15. nannofossil biostratigraphy for antarctic sediments ... · 15. nannofossil biostratigraphy for...

15. NANNOFOSSIL BIOSTRATIGRAPHY FOR ANTARCTIC SEDIMENTS,LEG 28, DEEP SEA DRILLING PROJECT

D. A. Burns, New Zealand Oceanographic Institute, Department of Scientificand Industrial Research, Wellington, New Zealand

INTRODUCTION

Leg 28 (DSDP) was the first attempt to drill into thedeeper layers of sediment beneath the Southeast IndianOcean and waters around Antarctica. Inasmuch as thenannofossil zonal schemes presently in use are based toa large degree on warm-water sequences, the distribu-tion of nannofossils at the high latitudes of Leg 28 hasbeen unknown. The nannofossil assemblages recoveredfrom Leg 28 are dealt with in detail below. Each site isconsidered separately and the basis for biostratigraphicage assignment is discussed. It should be noted that thezonal numbers suggested by Martini and Worsley (1970)are not used, although in some cases a zone fossil is pre-sent in the sediment. Such omission is a means of stress-ing that the sporadic occurrence of one or twospecimens of a zone fossil is not taken as an indicationthat the enclosing sediment is equivalent to the com-plete zone of Martini and Worsley. Similarly, the abso-lute age limits for such a zone cannot necessarily be ap-plied to the present sections.

SITE 265Site 265 is situated on the southern flank of the

Southeast Indian Ridge. The sediments cored rangefrom Recent to middle Miocene and can be divided intotwo distinct units: (1) an upper unit of sedimentsformed predominantly of siliceous microfossils, butwhich contain occasional specimens of nannofossils orlayers of nannofossil-bearing sediments; (2) a lower unitof sediments formed predominantly of nannofossils.

Upper Unit

In the upper, siliceous sediments (Sample 1-1, 50 cmto Sample 14-6-125 cm) it is difficult to position strati-graphic boundaries based on nannofossils because oftheir sporadic distribution.

In this upper section, the nannofossils, when present,are predominantly placoliths consisting of species suchas Emiliana huxleyi, Gephyrocapsa oceanica, Pseudo-emiliania lacunosa, Cyclococcolithus leptopoms, Helico-pontosphaera kamptneri, Coccolithus pelagicus, a smallGephyrocapsa species, Umbilicosphaera mirabilis,Gephyrocapsa caribbeanica, Reticulofenestra pseudoum-bilica, Cyclococcolithina macintyeri. Abundance general-ly varies from barren or very rare (three specimens perslide) to few, and preservation from poor to moderate.Detailed distribution of species is shown in Table 1.

QuaternarySample 1-1, 50 cm to Sample 2-6, 100 cm; E. huxleyi;

Pleistocene.

TABLE 1ADistribution of Nannofossils

at Site 265

Sample(Intervalin cm)

1-1, 501-2, 70

to2-5, 662-6, 752-6, 1003-1, 100

to3-3, 603-4, 1104-1, 274-2, 604-3, 605-1, 205-1,635-2, 605-3, 605-4, 1095-5, 605-6, 60

to6-4, 567-1, 407-2, 607-2, 1187-3, 607-4, 607-5, 567-6, 608-2, 608-3, 60

E. h

uxle

yi

+

G.

ocea

nica

+

P. l

acun

psa

C. l

epto

pom

s

+

H.

kam

ptne

ri

+

C. p

elag

icus

Smal

l G

ephy

roca

psa

sp.

Barren

++

++

++

++

++

Barren

vr+ A

Barren

++

++

++

++

vr+

Barren+++

+++

++

++ +

Barren

++

+ + ++

BarrenBarren

+++++

+++++

+++++

+++++

+++++

Note: +=Specimens of the speciescommonly present, but relativenumbers not assessed; A=Abun-dant; B=Base plate only present;R=Rare; F=Frequent; S=Several;X=One specimen only; C=Com-mon; VR=Very rare (2-3 speci-mens only in a complete traverseof the slide).

Sample 3-4, 110 cm to Sample 4-3, 60 cm;Gephyrocapsa sp.; Pleistocene.

Sample 5-1, 20 cm to Sample 9-4, 60 cm; P. lacunosa;Pleistocene.

589

D. A. BURNS

Pliocene/Pleistocene Boundary

It is impossible to locate or accurately position thePliocene/Pleistocene boundary on the basis of nan-nofossils at this site. Siliceous microfossil stratigraphyindicates that the boundary is contained within the in-terval between Sample 9-5, 55 cm and Sample 10-1, 60cm. This interval is barren of nannofossils (Table IB).Only the sediments above (Sample 9-4, 60 cm) andbelow (10-2, 60 cm) contain nannofossil specimens.However, even in these nannofossil-bearing sediments,the absence of Discoaster makes positioning of thePlio/Pleistocene boundary impossible. Hence, detailedage assignment for the interval from 9-1, 60 cm to 13-1,0 cm is difficult. The only age indication given for thisinterval by the nannofossils is the first occurrence of the

lower Pleistocene zone fossil Pseudoemiliania lacunosa.However, as the lower range of this species is usuallywell into the Pliocene, this first occurrence of P.lacunosa may only be taken as having a limited strati-graphical significance and suggests that the sedimentsbelow this point may be of late Pliocene age or older.

Pliocene

Sample 10-2, 60 cm to Sample 13-1,0 cm; discoastersabsent, P. lacunosa present; upper Pliocene or older.

Sample 13-1,0 cm; R. pseudoumbilica, discoasters ab-sent; lower Pliocene.

Sample 13-2, 139 cm; R. pseudoumbilica, Discoasterasymmetricus, D. brouweri', lower Pliocene.

TABLE IBDistribution of Nannofossils at Site 265


8-4, 608-5, 809-1, 609-2, 609-3, 609-4, 609-5, 55

to10-1,6010-2, 6010-3, 6010-4, 6010-5,60Core 11

toCore 1213-1, 13013-2, 13913-3, 14314-1, 75

to14-5, 12514-6, 12515-1,4615-2, 3015-3, 12215-4, 11015-5, 11215-6, 3315-6, 11316-1, 3616-2, 1616-3, 2916-4, 6916-5, 3516-6, 115

E.

huxl

eyi

G. o

cean

ica

+

P. l

acun

osa

G.

lept

opor

us

+

H.

kam

ptne

riC.

pel

agic

us

+

Smal

l G

ephy

roca

psa

sp.

C. m

acin

tyer

iR

. ps

eudo

umbi

lica

D.

asym

met

ricu

sD

. bro

uwer

iD

. ham

atus

D. v

aria

bilis

C.

mio

pela

gicu

sC.

coa

litus

Ret

icul

ofen

estr

a sp

.d.

cf.

dia

latu

sD

. ste

llulu

sD

. de

fland

rei

C.

florid

anus

Barren++++

+

++

+ +

++

Barren

+++ +

+

+

Barren

Barren

+++

+++

++

++ + +

Barren

+++++

+++++

++++++++

++++++++++++++

++++ +

++

+++

+

+

+

+

++++

+++

++++++++

+++

+

+

++

+

+

+

+

++

++

Note: See Table 1A for explanation of symbols.

590

NANNOFOSSIL BIOSTRATIGRAPHY FOR ANTARCTIC SEDIMENTS

Sample 14-1, 75 cm to Sample 14-6, 125 cm; R.pseudoumbilica, C. macintyeri; lower Pliocene of un-known specific age.

The Pliocene is extremely difficult to recognizebecause of the general absence of Discoasters. Thepresence of Reticulofenestra pseudoumbilica in Sample13-1, 0 cm certainly indicates that this sediment andthose below are at least of Pliocene age. However, in theabsence of D. brouweri, D. surculus, or D. pentaradiatusabove this horizon, it is impossible to know which partof the Pliocene this sediment represents. It would beerroneous to equate it directly with the R. pseudoum-bilica lower Pliocene zone (NN15) of Martini andWorsley (1970) as there is no clear indication as to thetop of the zone. However, the presence in the section ofD. asymmetricus along with D. brouweri suggests thatsome part of this sequence (Cores 12 and 13) cor-responds to the lower Pliocene age equivalent to theNN15 Zone of Martini and Worsley. The presence of D.asymmetricus in Sample 13-2, 139 cm also suggests thatthese sediments are of lower Pliocene age.

Miocene/Pliocene BoundarySiliceous microfossil stratigraphy indicates that the

Miocene/Pliocene boundary at Site 265 is locatedbetween the middle of Core 14 and the top of Core 15.Accurate selection of the position of this boundary isimpossible using nannofossil stratigraphy as the sedi-ments at the base of Core 14 are either barren (Sample14-1, 75 cm to Sample 14-5, 125 cm) or contain onlygeneral, lower Pliocene/upper Miocene, backgroundplacoliths (C. pelagicus, R. pseudoumbilica in Sample 14-6, 75 cm). The Ceratoliths diagnostic of the boundaryare absent. The uppermost sediments of Core 15 (15-1,46 cm) are definitely of upper Miocene age. Consequent-ly, the Miocene/Pliocene boundary is either in thelowest section of Core 14 or in the interval not sampledbetween Cores 14 and 15.

Lower UnitCores 15 and 16 contain the second type of sediment

which is predominantly formed of nannofossils andcalcareous material, but which still contain somesiliceous microfossils. The nannofossil assemblages ofthis section are again dominated by placoliths, butseveral Discoaster specimens can be found in the as-semblages. This section of sediments affords good nan-nofossil stratigraphic control and contains the up-per/middle Miocene boundary.

The sediments can be stratigraphically subdivided asfollows:

Sample 15-1, 46 cm; Discoaster quinqueramus; upperMiocene.

Sample 15-2, 30 cm to Sample 15-4, 110 cm; D.hamatus; middle Miocene.

Sample 15-5, 112 cm to Sample 16-1, 37 cm;Catinaster coalitus; middle Miocene.

Sample 16-2, 16 cm to Sample 16-6, 115 cm; D. deflan-drei; middle Miocene.

The presence of specimens of D. hamatus, C. coalitus,and D. quinqueramus allows these Antarctic calcareoussediments to be positioned relative to the known

biostratigraphic framework and give some comparisonof this area with more northerly warm areas. However,the low numbers of these zone fossils in the samplesanalyzed and their rare occurrence in the sediments donot allow the recognition of unequivocal zonal bound-aries.

In general, the sediments at this site appearautochthonous. Minor amounts of reworked materialwere seen in one sample (Sample 13-3, 143 cm), whichcontains a few specimens of Cyclicargolithus floridanusand D. deflandrei.

SITE 266Site 266 was drilled in the south flank of the Southeast

Indian Ridge, about 800 km from the ridge crest. Thesediments cored range from Recent to lower Miocene.They can be subdivided into three distinct units: (1) theupper, exclusively siliceous sediments; (2) the middlesediments containing predominantly siliceous micro-fossils, but also a small number of calcareous micro-fossils; and (3) the lower sediments containing somesiliceous microfossils, but also containing significantamounts of calcareous microfossils.

Upper UnitUpper siliceous unit (Samples 1-1, 60 cm to 9-2, 63

cm): Stratigraphic ages or zones based on nannofossilscannot be assigned to this upper unit. Only one horizoncontains sparse nannofossils (Sample 1-4, 90 cm)(Tables 2A-D) and these were poorly preserved speci-mens of the placolith species Cyclococcolithus lepto-porus and a small Gephyrocapsa species.

Middle UnitMiddle siliceous unit (Samples 9-3, 64 cm to 12-3, 90

cm): In this unit poor preservation of the nannofossilsmakes species identification and hence accurate ageassignment difficult. Abundance varies greatly withinshort distances between samples, but nannofossils aregenerally rare to few. Despite this low abundance, somediagnostic species are present which allow a strati-graphic subdivision of the section.

Lower Pliocene (Samples 9-3,64 cm to 9, CC)Siliceous microfossil stratigraphy indicates a lower

Pliocene age for this interval. A lower Pliocene age isalso suggested for these two samples by the presence ofD. brouweri and D. pentaradiatus. Furthermore, thepresence of occasional specimens of C. leptoporus D.pansus, D. variabilis, and R. pseudoumbilica is consistentwith the lower Pliocene age. However, this same overlapof nannofossil species can also be found in upperMiocene sediments, and in the absence of the lower Plio-cene/upper Miocene zone fossils Ceratolithus rugosus,C. tricorniculatus, D. quinqueramus the lower Plio-cene/upper Miocene cannot be separated on the basis ofnannofossils. By correlation with the siliceous micro-fossil stratigraphy, this part of the core is assigned alower Pliocene age.

Upper Miocene (Samples 10-1,60 cm to 12-3,90 cm)

As at Site 265, Site 266 contains D. stellulus in theupper Miocene. In general, diagnostic upper Miocene

591

D. A. BURNS

TABLE 2ADistribution of Nannofossils at Site 266


C. p

elag

icus

Smal

l G

ephy

roca

psa

sp.

C. l

epto

poru

sR

. ps

eudo

umbi

lica

D. p

enta

radi

atus

D. p

ansu

sD

. var

iabi

lisD

. bro

uwer

iC.

mac

inty

eri

D. s

tellu

lus

D. c

alca

ris

Ret

icul

ofen

estr

a sp

.D

. tor

alus

D. a

sym

met

ricu

sC.

flo

rida

nus

1-1,60to Barren

1-3, 601-4, 90 + +2-2, 60

to Barren9-2, 639-3, 649-4, 14810-1,6010-2,6010-2, 13010-3,4010-3, 11010-4, 4510-5, 4010-5, 10810-6,4110-6, 11011-1,4011-1, 11011-2,4111-2, 11111-3,4011-3, 11011-4, 30

++++

+

+

+++

++

RBBBBB

+++++++++++++++++++

RR

R RX

RR

FSSS

S

s

XR

BBBBBB

B

B

FFFFFFFFFF

F

RRR

XX

X

FFFFFFF

XX

11-4, 10611-5,4111-5,110 B a r r e n

11-6, 3012-1, 11012-2, 13012-3, 39

+++

+

ss

RR


nannofossils are absent from this site, except for thepresence of occasional specimens of D. calcaris inSamples 10-5, 108 cm; 10-6, 41 cm; and 11-1, 40 cm.Sample 11-3, 110 cm contains a few specimens of D.asymmetricus, a species more commonly associated withlower Pliocene sediments but which has its lower rangein the Miocene. Sample 11-4, 30 cm contains one goodspecimen of D. toralus. The remaining nannofossils pre-sent are generally long-ranging species such as D.variabilis and R. pseudoumbilica. The only other signifi-cant stratigraphical range is the lowermost occurrenceof C. leptoporus (Sample 10-3, 40 cm) and C. macintyeri(Sample 10-5, 40 cm).

Several reworked species are present throughout thisupper Miocene section: D. deflandrei (10-2, 60 cm), C.miopelagicus (10-2, 150 cm to 10-5, 108 cm), C. flori-danus (10-3, 110 cm), and R. cf. hillae (11-3, 40 cm).

There is an interval of core which is barren of nan-nofossils in the lower part of this section (11-4, 106 cmto 11-6, 30 cm). The upper Miocene age for this sectionbased on nannofossil stratigraphy corresponds closelywith that based on siliceous microfossils.

Middle Miocene (Samples 12-1,110 cm to 17-1,110 cm)Recognition of middle Miocene sediments and posi-

tioning of the middle/lower Miocene boundary is rela-tively well defined on nannofossil distribution. The mid-dle Miocene zone fossil Discoaster exilis is present inSamples 13-2, 41 cm to 13-6, 115 cm. The middle/lowerMiocene boundary is marked by the lowest occurrenceof Sphenolithus heteromorphus (17-1, 110 cm), thisspecies being present in Samples 16-1, 61 cm to 17-1, 110cm. This positioning of the boundary is further indi-cated by the close correlation with foraminifer distribu-tion in this core, the extinction of the foram Catapsy-drax dissimilis (early Miocene) being just below thislevel.

Middle/Lower Miocene boundaryThis is the only site in which the middle/lower

Miocene boundary was sampled in the sites drilled onLeg 28. However, although the middle Miocene speciesS. heteromorphus occurs at this site, the positioning ofthe boundary between the middle and lower Miocene isstill arbitrary and complex. The complexity of positionis still further magnified when correlation with siliceousmicrofossils is attempted.

When dealing with nannofossil stratigraphy, there isconsiderable difference of opinion as to where thisboundary should be placed. Martini and Worsley (1970)position the boundary coincident with the lower bound-ary of the S. heteromorphus Zone, as does Bukry(1971). However, Berggren (1972) positions the mid-dle/lower Miocene boundary within the S. hetero-morphus Zone at 16 m.y. Hence, there is apparently twodifferent positions at which this boundary can be posi-tioned relative to the occurrence of S. heteromorphus atSite 266. However, the situation is further complicatedat Site 266 by the inability to accurately position thelower boundary of the S. heteromorphus Zone. Thelower boundary of the S. heteromorphus Zone wasoriginally defined by Martini and Worsley as the posi-tion of the last occurrence of Helicopontosphaera ampli-apetra (lower Miocene). However, H. ampliapetra doesnot occur in sediments at Site 266. Beneath the sedi-ments containing S. heteromorphus there is a section ofsediment which does not contain any species which fitinto the known zonal schemes. Beneath this level is asection of sediment which contains the lower Miocenezone fossil S. belemnos. It may well be that the intervalbetween the occurrences of S. heteromorphus and S.belemnos represents and is equivalent to the H.ampliapetra Zone of lower latitudes, but in the absenceof the species itself, it is incorrect to make this assump-tion definitely.

Some further indication, however, of the correct posi-tioning of this boundary is given by the youngest occur-rence of S. dissimilis in Sample 18-2, 40 cm. This species

592


TABLE 2BDistribution of Nannofossils at Site 266


12-3, 9013-1,4513-1, 12013-2,4113-2, 11113-3, 3013-3, 10613-4, 4013-4, 11513-5,4013-5, 11513-6, 4013-6, 115

C. p

ealg

icus

++

++++++++

Smal

l G

ephy

roca

psa

sp.

C. l

epto

poru

sR

. ps

eudo

umbi

lica

D.

pent

arad

iatu

sD

. pa

nsus

D.

vari

abili

s

S++

+++

++

+

D.

brou

wer

iC

. m

acin

tyer

iD

. st

ellu

lus

D.

calc

aris

Ret

icul

ofen

estr

a sp

.D

. to

ralu

sD

. asy

mm

etri

cus

C.

flori

danu

s

RS

s+++++++++

D.

exili

s

R

R

RR

X

Sphe

nolit

hus

sp.

+

+

+++

D.

defla

ndre

i

X

R+++++

+

S.

mor

iform

isC

. m

iope

lagi

cus

S. h

eter

omor

phus

14-1, 73 Barren14-1, 13014-2, 4014-2, 11514-3, 4014-3, 11514-4, 4014-4, 11515-1,4015-1, 11015-2, 4015-2, 11015-3,4015-3, 11016-1,6116-2, 4016-2, 11017-1, 10017-2,4117-2, 109

+

+

+

++

+

++++++

+

+++

+

+++++++++++++++++++

++++++++++++

+

+

+

+

+

++

+


described by Bukry and Percival (1971) has previouslybeen recognized from lower Miocene sediments of thePacific Ocean. This information taken in conjunctionwith the distribution of the lower Miocene foraminiferaCatapsydrax dissimilis in Core 18 clearly indicates thatCore 18 is lower Miocene. For these reasons, themiddle/lower Miocene boundary is placed at the lowestoccurrence (down the core) of S. heteromorphus (Sample17-1, 100 cm).

It should be noted that this positioning of the bound-ary does not correlate with that based on siliceousmicrofossils, particularly that of silicoflagellates. How-ever, this conflict in correlation has been discussed infull in the Introduction (this volume).

Lower MioceneThe uppermost lower Miocene nannofossil zone

(NN4) cannot be positioned at this site as the zone fossil

H. ampliapetra is not present in the sediments. Forreasons explained above, the age gap between the firstoccurrence of S. heteromorphus and last occurrence of S.belemnos may possibly be equated to this zone (Samples17-2, 40 cm to 19-1, 40 cm). The lower Miocene S.belemnos Zone (NN3) can be recognized at this site bythe presence of the nominate zone fossil in Samples 19-1,115 cm to 19-6, 115 cm. Beneath this zone accurateassignment of the sediments to fit previously describedzonal schemes is impossible because of the absence ofzone fossils, particularly the species Triquetorhabduluscarinatus and good specimens of D. druggi. Somespecimens approximating to D. druggi were present inSamples 10-1, 70 cm, 20-2, 40 cm, 20-4, 40 cm, and 21-1,115 cm, but the preservation of these discoasters is poor,and accurate identification is therefore doubtful.

Some age indication can be deduced from this section,however, by the presence of considerable numbers of D.trinidadensis (Sample 20-2, 40 cm to Sample 22-4, 115

593

D. A. BURNS

cm) in conjunction with the persistent presence of num-bers of D. deflandrei (Table 2). This overlap of speciesindicates that the lower section of the site is near to theMiocene/Oligocene boundary. Because of the absenceof the zone fossil T. carinatus, whose range straddles thisboundary, and the lower range of D. deflandrei and D.trinidadensis in the upper Oligocene, it is extremely dif-ficult to know which side of the boundary thesesediments should correctly be placed. However, theabsence of the upper Oligocene species Dictyococcitesabisecta indicates that this section is definitely earlyMiocene in age. The base of Site 266 is therefore assign-ed to the D. deflandrei Zone of Bukry (1971) with an ab-solute age determination of 21 m.y.

The presence of enormous quantities of C. mio-pelagicus in the lowest horizons at this site (Sample 22-2-40 to Sample 22-4-115) is probably an environmentaleffect and cannot be given any true stratigraphical sig-nificance.

SITE 267Site 267 is located in the deep basin south of the

Southeast Indian Ridge and about 600 km north of theWilkes Land continental shelf. The sediments cored atthis site range in age from Recent to lower Oligocene. Asat the other sites, they can be subdivided into units: (1)upper siliceous section and (2) lower calcareous section.

Upper Unit

Upper siliceous section (Sample 1-1, 122 cm to Sam-ple 4-1, 52 cm): No nannofossils were present in thissection.

Lower Unit

Lower calcareous section (Sample 4-1, 115 cm to Core6): The contact between siliceous and calcareous sedi-ments was not cored at this site. It cannot therefore beestimated whether the transition from the Miocene sili-ceous sediments in Core 3 to the calcareous Oligocenesediments in Core 4 is a gradual or abrupt change. Ittherefore remains unknown whether the Miocene sedi-ments rest unconformably on the Oligocene sediments.

The lower calcareous section generally contains abun-dant, moderately well-preserved nannofossils.

Upper OligoceneThe nannofossil-bearing sediments at this site cannot

be positioned relative to the zonal scheme proposed byMartini and Worsley (1970) or Bukry (1971) as they lackthe diagnostic Oligocene species Sphenolithus ciperoen-sis, S. distensus, and S. predistensus. However, the spe-cies which are present, their abundance, range, andoverlaps of range when compared with the Oligocenestratigraphic framework proposed by Roth et al. (1970)allows a stratigraphic subdivision for these sediments atSite 267. However, once again there are problems inarriving at a stratigraphic subdivision of these antarcticsediments as the previously described zoned sections arebased on warm-water assemblages. Hence, in these highlatitude assemblages many of the major diagnosticspecies described by Roth et al. must be ignored and in-

TABLE 2CDistribution of Nannofossils at Site 266


17-3,4017-3, 11017-4,4017-4, 11017-5,4017-5, 11018-1, 10218-2,4018-2, 11018-3,5318-4, 13013-4, 4018-4, 11018-5,4018-5, 11519-1,4019-1, 11519-2, 4019-2, 11519-3, 4019-3, 11519-4,4019-4, 11519-5,4019-5, 11519-6, 4019-6, 11520-1, 7020-1, 13020-2, 4020-2, 115

C. p

elag

icus

++

+

++++++++++++++++++

++++

C.

florid

anus

+++++++++++++++++++++++++++++++

D.

exili

sSp

heno

lithu

s sp

.D

. de

fland

rei

+++++++++++++++++++++++++++++++

S. m

orifo

rmis

C.

mio

pela

gicu

s

+

++

++++

+++

+++++++++

S. h

eter

omor

phus

S. d

issi

mili

s

+++

+++

+++

+++++++++

D.

calc

ulos

us

+++

S. b

elem

nos

+++++++++

D.

cf.

drug

gi

+

+

D.

trin

idad

ensi

s

++


stead the overlap of ranges of the background placolithspecies must be compared with the assemblages at Site267. In this way reasonably reliable age determinationscan be made for Site 267 calcareous sediments.

As at Site 266, the lack of the lower Miocene/upperOligocene zone fossil T. carinatus makes it difficult toassess whether the uppermost sediments of Core 4 arelower Miocene or upper Oligocene in age. However, thecommon presence of C. altus, a particularly importantand useful stratigraphic species for southern PacificOligocene sediments, gives clear indication that the sedi-ments of Core 4 are Oligocene in age. This age is furtherindicated by the presence of C. floridanus and Dictyococ-cites scrippsae in Core 4. The presence of occasionalspecimens of S. cf. dissimilis in Samples 4-1, 111 cm; 4-3,122 cm; and 4-4, 122 cm suggests that the uppermostsediments of Core 4 are uppermost Oligocene in age andthis is further indicated by the continued presence ofsmall numbers of D. deflandrei in Samples 4-1, 115 cm to4-4, 52 cm.

The most useful indication for subdivision of thelower parts of this calcareous section is given by the

594


TABLE 2DDistribution of Nannofossils at Site 266


20-3, 4320-3, 11520-4, 4020-4, 11521-1,4021-1, 11521-2,4021-2, 11521-3,4021-3, 11521-4,4021-4, 11521-5,4021-5, 11521-6,4021-6, 11522-1,4022-1, 11522-2, 4022-2, 11522-3, 4022-3, 11522-4, 4022-4, 115

C. p

elag

icus

++++++

C.

flori

danu

s

++++++++++++++++++++++++

D. e

xilis

Sphe

nolit

hus

sp.

D.

defla

ndre

i++++++++++++++++++++++++

S. m

orifo

rmis

C. m

iope

lagi

cus

++++++++++++++++++C

ccccc

S. h

eter

omor

phus

S. d

issi

mili

s+

+

+

+

D.

calc

ulos

usS.

bel

emno

s

•

D.

cf. d

rugg

i

+

+

D.

trin

idad

ensi

s

++++++++++++++++++++++++


overlap in the ranges of the two species, Dictyococcitesabisectus and D. bisectus. This overlap gives a general in-dication of the position of the boundary between upperand mid Oligocene (Roth, 1970). Such an overlap occursin the base of Core 4 at Site 267 and suggests that Core 4is upper Oligocene and Core 5 is mid Oligocene in age.

It should be noted that although the Oligocene isoften subdivided only into late and early stages (Berg-gren, 1972), the term mid Oligocene is used here, as thecorrelations and age determinations have been based onthe zonation indicated by Roth (1970a, 1970b), whichemploys an upper, mid, and lower Oligocene subdivi-sion of the section.

In the absence of the Oligocene zonal Sphenolithspecies, further refinement of the correct stratigraphicpositioning of the calcareous sediments of Core 5 can beachieved by correlation with Roth et al. (1970). At thebottom of Core 5 there is no R. umbilica present andspecimens of D. abisectus are extremely rare. This dis-tribution positions the sediments within the S. predisten-sus Zone with a probable absolute age of 27-30 m.y.(Bukry, 1973) or 28-34 m.y. (Berggren, 1972).

Similar difficulties are encountered in attempting toposition the lowermost calcareous sediment in contactwith the basement basalt in Core 6. In the one sampleanalyzed from this core, R. umbilica is commonly pre-sent, along with rare specimens of S. moriformis, Chi-astomolithus oamaruensis, C. altus, and R. hillae. Speci-

mens of D. bisecta are also common and are accom-panied by rare specimens of Ericsonia subdisticha. It isclear from the great increase in R. umbilica in the samplethat Core 6 is stratigraphically below the S. predistensusZone of Core 5. However, in the absence of the lowerOligocene zone fossil Helicopontosphaera reticulata andupper Eocene zone fossil Discoaster barbadiensis fromthese high-latitude sediments, the accurate positioningof the sample in the lower Oligocene or upper Eocene isdifficult to assess. The presence of E. subdisticha in thesample would suggest that Core 6 is the lower Oligocenesubzone of the H. reticulata Zone (Bukry, 1971) or theE. subdisticha Zone of Roth et al. (1970). However, forthe assemblage to conform to these zones, there shouldbe considerable numbers of C. formosa present. Thisspecies was not found in Core 6. Further assistance can-not be gained from correlation with the species rangesindicated by Roth et al. (1970) as S. pseudoradians (lateEocene subzone) was not identified in these southernsediments and the lower Oligocene H. reticulata Zone,subzonal fossils R. laevis and C. margaritae were notidentified in this material.

On the presence of E. subdisticha in Core 6, therefore,the sediment/basalt contact at this site must be posi-tioned in the lower Oligocene (E. subdisticha Subzone),which would give this contact an absolute age of 35-37m.y. (Berggren, 1972) or 37-38 m.y. (Bukry, 1973). Theabsence of C. formosa from these sediments musttherefore be attributed to an environmental effect.

No nannofossils were present in the sediments sam-pled at Hole 267A.

HOLE 267BHole 267B was situated a few kilometers south of

Holes 267 and 267A. The greater portion of sedimentscored consisted of an upper sequence of predominantlysiliceous microfossil-bearing sediments (Core 1 to Core9). Within this section a few sporadic thin horizons con-taining calcareous nannofossils occured, but the floraswere very sparse and mainly consisted of very poorlypreserved small Reticulofenestra species which affordedno age definition. In Core 10 there was a change tocalcareous sediment which contained abundant nan-nofossils. This calcareous sequence was only short andrested on basalt basement.

When attempting an accurate age assignment for thecalcareous nannofossil assemblages found at this site(Core 10), the same difficulties are encountered as at Site267. The previously described upper Eocene zone fossilsS. pseudoradians, D. barbadiensis, D. saipanensis (Mar-tini and Worsley, 1970; Roth, 1970; Bukry, 1971) andthe lower Oligocene zone fossil H. reticulata are all miss-ing from these Antarctic sediments. The only nan-nofossil species present in the sediment which haspreviously been designated as a zonal species is Isthmo-lithus recurvus (Martini and Worsley, 1970), a speciestypically found in sediment formed in cold water.Specimens of the genus Chiastomolithus are common inCore 10, but the greater number of such specimens arepresent as rims only, the specimens having lost their cen-tral cross. However, several well-preserved specimens of

595

D. A. BURNS

Sample(Interval

in cm)

Hole 267

1-1, 122to

4-1, 524-1, 1154-2, 524-2, 1224-3, 524-3, 1224-4, 524-4, 1224-5, 524-5, 1224-6, 554-6, 1225-1, 905-2, 555-2, 1155-3, 535-3, 123Core 6 a

Hole 267B

10-1,8210-1, 9510-1, 110

Co3K

!

.15

TABLE 3Distribution of Nannofossils at Site

toau

sa,tj

Sc<_=o

"3<o

!1

Co

"3

1

Co10

εi

s

C) OS

Co

3

&

<O

18

g

aas

267

to

a

I-SN

CO

á.ço

CO

aC 1Io

CO

iε

O3

Co3

"3

u

1,co

•3S

Barren

+

++++++++

+

RVR

+++++

RRRRRRR

R

VR

X

RRRRR

VRRRRRRR

VRVRVR+

C

cccccccccc++++++

+

XXX

X

X

X

X

RRRRRRRFRRR+++++

X

X

X

s

XRF

F

+++

RRR+

+++++

RF+

+++++

+

X

R

R

R

R

+

+

X

RX

X

R

+ +

RRR

FFF F

FFF

XX

RRR

CCC

XR X

C

cc

Note: See Table 1A for explanation of symbols.aSample from sediment/basalt contact.

C. altus are present in the assemblages and from com-parison of size and rim features of these with theChiastomolithus specimens minus the central cross, itwould appear that most of these latter forms belong toC. altus. Only very rare specimens of C. oamaruensis arepresent. In the upper part of the short calcareous section(Sample 10-1, 82 cm) the assemblage contains no C. for-mosa, but in the lower sediments (Sample 10-1, 120 cm)several specimens of C. formosa can be found. Similarly,in Sample 10-1, 110 cm, just above basalt, this species ispresent in higher numbers. R. umbilica is presentthroughout Core 10 (Table 3), as is R. hillae.

From comparison with the species ranges andoverlaps indicated by Roth et al. (1970) these sedimentsin Core 10 could be placed in the lower Oligocene, H.reticulata, or E. subdisticha zones because of the lack ofC. formosa in these assemblages. However, the in-dications from the lower Oligocene sediments at Site 267are that the lack of C. formosa is an environmental re-sponse and not an age one. Furthermore, the presence ofsubstantial numbers of /. recurvus in the sediments ofHole 267B, but not in 267, clearly indicate that thesediments of Core 10, Hole 267B are stratigraphicallylower than those of Core 6, Site 267, although the upper

range of /. recurvus is in the Oligocene (Roth et al.,1970).

For this reason the sediments of Core 10, Hole 267Bmust be placed in the upper Eocene. This stratigraphicposition, however, cannot be correlated with the /.recurvus Zone of Martini and Worsley or Roth et al. asthe zone fossil for the uppermost Eocene (S. pseudo-radians) has not been identified in Antarctic sediments.In the absence of such zone fossils, it is possible thatthese sediments could represent any position in the up-per Eocene within the range limits of /. recurvus.

SITE 268

Site 268 was drilled on the lower continental rise justnorth of the Knox coast of Antarctica. Unlike the othersites (264 to 267), at Site 268 there was no lithologicchange from an upper siliceous section to a lower cal-careous section. In contrast to the other sites, Site 268was generally unfossiliferous through its whole length.

Nannofossils were found occasionally in sporadic thinlayers down the cores, but generally they were low innumber and the species present were poorly preservedand often nondiagnostic of age. However, a few hori-zons contained nannofossils which give some indi-

596


TABLE 4Distribution of Nannofossils at Site 268

Sample(Interval

in cm)

1-1-topto

9, CC10-1, top10-1, 1010-1, 12

to13-1, 2213-1, 2313-1, 25

to16, CC17-1, top17-1,3

to17-2, 12917-2, 13017-2, 15017-3, 9

C. m

iope

lagi

cus

Sml.

Ret

icul

ofen

stra

D.

defla

ndre

iC.

flo

ridan

usD

. cf

. tr

inid

aden

sis

C. e

opel

agic

usD

. abi

sect

usD

. bi

sect

usC

hias

t. al

tus

D.

scri

ppsa

eR

. cf

. gar

tner

eiS.

m

orifo

rmis

C. p

elag

icus

R. h

illae

Barren

AA

CC

XX

Barren

x IF | X | C IX

Barren

+ + + + x +

Barren

++ R +

X++

+C+

++

+

X

+

X

TABLE 5Distribution of Nanno-

fossils at Site 270


cations of age (Table 4). Sample 10-1, 10 cm containedspecies such as C. miopelagicus and D. deflandrei, sug-gesting a mid to early Miocene age. A calcareous "spot"in Core 13, Section 1 contained D. deflandrei, C. flori-danus, D. trinidadensis, C. eopelagicus, D. abisectus, andS. moriformis indicating an early Miocene age. Core 17,Section 1 contained a thin horizon with a nannofossilassemblage containing C. floridanus, C. eopelagicus, D.abisectus, D. bisectus, and Chiastomolithus altus in-dicating an upper mid Oligocene age. Core 17, Section 2contained two horizons which gave sparse nannofossilassemblages, containing specimens of C. floridanus, C.eopelagicus, D. abisectus, D. bisectus, considerablenumbers of C. altus, and occasional specimens of D.scrippsae, S. moriformis, R. cf. gartneri, and R. hillae, in-dicating a mid Oligocene age. The lowest nannofossil-bearing horizon was Sample 17-3, 9 which also con-tained a sparse assemblage with specimens of D. bisec-tus, C. altus, and R. hillae, suggesting a lower midOligocene. The sediments below this horizon (Cores 18-20) were barren of all microfossils.

SITE 269No nannofossils were seen at this site.

SITE 270The sediments cored at Site 270, the first site drilled in

the Ross Sea, contain little calcareous material. Onlytwo thin calcareous horizons were found to contain nan-nofossil assemblages. Sample 18-2, 69 cm contained afew specimens of a small Reticulofenestra species and C.floridanus, suggesting a Miocene or Oligocene age. The

Sample(Interval

in cm)

18-2, 6922-3, 126

Ret

icul

ofen

estr

a sp

.

++

C.

florid

anus

+

C. p

elag

icus

+

Note: See Table 1A forexplanation of symbols

second horizon, Sample 22-3, 120 cm, contained oc-casional specimens of a small Reticulofenestra speciesand C. pelagicus, neither species giving any age indica-tion (Table 5). Preservation of the few specimens presentwas generally very poor.

SITE 274Nannofossils were present only in isolated horizons

and burrows in a short section (Cores 21 to 28) at Site274. Poor assemblages were present in Samples 21-1, 93;21-3, 70; 21-3, 100; 27-4, 104. The best assemblages werein Samples 21-1, 93 and 21-3, 70 and these weredominated by C. altus suggesting an Oligocene age.Other species present in low numbers were C. pelagicus,D. scrippsae, and a small Reticulofenestra species (Table6).

TABLE 6Distribution of Nanno-

fossils at Site 274


21-1, 9321-3, 7021-3, 10027-4, 104

Chi

as.

altu

s

C

c++

Smal

l R

etic

ulof

enes

tra

CC++

C. p

elag

icus

F

Note: See Table 1A forexplanation of symbols

REFERENCESBerggren, W.A., 1972. A Cenozoic time scale—some im-

plications for regional geology and paleobiogeography.Lethaia v. 5, p. 195-215.

597

D. A. BURNS

Bukry, D. 1971. Cenozoic calcareous nannofossils from thePacific Ocean: San Diego Soc. Nat. Hist., Trans., v. 16, p.303-28.

, 1973. Coccolith stratigraphy, eastern EquatorialPacific, Leg 16 Deep Sea Drilling Project. In van Andel,T.H., Heath, G.R., et al., Initial Reports of the Deep SeaDrilling Project, Volume 16: Washington (U.S. Govern-ment Printing Office), p. 653-711.

Bukry, D. and Percival, S.F., 1971. New Tertiary calcareousnannofossils: Tulane Stud. Geol. Paleontol., v. 8, p. 123-46.

Martini, E., 1970. Standard Paleogene calcareous nan-noplankton zonation: Nature, v. 226, p. 560-61.

Martini, E. and Worsley, T., 1970. Standard Neogene calcare-ous nannoplankton zonation: Nature, v. 225, p. 289-90.

Roth, P.H., 1970. Oligocene calcareous nannoplankton bio-stratigraphy: Eclog. Geol. Helv., v. 63, p. 799-881.

Roth, P.H., Baumann, P., and Bertolino, V., 1970. LateEocene-Oligocene calcareous nannoplankton from Centraland Northern Italy: In Farinacci, A. (Ed.), Plankt. Conf.Proc, 2nd. Rome (Tecnoscienza), p. 1069-1097.

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