| | Tephrochronology in the Dry Valleys A major problem in Antarctic science is the development of the Transantarctic Mountains. This project addresses the geomorphic evolution of the central Transantarctic Mountains (Dry Valleys block) using 40Ar/39Ar analyses of surficial ash deposits (back to at least middle Miocene) in the Dry Valleys region of southern Victoria Land. The isotopic age and areal distribution of in-situ ashes have been used to determine the chronology and rate of landform development in the Dry Valleys and provide age control on widespread geomorphic surfaces. In addition, the depositional setting and the degree of weathering of in-situ surficial ash deposits also provides detailed information on local and regional paleoclimate conditions at and since ash deposition (e.g. Marchant et al., 1993; 1996). Dozens of ash analyses have been conducted throughout the Dry Valleys, spanning a variety of geomorphic settings at different elevations (e.g. Quartermain Mountains, Asgard Range, Olympus Range, and McKelvey Valley). These ash analyses have shown that the overall Dry Valleys morphology represents a relict, semi-arid landscape that formed prior to the build-up of continental ice sheets during middle Miocene time and that subsequent slope modification has been limited to minor glacial scouring concentrated at valley heads, glacier confluences, and deep-valley troughs. Assumptions of this theory are (1) the present geomorphic processes are ineffective denudational agents, (2) that widespread land surfaces within tectonically uniform blocks reflect base-level changes at the Transantarctic Mountain front, and (3) that geomorphic landforms of the Dry Valleys that superficially resemble box canyons, escarpments, mesas, and buttes of desert regions in the American southwest formed by denudational processes no operating in the Dry Valleys. The current 40Ar/39Ar chronology of landscape evolution for the Dry Valleys region provides constraints for models of geomorphic evolution in cold-desert regions. More importantly, these constraints have implications for models of landscape development and uplift history of the Transantarctic Mountains | |
