藏东芒康晚中新世卡均植物群及其古环境重建

Cenozioc floras from Xizang are vital to understand the evolution of vegetation and paleoenvironment changes in Qinghai-Tibet Plateau, but fossil floras have been largely uninvestigated in Xizang until now. Recently, we found a new plant fossil locality at an elevation of about 4000 m in the Upper Miocene Lawula Formation of Kajun village, Mangkang county, eastern Xizang. This locality is rich in plant fossils in several layers; among them, two layers bear fossils in the best preservation condition and have the highest number of species. According to our prelimenary observation, the floristic asseblages are obviously differnt between these two layers. In the lower layer, ring-cupped oaks (Quercus subgenus Cyclobalanopsis) are the most abundant, together with other species, e.g., Alnus, Elaeagnus and Populus, presenting a mixed evergreen-deciduous forest. In the upper layer, Salix is dominant, together with others, e.g., Cotoneaster, Equisetum, Picea and Rosa, presenting a deciduous forest. Besides, leaves in the lower layer are much bigger in size than these in the upper layer. The difference of floristic assemblage and leaf size between two layers indicates significant paleoenvironment change during the late Miocene. In this project, we will mainly focus on these two fossil-rich layers. The species list will be complied by the identification of fossils with culticle analysis and clearing leaf technique. Vegetation type will be reconstructed by the methods of Biome Reconstruction and Integrated Plant Record. The biogeographical implications will be discussed in details for some important taxa, e.g., Ealeagnus in the family Elaeagnaceae (the first leaf fossil record of this genus in the world); fossil ring-cupped oaks (the first discovery of fossils in this group from Xizang). Besides, paleoclimate will be quantitatively reconstructed with three methods, i.e., Leaf Margin Analysis, Climate-Leaf Analysis Multivariate Program, as well as Coexistance Approach. Paleoelevation will be calculated using the enthalpy palaeoaltimeter. By comprising these results of two layers, as well as combining with previous studies, this project could provide important evidence on several lines of important scientific issues for Qinghai-Tibet Plateau: the evolution of vegetation, paleoclimate change and mountainous uplift, as well as plant biodiversity in response to paleoenvironmental change.

西藏地区新生代植物群对于认识青藏高原的植被演变和古环境变化过程尤为重要，但是目前鲜有该地区化石植物群的报道和深入研究。近期，申请人在西藏东部芒康县海拔近四千米的卡均村上中新统拉屋拉组地层中，发现了大量植物化石，其中有两层化石保存状况最佳，物种也最为丰富。上、下层植物化石无论是叶片形态特征还是物种组成，都存在着明显差异。本项目拟系统研究这两层植物化石，通过透明叶对比和角质层技术准确鉴定化石，认识植物群的区系组成，并探讨重要化石类群的生物地理学意义；在此基础上，利用生物群区化法和整合植物记录分析法恢复古植被；共存分析法、叶缘分析法和气候-叶片多变量分析程序定量重建古气候；湿静态能平衡原理重建古海拔。通过对比上、下层位植物群的古环境重建结果，并结合已有研究资料，探讨藏东地区晚中新世以来的植被演变过程、古气候变化与海拔抬升历史，为青藏高原的古环境变化对植物多样性的影响提供重要证据。

西藏地区新生代植物群对于认识青藏高原的植被演变和古环境变化过程尤为重要，但是目前鲜有该地区化石植物群的报道和深入研究。本项目在西藏东部芒康县海拔近四千 米的卡均村拉屋拉组地层中，采集到大量植物化石，其中有两层化石保存状况最佳，物种也最为丰富。本项目利用氩-氩法对地层中的火山凝灰岩进行了测年，结果表明位于下部的MK3层所代表的地质年代为34.6 ± 0.8 Ma，而位于上部的MK1层所代表的年代为33.4 ± 0.5 Ma。这段时期地球历史恰巧经历了始新世到渐新世的转折期（Eocene-Oligocene Transition，时间界限为33.9 Ma）。上、下层植物化石无论是叶片形态特征还是物种组成，都存在着明显差异。本项目系统研究了这两层植物化石，通过透明叶对比和角质层技术准确鉴定化石 ，认识了植物群的区系组成，并探讨重要化石类群的生物地理学意义，发表新分化石类群四个;在此基础上，提出青藏高原东南缘植物多样性现代化面貌在晚始新世已经形成。本项目还利用气候叶相多变量分析程序和热力学原理定量重建了化石植物群的古气候与古海拔，表明始新世-渐新世之交，青藏高原东南缘气候逐渐变冷、变干，并经历了继续的抬升，接近或达到现在的高度。综上所述，本项目为青藏高原东南缘植被演变过程 、古气候变化与海拔抬升历史提供了重要的新证据。