ICE SHEET DYNAMICS OF THE PAST 17 MA IN SOUTHERN MCMURDO SOUND, ANTARCTICA: A HEAVY MINERAL ANALYSIS

The Antarctic geologic drilling program (ANDRILL) drilled sediment cores from a sea ice platform in the Ross Sea in southern McMurdo Sound (SMS), Antarctica in late 2007. The southern McMurdo Sound is a depositional site that is surrounded by the Transantarctic Mountains and the volcanoes of the McMurdo Volcanic Group, and it has received sediment supplied by both the East and the West Antarctic Ice Sheet and Ross Ice Shelf. The core site is located adjacent to the Transantarctic Mountains along the western margin of a half graben and is a site of heavy sedimentation from the surrounding glaciers. The top 650 m of the core were analyzed for heavy minerals, which have a density of 2.89 g/cm³ or higher. By completing an analysis of heavy minerals from these cores and tracing them back to their sources, the recent history (Middle Miocene, 17 Ma to present) of ice sheet drainage patterns and dynamics can be determined. A heavy mineral analysis is a great way to study ice dynamics because they can record multiple ice sheet advances and they are excellent indicators of source rock types. Grain mounts of the fine sand sized (63-250 microns) heavy mineral fraction of 23 intervals were created and approximately 300 grains were identified per slide. Results show the presence of diverse mineral assemblages, including different types of pyroxenes, amphiboles, epidote, garnet, sillimanite, monazite, volcanic glass with inclusions, and others. The data represent several changes in sediment provenance associated with the Middle Miocene climate optimum and transition (14-16 Ma). There are also changes in mineral assemblages that may be related to changes in sea level and volcanic eruptions.