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

该奖项支持一项研究跨南极山脉干旱河谷地区地貌演变的计划。 将利用火山灰沉积物的同位素年龄和区域分布来确定地貌发展的年代和速度，并帮助量化地貌表面的年龄。 火山灰的沉积环境和风化程度也将有助于限制火山灰沉积期间和之后的区域古气候条件。 这项工作将集中在夸特梅因山脉，阿斯加德山脉，奥林巴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含有各种地貌环境。 本项目将试图检验以下假设的基础假设：干谷地区代表了一个残留的半干旱景观，在中新世中期大陆冰盖形成之前形成，随后的斜坡改造仅限于集中在谷头、冰川汇流和深谷槽的轻微冰川冲刷。 这些假设包括：1）目前的地貌过程是无效的剥蚀剂，2）构造均匀块体内广泛的陆地表面反映了横贯南极山脉前沿的基准面变化，3）表面上类似于箱形峡谷、悬崖、台地的干谷地貌，以及美国西南部沙漠地区的孤峰，这些孤峰是由现在科罗拉多高原的剥蚀过程形成的。 该项目产生的同位素年龄信息将为寒冷沙漠地区地貌演化模型提供约束，并将对跨南极山脉的景观发展和隆升历史模型产生影响。 如果古代半干旱侵蚀，其次是轻微的冰川切割的假设证明是正确的干河谷地区，那么基准面的变化，在山谷中的同位素定年的土地表面所定义的，将提供一个独立的热年代学研究已经完成的晚新生代山脉演化和隆起的年表。 这是很重要的，因为热年代学研究，虽然很适合于确定长期的隆升速率，不适合区分早期和晚期新生代隆起。 在这项研究过程中建立的火山灰数据库也将有助于麦克默多火山区的研究。

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.