Tephrochronology Applied to Late Cenozoic Paleoclimate and Geomorphic Evolution of the Central Transantarctic Mountains

该奖项支持一个研究横贯南极山脉干谷地区地貌演化的项目。火山灰沉积物的同位素年龄和区域分布将用于限制地形发育的年代学和速率，并有助于量化地貌表面的年龄。火山灰的沉积环境和风化程度也有助于约束火山灰沉积期间和沉积后的区域古气候条件。这项工作将集中在夸特曼山脉、阿斯加德山脉、奥林匹斯山脉和麦凯维山谷，因为这些地区已知含有一些火山灰沉积物，因为它们在相当大的海拔范围内包含各种地貌设置。该项目将尝试检验以下假设的基础：干谷地区是在中新世中期大陆冰盖形成之前形成的一个废弃的半干旱景观，随后的斜坡改造仅限于集中在山谷头、冰川汇合处和深谷槽的小冰川冲刷。在这些假设中，1)目前的地貌过程是无效的剥蚀作用；2)在构造均匀的地块内广泛分布的陆地表面反映了横贯南极山脉锋面的基准面变化；3)干谷的地貌表面上类似于美国西南部沙漠地区的箱形峡谷、悬崖、台地和丘顶，这些地貌是由现在在科罗拉多高原上进行的剥蚀过程形成的。该项目产生的同位素年龄信息将为寒沙漠地区地貌演化模型提供约束条件，并将对跨南极山脉的景观发展和隆升历史模型产生影响。如果古半干旱侵蚀之后是小冰川切口的假设在干谷地区被证明是正确的，那么根据谷中陆地表面的同位素定年确定的基准面变化将提供一个晚新生代山脉演化和隆起的年代学，而不依赖于已经完成的热年代学研究。这一点很重要，因为热年代学研究虽然很适合确定长期的隆升速率，但并不适合区分早新生代和晚新生代的隆升。在本研究过程中建立的火山灰数据库也将对麦克默多火山省的研究有用。

This award supports a program to study the geomorphic evolution of the Dry Valleys region of the Transantarctic Mountains. The isotopic ages and areal distribution of volcanic ash deposits will be used to constrain the chronology and rates of landform development and to help quantify the age of geomorphic surfaces. The depositional setting and degree of weathering of the ash will also help to constrain regional paleoclimatic conditions during and after deposition of the volcanic ash. This work will focus on the Quartermain Mountains, Asgaard Range, Olympus Range, and McKelvey Valley because these regions are known to contain some volcanic ash deposits and because they contain a variety of geomorphic settings over a substantial elevation range. This project will attempt to test assumptions that underlie the hypothesis that the Dry Valleys region represents a relict, semi- arid landscape that formed prior to build up of the 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. Among these assumptions are 1) that present geomorphic processes are ineffective denudation agents, 2) that widespread land surfaces within tectonically uniform blocks reflect base-level changes at the Transantarctic Mountains 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 denudation processes now operating in the Colorado Plateau. The isotopic age information generated by this project will provide constraints for models of geomorphic evolution in cold- desert regions and will have implications for models of landscape development and uplift history of the Transantarctic Mountains. If the hypothesis of ancient semi-arid erosion followed by minor glacial incision proves correct for the Dry Valleys re gion, then changes in base level, as defined by isotopically dated land surfaces in the Valleys, will provide a chronology of late Cenozoic mountain evolution and uplift independent of thermochronological studies that have been completed. This is important because the thermochronology studies, although well suited for determining long-term uplift rates, are not well suited to distinguishing early from late Cenozoic uplift. The volcanic ash data base developed in the course of this study will also be useful for studies of the McMurdo volcanic province.