SR-ND-PB RADIOGENIC ISOTOPE SIGNATURES OF PLEISTOCENE TILLS AND MIOCENE SIRIUS GROUP SEDIMENTS FROM ANTARCTICA: IMPLICATIONS FOR ICE SHEET HISTORY

Glacially deposited sediments shed light on subglacial processes and provide a link to bedrock sources buried beneath the Antarctic Ice Sheet, expanding knowledge of bedrock geology. Provenance analysis of glacial sediments can yield valuable information on past ice sheet behavior. Approximately half of Antarctic ice drains through the Ross and Weddell Sea embayments, so sediments from exposed mountain ranges and nunataks near these ice streams can be used to study a wide swath of the East Antarctic Ice Sheet (EAIS). To learn more about subglacial geology and ice sheet behavior, we analyzed Sr, Nd, and Pb radiogenic isotope ratios and major/trace element concentrations of fine-grained (<5 μm) sediments collected from the Transantarctic Mountains (TAM) in the Ross Sea drainage and the Whichaway Nunataks, Shackleton Range, Patriot Hills, and Patuxent Range in the Weddell Sea drainage. Geochemical analyses were performed on 16 Pleistocene till samples and 12 Miocene tillites from the Sirius Group, also within the TAM. Overall, samples have εNd = -16.2 to -4.8, ⁸⁷Sr/⁸⁶Sr = 0.71 to 0.80, ²⁰⁶Pb/²⁰⁴Pb = 18.26 to 24.19, ²⁰⁷Pb/²⁰⁴Pb = 15.54 to 16.07, and ²⁰⁸Pb/²⁰⁴Pb = 38.32 to 44.88, with only minor differences between the Ross and Weddell drainages. We did not observe any major differences in Sr-Nd-Pb compositions between Pleistocene tills and Sirius Group sediments in the central TAM, suggesting a similar mix of lithologic sources through time. We will evaluate several notably high ⁸⁷Sr/⁸⁶Sr values of 0.77 to 0.80 in light of potential bedrock sources and the chemical index of alteration to infer the degree of chemical weathering beneath the EAIS (i.e., loss of Sr relative to Rb). We will present the new provenance data in the context of existing bedrock, sediment, and marine core-top geochemical data, and will assess provenance signatures of the major drainages of the EAIS.