JURASSIC SPORA-POLLEN ASSEMBLAGES AND PALEOCLAMATE IN INNERMONGOLIA,GANSU,QINGHAI,CHINA

A larger part of Gansu,the west of Innermongolia and the northeast of Qinghai,divided into Alashan,Beiqilian-Hexizoulang,Zhongqilian and Qaidam stratigraphical divisions have been related.In this region there are widely well-developed Jurassic sediments,which include abundant coal and oil natural resources.Based on fully studing Jurassic spores and pollen grains in this area,with preceding achievement,seven spora-pollen assemblages have been established.The low Jurassic includes three assemblages: Protoconiferus-Taeniaesporites,Osmundacidites-Chasmatosporites-Disaccites and Classopollis-Cyathidites-Cycadopites.The Middle Jurassic includes three assemblages: Cyathidites-Quadraeculina-Cycadopites,Cyathidites-Callialasporites-Pinuspollenites and Classopollis-Cyathidites-Inaperturopllenites.The Upper Jurassic only establishes Classopollis assemblage.Using paleoecology of mother plant of spores and pollen,combing the range of special rocks implying paleoclimate in strata,Jurassic climate has been studied,which includes Jurassic climate structure and evolution rule.It is suggested that the Jurassic climate locates the subtropical-moderate climate zone.Under this background,there is a fluctuated temperature-rising and humidity-falling events occur in late early Jurassic(Toarcian).The late middle Jurassic climate is comparatively hot and arid.This hot and arid phenomenon is so further aggravate that the whole area is hot and arid in late Jurassic.The temperature is higher in Qaidam basin and Zhongqilian area than that of other place in the early-middle early Jurassic.The humidity in Yabulai basin is smaller than that of other place in the early middle Jurassic,but it is larger than that of other place in the late middle Jurassic in Qaidam basin.All of the research region are hot and arid in late Jurassic.The early-middle Jurassic is major period of assembling and generating coal and hydrocarbon with flourishing fauna and flora,coal bed and dark mudstone in Alashan,Zhongqilian and north of Qaidam basin.It is advantage for forming oil and gas-bearing depression,which is advantaged explorating area.