C11C-0773
Till Provenance for Whillans Ice Stream, West Antarctica: from Upstream B, Subglacial Lake Whillans, and the Grounding Zone
Monday, 14 December 2015
Poster Hall (Moscone South)
Rebecca Puttkammer1, Ross D Powell2, Timothy O Hodson1, Franco M Talarico3, Slawek M Tulaczyk4, Reed P Scherer1, Jason James Coenen1 and WISSARD Science Team, (1)Northern Illinois University, DeKalb, IL, United States, (2)Northern Illinois Univ., De Kalb, IL, United States, (3)University of Siena, Department of Physical Sciences, Earth and Environment, Siena, Italy, (4)University of California Santa Cruz, Earth and Planetary Sciences, Santa Cruz, CA, United States
Abstract:
The Whillans Ice Stream Subglacial Access Research Drilling (WISSARD) project recovered sediment cores from Subglacial Lake Whillans (SLW) in 2013 and Whillans Grounding Zone (WGZ) in 2015. Coarse particles were extracted from cores of till for quartz sand gain surface microtexture analysis and pebble shape, texture, and lithology analyses. Limited research has been previously done on the subglacial coarse sediments of subglacial lakes and grounding zones in the Antarctic to infer subglacial sediment transport processes and sources along an ice stream. The subglacial coarse sediment at the three research sites is glacially transported as indicated by quartz sand grain microtexture analysis. Subglacial water drainage does not fluvially transport the coarse sediment as shown by: (1) a lack of V-shaped percussion cracks as surface microtextures on quartz sand grains, (2) high relief, (3) angularity, (4) conchoidal fractures, and (5) arc-shaped steps having high frequency occurrences; all indicating that glacial processes in till dominate coarse sediment subglacial transport at the three sites. Pebble shape and texture analyses concur with those findings with 76% of pebbles spherical or discoid and over 90% subangular to angular at WGZ and SLW. Faceting occurred on 50% of pebbles at upstream Whillans (UpB), 56% at SLW, and 42% at WGZ and striae are present on fine-grained pebbles. No stratigraphic changes in transport mechanisms are apparent from coarse sediment analyses by depth at the three sites. The subglacial sediment lithology from UpB to SLW indicates the same source beds composed largely of low-grade metamorphics and plutonics. Stratigraphic variation at WGZ shown in the compositional analysis indicates the provenance for the sediments vary by depth. Variation in subglacial sediment sources suggest changing source beds due to shifting glacial flow lines or varying input from Mercer Ice Stream at the upstream convergence zone.
