THE FLOW OF THE FERRAR GLACIER CONSTRAINED BY THE PROVENANCE OF GLACIAL TILL IN VERNIER VALLEY, ANTARCTICA

We use provenance tools to test for changes in the source area of glacial tills in Vernier Valley, Antarctica, which would indicate changes in the flow patterns of the Ferrar Glacier. Vernier Valley is a small, ice-free valley in the Wilkniss Mountains of Antarctica (~78°S, 161°E) that contains four glacial drifts mapped and dated by Staiger et al. (2006). The tills and their minimum ages are: F1 (50 ka), F2 (670 ka), F3 (1100 ka), and F4 (3400 ka). We collected samples of these tills from shallow, hand-dug soil pits, as well as debris from the modern ice face and from colluvium beyond the glacial limit in the valley. For each pit, we collected two samples in a “T” profile. The upper sample was collected in a wide and shallow method to capture the horizontal variability of the sediments. The lower sample was collected in a narrow and wide method to capture the vertical variability of the sediments. At each sedimentary unit, we collected samples from 4-5 pits with this “T” method. This sampling method allows us to examine the spatial variability in the tills, as well as post-depositional changes in the tills. For example, in the cold, hyperarid, and polar conditions of this valley, aerosols accumulate in the soils, and cryoturbation slowly turns over the surface. We have measured the grain size distribution, organic carbon content (mass lost on ignition), and bulk geochemistry of the samples. We have begun to separate detrital zircon from each sample in order to determine the zircon U/Pb age distribution contained in each till.

Preliminary results show an increase in organic carbon from an average of 0.6% in the youngest till to an average of 1.7% in the oldest till. The lower samples show higher percentages of mass lost on ignition, and the oldest till shows the widest range of mass lost on ignition, suggesting that cryoturbation is actively mixing organic carbon to depth in these tills. The grain size data show lower amounts of fines in the older tills, consistent with the idea that aeolian activity removes fines from the tills over time. The bulk geochemistry of the samples shows that all samples have the same general geochemical signatures, suggesting there may not be changes in the provenance of the tills over time. The detrital zircon age populations will be used to further explore this finding, as that has proven to be a more robust method.