biogenic sedi-mentation during stage 4 is well expressed,

5. The latest deposits, Campanian chert to Cenozoic red clay(stages 5 and 6), contain a detrital component.

Detailed geochemical discrimination between the successive bio-siliceous sediments is given by Karl et al. (this volume).

These geochemical specifics are also shows by the Ti and Ferelationship (Fig. 8), which emphasizes iron enrichment of the prod-ucts of altered basalt, particularly the interpülow celadonite, the ironenrichment of the basal red radiolarite with respect to the othersiliceous sediments, and the titanium enrichment of the altered vol-caniclastics with respect to the tholeiitic basalt reference. These highTi contents, as well as the higher Zr contents, could also reflect aspecific magmatic source for the volcanogenic phase. The red radio-larite samples are located between the hydrothermal trend in the basalticcrust and the halmyrolytic trend represented within the volcaniclasticdeposits and Cenozoic pelagic clay. The latter are distinguished fromeach other by their Al contents. Possible contamination by a Fe-Zn-Crcomponent is suspected in the uppermost superficial red clay core-catcher sample: this does not affect the ratio between other elements.

A ternary plot of Al-Fe-Mn allows the Pigafetta Basin deposits andother oceanic facies to be compared (Fig. 9). The data points for Cenozoicpelagic clay, Upper Cretaceous chert, and Aptian-Cenomanian chert and

limestone (stages 6, 5, and 4) are within the field of biogenic oozes,between the terrigenous end-member and the diagenetic deep-seabrown clays field. The points representative of the Lower Creta-ceous to Upper Jurassic radiolarite and claystone (stage 2) reachthe field of metalliferous sediments (EPR and Bauer Deep deposits).The Callovian-Bathonian basal radiolarite samples have their pointsbetween the basaltic pole and the Fe apex of the hydrothermal field.This trend appears to be that of the highly siliceous sediments formedclose to basaltic basement. The metasediments, siliceous ochre, andalteration products from the crustal sequence lie within the hydrother-mal field, which is also that of the interlava flow sediments from theOman ophiolite (Robertson and Fleet, 1986; Karpoff et al., 1988).

The Bonatti ternary diagram [Fe-Mn-(Ni + Co + Cu) x 10] (Fig. 10)is primarily used as a classification to discriminate among thevarious oceanic metalliferous concretions and nodules as hydroge-nous (from seawater), hydrothermal, or diagenetic (seawater-sedimentsinteraction). With increasing data on such phases and on their hostsediments, the apex significance and trends can be specified (Toth, 1980;Karpoff et al., 1985; Karpoff, 1989). The Fe apex area is characteristic ofhydrothermal metallic ores and biogenic oozes. The diagenetic evolutionof the latter yields the segregation between deep-sea nodules (hydroge-nous and oxic diagenetic apex) and their host red clays. The Mn zone isthe field of transition-element-poor hydrothermal crust, but also ofbiogenic origin and crusts formed at shallow depths (suboxic diageneticenvironment). In these cases, the Mn concretions are enriched in othertrace elements, particularly Ba and Sr.

The data confirm the hydrothermal character of the alterationproducts in the basaltic sequence, and also that of the Middle Jurassicbasal red radiolarite (stage 1). The subsequent sediments (radiolarite

18


Table 8. Chemical composition of bulk samples of sediments from Site 800: major elements (wt%).

Sample(cm, top)

128-800 A-

1R-CC, 13R-1, 1364R-1, 974R-3, 804R-4, 176R-1.76R-1, 37 Clear6R-l,38Dark7R-1, 668R-1, 18R-1.229R-1, 1

10R-1, 1311R-1, 90 Clear11R-1,91 Dark12R-1.3713R-1.4614R-1, 10117R-1.2518R-1.7018R-1, 12119R-1, 119R-1, 3721R-l,54Gray21R-1, 56 White21R-2, 822R-1, 1924R-1.3026R-1.426R-1, 10626R-2, 1227R-1.3028R-1, 8228R-2, 4828R-4, 229R-3, 7230R-2, 2533R-2, 14633R-7, 6335R-2, 9836R-2, 3936R-3, 2837R-CC, 138R-1, 1238R-1.2438R-1, 29 Nodule39R-2, 11141R-1.9350R-1, 5951R-1, 8851R-1, 135 Clear51R-1, 136 Dark52R-1, 14152R-2, 8652R-2, 86 Fissure53R-1, 11753R-2, 25 Pink53R-2, 27 Brown55R-1, 126

Depth(mbsf)

0.2811.9621.2724.0024.8739.6739.9739.9849.8658.9159.1268.5178.3388.7088.7197.67

107.26117.21144.45154.40154.91162.91163.27181.84181.86182.88191.19210.20228.64229.66230.22238.30248.02249.18251.72260.22267.65290.46296.33308.88317.79319.18328.02334.62334.74334.79337.15363.43440.79450.48450.95450.96460.21461.16461.20466.07466.65466.67480.36

SiO2

46.148.550.250.650.885.580.890.092.087.589.096.592.863.395.090.669.193.062.283.692.085.580.169.061.548.733.685.362.355.652.957.252.672.350.087.077.945.346.463.546.149.744.755.352.8

1.654.249.755.980.879.983.382.578.395.787.786.787.888.5

A12O3

14.615.314.714.314.04.45.33.21.52.92.50.21.50.60.42.40.71.50.83.91.53.55.59.01.30.56.73.38.38.99.7

10.29.47.4

10.02.84.7

10.49.57.9

11.39.09.59.79.80.68.69.3

11.25.95.63.75.25.80.92.72.93.03.4

MgO

3.033.153.182.772.921.041.360.730.420.900.830.080.330.290.140.750.250.540.361.280.511.241.903.610.530.312.271.204.446.569.936.08

12.303.29

11.201.411.826.08

10.805.876.90

17.4013.5011.708.430.20

11.6012.608.451.831.501.251.431.640.290.900.920.920.88

CaO

1.33.04.25.24.20.40.70.40.20.90.20.20.2

18.90.50.3

14.40.3

18.70.70.30.40.51.0

17.826.225.00.51.87.06.46.33.11.36.40.51.2

13.16.51.78.92.15.72.52.00.31.83.71.00.80.70.80.70.80.30.50.90.50.5

Fe2O3

15.87.66.65.45.72.02.51.41.01.51.30.31.70.50.31.30.51.10.52.91.12.54.46.80.90.35.22.77.67.9

10.39.5

10.73.79.52.45.2

10.09.39.6

10.010.111.79.7

10.70.39.9

11.88.33.73.84.13.55.20.92.32.92.92.2

Mn3O4

1.3102.6902.3402.1101.8200.2740.4380.2440.2040.2160.1130.0100.0100.0630.0100.0110.0280.0100.0810.0210.0130.0130.0330.0490.0460.0860.0680.0720.1370.1610.2390.1620.1700.0610.2260.0500.0920.1720.1620.0980.2160.1810.3050.1911.270

82.1000.1170.2220.0330.0890.1500.3081.1700.5370.3320.2840.0850.3570.143

TiO2

0.780.660.630.530.570.200.230.160.130.150.140.030.160.060.050.160.100.130.100.370.150.280.460.700.120.081.080.311.351.451.631.731.180.561.280.220.621.691.360.911.590.991.681.491.350.141.371.300.920.380.370.350.310.360.080.170.180.200.18

Na2O

3.583.693.103.162.331.001.140.660.390.700.700.090.370.210.160.510.220.440.240.920.500.690.971.490.380.171.270.732.322.282.052.632.332.052.680.681.392.181.641.701.472.831.922.382.280.052.241.951.491.000.870.700.770.990.270.360.360.660.61

K2O

2.693.523.714.193.871.071.380.780.440.660.690.100.480.300.220.880.260.570.281.140.501.131.682.550.330.110.840.932.861.790.430.981.691.470.800.930.741.182.951.812.901.000.861.211.520.051.041.386.331.601.541.141.351.710.300.780.890.971.13

P2O5

0.411.562.302.872.380.140.400.160.050.450.120.050.050.050.050.120.050.050.050.190.050.050.150.240.110.050.190.050.190.210.270.190.200.180.250.050.140.230.180.170.270.260.250.180.270.050.170.400.050.270.130.160.110.190.050.050.120.130.12

LOI

9.9310.839.619.01

10.314.305.543.622.743.903.501.712.85

16.331.822.62

13.332.52

16.523.632.333.595.005.67

16.4023.1024.20

3.287.127.525.285.195.736.406.113.374.759.929.856.53

10.956.878.416.828.21

13.607.256.824.783.833.632.873.243.710.942.612.472.632.49

Total

99.53100.50100.57100.1498.90

100.3299.79

101.3599.0799.7899.0999.27

100.45100.6098.6599.6598.94

100.1699.8398.6598.9598.89

100.69100.1199.4299.61

100.4298.3798.4299.3799.13

100.1699.4098.7198.4599.4198.55

100.2598.6499.79

100.60100.4398.53

101.1798.6398.9998.2999.1798.45

100.2098.1998.68

100.2899.24

100.0698.3598.43

100.07100.15

and claystone from the Late Jurassic-Early Cretaceous, stage 2) retainthis metalliferous specificity, with a high Fe/Mn ratio; however, theMn enrichment is followed by a slight trace element concentrationrelated to early oxic diagenesis (micronodules replacing tests). Thehigh Si content of the chert (stage 4), as well as the detrital feature ofthe Mn-enriched-pelagic clay (stage 6), disperse the representativepoints on both side of the biogenic-diagenetic trendline.

A peculiarity of the volcaniclastic deposits from Site 800 is themanganite which forms concretions and vein infillings. The chemicalcomposition of this manganese phase has a representative point lyingwithin the hydrothermal field; but, as with the Mn-microconcretions

from Site 550 Paleocene chert (Karpoff et al., 1985), this manganitehas a very high Ba content with lesser amounts of Sr. The AtlanticPaleocene micronodules are fecal pellets made up of diatomaceousfragments diagenetically replaced by well-crystallized todorokite.The manganite concretions at Site 800, like the pellets, are massiveand do not show any columnar or concentric layering of deep-seanodules; nevertheless, no traces of biogenic tests were found (Pl. 2,Fig. 1). A probable primarily biogenic origin of the manganese oxidesconcentration is suspected; these oxides could have formed at shallowdepths and settled with the turbidites beds. These concretions yieldeda secondary diagenetic transformation onto the better-crystallized

19

A. M. KARPOFF

Table 9. Chemical composition of bulk samples of sediments from Site 800: trace elements(ppin).

Sample(cm, top)

129-800 A-

1R-CC, 13R-1, 1364R-1.974R-3, 804R-4, 176R-1,76R-1, 37 Clear6R-l,38Dark7R-1.668R-1, 18R-1.229R-1, 110R-1, 1311R-1, 90 ClearllR-1,91 Dark12R-1,3713R-1.4614R-1, 10117R-1.2518R-l,7018R-1, 12119R-1, 119R-1.3721R-l,54Gray21R-1, 56 White21R-2, 822R-1, 1922R-1.3026R-1,426R-1, 10626R-2, 1227R-1.3028R-1.8228R-2,4828R-4, 229R-3, 7230R-2, 2533R-2,14633R-7, 6335R-2, 9836R-2, 3936R-3, 2835R-CC, 138R-1, 1238R-1.2438R-1, 29 Nodule39R-2, 11141R-1.9350R-l,5951R-1,8851R-1, 135 Clear51R-1, 136 Dark52R-1, 14152R-2, 8652R-2, 86 Fissure53R-1, 11753R-2, 25 Pink53R-2, 27 Brown55R-1, 126

Depth(mbsf)

0.2811.9621.2724.0024.8739.6739.9739.9849.8658.9159.1268.5178.3388.7088.7197.67107.26117.21144.45154.40154.91162.91163.27181.84181.86182.88191.19210.20228.64229.66230.22238.30248.02249.18251.72260.22267.65290.46296.33308.88317.79319.18328.02334.62334.74334.79337.15363.43440.79450.48450.95450.96460.21461.16461.20466.07466.65466.67480.36

Sr

195258256326262405930175719416

30612251951919466224471116189204542577436092674072597382766318428712015713112810818427112515213992746862105995062477049

Ba

45037539531734885150645962573921439214291841273244941605687143542581995228276206120988579843778864966343367542142526

81515116976468248255634789413329

V

188139120106101333725152219740119399201379283846871588026127202229206143121166415619923486158129161180606613912228634332436491027304028

Ni

2504555074953403844557231152253261328163566343766692211446561241094994658832730351942371921432903863503951

34028713148403762411931292723

Co

1402402301881642229166187105142116818112426141821141028193043643566264617164152363547414954194860222515821171116121613

Cu

3122642903462778713860328548144215720162012372159818316642291051251138010862965246469949107

497055185312333133120132116110

2745425445

Cr

7596050394419191812161483110830115213503125437021782291053994076674161135692875555378110293225780549325468096292483646192119716131514

Zn

18821671581232058198613857254104215113016151654203256118782010355728610196101568828636887838089941239933889179788957811021954506147

Zr

19017616615915454604027443672915123715291969294576118208

118481151121251811176118375213513212611486141121125111181045871735558841437444742

manganite phase. Further microprobe investigations will determinethe sites of barium within the oxide structure or as barite.

CONCLUSIONS

Mineralogical and chemical investigations conducted on a large setof samples from both Sites 800 and 801 allow the main trends of thesedimentation of the Pigafetta Basin since the Middle Jurassic to bedescribed and accurately defined with six major stages and events. At thisstage of the study, it would be pretentious to declare all the mysteries and

details of these sediments resolved. The results are good preliminary datafor further work with two different objectives: (1) on a small scale, todetermine the complex seawater-rock interactions and the conditions offormation of the specific minerals found in the deposits (i.e., apatite,manganite, celadonite, and zeolites) and thus to specify the environmentsof deposition and of the conditions of subsequent diagenesis (see alsoBehl and Smith, and France-Lanord et al., both this volume), and (2) ona large scale, to compare this complete sequence with those deposited atthe same time elsewhere in the mega-Pacific, and thus to relate the platemotion and subsidence story (see Larson and Lancelot, this volume).


Table 10. Chemical composition of bulk samples of sediments and basement alteration products from Site 801: major elements

Sample(cm, top)

129-801A-

1R-1,4O3R-1,633R-2, 1455R-1, 135R-1, 155R-1,625R-1,637R-1,677R-CC, 1

10R-1, 1116R-1.416R-1, 14019R-1,5519R-l,70

129-801B-

2R-1.413R-1, 1005R-1, 50 Green5R-1, 52 Brown5R-2, 846R-4, 627R-1.348R-1, 1308R-5, 102

14R-l,24Gray14R-1, 25 Pink18R-1.2424R-1,5425R-1, 127R-1, 3033R-1.4333R-2, 4835R-2, 12035R-2, 14035R-3, 1 Red35R-3, 3 Yellow35R-3, 1944R-1, 125 Brown44R-1, 126~Green44R-1, 132

129-801C-

4R-1.734R-2,1014R-2, 102 White5R-2, 99 Green5R-5, 124 Green7R-3, 1208R-1.239R-2, 97

Depth(mbsf)

8.4021.0323.3539.7339.7540.2240.2359.6763.9687.61

145.64147.00175.25175.35

203.91213.90232.20232.22234.04246.42251.34262.00267.72318.54318.55356.04401.14405.21415.00443.23444.78455.00455.20455.31455.33455.49502.95502.96503.03

522.43524.08524.09533.45537.93554.18559.73565.57

SiO2

48.347.949.350.79.48.2

51.657.290.890.553.652.659.374.9

50.251.367.856.050.057.050.955.763.082.584.185.485.385.996.881.483.756.364.866.767.069.875.6

2.185.9

83.895.494.140.641.490.444.050.2

A12O3

16.014.816.114.72.42.1

14.015.11.92.19.1

10.18.25.7

10.09.56.09.29.18.78.49.59.74.83.93.73.23.40.34.53.0

11.38.38.46.37.80.30.30.9

0.20.20.25.41.90.14.7

14.2

MgO

2.793.083.243.170.760.703.113.350.530.546.019.554.572.86

11.6012.905.417.16

10.607.147.877.523.501.421.190.900.970.880.061.110.772.841.962.141.631.760.76

14.101.07

0.090.080.114.974.200.254.876.77

CaO

1.72.41.93.3

45.446.9

3.41.40.50.35.66.15.12.6

5.42.73.14.35.03.45.71.61.70.60.60.50.40.60.30.50.41.40.80.70.60.6

10.531.53.3

0.20.21.81.7

11.32.81.5

12.1

Fe2O3

8.78.27.26.31.21.06.06.11.11.29.4

10.77.95.1

11.010.36.08.5

10.59.7

10.111.15.73.42.72.42.72.80.55.75.4

15.313.311.112.79.81.06.52.9

14.02.41.9

32.519.92.6

25.411.6

Mn3O4

1.5202.8602.1001.7200.1450.1191.4900.7700.1350.1180.1280.1750.1210.082

0.1250.1600.0970.1890.1890.1500.2410.1920.1220.5610.2280.3030.5280.4280.1100.0400.0390.4020.1570.1490.1490.0700.5241.0400.181

0.0160.0100.0100.1300.2950.0630.2860.190

TiO2

0.860.550.540.530.140.120.500.510.100.162.122.241.451.04

2.121.541.112.862.111.711.691.981.140.300.220.210.170.210.050.310.200.850.560.590.390.540.060.050.10

0.020.020.020.100.020.020.221.40

Na2O

4.673.983.213.120.380.283.092.980.420.552.772.142.461.66

3.662.892.123.452.531.912.192.582.481.191.040.800.800.880.190.880.681.431.411.371.131.130.070.110.09

0.080.100.120.700.340.020.712.59

K2O

3.313.683.914.510.020.024.243.940.490.512.580.612.641.66

0.711.831.601.672.554.113.772.673.101.361.151.150.940.990.131.631.223.672.783.062.382.700.020.020.38

0.060.230.284.455.630.244.010.02

P2O5

0.631.070.921.660.290.281.310.700.180.130.370.430.270.24

0.330.410.260.320.440.350.260.340.390.050.050.120.050.050.050.050.050.210.220.170.260.100.050.050.05

0.200.170.990.220.050.050.130.20

LOI

10.1010.209.718.86

39.0939.72

9.688.322.502.688.386.289.035.28

5.056.515.647.337.126.949.446.927.534.514.053.773.213.721.604.013.556.856.175.835.705.19

10.3743.16

4.49

2.360.740.519.93

15.403.21

12.721.13

Total

98.698.798.198.699.299.498.4

100.498.798.8

100.1100.9101.0101.1

100.2100.099.1

101.0100.1101.1100.6100.198.4

100.799.299.398.399.9

100.1100.199.0

100.6100.5100.298.299.599.398.999.4

101.099.6

100.0100.7100.499.898.5

100.4

The hydrothermal alteration of the upper crustal sequence, duringthe latest stages of the setting of upper tholeiitic lava flows, pillows,and alkali lava flows, is fairly comparable to that of the Cyprus andOman ophiolites. Peculiarly, the siliceous and ferruginous hydrothermaldeposit, with scarce apatite, is similar to the Cyprus hydrothermal ochre.

The basal Callovian-Bathonian red sediments (stage 1) are iden-tical to the commonly observed metalliferous deposits found as alayer between the basement and the overlying true pelagic sedimentsin oceanic basins. Biogenic siliceous tests are mixed with the ironsupply from the hydrothermal activity of the nearby ridge crest(oxidation of hydrothermal metallic ores, alteration of basalts). ThePigafetta Basin basal red radiolarite is like the basal red radiolaritesfound over Tethyan ophiolites (i.e., Oman, Apennines). Withoutsecondary tectonic metamorphism, their "simple" two phases, Siand Fe, both relate to the variability of the episodic inputs. A ridge

crest oxic environment also seems more favorable for the preserva-tion of the primary biogenic markers as Ba and Sr during earlydiagenetic processes.

Mesozoic sedimentation in the open Pacific Ocean was dominatedby siliceous biomineralization, making it significantly different fromthe Atlantic realm (stages 2, 4, and 5). The supply of biogenic phasesis a function of productivity, and the siliceous trend follows thepaleolatitudinal migration of the sites. The heaviest biogenic (Si andCa) contribution to sedimentation occurred during the Albian-Cenomanian at Site 800 when it was at a subequatorial location.

The middle Cretaceous event (stage 3) is well recorded in bothsedimentary sequences. A "mineral stratigraphy" related to the typeof the redeposited volcaniclastic facies (as a function of the proximityto the volcanic source) allows the upper part of the section at Site 800and the lower part of that at Site 801 to be correlated. Thus, the sites

21

A. M. KARPOFF

Table 11. Chemical composition of bulk samples of sediments and basement alterationproducts from Site 801: trace elements (ppm).

Sample(cm, top)

128-801A-

1R-1,4O3R-1,633R-2, 1455R-1, 135R-1, 155R-1,625R-1.637R-1,677R-CC, 110R-l,ll16R-1.416R-1, 14019R-1,5519R-1.70

129-801B-

2R-3R-5R-5R-5R-:6R-7R-8R-8R-14R-14R-18R-24R-25R-27R-33R-

,41, 100, 50 Green, 52 Brown.,84µ, 62,34, 130. 102, 24 Gray, 25 Pink,24.54, 1.30.43

33R-2, 4835R-2, 12035R-2, 14035R-3, 1 Red35R-3, 3 Yellow35R-3, 1944R-1, 125 Brown44R-1, 126 Green44R-1, 132

129-801C-

4R-1.734R-2, 1014R-2, 102 White5R-2, 99 Green5R-5, 124 Green7R-3, 1208R-1.239R-2, 97

Depth(mbsf)

8.4021.0323.3539.7339.7540.2240.2359.6763.9687.61145.64147.00175.25175.35

203.91213.90232.20232.22234.04246.42251.34262.00267.72318.54318.55356.04401.14405.21415.00443.23444.78455.00455.20455.31455.33455.49502.95502.96503.03

522.43524.08524.09533.45537.93554.18559.73565.57

Sr

196227171195856

2031762826413227336187

199194297647216148269228494S25856787211754210811411296924019133

16213741741118

Ba

26734737131855503422804310026070226158

1951074111181116189155223236142

10592629154488

184992312272560244922972036171828

191051176

V

15513112110218159292141818123312981

2031351112441802031691702342932353334781102157172146210125167533

811713

41226424228369

Ni

228414433399464531714734231211377863

29227112815131115118617211446293029181292914282768560104334

26172014810559570

Co

17624420216286

13852111134392628

444737425339424544128101085111219241522157178

1489211855344

Cu

3083424293416454299308774273927857

638049969680941601296246647369325994137119871286211111

159848956274

Cr

70506043873944129

312567199136

6713462447255763324322501731112161481

201654394332137275

6108

15156339199

Zn

13214819017235231561591632125997963

1081036212199748416676781065147664663915912410913710478318

1457

130781

9389

Zr

18217916215732281451352314

215187152109

19115911624020416615719913568585346491086731481551401401123118544

11119503264894

successively occupied the same geological setting, at a relativelydistal location from a fixed volcanic source (hotspot edifice[s]). Theactivity of the source was recorded from the early Aptian to Cenoma-nian by the deposits of the Pigafetta Basin, at the time when both siteswere at their southernmost paleoposition.

Detrital and eolian terrigenous input began to be significant duringthe Late Cretaceous and early Cenozoic. The surficial, condensed redclay (stage 6) exhibits a "zeolite stratigraphy" with older clinoptiloliteand recent phillipsite. This surface deep-sea clay has a higher detritalcontent than its central Pacific equivalent.

ACKNOWLEDGMENTS

This article is dedicated to the memory of Professor GeorgesMillot. I am grateful to Y. Lancelot, who gave me the opportunity to

discover the "Old Pac" realm. Sincere thanks are due to the Leg 129Scientific Party and the ODP Technical and Operations staff for thesuccessful cruise. This article has benefited from the review anduseful corrections of T. A. Davies, M. Underwood, and E. L. Winterer.I am indebted to A. Fisher for careful improvement to the Englishversion of the manuscript. The analytical work was performed usingfacilities at Centre de Géochimie de la Surface (CNRS), Strasbourg.This study was supported by a INSU-IST Grant, 90/ATP/781/AP90-803911-GEO307.

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and geochemistry of sediments from Galapagos Hydrothermal mounds,Leg 70, Deep Sea Drilling Project. In Honnorez, J., Von Herzen, R. P., etal., Init. Repts. DSDP, 70: Washington (U.S. Govt. Printing Office),225-233.

Lancelot, Y, Larson, R. L., et al., 1990. Proc. ODP., Init. Repts., 129: CollegeStation, TX (Ocean Drilling Program).

Larson, R. L., Moberly, R., et al., 1975. Init. Repts. DSDP, 32: Washington(U.S. Govt. Printing Office).

Lenotre, N., Chamley, H., and Hoffert, M., 1985. Clay stratigraphy at DeepSea Drilling Project Sites 576 and 578, Leg 86 (Western North Pacific). InHeath, G. R., Burckle, L. H., et al., Init. Repts. DSDP, 86: Washington (U.S.Govt. Printing Office), 571-579.

Manghnani, M. H., Schlanger, S. O., and Milholland, P. D., 1980. Elasticproperties related to depth of burial, strontium content and age, anddiagenetic stage in pelagic carbonates sediments. In Kuperman, W. A., andJensen, F. B. (Eds.), Bottom-Interacting Ocean Acoustics: New York(Plenum), 41-51.

McKenzie, J. A., Isern, A., Karpoff, A. M., and Swart, P. K., 1990. Basaldolomitic sediments, Tyrrhenian Sea, Ocean Drilling Program, Leg 107.In Kastens, K. A., Mascle, J., et al., Proc. ODP, Sci. Results, 107: CollegeStation, TX (Ocean Drilling Program), 141-152.

McMurtry, G. M., and Yeh, H.-W., 1981. Hydrothermal clay mineral forma-tion of the East Pacific Rise and Bauer Basin sediments. Chem. Geol,32:189-205.

Palmer, A. R., 1983. The decade of North American geology. 1983 geologicaltime scale. Geology, 11:503-504.

Pisciotto, K. A., 1981. Distribution, thermal histories, isotopic composition,and refection characteristics of siliceous rocks recovered by the Deep SeaDrilling Project. In Warme, J. E., Douglas, R. G., and Winterer, E. L., etal. (Eds.), The Deep Sea Drilling Project: A Decade of Progress. Spec.Publ.—Soc. Econ. Paleontol. Mineral., 32:129-148.

Robertson, A.HF., and Fleet, A. J., 1986. Geochemistry and palaeo-oceano-graphy of metalliferous and pelagic sediments from the Late CretaceousOman ophiolite. Mar. Pet. Geol, 3:315-337.

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Samuel, J., Rouault, R., and Besnus, Y., 1985. Analyse multiélémentairestandardisee des materiaux géologiques en spectrométrie d'emission parplasma à couplage inductif. Analusis, 13:312-317.

Shipboard Scientific Party, 1990a. Site 800. In Lancelot, Y., Larson, R. L., etal., Proc. ODP, Init. Repts., 129: College Station, TX (Ocean DrillingProgram), 33-89.

, 1990b. Site 801. In Lancelot, Y., Larson, R. L., et al., Proc. ODP,Init. Repts, 129: College Station, TX (Ocean Drilling Program), 91-170.

Thiede, J., Vallier, T. L., et al., 1981. Init. Repts. DSDP, 62: Washington (U.S.Govt. Printing Office).

Toth, J. R., 1980. Deposition of submarine crusts rich in manganese and iron.Geol. Soc. Am. Bull., 91:44-54.

Veizer, J., and Demovic, R., 1974. Sr as a tool of facies analysis. /. Sediment.Petrol., 44:93-115.

Date of initial receipt: 6 June 1991Date of acceptance: 6 January 1992Ms 129B-110

10 -–

0.0 0.2 0.3 0.4

AI/AI + Fe + Mn

0.5 0.7

Figure 7. Relationship between Al/Al + Fe + Mn and Fe/Ti in lithologic faciesfrom Sites 800 and 801 (after Boström, 1970, 1983). Ideal mixing curves: fromhydrothermal and EPR deposits (H) to mean value of continental crust orterrigenous material (C), and to mean value of oceanic crust or basalts (B).Same symbols as in Figure 6.


2.5 - r

0.5 -–

0.0

10 15 20 25 30

Fe2O3

35

Figure 8. Relationship between Fe and Ti oxides contents in the sedimentary deposits from Sites 800 and 801. A. Basaltic alteration trend (hydrothermalism). B.Basal red radiolarite trend. C. Volcaniclastic deposits and detrital trend (halmyrolysis). Same symbols as in Figure 6.

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A. M. KARPOFF

Pelagic Oozes

Fe

Ni +C0 + C11×10

Noduleso

etalliferous Sediments EPR

V H.D. Manganite

Mn Fe Mn

Figure 9. Ternary diagram for the relation between Fe, Mn, and Al contents ofoceanic sediments (after Dymond et al., 1973; Toth, 1980; Karpoff et al., 1988;Karpoff, 1989). T = terrigenous sediments pole in the upper part of the biogenicoozes field. EPR = metal-rich deposits from the East Pacific Rise axial zone.Metalliferous sediments field: (1) EPR crest and ridge flanks sediments, (2)Bauer deep surface sediments. H = hydrothermal deposits field between Feand Mn apices. Om = interlava flow metalliferous sediments from Omanophiolite. Nodules = Central East Pacific hydrogenous polymetallic nodules.Same symbols as in Figures 4 and 5.

Figure 10. Ternary diagram [Fe-Mn-(Ni + Co + Cu) x 10] (after Bonatti et al.,1972; Toth, 1980; Karpoff et al., 1985;Karpoff, 1989) for lithologic facies fromSites 800 and 801 and their relationship with oceanic facies. H.D. = hydrother-mal deposits between Fe and Mn apices. EPR = East Pacific Rise basalmetalliferous sediments from various sites: from left (higher Fe values) to right(Mn enrichment), deposits from the axial zone, crest sides, and deeper ridgeflanks. B.D. = Bauer Deep surface metal-rich sediments and brown clays fromthe high productivity zone. Red clays = surficial red clays from central EastPacific Ocean and their associated polymetallic nodules (nodules). Lowermostarea near Fe apex = biogenic siliceous and calcareous oozes. Si-C = siliceousconcretion from Pliocene clayey siliceous ooze at Site 464, DSDP Leg 62.P = manganese pellet from Paleocene brown clay at Site 550, DSDP Leg 80.Same symbols as in Figure 9.


05 µm 10 µm

Plate I. Jurassic basement and basal deposits at Site 801. 1. SEM photomicrograph of the ochre hydrothermal layer with quartz and goethite globule (Sample129-801C-4R-2, 101 cm). 2. Bipyramidal quartz and larger apatite crystals from the white lamina of the hydrothermal layer (Sample 129-801C-4R-2, 102 cm,SEM). 3. TEM microphotograph ofthe untreated clay fraction ofthe basal red radiolarite (Unit V, stage 1; Sample 129-801B-35R-3,1 cm): flaky smectite particles(S) and small iron oxide grains. 4. Valanginian brown radiolarite (Unit IV, stage 2; Sample 129-801B-14R-1, 24 cm, SEM): Mn-oxide rods around opalinelepispheres from a radiolarian test.

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A. M. KARPOFF

20 µm 10µm

Plate 2. SEM microphotographs of the Cretaceous volcaniclastic turbidite deposits (stage 3). 1. Well-crystallized manganite (Site 800, Unit IV; Sample129-800A-38R-l,29cm). 2. Authigenic Mg-rich smectite and K-zeolite crystals (Site 800, Unit IV; Sample 129-800A-41R-l,93cm). 3. Authigenic honeycombsmectites and small zeolite crystals (Site 800, Unit IV; Sample 129-800A-33R-2, 146 cm). 4. Clayey layer in the volcaniclastic turbidite at Site 801 (Unit III;Sample 129-801B-5R-2, 84 cm): clay-replaced and quartz-filled radiolarian test and very small clinoptilolite crystals in the matrix (arrow).


1 µm 0.5 µm

Plate 3. TEM microphotographs of untreated clay fractions (< 2 µm) of the Cretaceous volcaniclastic turbidite deposits (stage 3). 1. The two types of smectite particleswith flakes and thin laths (Sample 129-800A-38R-1,12 cm). 2. Flaky particles and diffuse laths of smectite and halloysite cylinder (H) (Sample 129-800A-36R-2, 39cm). 3. Slightly crumpled smectite particle, clinoptilolite fragment (C), and celadonite platelets (ce) in the background (Sample 129-800A-26R-1, 4 cm).

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A. M. KARPOFF

•

05 µm

1 µm

Plate 4. TEM microphotographs of untreated clay fractions (< 2 µm). 1. Late Albian radiolarian chert (stage 4; Sample 129-800A-19R-1, 37 cm): smectiteparticle with diffuse lath-shaped edges and curled overgrowths commonly observed for authigenic and/or diagenetically transformed smectites, longer laths ofpalygorskite, and aggregates of siliceous globules. 2. Cenozoic pelagic red clay (stage 6; Sample 129-801A-7R-1, 27 cm): small flaky smectite particles and rarethin and short palygorskite fibers.

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1. cenozoic and mesozoic sediments from the … · the mesozoic magnetic anomaly sequence) and the...

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