云南中新世南锋木化石及其古环境意义

In times of great concerns for Global Change, palaeobotany has already brought a lot of key results in our understanding of past climate changes. The contribution of palaeobotany to the study of Neogene palaeoclimates in China has mostly been limited to leaf and pollen assemblages. In this project, we focus on the late Miocene Nanfeng wood assemblage in Yunnan for the new information wood fossil can bring. Indeed, all plant organs have different preservation potential, and wood fossils can bring different floristic information compare to leaves and pollen. Moreover, the annual variations of the climate are registered in tree rings. By studying the late Miocene tree rings, we can understand the annual variability of the monsoon at that time. The late Miocene of Nanfeng is of great importance because the Neogene is the time of development of the monsoon and of uplift of the nearby Tibetan Plateau and adjacent areas. In this project, we will use fossil woods to reconstruct the palaeoenvironment, and particularly four components: the floristic, the climate, the annual variations of the climate, and the vegetation. Because the Nanfeng coalmine already yielded several hundred specimens, with a broad taxonomic diversity, the project is feasible. The identification of the fossil wood is made through sections of the sample along three planes: transversal, radial and tangential. More detailed characters are observed under a scanning electronic microscope. A comparison with modern samples allows identification generally at least at the genus level. Two methods are used to reconstruct the palaeoclimate: wood physiognomy, which is based on the link between wood features and climate; the coexistence approach, which looks at the climatic requirements of the nearest living relatives. For the largest specimens which exhibit tree rings, we will polish radial section and measure all rings. Comparison of the measurements through classic methods of dendrochronology will allow us to identify the annual variations of the late Miocene climate. The reconstruction of palaeovegetation is made according to two methods: the integrated plant record and the biome reconstruction. Both are based on the ecology of the nearest living relatives, but look at different characteristics. They are complementary because one is very precise, but the other allows better comparison with other sites. Combining the results of all these methods, we will have a good understanding of the late Miocene Nanfeng palaeoenvironment. In complement with other studies, it will bring useful information for our understanding of the Neogene Yunnan palaeoclimates and monsoon history.

木材化石能够提供丰富的植物系统演化及其独特的气候环境演变信息。植物化石在我国较为丰富而研究相对薄弱。本项目以采自云南晚中新世小龙潭组南锋煤矿的木化石为研究对象，通过木化石的解剖学和比较形态学研究，准确鉴定化石属种，认识该植物群的物种组成；采用整合植物记录分析法和生物群重建法，了解该植物群的植被类型；利用共存分析法和木相分析法，定量重建年均温、年降雨量等古气候要素；同时，测量并分析木化石树轮的年际变化，通过木化石树轮的年纪变化与气候变化的相关性，研究晚中新世气候在年际间的变化规律，探寻季风形成和演变的直接证据以及可能的地史时期极端天气事件。综合分析本项目研究结果，并结合已有研究成果，深入认识云贵高原新近纪以来生物多样性和环境演变的相互关系，并探讨亚洲季风的形成与演变过程，为新近纪全球由温室气候向冰期过渡的研究，以及人类认识地质时期气候变化历史及其规律提供证据。

通过数次野外调查，在南方煤矿收集木材化石600多件。项目对这些木材化石进行了研究，从中鉴定并在国际期刊上发表化石新种4个，未定种2个：Tsuga nanfengensis 、Pinus uniseriata 、Pinus nanfengensis、Pinus sp.、Abies nanfengensis和Prunus sp。 在此基础上讨论了南锋植物群代表的古气候认为：目前鉴定出来种类多少尚不能完全真实地反映出地质历史时期的植被状况，但依然能提供可靠的证据，化石的最近亲缘种中有代表温暖、湿润的气候条件的种类以及高海拔的类群，认为南峰已有较大海拔分异的山地环境，在湖泊边是要求水热条件较好的Pinus uniseriata和P. nanfengensis针叶林，稍高海拔段是Tsuga nanfengensis和Pinus sp. 组成的针叶林，最高海拔段是Abies nanfengensis为优势的针叶林。 项目还发现锦葵科的Wataria属的化石，这是该属化石在中国的首次报道。此外项目还得云南中新世的古海拔进行了重建，认为晚中新世云南的地貌已经有了较大的分化。项目培养博士研究生一名，硕士研究生一名，发表SCI论文21篇，实现了预期目标。