东海盆地西湖凹陷B1井中始新世微体古生物及其古环境意义

EOCENE MICROPALEONTOLOGY AND ITS EOENVIRONMENTAL SIGNIFICANCE IN WELL B1,XIHU SAG,EAST CHINA SEA BASIN

通过对东海盆地西湖凹陷B1井3370~3799 m井段宝石组19个样品多门类微体古生物的分析,发现了丰富的孢粉,少量有孔虫、沟鞭藻、盘星藻以及钙质超微化石等。孢粉化石以杉科繁盛,松科和榆科花粉发育,金缕梅科、桦木科、壳斗科花粉以及水龙骨科孢子也有一定含量为主要特征,可称为杉粉Taxodiaceaepollenites-双束松粉Pinuspollenites-榆粉Ulmipollenites-栎粉Quercoidites组合,与相邻地区的孢粉组合对比结果表明,该孢粉组合时代为中始新世。此外,该段地层含沟鞭藻Operculodinium centrocarpum和Hystrichokolpoma granulatum等种类,发现Dictyococcites bisectus和Cyclicargolithus floridanus等钙质超微化石,以及个别浮游有孔虫Parasubbotina griffinae等。根据孢粉组合时代,结合浮游有孔虫、沟鞭藻和钙质超微化石特征种的分布时限,B1井3370~3799 m井段的地层时代为中始新世。综合各门类微体化石组合面貌特征,推测中始新统为近岸滨海海湾沉积。

19 samples were collected for micropaleontology analysis from the interval 3370~3799 m of Well B1 in the Xihu Sag,East China Sea Basin.Abundant pollen,a small amount of foraminifers,dinoflagellates,discostellaria and calcareous nannofossils were found.The pollen are characterized by the flourishing taxaceae,moderate pinaceae and ulmus pollen,and less hamamelidaceae,betulaceae and fagaceae pollen and less hydrosauria spore.It can be recognized as Taxodiaceaepollenites-Pinuspollenites-Ulmipollenites-Quercoidites assemblage.Comparing with the sporopollen assemblage in the adjacent region,the age of this studied assemblage is the Middle Eocene.In addition,there are dinoflagellates Operculodinium centrocarpum and Hystrichokolpoma granulatum in this formation.Calcareous nannofossils such as Dictyococcites bisectus and Cyclicargolithus floridanus were found,as well as planktonic foraminifera Parasubbotina griffinae.Combined with the occurrence of foraminifers,dinoflagellates and calcareous nannofossils,the age of the interval 3370~3799 m from Well B1 is the Middle Eocene.According to the micropaleontological assemblages,it is interpretted that the middle Eocene strata was mainly deposited under the nearshore coastal bay.