古近纪重大气候事件及其生物响应

古近纪气候演化是由“温室气候”向“冰室气候”转变的过程,大致可划分为3个阶段:古新世-始新世早期的升温期,始新世中期-始新世末期的稳定降温期及渐新世-中新世早期的冰室气候期.在此期间发生了3次显著的气候事件,分别为PETM极热事件、Oi-1骤冷事件和Mi-1降温事件.这3次大的气候事件引起了生物圈的巨大波动:PETM期间发生了全球底栖大有孔虫灭绝事件及浮游有孔虫的辐射演化,并且是哺乳动物演化的关键时期；Oi-1期间全球植物群落由热带型密集雨林向寒冷干燥的森林草原过渡,在欧亚大陆出现了哺乳动物种群大规模改变的Grande Coupure和Mongolian Remodelling事件,也发生热水型浮游及底栖有孔虫的灭绝事件；Mi-1前后,浮游有孔虫部分属种绝灭,钙质超微化石也出现暖水种数量的急剧减少,现代植物群落在这一时期开始形成.古近纪气候的大幅波动和转折由诸多因素控制,主流观点认为PETM事件与天然气水合物的大量释放有关,但其喷发机制尚不明确；降温事件则与区域性构造隆升、洋流榕局变化等因素有关.

Significant Climate Events in Paleogene and Their Biotic Response

The climate change during the Paleogene is a process from "green house" to "ice house".This process can be divided into 3 stages: the Paleocene-early Eocene which is the period of steadily temperature growing;middle Eocene-late Eocene in which the temperature was steadily droping;and the glacial in Oligocene-early Miocene.There are 3 significant climate events during these periods and each of them had caused significant fluctuation to the whole biosphere.The PETM had caused the largest benthic foraminiferal extinction event and rapidly diversification of plankton foraminifera,which is also the vital period of mammalian evolution.During the Oi-1,the global flora changed from dense rain-forest to cold dry forest steppe,and there are mammalian turnover events(Grande Coupure,Mongolian Remodelling) founded in Eurasia as well as extinction of warn planktonic and benthic foraminifera.After Mi-1,some genus of planktonic foraminifera became extinct.Thermo-water species of calcargeous nannofossils reduced their number sharply and modern floral pattern began forming.There are many factors which controlled the fluctuation and changes of Paleogene climate.The mainstreaming associated PETM with the release of methane hydrate.But the origin of the gas is not clear yet.The glacials may have relationship with the regional tectonic uplift and changes of ocean circulation.