A Local Provenance for Glacial Tills at the Margin of the East Antarctic Ice Sheet, Transantarctic Mountains, Antarctica
The Nd and Sr isotopic compositions of fine-grained (<63 micron) fractions from tills transported by the Byrd Glacier and its tributaries in the Transantarctic Mountains were determined to asses the nature of crustal rocks underlying the East Antarctic ice sheet (EAIS) and to investigate changes in the sources of glacial detritus as a function of position along an active glacial flow path. Our data reveal that the tills have isotopic compositions that typically reflect variations in the composition of local bedrocks. The furthest upstream samples, from the Lonewolf Nunataks, have the lowest measured ∊Nd values (~-20) and highest 87Sr/86Sr (0.725 to 0.736) of any of the sampled tills. Although the local bedrock is mapped as Late Paleozoic to Mesozoic Beacon Group sedimentary rocks, the measured values likely reflect erosion of Precambrian crust similar to that exposed in nearby areas (Miller Range). Northern tributaries to the Byrd Glacier (along Brittania Ridge and the Bates Nunatak) have significantly higher measured ∊Nd (-8 to -15) and lower 87Sr/86Sr (0.712 to 0.723) that correspond to erosion of the Beacon Group rocks exposed in these regions. These results indicate that the tills deposited along nunataks do not necessarily represent far-traveled glacial detritus transported from the interior of the EAIS but are often products of more local bedrock erosion. Fine grained material in lateral moraines along the Byrd Glacier have ∊Nd values from -14 to -17 and 87Sr/86Sr from 0.729 to 0.739 that are consistent with their derivation from material eroded along the main glacier, combined with variable amounts of detritus provided by the tributary glaciers. Overall, our data support the assertion that outlet glaciers draining major continental ice sheets deliver detritus to continental margins that represents a complex mixture of the rocks glacially eroded within its entire catchment, and may be dominated by material eroded at or near the continental margin, itself.
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- 0726 Ice sheets;
- 0790 Weathering (1625;
- 1040 Radiogenic isotope geochemistry