Research Objectives:
Hyperarid cold conditions have prevailed in the Dry Valleys for over ten million years (Myr) based on suggested in situ preservation of ancient volcanic ash, overlying till and colluvium. This extreme stability of the sediments also argues against any influx of warm based ice into the valley system and attests to the relatively dry climate and minimal ice sheet expansion. However, other evidences suggest that Dry Valleys may have experienced much more sediment erosion than generally believed: 1) The cosmogenic exposure ages of inner valley boulders and bedrock all show generally younger ages than volcanic ash deposits that are suggested to give the minimum age to moraines and drifts, 2) There is an apparent discrepancy between the suggested extreme preservation of slope deposits (>10 Myr) adjacent to bedrock that has in the same time period eroded 2.6 to 6 meters.
The fact that the till and moraine exposure ages generally post date the overlying volcanic ash deposits (a clear contradiction) can be explained by documented expansion of continental ice sheet in the Dry Valleys sector to inundate the valleys with cold based ice, thus preserving the landscape and shielding the surfaces from cosmic radiation. Another probable explanation for the young cosmogenic exposure ages is erosion of the sediments and gradual exhumation of young boulders to the surface.
The cosmogenic isotope systematics are especially well suited to address questions of temporal shielding and sediment stability.
This project will measure the accumulation of cosmogenic isotopes in the rocks at or near soil surface to determine the minimum sediment exposure ages, soil stability or mixing, and shielding history of surfaces by cold based ice. Additional benefits include directly verifying the extreme preservation of soils and assigning absolute minimum ages to key deposits.
