glaciation, subtracting the eustatic sea level drop due toglaciation, and then performing a density calculation. Recentglacial reconstructions in Ross Sea predict greater groundedice thicknesses than would be determined with density calcu-lations (Denton, Prentice, and Burckle 1991). Thus, the icethickness in Bransfield Basin could have been much greaterthan the calculated 700 m.

Financial support for this project was provided byNational Science Foundation grant OPP 91-19683 awarded toJohn B. Anderson.

References

Anderson, J.B., and L.R Bartek. 1992. Cenozoic glacial history of theRoss Sea revealed by intermediate resolution seismic reflectiondata combined with drill site information. In J.P. Kennett and D.A.Wamke (Eds.), The antarctic paleoenvironment: A perspective onglobal. (Antarctic Research Series, Vol. 56.) Washington D.C.:American Geophysical Union.

Belknap, D.F., and R.C. Shipp. 1991. Seismic stratigraphy of glacialmarine units, Maine inner shelf. In J.B. Anderson and G.M. Ashley(Eds.), Glacial marine sedimentation: Paleoclimatic significance.Boulder, Colorado: Geological Society of America.

Denton, G.H., M.L. Prentice, and L.H. Burckle. 1991. Cainozoic histo-ry of the antarctic ice sheet. In R.J. Tingey (Ed.), The geology ofAntarctica. Oxford: Clarendon Press.

King, L.H. 1993. Till in the marine environment. Journal of Quater-nary Science, 8(4), 347-358.

King, L.H., and G.B.J. Fader. 1986. Wisconsinan glaciation of theAtlantic Continental Shelf of southeast Canada. Supply and Ser-

vices Canada, Ottawa: Canadian Government Publishing Centre.King, L.H., K. Rokoengen, G.B.J. Fader, and T. Gunleiksrud. 1991. Till-

tongue stratigraphy. Geological Society of America Bulletin, 103,637-659.

Mosher, D.C., D.S.W. Piper, G.V. Vilks, A.E. Aksu, and G.B. Fader.1989. Evidence for Wisconsinan glaciations in the Verril Canyonarea, Scotian Slope. Quaternary Research. 31(1989), 27-40.

Stewart, F.S., and M.S. Stoker. 1990. Problems associated with seismicfacies analysis of diamicton-dominated, shelf glacigenicsequences. Geo-Marine Letters, 10(1990),151-156.

Stoker, M.S. 1990. Glacially-influenced sedimentation on theHebridean slope, northwestern United Kingdom continental mar-gin. In J.A. Dowdeswell and J.D. Scourse (Eds.), Glacimarine envi-ronments: Processes and sediments. London: Geological Society ofLondon.

Stoker, M.S., F.S. Stewart, M.A. Paul, and D. Long. 1992. Problemsassociated with seismic facies analysis of quaternary sediments onthe northern UK continental margin. Underwater Technology,18(4).

Vail, P.R., R.M. Mitchum, Jr., R.G. Todd, J.M. Widmier, S. ThompsonIII, J.B. Sangree, J.N. Bobb, and W.G. Hatlelid. 1977. Seismicstratigraphy and global changes of sea level. In C.E. Payton (Ed.),Seismic stratigraphy—Applications to hydrocarbon exploration.Tulsa: American Association of Petroleum Geologists.

Vorren, T.O., M. Hald, and E. Lebesbye. 1988. Late Cenozoic environ-ments in the Barents Sea. Paleoceanography, 3(5), 601-612.

Vorren, 1.0., E. Lebesbye, K. Andreassen, and K.B. Larsen. 1989.Glacigenic sediments on a passive continental margin as exempli-fied by the Barents Sea. Marine Geology, 85(1989), 251-272.

Vorren, T.O., E. Lebesbye, and K.B. Larsen. 1990. Geometry and gene-sis of the glacigenic sediments in the southern Barents Sea. In J.A.Dowdeswell and J.D. Scourse (Eds.), Glacimarine environments:Processes and sediments. London: Geological Society of London.

A geochemical sedimentological analysis of glacial marinesediments from the Palmer Deep Basin,

Bellingshausen Sea, AntarcticaANTONIO B. RODRIGUEZ, Department of Geology and Geophysics, Rice University, Houston, Texas 77251

EUGENE W. DOMACK, Department of Geology, Hamilton College, Clinton, New York 13323

The sediments off the Antarctic Peninsula contain a historyof the advance and retreat of glaciers and paleoclimate

change. The Palmer Deep Basin is located on the Beffingshau-sen Sea Continental Shelf, 5 kilometers south of Anvers Island(figure 1). Piston core PD92-30 was collected from the basinduring the R/V Polar Duke 92-2 research cruise. This studyfocuses on the geochemical, magnetic susceptibility (MS), andtotal organic carbon (TOC) variations in the core.

In the Antarctic Peninsula, MS has proved to be a usefulpaleoclimatic indicator due to distinct sediment sourcechanges that accompany changes in climate (Domack and Ish-man 1992). A low MS value corresponds to a high biogeniccontent and low terrigenous material (Domack and Ishman1992). High MS values are not found where ice-rafted debris iswithin the core; therefore, high MS values for core PD92-30 area product of the fine-grain hemipelagic component of deposi-tion (Kirby 1993).

The depth vs. MS graph (figure 2) for core PD92-30 showswide variations in MS for the upper 580 centimeters. From 580centimeters down, a trend of low MS values with small fluctua-tions is apparent. The MS variations are related to variations inbiogenic material in the core (Domack and Ishman 1992). Togain a better understanding of the relation between MS andbiogenic material, a geochemical analysis of the core was per-formed at various depths. Nine samples from alternating lowand high MS were analyzed by x-ray fluorescence for themajor and trace earth elements (table). The plots of stron-tium/MS (Sr/MS), aluminum oxide/MS (Al 203 /MS), calciumoxide/MS (CaO/MS), potassium oxide/MS (K20IMS), magne-sium oxide/MS (MgO/MS), and titanium oxide/MS (Ti02/MS)have a direct, positive sloped, linear relationship to MS. Thegraph of silica/MS (Si02/MS) has a direct, negative sloped, lin-ear relationship to MS (figure 3).

The observed TOC of core sediments is controlled by the

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0

-gCI) M

0CM

0

Depth (cm)

Figure 2. Depth vs. magnetic susceptibility in core PD92-30. Locations in thecore where nine samples were taken are marked by arrows. (CSG denotescentimeter-gram-second.)

Figure 1. Map of the Antarctic Peninsula region and the SouthShetland Islands showing location of piston core PD92-30.

quantity of organic carbon vertically settling and the amountof dilution of this organic carbon due to terrigenous sedimen-tation (Domack et al. 1993). The plot of TOG vs. depth showsapproximately 12 cycles of low and high TOG percentagesthroughout the core. These cycles become more spread out asthey progress down core. TOG generally varies inversely withMS. Graphs of Sr/TOG, Al 203 /TOG, GaO/TOG, K20/TOG,MgO/TOG, and Ti0 2 /TOG show no distinct clear linear rela-tionship; however, there is an apparent negatively sloped

72

71

70

CMC69

68

670102030405060708090100

MS

Figure 3. Si02 vs. magnetic susceptibility. Notice the negativelysloped best fit line.

characteristic to the trend. The graph 5i0 2 /TOG portrays a rel-atively positively sloped trend.

Low MS corresponds to high TOG. The concentrations ofSr, Al203, CaO, 1(20, MgO, and Ti02 all increase with increas-ing MS and show a general decreasing trend with increasingTOG. These elements make up some portion of the hemipelag-ic sedimentation component. Since MS is a measure of thevariations in the hemipelagic component of sedimentation(Kirby 1993), two scenarios can be inferred: the cause for anincrease in terrigenous sedimentation depresses the organicproductivity, or the cause for an increase in productivitydepresses the terrigenous sedimentation. The mechanismsdescribing these causes, and the realization that the first sce-nario is most plausible, become apparent upon comparing thehemipelagic to pelagic components of sedimentation.

Diatoms are unicellular algae composed of siliceous tests.Upon death, these tests settle to the ocean floor and becomepreserved in the sediment. The concentration of SiO2 in corePD92-30 is a result of diatom productivity. Kirby (1993) visual-ly noted the abundance of diatom ooze layers in the core.Domack et al. (1993) hypothesized that high TOG, which is

associated with high silica values from diatom blooms,would correspond to low MS. The graph of Si0 2 vs. MS(figure 3) produces a negative slope, the graph of SiO2vs. TOG indicates a positive trend, and the inverse rela-tionship between TOG and MS supports Domack andIshman's hypothesis. When MS is low, there is a highconcentration of SiO 2 and high TOG, both of which cor-respond to high productivity for the area.

The initiation of high hemipelagic sedimentationcould be suppressing the values of TOG and SiO2through dilution and suppressing overall productivity.Increases in hemipelagic sedimentation could be theresult of large-scale storm cycles that suspend relict tillfrom the continental shelf and transport it into thebasin. This would result in a decrease in TOG and SiO2values, due to dilution caused by the newly transportedhemipelagic component, and a decrease in diatombloom size, due to deep mixing caused by strong winds.The preservation of turbidites was noted in cores fromtwo adjacent basins; their preservation could have beentriggered by large storms (Kirby 1993). During the sub-

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Concentrations of the major and trace earth elements in core PD92-30

Sample DepthSr

152256.012.893.241.822.872100219.971.082.801.642.543210247.612.553.201.772.794320245.712.503.251.772.915355219.811.172.821.582.57

419217.611.272.901.592.60

450234.312.013.081.722.70

560267.413.133.391.802.97

620213.771.542.791.562.56

0.7168.44648.35.67

0.6071.08549.25.13

0.6969.00552.15.46

0.7168.59563.25.83

0.6270.79557.95.37

0.6470.55505.05.38

0.6869.95587.85.42

0.7667.52570.85.92

0.6171.54533.35.06

sequent placid periods, blooms would increase in productivi-ty, and less suspension of relict till would take place.

The 12 cycles of low and high TOG percentages could pos-sibly represent 12 periods of large storms in the past. Twelvecycles of TOG were also noted by Domack and Ishman (1992)from a piston core collected in Andvord Bay, Antarctica. Themechanism causing these cycles could be the same for the twoareas. Once sedimentation rates have been studied for corePD92-30, the mechanism for the observed variations in sedi -mentation can be constrained.

This research was supported by National Science Founda-tion grant OPP 89-15977 to Hamilton College.

References

Domack, E.W., and S.E. Ishman. 1992. Magnetic susceptibility ofantarctic glacial marine sediments. Antarctic Journal of the U.S.,27(5),64-65.

Domack, E.W., T.A. Mashiotta, L.A. Burkley, and S.E. Ishman. 1993.300 year cyclicity in organic matter preservation in antarctic fjordsediments (Antarctic Research Series, Vol. 60). Washington, D.C.:American Geophysical Union.

Kirby, M.E. 1993. High resolution seismic stratigraphy and sedimen-tological analysis of Holocene glacial marine sediments in thePalmer Deep Basin, Bellingshausen Sea, Antarctica. (Senior pro-ject thesis, Hamilton College, Clinton, New York.)

Recent ostracodes from the fjord region of southern Chile:Applications to Holocene paleoenvironments

ANDREW V. SHUCKSTES, Byrd Polar Research Center, Ohio State University, Columbus, Ohio 43214

The purpose of this study is to determine quantitatively themodem distribution of benthic marine ostracodes (small

bivalved crustaceans) within the fjord region of Chile andrelate them to modern environmental data (water tempera-ture, salinity, depth, and composition of the substrate).Knowing the relationships between the modern distributionof ostracodes and the modern environment is useful fordetermining the bottom water conditions that existed duringdeposition of ancient sediments. During July 1993, aboardR/V Polar Duke cruise PD93-06, we retrieved 44 Smyth-McIn-tyre grab samples, 38 piston cores, and several gravity coresfrom the fjords and channels of southern Chile. The grabsamples and piston/gravity core catchers have yielded anabundant and diverse benthic ostracode fauna. Samplesrange between 54.288 0S to 45.345 0S. Water depths of samplesites range from 58 to 1,140 meters. Ostracodes were abun-dant in 23 of the Smyth-McIntyre grab samples (table). Theconsensus data obtained from these samples make up themodern Chilean ostracode database (MCOD). Common

species present in the samples include Bradleya normani,Krithe spp., Hemingwayella pumilo, Munseyella sp. A., Patago-nacythere longiducta?, Procythereis spp., Henryhowella spp.,Pseudocythereis sp., and Cytheropteron spp. (figure 1).

Associations between environmental parameters of sam-ple sites and ostracode assemblage are determined throughcluster analysis of samples and through single speciesdepth/latitude limits. Ostracode distribution is generally con-trolled by bottom water temperature, salinity, and substratecomposition (Cronin 1991; Dingle and Giraudeau 1993). Clus-ter analysis of the MCOD was completed using SYSTAT withsingle linkage, (nearest neighbor) Euclidean distance method.Four primary groups are immediately apparent and demon -strate the importance of both latitudinally and bathyrnetrical-ly controlled parameters (such as bottom water temperature).Group one contains very shallow samples (less than 200meters) from the northern part of the field area. The secondgroup contains samples from intermediate depth (200 to 400meters), northern sites. The third group includes intermedi-

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