甘肃华亭中侏罗统延安组植物群组成及古气候指示

FOSSIL PLANT ASSEMBLAGE FROM THE MIDDLE JURASSIC YAN'AN FORMATION IN HUATING,GANSU PROVINCE AND ITS PALEOCLIMATIC IMPLICATION

对甘肃华亭延安组植物化石进行了宏观形态和表皮构造分析,经鉴定共有24属49种。该植物群组成为:真蕨纲(28.6%)、银杏纲(38.8%)繁盛,松柏纲(16.3%)、楔叶纲(8.2%)和苏铁纲(4.1%)占一定比例,石松纲和种子蕨纲未见。与国内、外侏罗纪植物群或组合,特别是与我国北方中侏罗世11个研究较为系统的植物群进行了详细的对比和分析。结果表明,当前植物群明显具有中国北方Coniopteris-Phoenicopsis植物群早期组合的特点,其地质时代归为中侏罗世早期,大致相当于阿林期(Aalenian)至巴柔期(Bajocian)。华亭延安组化石植物以温暖湿润气候下繁盛的植物类型为主,兼具少数亚热带、热带气候下的植物成分,说明甘肃华亭地区中侏罗世为偏湿润的暖温带气候。

On the basis of morphological and cuticle analysis, a total of 24 genera and 49 species of plant fossils were identified from the Middle Jurassic Yan＇an Formation of Huating, Gansu Province. The results show that Ginkgopsida （38. 8%） and Filicopsida （28.6%） are dominated in this flora, Coniferopsida （ 16. 3 %）, Sphenoposida （ 8. 2 %） and Cycadopsida （4.1% ） have an important proportion while Lycopsida and Pteridospermopsida are absent. On the basis of the comparison of fossil compositions with other Jurassic floras, including 11 Middle Jurassic floras from North China which had been investigated in detail by previous researches, we conclude that the present Yan ~ an Formation flora of Huating belongs to the early assemblage of the Coniopteris-Phoenicopsis flora in North China, with a geological age of Middle Jurassic （likely Aalenian to Bajocian）. Meanwhile, most species from the Yan＇an Formation were distributed in a zone of warm and humid conditions with some exceptions that existed in tropical or subtropical zones. Therefore, the regions of Huating, eastern Gansu Province might have experienced a humid and warm- temperate climate during the Middle Jurassic.