西藏亚东堆纳地区始新世钙藻化石

始新世是西藏特提斯消亡的时期,因此在该地史时期形成了最年轻的海相沉积即最高海相层。最高海相层的时代代表了残留海盆消亡的时间。藏南亚东地区保存着最年轻的海相沉积,即遮普惹组。通过对亚东堆纳地区日阿东剖面遮普惹组中灰岩段的上部和砂页岩段的中下部灰白色块状生物碎屑灰岩夹层中的钙藻化石进行详细的分析和研究,共鉴定出18属27种(包括红藻门6属9种,绿藻门12属18种),据其分布特征划分出3个化石组合:1 Jania denotata-Amphiroa iraquensis组合,2 Ovulites margaritula-Fucoporella diplopora组合,3 Lithoporella melobesioides-Polygonella minima组合。根据所含钙藻化石组合的相关特征,推测堆纳地区在始新世处于浅海陆棚环境,海水深度最深不超过30m。

EOCENE CALCAREOUS ALGAE FROM DUINA,YADONG,SOUTHERN TIBET,CHINA

Eocene is the demise period of the TibetanTethys,during which the youngest marine sediments(the highest marine layer,HML)was formed.The age of the HML stands for the final closing age of the residual sea basin.The HML is well outcropped in Yadong,southern Tibet,China,which was named as the Zhepure Formation.Based on the detailed analysis and study on the calcareous algal fossils from the East Ria Section,Duina,Yadong,27 species of 18 genera have been identified and three assemblages have been recognized from the Zhepure Formation,which in ascending are as follows:1 Jania denotata-Amphiroa iraquensis assemblage,2 Ovulites margaritula-Fucoporella diploporaassemblage,3 Lithoporella melobesioides-Polygonella minima assemblage.Based on the study of the characteristics of calcareous algal assemblages,it is referred that during the Eocene the Duina region should be located in a shallow shelf environment with a water depth less than 30 m.