(I) Introduction to the Problem and BackgroundLGM flow dynamics of the East Antarctic Ice Sheet (EAIS) and West Antarctic Ice Sheet (WAIS) are not well constrained. The expanded LGM Ross Ice Sheet followed Ross Sea Floor bathymetry via troughs, however the origin of the ice filling the troughs remains uncertain. Currently, disagreement exists surrounding the EAIS and WAIS contribution to the expansion of the LGM Ross Ice Sheet. Contrasting models predict either a predominantly WAIS (Fig. 1), or a somewhat even contribution from both the EAIS and WAIS (Fig. 2 & 3).

Previous investigations aimed at characterizing LGM Ross Sea till do not directly correlate the till with an East or West Antarctic source (i.e. Balshaw, 1981; Anderson et al., 1992). Since these previous studies, several improvements have been made in Ross Sea core coverage and till availability from beneath the WAIS. In this study, the sand petrography of West and East Antarctic till is Ross Sea till is then compared to these source terranes to determine the most likely provenance. The results from this study can be used in determine the paleo flow-dynamics of the LGM Ross Ice Sheet.

(IV) Methodology• Obtained till from six regions in East Antarctica and from

beneath the Whillans Ice Stream and Ice Stream C in West Antarctica

• Obtained till from sixteen cores from across the Ross Sea• Petrographically analyzed the 500 – 2000 μm sand fraction

using Indiana Method of point counting method. Indiana Method categorizes lithic fragments according to

their mineralogy, whereby a grain with two+ mineral fragments is classified as a lithic fragment.

• Plotted data according to their normalized quartz, feldspar, and mafic intrusive lithic fragment (QFM) and quartz, mafic intrusive, and sedimentary lithic fragment concentrations (QSM) (Figure 5).

• Statistically analyzed results with cluster analysis (Figure 6) and discriminant analysis (Figure 7)

• Contains till deposited during the LGM ice sheet expansion.• Characterized by NE-SW trending troughs and ridges interpreted

to be remnant glacial features.• CRS and ERS troughs contain paleo ice-flow features (i.e.

drumlins, lineations, etc. (Shipp et al., 1999).

(III) Ross Sea

Abstract No: 55816

Provenance of Ross Sea TillJason Lederer, Kathy J. Licht, R. Jeffery Swope

Geology Department, Indiana University-Purdue University, Indianapolis Indianapolis, IN 46202 USA

jlederer@iupui.edu, klicht@iupui.edu, rjswope@iupui.edu

Denton and Hughes (2000)

Figure 3

180o

Figure 3

180o

Licht and Fastook (1998)

WA

EA

Figure 2

Stuiver et al., 1981Stuiver et al. (1981)

E

180o

180o

WA

EA

Figure 1Stuiver et al. (1981)

The exposed bedrock in East and West Antarctica is compositionally different, thus the till from the two regions should be different as well. We assume that the composition of the till reflects the composition of the rocks over which ice flowed. Though not shown on this map, West Antarctic rocks are rift associated flood basalts Behrendt et al., 1994) overlain by unlithified sediment derived from marine and terrigenous input (Rooney et al., 1991).

Pre-Cretaceous strata,upper Paleozoic and/orlower Mesozoic

RISP

David Glacier

Ice Stream D

Drygalski Ice Tongue

Figure 4

Ice Stream E

From American Map Folio series, 1970 – American Geographical Society

McMurdo Volcanic Group (olivine basalt, trachyte, kenyte, pyroclastic deposits)

Ferrar Group (tholeiitic flows, sandstone lenses, agglomerate tuff, volcanic conglomerateGranite Harbour Intrusives (biotite-hornblende granodiorite and hornblende granite)

Byrd Group (marble, limestone, oolitic limestone, quartzite, conglomerate, sandstone, volcanic rocks

Nimrod Group (quartzite, marble, schist, diorite, gneiss, ecologite lenses)

Beardmore Group (pelitic schist, hornfels, metagraywacke, argillite)

Beacon Group (sandstone, shale, coal measures with tholeiitiic dikes, sills, and plugs

Basement Complex – metasedimentary rocks

(II) Regional Bedrock Geology (Figure 4)

Acknowledgements:Contributors: H. Engelhardt – California Institute of Technology, J. Bockheim – University of Wisconsin – Madison, G. Faure – The Ohio State University, T. Janecek – Florida State University, Antarctic Research FacilityFunding from the Geological Society of America, NSF Office of Polar Programs, IUPUI Geology and Graduate SchoolDr. Kathy Licht, Dr. R. Jeffery Swope, Dr. Andy Barth, Dr. Joe Pachut (statistics), Bob E. Hall and Dr. Jeffery Wilson (GIS)

(VI) Conclusions• East and West Antarctic source areas have distinct petrologic signatures.• Ross Sea till exhibits E-W petrologic variability.• WRS till exhibits petrographic similarities to adjacent areas of East Antarctica• ERS till exhibits petrographic similarities to adjacent West Antarctica • Although ERS and WRS are compositionally similar to adjacent areas of

Antarctica, transport by ice has caused maturation of the lithologic and mineralogic counterparts. (Note: Particle size analysis results not presented here show that Ross Sea till has a smaller average particle-size than East and West Antarctic till)

• CRS till exhibits compositional similarities to both ERS and WRS tills which can be used as proxies for East and West Antarctic source areas. Several Ross Sea till samples contain distinctive provenance indicators (i.e. oolitic limestone, calcite, marble, etc.)

• Distinctive lithic fragments serve as tracers• Results suggest an moderately even contribution from the EAIS and WAIS to

the expansion of the LGM Ross Ice Sheet, correlating well with the models of Fastook and Licht (1998) and Denton and Hughes (2000) following Ross Sea troughs (consistent with Shipp et al. (1999) paleo ice-flow directional indicators).

ReferencesAnderson, J.B., Shipp, S.S., Bartek, L.R., and Reid, D.E., 1992, Evidence for a grounded ice sheet on the Ross Sea continental shelf during the Late Pleistocene and preliminary paleodrainage reconstruction.

Marine Geology, v. 57, p.295 – 333.

Balshaw, K.M., 1980, Antarctic glacial chronology reflected in the Oligocene through Pliocene sedimentary section in the Ross Sea. Ph.D. Thesis, Rice University, 140 p.

Licht, K.J., and Fastook, J., 1998, Constraining a numerical ice sheet model with geologic data over one ice sheet advance/retreat cycle in the Ross Sea. Chapman Conference on the West Antarctic Ice Sheet, University of Maine, p.25-26.

Shipp, S.S., Anderson, J.B., and Domack, E.W., 1999, Seismic signature of the Late Pleistocene fluctuation of the West Antarctic Ice Sheet system in the Ross Sea: A new perspective, Part 1. Geological Society of America Bulletin, V.111, n.10, p.1486 – 1516.

Stuiver, M., Denton, G.H., Hughes, T.J., and Fastook, J.L., 1981, History of the marine ice sheets in West Antarctica during the last glaciation: A working hypothesis. In Denton, G.H. and Hughes, T.J.eds, The last great ice sheets: New York, Wiley-Interscience, p.319-439.

a.

Function 1:felsic igneous fragmentsIntermediate igneous fragmentsextrusive volcanic fragmentsopaque mineralscalcitepotassium feldsparplagioclasemudstone fragmentssandstone fragmentsclaystone fragments

Function 2:metamorphic igneous fragmentsmafic igneous fragmentsbiotiteiron orequartzolivinechlorite

Function 1:intermediate igneous fragmentsmetamorphic fragmentsextrusive volcanic fragmentslimestone fragmentssandstone/siltstone fragmentsclaystone fragmentspyroxenepotassium feldsparbiotitechlorite

Function 2:mudstone fragmentsmafic fragmentsfelsic fragmentsolivineiron orecalcitequartz

Function 3:opaque mineralsmuscovite

Canonical Scores Plot

-6 -1 4 9FACTOR(1)

-6

-1

4

9

FAC

TOR

(2)

321

VARIABLE

Function 1

Fu

nct

ion

2

EA (1)

EAWARS

EA + RS (3)

Function 1 Function 2

Fu

nct

ion

3F

un

ctio

n 2

2a2b

2c

2d

• Confirms that the groups formed by cluster analysis are statistically distinct.

• Determines which mineral and lithic fragments components in the till are important factors in forming the cluster groups.

Figure 7. Discrminant analysis plots: ellipses represent the 95% confidence interval surrounding the average grouping score for each cluster.

East Antarctic and West Antarctic Till Composition• East and West Antarctic till reflect regional geology.• East Antarctic till is dominantly mafic intrusive, felsic

intrusive, metamorphic (quartzite, calcite), sedimentary (mudstone), volcanic extrusive.

• West Antarctic till is dominantly well rounded quartz, feldspar, felsic intrusive – distinctive feature to is biotite, quartz, hornblend, and/or chlorite – rich felsic intrusive fragments. Sediment likely derived from Transantarctic Mountains to the north during ice free conditions.

(V) Results

Magnification 100x

quartz

?

Figure 9

Ross Ice Shelf

RISP

Whillians Ice Stream

Binschadler Ice Stream

Kamb Ice Stream

MacAyel Ice Stream

Mt. Achernar

Beardmore Glacier

Nim

rod

Gla

cier

Byrd

Gla

cier

Darwin G

lacier

Hatherton Glacier

Allan Hills

David Glacier

Mercer Ice Stream

S

EA

WA

9902 - 04

Victoria Land

Marie ByrdLand

Holyoake Range

DryglaskiIce Tongue

Coulman Island

9902 - 05

9407 - 63

9501 - 24

9501 - 07EL - 32

WRSCRS

ERS

9501 - 179407 - 39

Dry

gals

ki T

roug

hPennellBank

EasternBasin

JOID

ES

B

asin

-500

9501 - 30

9401 - 01

9902 - 17

9902 - 08

9501 - 35

Magnification 400xSAL 3 – x-polars

hornblende

biotitequartz

SAL 540 - ppl

Oolitic limestone

Magnification 100x

?

Figure 8.

Figure 6. Resulting dendogram from cluster analysis of till samples from East Antarctica, West Antarctica and Ross Sea.

Sample Locations

Cluster Tree

0 5 10 15Distances

WASAL1WASAL3

WASAL122WASAL123

EASAL106

EASAL114

EASAL119

EASAL186EASAL187

EASAL192

EASAL193

RIPSSAL219RISPSAL222

EASAL226EASAL227

CRSK15CRSK23CRSK33

CRSK53

CRSSAL230

CRSSAL534

CRSSAL537

CRSSAL538

CRSSAL540CRSSAL543

WRSSAL306

WRSSAL368

WRSSAL369

WRSSAL371

WRSSAL373

WRSSAL374

WRSSAL375

WRSSAL376WRSSAL403

WRSSAL404

WRSSAL405

WRSSAL406

WRSSAL407WRSSAL408

ERSSAL138

ERSSAL141

ERSSAL142

ERSSAL169

ERSSAL177

ERSSAL178

A

B

C

D

DarwinUpper BeardmoreHatherton

Ice Stream CIce Stream CWhillans Ice StreamWhillans Ice StreamNBP9501 - 17DF80 - 193DF80 - 193NBP9501 - 11NBP9501 - 17NBP9501 - 17NBP9501 - 17RISPRISPNBP9501 - 24NBP9501 - 12NBP9501 - 07NBP9902 - 08NBP9902 - 17NBP9902 - 04NBP9902 - 04NBP9907 - 63NBP9902 - 16NBP9902 - 05Hatherton/DarwinNBP9501 - 35EL32 - 13NBP9501 - 35NBP9501 - 30EL32 - 13EL32 - 13DF80 - 193EL32 - 13Upper BeardmoreCentral Beardmore

NBP9401 - 01Darwin TerminusDF80 - 193NBP9501 - 11NBP9501 - 17NBP9401 - 01Mt. AchernarAllan Hills

1

2

3

Cluster

ERSSAL306

Three clusters form at a Euclidean distance of ~9.5.

• There are four subclusters of cluster 2 formed at a Euclidean distance of ~ 5.

• Weak clustering between source terrane and Ross Sea tills, however, some overlap does occur.

• The three areas of the Ross Sea cluster separately on dendogram.

• There is little overlap between East and West Antarctic source area tills indicating that they are distinct.

East AntarcticaWestern Ross SeaWest Antarctica

Eastern Ross SeaCentral Ross Sea

RISP

Figure 5

• East and West Antarctic samples do not exhibit overlap.

• Western Ross Sea (WRS) samples plot close to East Antarctic samples.

• Eastern Ross Sea (ERS) samples plot close to West Antarctic samples.

• Central Ross Sea (CRS) samples plot between ERS and WRS samples.

• RISP samples plot similarly to West Antarctic samples on QSM ternary and similarly to East Antarctic samples on QFM ternary.

Felsic igneous fragments with characteristic quartz, biotite, hornblende composition occur in West Antarctica and the CRS.

Oolitic limestone occurs in CRS LGM till and has one documented occurrence in Ross Embayment in the Shackleton Formation Limestone in the Holyoake Range near Nimrod Glacier (Fig. 9).

9501 - 12

9501 - 11

80 - 193

9501 - 39-2000

-1000