摘要
中间中新世的气候的最佳(MMCO；~ 15-17 ? 妈) 是标点的短期的气候的温暖的事件之一新生代长期的冷却趋势。因为有这个事件的很少的陆上的记录，大多数我们的理解来自海洋的核心。在这份报告，我们首先介绍修订标明日期的新 palaeomagnetic 数据我们的 400 ? 在 Wenshan (云南) 的 m 厚的湖的节，以前想了晚中新世。这些新数据建议老年， ca。15.2-16.5 ? 妈，与 MMCO 与一致。我们测量了 <sup>13</sup > 体积有机物上的 C (<sup>13</sup > C <sub > 器官的碳(TOC ) ，全部的氮(TN ) 和在高度的 C/N 比率取样的 org </sub>), 总数分辨率：(1 ) 重建在湖集水区域的 palaeoenvironmental 变化，并且(2 ) 推断为这些变化负责的机制。我们的结果证明所有四个 geochemical 参数证明一个强壮的环境变化发生在节的中间附近，立即在在 15.97 点的 C5Cn/C5Br 地磁气的颠倒和早 / 中间中新世的边界以后 ? 妈。我们建议环境移动可能由于在气候的一个变化的联合，它变得更凉爽，和在有机物在湖以内骑车的一个变化。这研究提供新卓见进 MMCO 并且证明尽管 MMCO 通常是一个温暖的事件，它也是气候的不稳定性和突然的环境变化的一倍。
The Mid-Miocene Climatic Optimum （MMCO; 15-17 Ma） was one of the short-term climatic warm events that punctuated the Cenozoic long-term cooling trend. Because there are very few terrestrial records of this event, most of our understanding comes from marine cores. In this report, we first present new palaeomagnetic data that revises the dating of our 400 m-thick lacustrine section in Wenshan （Yunnan）, previously thought to be Late Mio- cene. These new data suggest an older age, ca. 15.2-16.5 Ma, coinciding with the MMCO. We measured δ13C on bulk organic matter （3 Corg）, total organic carbon （TOC）, total nitrogen （TN） and C/N ratios at a high sample resolution to： （1） reconstruct the palaeoenvironmental changes in the lake catchment area, and （2） infer mechanisms responsible for these changes. Our results show that all four geochemical parameters demonstrate that a strong environmental change occurred around the middle of the section, shortly after the C5Cn/C5Br geomagnetic reversal and the Early/Middle Miocene boundary at 15.97 Ma. We propose that the environmental shift may be due to a combination of a change in climate, which became cooler, together with a change in organic matter cycling within the lake. This study provides a new insight into the MMCO and demonstrates that although the MMCO was generally a warm event, it was also a time of climatic instability and abrupt environmental changes.
基金
The authors are grateful to two anonymous reviewers for their constructive comments, which significantly improved the manuscript. The authors thank fellow members of staff of the Palaeoecology group in Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences for assistance during sample collection and productive critical discussions
Professor Yun Fu from the Central Laboratory of Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences for assistance during the TN mea- surements
Dr. Olesya V. Bondarenko, from the Russian Academy of Sciences, Vladivostok, for her help and support during sample preparation
Yi-Min Tian from the Faculty of Land Resource Engi- neering, Kunming University of Science and Technology, for her assistance when preparing and observing thin sections. The authors are grateful to Dr. Andrea Kern from the USGS and Dr. Dayou Zhai from Yunnan University for fruitful discussions and suggestions to improve the manuscript. This study was supported by National Nat- ural Science Foundation of China （U1502231）, the CAS 135 Program （XTBG-F01）, and a grant from the China Scholarship Council to J. Lebreton Anberr6e （2013GCX606）. Shihu Li and Chenglong Deng acknowledge support from the National Natural Science Foundation of China （41404056）, and the State Key Laboratory of Lithospheric Evolution （11431780）. Shu-Feng Li was supported by the Foundation of the State Key Laboratory of Paleobiology and Stratigraphy, Nanjing Institute of Geology and Paleontology, CAS （15310）. This work is part of the NECLIME （Neogene Climate of Eurasia） network.
