Landscape Evolution and Ice Sheet Stability: New Chronologies from the Transantarctic Mountains

该奖项由极地方案办公室南极地质和地球物理方案提供，支持获得和解释横跨北极山脉冰川沉积和地貌的新年代学数据的研究。其中一个焦点将是确定天狼星群沉积物的年龄，这些沉积物通常被认为记录了显著变暖的南极气候，这意味着东南极冰盖过去一直不稳定。由于东南极冰盖包含了地球上很大一部分淡水，这对于了解过去的气候变化至关重要。南极气候变暖的主要证据是在一些天狼星群岩屑中存在山毛榉化石树叶和木材。核心问题是这是什么时候发生的，天狼星群中的硅藻化石证据表明，这大约是300万年前，而地貌证据表明，它至少发生在1000万年前。为了获得这些重要冰川沉积物的最小年龄，将在天狼星群关键露头分离的单斜辉石矿物中测量宇宙射线产生的氦和霓离子(3He和21Ne)。这种方法通常被称为暴露年龄测年，它依赖于表面样品中3He和21Ne的积累与宇宙线照射有关的假设，因此与时间直接相关。这些研究将包括1995/1996年澳大利亚夏季田野季节采集的麦克默多海峡干燥山谷地区以及遥远的茂德皇后山脉(比尔德莫尔和沙克尔顿冰川地区)的样本。贝内特地台(沙克尔顿冰川)的初步年龄证明了该方法的可行性，产生的年龄约为1100万年。新的数据将有助于确定不同地区之间是否存在系统性的年龄差异，这可能有助于协调相互冲突的气候和地质模型。为了确定方法的可靠性，将对来自每个地点的多个样本进行分析，并将使用几种不同的宇宙源核素来检查一致性。初步数据已经表明，一些地点的年龄一致性很好(Bennett Platform和Table Mountain)，而其他地点则不是。将利用现场观测来评估该方法的假设，包括对相关基岩样品(应产生较老年龄)和屏蔽样品(应产生零年龄)的测量。基岩样本的暴露年龄数据将得出横贯北极山脉景观的最小年龄估计，并允许计算最大侵蚀速率，这两者都将检验横贯北极山脉的无冰景观至少有1000万年的历史，并且受到侵蚀的影响最小的假设。

This award, provided by the Antarctic Geology and Geophysics Program of the Office of Polar Programs, supports research to obtain and interpret new chronological data for glacial deposits and landforms in the Transantarctic Mountains. One focus will be to determine the age of the Sirius Group deposits, which are generally believed to record significantly warmer Antarctic climates, implying that the East Antarctic Ice Sheet has been unstable in the past. Because the East Antarctic Ice Sheet contains such a large fraction of the Earth's fresh water this is crucial to understanding past climate changes. The primary evidence for warmer Antarctic climates is the existence of fossil Beech leaves and wood within some Sirius Group tillites. The central question is when this occurred, with evidence based on fossil diatoms in the Sirius Group suggesting that it was roughly 3 million years ago, and evidence based on geomorphology suggesting it was at least 10 million years ago. In order to obtain minimum ages for these important glacial deposits, cosmic ray produced helium and neon (3He and 21Ne) will be measured in clinopyroxene mineral separates from key Sirius Group outcrops. The method, commonly referred to as exposure age dating, relies on the assumption that the accumulation of 3He and 21Ne in surficial samples is related to cosmic ray exposure, and hence is directly related to time. The studies will include samples from the Dry Valleys region of McMurdo Sound as well as those far to the south in the Queen Maude Mountains (Beardmore and Shackleton Glacier area) that were collected during the 1995/1996 Austral summer field season. Preliminary ages from Bennett Platform (Shackleton Glacier) demonstrate the viability of the method, yielding ages of approximately 11 million years. The new data will help determine whether there are systematic age differences between the various localities, which might help reconcile the conflicting climatic and geologic models. In order to establish the reliability of the methods, multiple samples from each locality will be analyzed, and several different cosmogenic nuclides will be used to check for consistency. The preliminary data already demonstrate that some locations yield excellent age consistency (Bennett Platform and Table Mountain) while others do not. Field observations will be used to evaluate the assumptions of the method, including measurements on associated bedrock samples (which should yield older ages) and shielded samples (which should yield zero age). The exposure age data for the bedrock samples will yield minimum age estimates for the landscapes in the Transantarctic Mountains and allow calculation of the maximum erosion rates, both of which will test the hypothesis that ice-free landscapes in the Transantarctic mountains are at least 10 million years old and are modified minimally by erosion.