Study On The Palaeoecology And Phytogeography Of Middle Jurassic Flora In Western Hills Of Beijing

The plant fossils discussed in this paper was collected from the Yaopo and Longmenformations of southern Jiulongshan in Western Hills of Beijing. There are 38 species in 22genera. These species are in different groups which comprise Sphenopsida, Filicopsida,Cycadopsida, Coniferopsida and Ginkgopsida. The flora may be designated as MiddleJurassic in age. The taphonomic types of the fossil plants are analyzed according to theirstates of preservation, sizes and characters. It is sure that most of them are autochthonousburial. So the flora characters could reflect paleoecological environment. The fossil plantsare divided into three plant assemblages, namely, Equisetum laterale-Equisetum beaniassemblage, Cladophlebis asiataca-Coniopteris beijingsis assemblage and Elatocladusmanchurica-Podozamites lanceolatus assemblage. In this essay, emphasis is laid on thestudy of climate reconstruction. There are two main approaches used in this paper, whichare Nearest-Living-Relatives-Method and Leaf-Physiognomy-Analysis. Results of thestudy show that the dominant groups are Filicopsida (31.6%) and Cycadopsida (23.7%),the proportion of entire margined species is 51.6%, mean annual temperature is 16.9℃.The flora indicates a humid-warm close to subtropical climate and also indicates awarming and drying climatic change in Middle Jurassic.The Middle Jurassic flora in Western Hills of Beijing also includes Mentougou florain Chenfen, Douyawei, Huangqisheng (1984) and Zhaitang flora in Duanshuying (1987)by comparison. Cladistic biogeography is used to interpret pattern of plant distribution.The Middle Jurassic flora in Western Hills of Beijing is compared with contemporaryfloras, such as, floras of western Liaoning, northern Chaidamu, Siberian and Yorkshire.The relatives of each flora are analyzed to conclude phytogeography. The result showsthat flora of western Liaoning is closer to flora in Western Hills of Beijing than to flora ofnorthern Chaidamu. The flora of Middle Jurassic in Western Hills of Beijing is near theboundary between the Siberian and Euro-Sinian phytogeographic regions. It is reasonablethat the flora of Middle Jurassic in Western Hills of Beijing is in Euro-Sinian phytochorialregion, just as the Southern floras of China.