Tephrachronology & Landscape Evolution 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 provide detailed information on local and regional paleoclimate conditions at and since ash deposition.
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 largely formed prior to the build-up of continental ice sheets during middle Miocene time. Subsequent slope modification has been limited to minor wind erosion, periglacial processes, and glacial scouring concentrated at valley heads, glacier confluences, and deep-valley troughs. Assumptions of this theory are (1) that present geomorphic processes are largely 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 similar denudational processes.
NSF Award Abstract
Top of Page
(* Student Advisee)
*Lewis, A.R., Marchant, D.R., Ashworth, A.C., Hemming, S.R., and Machlus, M.L. 2007. Major middle Miocene global climate change: evidence from East Antarctica and the Transantarctic Mountains. Geological Society of America Bulletin 119, (11/12), 1449-1461, doi: 10.1130B26134.1
*Lewis, A.R., Marchant, D.R., Baldwin, S.L, and Webb, L.E. 2006. The age and origin of the Labyrinth, western Dry Valleys, Antarctica: evidence for extensive middle Miocene subglacial floods and freshwater discharge to the Southern Ocean. Geology 34 (7), 513-516.
Marchant, D.R., *Lewis, A., Phillips, W.C., *Moore, E.J., Souchez, R., and Landis, G. P. 2002. Formation of patterned-ground and sublimation till over Miocene glacier ice in Beacon Valley, Antarctica. Geological Society of America Bulletin 114, 718-730.
Marchant, D.R., Denton, G.H., Swisher III, C.C., and Potter, N., Jr. 1996. Late Cenozoic Antarctic paleoclimate reconstructed from volcanic ashes in the Dry Valleys region, south Victoria Land. Geological Society of America Bulletin 108, (2) 181-194.
Sugden, D.E., Denton, G.H., and Marchant, D.R. 1995. Landscape evolution of the Dry Valleys, Transantarctic Mountains: Tectonic implications. Journal of Geophysical Research, 100 (B7), 9949-9967.
Marchant, D.R., Swisher III, C.C., Lux, D.R., West, D.P., Jr., and Denton, G.H. 1993. Pliocene paleoclimate and East Antarctic ice-sheet history from surficial ash deposits. Science 260, 667-670.
Top of Page