西藏南部古近纪放射虫研究进展

Advance Research of Paleogene Radiolarian in Southern Tibet

西藏南部的雅鲁藏布江缝合带及其相邻南部的沉积地层带中发育大量含有古近纪放射虫的地层。这些放射虫化石的研究,在解释缝合带复杂的地层层序、古海洋盆地演化以及揭示特提斯洋最终关闭及印-亚板块全面碰撞时间、过程等方面,可提供主要的微体古生物学证据。根据近10年已发表的文献、西藏南部1∶25万地质填图资料和我们正在研究的初步成果显示,西藏南部含古近纪放射虫地层的时代为古新世至始新世晚期。放射虫产于蹬岗组、桑单林组、者雅组、郭雅拉组和盐多组中,或者发育于泥砂质混杂岩、玄武(蛇绿)质混杂岩中的硅质岩、硅质泥岩(块)中。尽管西藏南部古近纪放射虫研究已取得一些成果,但系统的放射虫研究与地层或混杂岩研究仍然有待系统深入开展。

Paleogene radiolarian-bearing strata are wide-spread in southern Tibet.They belong to the Yarlung Zangbo suture and stratigraphic belt immediately to its south which is referred to as the ＂Tethyan Himalayan subprovince＂.The radiolarian provides important micropaleontological evidence in determining stratigraphic sequence,interpreting evolution of the oceanic basins,revealing the final Tethys closing time and complete India-Asia colliding in the Early Cenozoic.According to the reported data,available 1：250 000 geological mapping documents and our investigation,Paleogene radiolarian in southern Tibet ranges from Early Paleocene to Late Eocene in age.Paleogene radiolarian-bearing sedimentary rocks include Denggang Formation,Sangdanlin Formation,Zheya Formation,Guoyala Formation,Yanduo Formation and chert or siliceous mudstone of sand-muddy and basaltic（ophiolite） melánge.A systematic study of Paleogene radiolarian and radiolarian-bearing stratigraphy or melánge in southern Tibet,is to be carried out.