藏南亚东堆纳地区古近纪钙藻化石与沉积环境
Paleogene Calcareous Algae and Sedimentary Environment in Tüna Area of Yadong in Southern Tibet

摘要： 西藏南部发育着连续的海相古近纪地层,亚东地区是特提斯演化晚期残留海的居留地,保存着西藏最年轻的海相沉积(即最高海相层)，其时代标志着残留海盆消亡的时间。研究最高海相层可以为东特提斯晚期演化及其封闭时限提供良好信息。亚东堆纳地区古鲁浦剖面宗浦组顶部和遮普惹组含有较丰富的钙藻化石，本研究鉴定出红藻门珊瑚藻科7属11种(含3个未定种)，绿藻门粗枝藻科4属4种(含1个未定种)及松藻科1属1种，据其分布特征划分出3个化石组合，自下而上分别为： Lithoporella melobesioidesLithophyllum carpathicum、Lithoporella melobesioidesOvulites margaritula、Distichoplex biserialisJania denotata组合。推测堆纳地区在晚古新世至始新世时期总体处于浅海陆棚环境，海水逐渐变浅，在始新世晚期海水深度可能已不足30 m。
Abstract: Continuous Paleogene marine deposits are outcropped in southern Tibet. Yadong area in southern Tibet was once located in the Tethyan residence sea basin and developed the youngest wellexposed marine sediments (the highest marine layer, HML). The age of the HML stands for the final closing age of the residual basin. The study on HML in this area can provide direct information about the late evolutionary history and the closing age of eastern Tethys. Based on the detailed analysis on the calcareous algae fossils from the Gulupu section in Tüna of Yadong area, eleven species of seven genus of Corallinaceae, four species of four genus of Dasycladaceae, one species of one genus of Codiaceae have been identified and three assemblages have been recognized from the Zongpu Formation and Zhepure Formation, which are ranked from bottom to up as follows: Lithoporella melobesioidesLithophyllum carpathicum assemblage, Lithoporella melobesioidesOvulites margaritula assemblage, Distichoplex biserialisJania denotata assemblage. Based on the study of the characteristics of calcareous algae fossil assemblages, it is inferred that during Late Paleocene to Eocene Tüna region should be located in a shallow shelf environment and the depth of sea water might gradually decrease to be less than 30 m until Late Eocene