Collaborative Research: Spatially Varying Topographic and/or Climatic History of the Sierra Nevada Mountains

合作研究：内华达山脉空间变化的地形和/或气候历史

• 批准号: 0309011
• 负责人: C. Page Chamberlain
• 金额: $ 27.72万
• 依托单位: Stanford University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-07-01 至 2007-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0309011&HistoricalAwards=false
• 关键词: Collaborative; Research; Spatially; Varying; Topographic

There is considerable debate as to when the Sierra Nevada developed as a significant topographic feature and how it affected the past climate of this region. One view holds that the Sierra Nevada is a young mountain range, with net surface uplift of some 2km in the last 10 million years. In contrast, recent work suggests that the Sierra Nevada has been a long-standing topographic feature. Previous analysis of the hydrogen and oxygen isotope composition of smectite produced by the weathering of volcanic ashes from sections along the east side of the Sierra Nevada shows that, in the central Basin and Range, the oxygen isotopes of smectite increased slightly in the last 16 million years. This result contrasts with that of one section in the southern Basin and Range, which shows a large increase in oxygen isotopes from 14 to 6 million years. These results indicate that the Sierra Nevada has been a long-standing topographic feature at least for the past 16 million years. Moreover, if these isotopic shifts result solely from topographic change, then the Sierra has a spatially varying topographic history, with some 700 m of topographic loss in the northern Sierra and ~2000m of lowering of the southern Sierra in the Late Cenozoic. The data can also be explained by a strengthening of the summer monsoon in the Late Cenozoic that could result in isotopically heavier precipitation, particularly in the southern areas of the Basin and Range.This study is testing the hypothesis that the Sierra Nevada had a spatial varying topographic history by: 1) collecting isotopic data from the southern Basin and Range in order to separate topographic from climatic effects; 2) constructing a regional isotopic map of the Basin and Range to enhance understanding of the regional topographic and climactic history of this region; 3) sampling over a larger time range to determine what isotopic changes have occurred both in rocks younger than 2 million years and older than 16 million years; and 4) collecting isotopic data from other substrates, particularly fossil mammals, to reduce the uncertainty associated with any one isotopic proxy for paleoprecipitation.

关于内华达山脉何时发展为重要的地形特征以及它如何影响该地区过去的气候存在相当多的争论。 一种观点认为，内华达山脉是一座年轻的山脉，在过去 1000 万年中地表净隆起约 2 公里。 相比之下，最近的研究表明内华达山脉一直是一个长期存在的地形特征。 此前对内华达山脉东侧地段火山灰风化产生的蒙脱石氢、氧同位素组成的分析表明，在盆地中部，近1600万年来蒙脱石的氧同位素略有增加。年。 这一结果与南部盆地和山脉的一个剖面的结果形成鲜明对比，该剖面显示氧同位素从 14 到 600 万年大幅增加。 这些结果表明，至少在过去 1600 万年里，内华达山脉一直是一个长期存在的地形特征。 此外，如果这些同位素变化仅由地形变化引起，那么内华达山脉的地形历史在空间上有所变化，在新生代晚期，内华达山脉北部的地形损失约 700 m，而内华达南部的地形下降约 2000 m。 这些数据还可以通过新生代晚期夏季季风的加强来解释，这可能导致同位素降水量增加，特别是在盆地和山脉的南部地区。这项研究正在检验内华达山脉具有空间变化的假设地形历史：1）从南部盆地和山脉收集同位素数据，以便将地形与气候影响分开； 2）构建盆山区域同位素图，加深对该地区区域地形和气候历史的了解； 3) 在更大的时间范围内进行采样，以确定 200 万年以下和 1600 万年以上的岩石中发生的同位素变化； 4) 从其他基质，特别是哺乳动物化石中收集同位素数据，以减少与古降水的任何一种同位素代理相关的不确定性。