Cosmogenic beryllium-10 and neon-21 dating of late Pleistocene glaciations in Nyalam, monsoonal Himalayas
Cosmogenic beryllium-10 and neon-21 dating of late Pleistocene glaciations in Nyalam, monsoonal Himalayas
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DOI：
10.1016/j.quascirev.2007.10.014
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发表时间：
2008-02
影响因子：
4
通讯作者：
J. Schaefer;Peter Oberholzer;Zhizhong Zhao;S. Ivy‐Ochs;R. Wieler;H. Baur;P. Kubik;C. Schlüchter-C.-Schlücht
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文献类型：
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作者：
J. Schaefer;Peter Oberholzer;Zhizhong Zhao;S. Ivy‐Ochs;R. Wieler;H. Baur;P. Kubik;C. Schlüchter-C.-Schlücht
地表暴露年龄为末次冰期旋回晚期至少两次明显的冰川推进和一次或多次明显更古老的冰川作用提供了证据。古冰碛层序三脊的宇宙年龄分布与其地层顺序不一致。由于沉积物在冰碛表面沉积之前的暴露时间很短，因此年代学-地层学的不匹配表明，宇宙形成年龄并不能确定冰碛沉积的年代，而很可能是在第二次冰期旋回或更早的冰碛初始沉积之后，冰碛脊的剥蚀和相关的巨石挖掘。基于各种目前公认的产量标度方案的地表暴露年龄产生了高达35%的年龄差异，这反映了对低纬度/高海拔地区地球宇宙成因产量的认识不足。为了充分利用热带冰碛序列中记录的气候信息，迫切需要提高陆地宇宙核素产生速率及其在低纬度地区的尺度知识。
We present cosmogenic10Be and21Ne chronologies from 21 erratic boulders on three moraine sequences in Nyalam county, monsoonal Himalayas, southern margin of the Tibetan Plateau. The surface exposure ages provide evidence for at least two distinct glacial advances during the late stage of the last glacial cycle and for one or more significantly older glaciations. The distribution of cosmogenic ages from the three ridges of the old moraine sequence is inconsistent with their stratigraphic order. Because exposure periods of the erratics prior to deposition on the moraine surface is shown to be small, the chronology–stratigraphy mismatch suggests that the cosmogenic ages do not date moraine deposition but most likely significant moraine ridge denudation and related boulder exhumation after initial deposition of the moraines during the penultimate glacial cycle or earlier. The surface exposure ages based on various currently accepted production rate scaling protocols yield age differences of up to 35% reflecting the poor knowledge of terrestrial cosmogenic production rates at low latitude/high altitude sites. Even within this conservative uncertainty range, our results do not yield evidence for late Pleistocene glaciations in monsoonal Tibet to be asynchronous to those in mid-latitudes on both hemispheres. There is an urgent need to improve the knowledge of terrestrial cosmogenic nuclide production rates and their scaling to low latitude regions to fully exploit the climate information archived in tropical moraine sequences.