a number of sedimentary depocenters must exist beneath theantarctic ice sheet.

Four provenance areas for the Weddell Sea are recognized: (1)the Cretaceous-Tertiary prograding shelf of the Weddell Sea, (2)the recently uplifted Transantarctic Mountains, (3) the Pal-eozoic-Mesozoic Beacon sedimentary basin, and (4) the BruntMegatrough (Kamenov and Ivanov 1983). Correlation betweenthese provenance areas (as defined by geophysical data) and tillpetrologic provinces are remarkably good.

I wish to thank Dennis Cassidy for providing pebble samplesfor this study. This research was supported by National ScienceFoundation grant DPP 81-16623 to John B. Anderson.

ReferencesAnderson, J.B., CF. Brake, E.W. Domack, N.C. Myers, and R. Wright.

1983. Development of a polar glacial-marine sedimentation modelfrom Antarctic Quaternary deposits and glaciological information. InB.F. Molnia (Ed.), Glacial marine sedimentation. New York: PlenumPress.

Anderson, J.B., D.D. Kurtz, E.W. Domack, and K.M. Baishaw. 1980.Glacial and glacial-marine sediments of the Antarctic continentalshelf. Journal of Geology, 88, 399-414.

Kamenov, E. N., and V. L. Ivanov. 1983. Structure and outline of geologichistory of the southern Weddell Sea basin. In R.L. Oliver, P.R. James,and J.B. Jago (Eds.), Antarctic Earth science. Canberra: AustralianAcademy of Science.

Sedimentologic andpaleoceanographic implications of

terrigenous deposits on the MauriceEwing Bank, southwest Atlantic Ocean

S. E. MACDONALD

Department of GeologyRice University

Houston, Texas 77251

The Maurice Ewing Bank (MEB), representing the easternmostportion of the Falkland Plateau (figure 1), provides a remarkablyunique environment in which to study deep-sea clastic sedi-mentation. A number of key sedimentological problems in thisregion have not been previously addressed. One of the impor-tant questions concerns the existence of terrigenous deposits inthis deep-sea environment. Visual examination of piston coresreveals the presence of a widespread, coarse-lag deposit andsand bodies on the MEB. It has been well established that ter-rigenous material reached the bank as ice-rafted detritus (IRD)(Plafker, Bartsch-Winkler, and Ovenshine 1977; Bornhold 1983).Strong impinging currents, developed primarily as a result ofthe opening of Drake Passage, have subsequently eroded,

65 60 55 50

45 40 35 30

65 60 55 50 45 40 35 30

Figure 1. Bathymetric and physlographic map of the Falkland Plateau and adjacent environs (after Rabinowitz et al. 1978). Maurice Ewing Bankstudy area is outlined by rectangle. (Bathymetry measurements are in meters.)

94 ANTARCTIC JOURNAL

sorted, redistributed, and ultimately deposited this glaciallyderived material.

Studies of surface sediment distribution, micropaleontology,and oceanographic data were previously used to infer the lateMiocene to Recent oceanographic and climatic regimes influ-encing sedimentation on the MEB (Ciesielski and Wise 1977;Ciesielski, Ledbetter,and Ellwood 1982). Causal relationshipsbetween bottom scour, current intensification, and glacial epi-sodes were postulated. The purpose of this study was (1) toinvestigate sedimentary processes responsible for deep-seasand occurrences on the bank and (2) to explore the possibilitythat the observed form of sedimentation is related to intensifica-tion of circumpolar currents resulting from climaticfluctuations.

Grain-size distributions of sediment samples were used toidentify styles of sediment transport and current velocities atthe benthic boundary layer. These data, along with physicaloceanographic information, allowed for examination of the rela-tionship between sedimentation on the bank and circumpolarcurrents. Similar analyses were conducted for down-core sam-ples to investigate the history of bottom current flow.

Grain-size analysis indicates that modern sediment distribu-tion is controlled by both bottom and surface currents and ismodified by mass-flow processes. Present and past energy regi-mes acting on the Maurice Ewing Bank were determined using anewly derived velocity curve (Singer and Anderson 1984) relat-ing grain size to current speeds. Results of this data suggest auniform energy regime of 8-12 centimeters per second over thebank. Physical oceanographic data, in the form of temperatureversus depth profiles and geostrophic velocity profiles, wereused to locate the bank spatially within the Antarctic Circum-polar Current system. The MEB is situated within the PolarFrontal Zone. Geostrophic velocity profiles constructed fromhydrographic stations over the bank indicate current speeds onthe order of 5-10 centimeters per second, which is in reasonableagreement with the velocities derived from the grain-size data(8-12 centimeters per second).

The results of this study also demonstrate that misinterpreta-tions regarding current velocities may result when statisticalparameters such as mean grain size and standard deviation(sorting) are used as indicators of bottom current strength.Sediment distribution on the bank is one in which the gravel,sand, silt, and clay concentrations vary in a rather randomfashion, and grain-size parameters fail to show any coherentpattern. However, total grain-size data, examined in light ofsediment transport modes and current velocities, along withhydrographic information, indicate a constant energy regimeacting on the MEB.

Current velocities assigned to down-core samples indicatethat no major fluctuations in circumpolar current flow over thebank have occurred since Plio-Pleistocene time (figure 2). Theseresults refute the previously inferred causal relationship be-tween current intensification and glacial conditions based onthe identification of biostratigraphic hiatuses. An alternate ex-planation to bottom erosion and the subsequent creation ofhiatuses is suggested by the abundant occurrence of soft sedi-mentary clasts, which are largely composed of glauconite andice-rafted quartz grains. The presence of these clasts withinpelatic units, containing virtually no IRD, strongly indicatesslumping and debris flow transport. Misinterpretations con-cerning the existence of hiatuses could result from mass-flowdeposits. The source material on the bank spans Miocene toPlio-Pleistocene time. Therefore, mass-flow deposits of dif-ferent ages and from different sources could separate sediments

INFERRED CURRENT VELOCITIES (cmls)

1014 11014 101411111011111

011111

2 2

E - - -

WCr -0 - -C)

z -- -

I - -

a. -

0 8 - 8-80

EL9-21 1176-10 1176-12

10140

1014 61I014II I IIIIIIIIIII I

IUJ 4 --00 -

60—z -

- 12 - 120—

I-0.W -0

1 0775-54

1

0775-43 V22-84

Figure 2. Current velocities assigned to down-core samples from theMaurice Ewing Bank. Cores contain Pliocene Pleistocene to Recentsediment. ("cm" denotes centimeters. "cm/s" denotes centimetersper second.)

that were deposited in place. In this fashion, the time stratigra-phy of the sedimentary units could be artificially altered.

A plausible hypothesis for the MEB is that during Plio-Pleistocene time, IRD accumulation increased markedly. Afterthe fine material had been winnowed from the sediment, ar-mouring occurred which prevented further erosion. Tectonicactivity in the area most likely initiated mass movement allow-ing clasts, composed of current-sorted IRD, to be incorporatedinto the underlying pelagic oozes as they flowed down slope.Ice-rafted gravels and sands were still accumulating during thistime and were redistributed over the bank and across the sur-face of mass-flow deposits by moderate bottom currents.

This study has shown that the application of grain-size dis-tributions to identify styles of sediment transport and currentvelocities at the benthic boundary layer, along with physicaloceanographic information, can yield meaningful informationin terms of the sedimentologic and paleoceanographic historyof deep-sea environments. This approach is particularly usefulfor regions that are characterized by deposition of poorlysorted, glacially derived sediments and where the dynamics ofcircumpolar currents are poorly understood.

This research was supported by National Science Foundationgrant DPP 81-16623 to John B. Anderson.

References

Bornhold, B.D. 1983. Ice-rafted debris in sediments from Leg 71, South-west Atlantic Ocean. In W.J. Ludwig, V.A. Krasheninnikov, et al.,

1984 REVIEW 95

Initial Reports of the Deep Sea Drilling Project, Vol. 71. Washington,D.C.: U.S. Government Printing Office.

Ciesielski, P.F., M.T. Ledbetter, and B.B. Ellwood. 1982. The develop-ment of Antarctic glaciation and the Neogene paleoenvironment ofthe Maurice Ewing Bank. Marine Geology, 46, 1-51.

Ciesielski, RE, and S.W. Wise. 1977. Geologic history of the MauriceEwing Bank of the Falkland Plateau based on piston and drill cores.Marine Geology, 25, 175-207.

Plafker, G., S. Bartsch-Winkler, and A.T. Ovenshine. 1977. Paleoglacial

implications of coarse detritus in DSDP Leg 36 cores. In P.F. Barker,I.W.D. Daiziel etal., Initial Reports of the Deep Sea Drilling Project, Vol.36. Washington, D.C.: U.S. Government Printing Office.

Rabinowitz, P.D., M. Delach, M. Truchan, and A. Lonardi. 1978.Bathymetry Chart Argentine Continental Margin. AAPG ArgentineMap Series.

Singer, J.K., and J.B. Anderson. 1984. Use of total grain size distribu-tions to define bed erosion and transport for poorly sorted sedimentundergoing simulated bioturbation. Marine Geology, 57, 335-359.

Paleoclimatological indices in thesouthern ocean based on

morphological parameters in theradiolarian genus Antarctissa

A. GRANLUND

Department of GeologyStockholm University

S-106 91 Stockholm, Sweden

Relationships between radiolarian assemblages and climaticparameters have been noted by many workers (Hays 1965;Keany 1973; Lozano and Hays 1976). Such relationships havebeen used for establishing paleoclimatologic equations (transferfunctions) (Williams and Keany 1977). In this study, the mor-phology of the radiolarian genus Antarctissa (A. denticulata—A.strelkovi complex) is analyzed in relation to physical parameters.The Antarctissa complex is very abundant in the southern ocean;it is one of the most common representatives of the Antarcticradiolarian fauna (Hays 1965; Nigrini 1967; Petrushevskaya1967; Keany 1973; Lozano and Hays 1976; Williams and Keany1977). This group is, therefore, suitable for a morphometricstudy.

The study area is a latitudinal transect from the southernIndian Ocean sector of the southern ocean (45°S to 65°S). A pilotstudy of five core-top samples from each of the South AtlanticOcean, South Pacific Ocean, and southern Indian Oceanshowed that morphologic gradients do not differ among theseoceans. Since more core-top material is available from thesouthern Indian Ocean, this ocean was chosen to represent thesouthern ocean.

Initially, 50 core-top samples were selected for this study.Only those 21 samples that contained more than 100 specimensof Antarctissa per gram sediment were included. These samplesare from an area between 45°S and 65°S. The remaining 29samples mainly came from the north of 45°S.

To determine whether the core-tops are Recent, counts weremade of the relative abundances of Cycladophora davisiania. Innone of the samples, C. davisiana exceeded 5 percent. Thus,they reflect Recent conditions (Lozano and Hays 1976). Theabsence of Stylatractus universus in all samples indicated thatthey are not older than 400,000 years (Hays and Shackleton1976). The greater than 60-micrometer fraction was used for themorphologic study. The samples were prepared using an im-proved version of Moore's (1973) settling technique (Granlund1983), which provides 32 slides with equally distributed radi-olarian faunas from each sample. For the measurements, 10slides, containing about 100 specimens, were randomly se-lected from each sample.

Seven morphological characters were measured on eachspecimen (cephalis width, contour width, thorax width, length

Correlation coefficients for two morphological parameters versus some physical parameters for the South Indian Ocean transect In thesouthern ocean

Physical parametersMorphological SilicaPhosphate .Oxygenparameters TemperatureTemperatureTemperature(micromoles(micromole (microlitersA° Bb Cc

per liter)per liter) per liter)

—0.200

—0.153

Width of cephalis(in micrometers)(Vi) _0.662d

Width of thorax(in micrometers)(V2) 0.715'

_0.631e_0.685d

0.696'_0.723d

0.223_0.695d0.6430

0.309- 0.5320.487

a Annual average temperature, °Cb Winter temperature, °C

Summer temperature, °Cd Denotes significance at the 0.1 percent level.

Denotes significance at the 1.0 percent level.Denotes significance at the 5.0 percent level.

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