太白山第四纪冰川地貌演化与年代学研究

Thanks to new dating techniques, such as cosmogenic radionuclides (CRN), optically stimulated luminescence (OSL) and electron spin resonance (ESR) have been developed and refined in glacial chronology, Quaternary glaciations research in China has entered a crucial period with the characteristics of dating technology. Qinling mountain range is a natural barrier of Chinese north-south, also the link that connecting the east-west, the geographical position is extremely important and special. During the Quaternary period, Taibai Mountain has developed obvious glaciations, and retained lots of clear glacial erosion and accumulation landforms. It’s a ideal place to reconstruct ancient glacial sequence and recover glacier landforms evolution, especially to verity the Tibetan Plateau and surrounding mountains’ glacier development mechanism-tectonic and climate coupled model. This project will use OSL、ESR、CRN dating techniques to research chronology with typical glacial deposits in Taibai Mountain, and the key is finding MIS3/4 evidence of glacial advance. This study determined the Taibai Mountain ancient glacial sequence, nature and scale, it can recover glacier landforms evolution. Combined with other climate records for this area, and extensive contrast surrounding the other mountains, we will try to construct the temporal and spatial patterns of glacier evolution in the eastern margin of the Tibetan Plateau.

得益于CRN、OSL、ESR等测年手段在冰川年代学的发展与应用，第四纪冰川研究已经进入了以技术定年为特征的关键时期。秦岭为我国南北的天然屏障和连接东西的纽带，地理位置极为重要和特殊，其主峰太白山在第四纪期间发育过明显的冰川作用，且保留了形态清晰的冰川侵蚀和堆积地貌，是重建古冰川序列和恢复冰川地貌演化过程，特别是验证青藏高原及周边冰川发育机制—构造和气候耦合模式的理想场所。本项目将运用OSL、ESR、CRN等技术测年手段对太白山典型冰川沉积进行年代学研究，重点找寻MIS3/4的冰进证据。本研究确定的太白山古冰川序列、性质和规模，能够恢复冰川地貌的演化过程，结合该区其他气候记录，并广泛对比周边其他山地，尝试构建青藏高原东缘冰川演化的时空模式。

秦岭主峰太白山地处我国南北分界的关键地带, 地理位置极为重要和特殊, 其山顶3000 m以上分布的串珠状冰斗和多道冰碛垄显示这里在末次冰期经历过次级的波动或阶段性的停顿, 是深入研究末次冰期时限、规模与气候响应机制的理想地点之一. 本课题利用10Be暴露测年确定太白山末次冰期序列, 进而探讨冰川发育的演化过程, 并与周边山地冰进时代进行对比. 主要结论如下: 冰川漂砾和冰坎基岩10Be暴露测年说明太白山至少发生过2冰进，最早为～37.9 ka, 对应末次冰期中期(MIS 3), 第二次为23.4～21.7 ka, 对应全球末次冰盛期(LGMg), 其中，LGMg时有两次千年尺度的波动停顿, 此后进入末次冰消期, 暴露年代依次为18.1 ka, 17.6 ka, 17.3 ka, 呈现出很好的退缩趋势和阶段性, 冰川在16～15 ka左右消失殆尽. 通过与青藏高原腹地和东北缘的典型山地进行冰期序列对比得出, MIS 4冰进只出现在海拔超过6000 m高山, MIS 2冰进在各地均有发生, 而MIS 3冰进可能并不具有普遍性. 与全球多处利用基岩和漂砾暴露年代恢复末次冰消期时限的山地比较得出: 末次冰消期时, 全球增温导致的冰川消融具有大约相同的时间框架, 但期间具有千年尺度的波动; 此外, 研究区绝大多数冰川底部基岩侵蚀面、磨光面的暴露年代相对集中, 表明LGMg期间的冰川侵蚀足以去除槽谷底部基岩之前表面暴露积累的宇宙成因核素, 导致基岩暴露年代只能记录末次冰消期这一次冰川消融事件.

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