13. CENOZOIC PLANKTONIC FORAMINIFERA FROM ANTARCTIC DEEP-SEA SEDIMENTS, LEG 28, DSDP Ansis G. Kaneps, Scripps Institution of Oceanography, La Jolla, California INTRODUCTION In general, the degree of our knowledge of the strati- graphic distribution of planktonic foraminifer assemblages and their species composition is an inverse function of geographic latitude. Whereas the lower latitude faunas have been extensively studied, those of the high-latitude oceanic regions, especially around Antarctica, have remained virtually unknown. This has been due mainly to the inaccessibility of older sediments to piston coring and other sampling techniques prior to the Deep Sea Drilling program. Leg 28, the first venture of Glomar Challenger into extremely high southern latitudes, thus promised to be a unique opportunity to study the history of high-latitude planktonic foraminifers and how it has been influenced by the associated environmental parameters of low temperature and high nutrient levels and associated high phytoplankton productivity. Another aim would be to determine how long these environmental conditions have existed and if they have changed with time. The results were, unfortunately, somewhat disap- pointing. Foraminifers occur sporadically in the Antarc- tic sections cored during Leg 28; where present, they make up a minor portion of the microfossil assemblage and are of very low diversity. In addition, most assemblages show the effects of carbonate dissolution. The drill sites in the Ross Sea, which might have been expected to yield less dissolved assemblages, are mostly barren of planktonic foraminifers, apparently for paleoenvironmental reasons. Nevertheless, two general conclusions seem warranted on the basis of Leg 28 results. (1) Antarctic foraminifer assemblages have had a characteristically polar aspect since the Oligocene. That is, they are of ex- tremely limited diversity, and some of the species pre- sent are morphologically similar to Globigerina pachyderma (Ehrenberg), which is presently the domi- nant species in high-latitude waters. (2) The major change in planktonic foraminifer ecology in the Antarc- tic area took place at or near the Eocene-Oligocene boundary. This is evidenced by the recovery of a diverse upper Eocene assemblage at Hole 267B, at 59° south latitude which is in marked contrast to the sparseness of younger faunas. This change is most likely related to the initiation of glacial conditions on Antarctica (see General Synthesis, Hayes and Frakes, this volume). Leg 28 drill sites in the Antarctic are shown in Figure 1, and site data are given in Table 1. Site 264, the first Leg 28 site, was drilled on the Naturaliste Plateau, close to port. It was primarily a test site to check the opera- tion of the drill rig and is not included in the present report; a discussion of the planktonic foraminifers at this site can be found in the site report for Site 264 (Chapter 2), and in the report by Kennett (this volume). A distribution chart of planktonic foraminifers at this site is given in Table 2 of the present report. Distribution charts of planktonic foraminifers are given for Sites 265 and 266 in Tables 3 and 4, respective- ly. Occurrence data for the other sites (267-274) are given at the end of this chapter in the form of species lists. Selected species are illustrated in Plates 1 and 2. COMPARISON TO PREVIOUS WORK Tertiary foraminifer assemblages from the subantarc- tic Pacific Ocean (north of the Antarctic Convergence) have been described by Riedel and Funnell (1964) and Margolis and Kennett (1971). Margolis and Kennett have, in addition, constructed a paleoenvironmental curve for the Southern Ocean based on trends in foraminifer diversity, expressed as the number of species present. Their results indicate low diversity in the Oligocene which increases to a maximum in the middle Miocene. Although the assemblages seen in the present study are in general less diverse than those from north of the Antarctic Convergence, they exhibit a probable identical diversity pattern. The lower Oligocene assemblage consists of a single species. This increases to two higher in the Oligocene, two to occasionally four in the lower Miocene, and four in the middle Miocene. Upper Miocene assemblages (not recorded by Margolis and Kennett, 1971) have mostly been destroyed by dis- solution, but the two samples from which foraminifers were recovered contained one species each. Pliocene assemblages in general are monospecific, while the Pleistocene shows two diversity peaks, one in the lower Pleistocene and one in the upper Pleistocene. SUMMARY OF ANTARCTIC FAUNAS BY AGE The following section outlines the general nature of the recovered faunas by age. Not surprisingly, a number of the species seen in Antarctic sediments were originally described from Tertiary rocks of New Zealand. Except in a broad sense, the planktonic foraminifers were not found useful for age determination; for Leg 28 reliance was placed on the siliceous fossil groups (radiolarians, diatoms, and silicoflagellates). Eocene (Determinations by P.N. Webb) An upper Eocene planktonic fauna was recovered in Core 10 of Hole 267B. It includes Chiloguembelina cubensis (Palmer), C. martini (Pijpers), Catapsydrax echinatus Bolli, Globigerina (Subbotina) linaperta Finlay, G. (S.) angiporoides Hornibrook, Globorotalia {Tur- borotalia) spp., ?Globigerapsis index (Finlay), and a single broken specimen of Hantkenina sp. (perhaps H. 573
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13. CENOZOIC PLANKTONIC FORAMINIFERA FROM ANTARCTICDEEP-SEA SEDIMENTS, LEG 28, DSDP
Ansis G. Kaneps, Scripps Institution of Oceanography, La Jolla, California
INTRODUCTION
In general, the degree of our knowledge of the strati-graphic distribution of planktonic foraminiferassemblages and their species composition is an inversefunction of geographic latitude. Whereas the lowerlatitude faunas have been extensively studied, those ofthe high-latitude oceanic regions, especially aroundAntarctica, have remained virtually unknown. This hasbeen due mainly to the inaccessibility of older sedimentsto piston coring and other sampling techniques prior tothe Deep Sea Drilling program. Leg 28, the first ventureof Glomar Challenger into extremely high southernlatitudes, thus promised to be a unique opportunity tostudy the history of high-latitude planktonicforaminifers and how it has been influenced by theassociated environmental parameters of lowtemperature and high nutrient levels and associated highphytoplankton productivity. Another aim would be todetermine how long these environmental conditionshave existed and if they have changed with time.
The results were, unfortunately, somewhat disap-pointing. Foraminifers occur sporadically in the Antarc-tic sections cored during Leg 28; where present, theymake up a minor portion of the microfossil assemblageand are of very low diversity. In addition, mostassemblages show the effects of carbonate dissolution.The drill sites in the Ross Sea, which might have beenexpected to yield less dissolved assemblages, are mostlybarren of planktonic foraminifers, apparently forpaleoenvironmental reasons.
Nevertheless, two general conclusions seemwarranted on the basis of Leg 28 results. (1) Antarcticforaminifer assemblages have had a characteristicallypolar aspect since the Oligocene. That is, they are of ex-tremely limited diversity, and some of the species pre-sent are morphologically similar to Globigerinapachyderma (Ehrenberg), which is presently the domi-nant species in high-latitude waters. (2) The majorchange in planktonic foraminifer ecology in the Antarc-tic area took place at or near the Eocene-Oligoceneboundary. This is evidenced by the recovery of a diverseupper Eocene assemblage at Hole 267B, at 59° southlatitude which is in marked contrast to the sparseness ofyounger faunas. This change is most likely related to theinitiation of glacial conditions on Antarctica (seeGeneral Synthesis, Hayes and Frakes, this volume).
Leg 28 drill sites in the Antarctic are shown in Figure1, and site data are given in Table 1. Site 264, the firstLeg 28 site, was drilled on the Naturaliste Plateau, closeto port. It was primarily a test site to check the opera-tion of the drill rig and is not included in the presentreport; a discussion of the planktonic foraminifers at
this site can be found in the site report for Site 264(Chapter 2), and in the report by Kennett (this volume).A distribution chart of planktonic foraminifers at thissite is given in Table 2 of the present report.
Distribution charts of planktonic foraminifers aregiven for Sites 265 and 266 in Tables 3 and 4, respective-ly. Occurrence data for the other sites (267-274) aregiven at the end of this chapter in the form of specieslists. Selected species are illustrated in Plates 1 and 2.
COMPARISON TO PREVIOUS WORKTertiary foraminifer assemblages from the subantarc-
tic Pacific Ocean (north of the Antarctic Convergence)have been described by Riedel and Funnell (1964) andMargolis and Kennett (1971). Margolis and Kennetthave, in addition, constructed a paleoenvironmentalcurve for the Southern Ocean based on trends inforaminifer diversity, expressed as the number of speciespresent. Their results indicate low diversity in theOligocene which increases to a maximum in the middleMiocene. Although the assemblages seen in the presentstudy are in general less diverse than those from north ofthe Antarctic Convergence, they exhibit a probableidentical diversity pattern. The lower Oligoceneassemblage consists of a single species. This increases totwo higher in the Oligocene, two to occasionally four inthe lower Miocene, and four in the middle Miocene.Upper Miocene assemblages (not recorded by Margolisand Kennett, 1971) have mostly been destroyed by dis-solution, but the two samples from which foraminiferswere recovered contained one species each. Plioceneassemblages in general are monospecific, while thePleistocene shows two diversity peaks, one in the lowerPleistocene and one in the upper Pleistocene.
SUMMARY OF ANTARCTIC FAUNAS BY AGEThe following section outlines the general nature of
the recovered faunas by age. Not surprisingly, a numberof the species seen in Antarctic sediments were originallydescribed from Tertiary rocks of New Zealand. Exceptin a broad sense, the planktonic foraminifers were notfound useful for age determination; for Leg 28 reliancewas placed on the siliceous fossil groups (radiolarians,diatoms, and silicoflagellates).
Eocene (Determinations by P.N. Webb)An upper Eocene planktonic fauna was recovered in
Core 10 of Hole 267B. It includes Chiloguembelinacubensis (Palmer), C. martini (Pijpers), Catapsydraxechinatus Bolli, Globigerina (Subbotina) linaperta Finlay,G. (S.) angiporoides Hornibrook, Globorotalia {Tur-borotalia) spp., ?Globigerapsis index (Finlay), and asingle broken specimen of Hantkenina sp. (perhaps H.
573
A. G. KANEPS
160c 170°
AUSTRALIA
40° 50° 60
Figure 1. Location map of sites drilled during DSDP Leg 28.
alabamensis compressa Parr). This fauna is notable forits high diversity as compared to Oligocene and youngerassemblages.
TABLE 1Site Data
Site
264
265
266
267, 267A
267B
268
269
270
271
272
273
274
Latitude
34°58.13'S
53° 32.45 'S
56° 24.13'S
59° 15.74'S
59° 14.55'S
63°56.99'S
61°40.57'S
77° 26.48'S
76°43.27'S
77°07.62'S
74° 32.29'S
68°59.81'S
Longitude
112°02.68'E
109° 56.74'E
110° 06.70'E
104° 29.30 'E
104°29.94'E
105° 09.34'E
140° 04.21'E
178°30.19'W
175° 02.86 TV
176°45.61rW
174°37.57'E
173° 25.64'E
Water Depth (m)
2873
3582
4173
4564
4539
3544
4285
634
554
629
495
3326
OligoceneThe characteristic element of Oligocene Antarctic
assemblages is Globigerina angiporoides Hornibrook. Aspointed out by Hornibrook (1965) in the originaldescription of this species, there is considerable varia-tion in the size and shape of the final chamber. In thepresent specimens, it ranges in degree of inflation from abulla to a normal, full-sized chamber (see Plate 1). In ad-dition, the shape of the aperture ranges from a low slit(in the majority of specimens) to a high arch.
G. angiporoides was found in Cores 5 and 6 of Site267, and Core 21 of Site 274. In Core 5 of Site 267Catapsydrax dissimilis (Cushman and Bermudez) wasalso found. This is the only other species recorded fromLeg 28 Oligocene assemblages. Although there is no wayto determine the degree of dissolution these assemblageshave undergone, the specimens appear to be fairly wellpreserved (see Plate 1). Thus, the low diversity probablyreflects original faunal composition.
Miocene
Lower MioceneLower Miocene assemblages are slightly more diverse
than those of the Oligocene. Their characteristic element
574
CENOZOIC PLANKTONIC FORAMINIFERA
TABLE 2Distribution of Planktonic Foraminifers at Site 264
MINERAL GRAINSSILICEOUS FOSSILSPLANKTONIC FORAMSBENTHONIC FORAMS
O r- r- «*
1 1 1 1in in in <to •— •— < a•
N ro <t ID
XX X
XX X
X X
X
Tr - - -A A A AF C - R
3
43- 45
4
68- 70
5
70- 72
6
100-102
XX
X XX
X
XXXXX
- - Tr -A A A C- R - A
Tr Tr - Tr
r~. m CM CM CMOO O CO r— CM
1 1 1 1 1in CM o o ooo o oo <— CM
CM i — CM OO ^ J
CM CO
Tr? - Tr Tr -A A A A F
- - - Tr -
4
1
21- 23
2
40- 42
3
100-102
?XX X
X X X
X XX
- C -F A CA R R
Tr - -
5
1
68- 70
2
40- 42
3
40- 42
4
40- 42
5
40- 42
6
30- 32
X X
X X X XX
X
X
X X
- - - R - TrF A A F R CA - F - A R
6
2
30- 32
3
30- 32
4
30- 32
- R TrC F F
7
2
30- 32
3
30- 32
X X
R -F FF TrR Tr
*probably contamination
is Catapsydrax dissimilis (Cushman and Bermudez),which ranges nearly to the top of the lower Miocene. C.dissimilis is accompanied through most of the lowerMiocene by Catapsydrax unicavus Bolli, Loeblich, andTappan. The latter disappears at a level somewhat lowerthan the last occurrence horizon of C. dissimilis. Otherspecies that occur sporadically in the lower Miocene areGloborotalia zealandica Hornibrook, Globigerina sp. cf.G. woodi Jenkins, Globorotaloides suteri Bolli, andGlobigerina sp. cf. G. bulloides d'Orbigny.
It should be noted that C. dissimilis seems to have anextended stratigraphic range in the Antarctic as com-pared to the lower latitude areas from which it wasoriginally described. In warm-water sequences its upperlimit is in the mid-lower Miocene while at Site 266 itranges to nearly the top of the lower Miocene. Thisseems reasonable in view of its cosmopolitan nature andtolerance for cold-water masses. This has significance inthat the C. dissimilis last occurrence datum is commonto several zonal schemes. On the basis of the presentresults, however, it appears that this datum may slopestratigraphically upward toward the poles.
Middle MioceneMiddle Miocene assemblages were recovered at Sites
265 and 266. The species composition differs at the twosites. This is probably a result of age difference, as theforaminifer-bearing sediments at Site 265 are youngerthan those at Site 266, according to the siliceous fossils.
However, paleoenvironment may also be a factor sincethe sites have a north-south separation of about 260 km.
The common element in both assemblages isGlobigerina woodi Jenkins. Site 266, the higher latitudesite, and the older assemblage, contains, in addition, aspecies of Globorotalia that most closely resembles G.miozea Finlay, but is more compact. The younger mid-dle Miocene of Site 265 is more diverse, containing inaddition to G. woodi, Globigerina bulloides, Globigerinitauvula (Ehrenberg), Globorotalia conica Jenkins,Globorotalia continuosa Blow, and Globigerina sp.
Upper MioceneUpper Miocene sediments were recovered at Sites 265
and 266. At Site 265 the upper Miocene is representedby only one sample in which a specimen of Globigerinitauvula was found. At Site 266, the upper Miocene, thoughthicker, is mostly barren; a specimen of Globigerinasimilar to Globorotalia continuosa was found in one sam-ple. The scarcity of foraminifers in the upper Miocenecan most likely be attributed to calcite dissolution.
Pliocene
Pliocene assemblages were seen only at Site 265. Ex-cept for a single occurrence of Globorotalia puncticulataDeshayes, the fauna consists solely of Globigerinapachyderma, the species which presently lives in thisarea.
576
CENOZOIC PLANKTONIC FORAMINIFERA
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Pleistocene
The Pleistocene assemblages of Site 265 are on thewhole more diverse than those of the Pliocene. Twodiversity peaks occur: one in the middle lowerPleistocene, and another in the middle upper Pleistocene(Table 3). Found along with G. pachyderma, the mostcommon species, are G. bulloides, Globigerinita uvula, G.quinqueloba Natland, and Globorotalia inflata (d'Or-bigny). In addition, lower latitude forms such asGlobigerinita glutinata (Egger), Turborotalita humilis(Brady), Globorotalia scitula (Brady), and G. trun-catulinoides (d'Orbigny) occur in the mid-upperPleistocene diversity peak, indicating an expansion ofmid-latitude water masses at this time. This foraminiferdiversity peak occurs in the lower part of the Emilianiahuxleyi nannofossil Zone and thus is somewhat youngerthan 170,000 y. (Gartner, 1973). Its correlative may bethe interglacial X Zone of Ericson et al. (1961), in-dicating a significant expansion of warmer water massesat this time.
At Site 266, only three Pleistocene samples containplanktonic foraminifers, and in each case the onlyspecies present is G. pachyderma.
OCCURRENCE OF FORAMINIFERS ATSITES 267-274
The following isolated occurrences of planktonicforaminifers were noted at Sites 267 through 274. In-sofar as could be determined on the basis of core-catcher
samples, and other samples which were reported by theshipboard sedimentologists to contain carbonate, theremainder of the sections are barren. Some of these oc-currences represent the processing of up to 0.5 kg ofsediment and testify to the general scarcity offoraminifers in circum-Antarctic deep-sea sediments. Itwould be hoped that future drilling in a shallower areasuch as the Kerguelen Plateau might overcome the dis-solution problem and add materially to our knowledgeof Antarctic planktonic foraminifers.
Site 267Core 5, CC: Globigerina angiporoides, Catapsydrax
Oligocene)Core 10B, CC: Chiloguembelina cubensis (Palmer), C.
martini (Pijpers), Catapsydrax echinatus Bolli,Globigerina (Subbotina) linaperta Finlay, G. (S.)angiporoides Hornibrook, Globorotalia (Tur-borotalià) spp., ?Globigerapsis index (Finlay), anda single broken specimen of Hantkenina sp.(perhaps H. alabamensis compressa Parr). (Deter-minations by P.N. Webb). (Age: upper Eocene)
Site 268Core 1: Globigerina pachyderma (Age: Quaternary)Core 8, CC: Catapsydrax dissimilis, C. unicavus (Age:
lower Miocene)
577
-000
TABLE 4Distribution of Planktonic Foraminifers and Other Components of the Coarse Fraction at Site 266
SAMPLEINTERVAL
SECTION
CORE
SPECIES
Globigerina paahydermaG. sp.G. woodiG. c f . G. bulloidesG. c f . G. ampliaperturaGlobovotalia c f . G. siakensisG. zealandicaCatapsydrax uniaavusC. dissimilisGloborotaloid.es suteri
MINERAL GRAINSSILICEOUS FOSSILSPLANKTONIC FORAMSBENTHONIC FORAMS
INCERTAE SEDIS*SERIES
CNJ
o
r -
-
FA
-
CNJ CNJ
1 1
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CNJ C O
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CNJCNJ
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X
_
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o•—
CM
CNJ
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_
c
R
CM
•—
O
"―co
X
cA
PLEISTOCENE
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CM
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CM
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Tr
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σ
σ
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cn
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CM
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TrF
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•—
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<->
i
CM
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o—
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C
CM
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_
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7
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TABLE 4 - Continued
SAMPLEINTERVAL
SECTION
CORE
SPECIES
Globigevina paahydermaG. sp.G. woodiG. c f . G. bulloidesG. cf. G. ampliaperturaGloborotalia Cf. G. siakensisG. zealandiaaCatapsydrax uniaavusC. dissimilisGloborotaloides suteri
MINERAL GRAINSSILICEOUS FOSSILSPLANKTONIC FORAMSBENTHONIC FORAMSINCERTAE SEDIS*
Site 270Core 28, CC: Globigerinoides trilobus (most probably
a contaminant from the shipboard laboratory asno other species were found in this sample, and itis highly unlikely that G. trilobus has ever lived atthe latitude of this site)
REFERENCESEricson, D.B., Ewing, M., Wollin, G., and Heezen, B.C.,
1961. Atlantic deep-sea sediment cores: Geol. Soc. Am.Bull., v. 72, p. 193-286.
Gartner, S., 1973. Absolute chronology of the late Neogenecalcareous nannofossil succession in the equatorial Pacific:Geol. Soc. Am. Bull., v. 84, p. 2021-2034.
Hornibrook, N. de B., 1965. Globigerina angiporoides n. sp.from the upper Eocene and lower Oligocene of NewZealand and the status of Globigerina angipora Stache,1865: New Zealand J. Geol. Geophys., v. 8, p. 834-838.
Margolis, S.V. and Kennett, J.P., 1971. Cenozoic paleoglacialhistory recorded in subantarctic deep-sea cores: Am. J. Sci.,v. 271, p. 1-36.
Riedel, W.R. and Funnell, B.M., 1964. Tertiary sedimentcores and microfossils from the Pacific Ocean floor: Quart.J. Geol. Soc. London, v. 120, p. 305-368.
579
A. G. KANEPS
PLATE 1Globigerina angiporoides Hornibrook
Figures 1-3 Site 267, Core 5, CC.1. X185.2, 3. X187.