藏南岗巴—定日地区始新世微体化石与特提斯的消亡

印度与亚洲板块之间的碰撞也许是自中生代末期以来所发生的意义最为深远的构造事件 ,但目前对于碰撞的起始时间尤其是陆间海相沉积最终消亡的时间的把握仍十分不确定。西藏特提斯晚期演化史的研究及其封闭时间的确定 ,可为印度与亚洲碰撞发生过程的研究提供极为重要的直接性的依据。藏南地区发育着西藏地区最晚期的海相沉积 ,岗巴—定日地区曾是西藏特提斯演化晚期——残留海盆的居留地 ,可提供关于西藏特提斯演化晚期及其最终封闭时间的良好信息。对岗巴—定日地区内始新世地层剖面作了极为详细的研究工作 ,发现并鉴定了数量较为丰富的微体化石 ,在此基础上对西藏特提斯晚期沉积环境的演变进行了较为详细的分析 ,认为岗巴地区遮普惹组砂页岩段的时代与定日遮普惹组砂页岩段的时代相同或略晚于后者 ,两者基本上属同期异相沉积 ,含相同的浮游有孔虫 Morozovella spinulosa- Acarinina bullbrooki组合 ;藏南最高海相层——遮普惹组砂页岩段顶部的时代应为晚始新世 Priabonian早期 ,它代表着西藏—特提斯海在藏南最终消亡的时间。

EOCENE MICROFOSSILS IN SOUTHERN TIBET AND THE FINAL CLOSING OF THE TIBET-TETHYS

The collision of India with Asia has been perhaps the most profound tectonic event since the end of the Mesozoic Era. The age of initiation of this collision,however, particularly the age of the latest marine deposits, remains uncertain. Study on the late evolutionary history and final closing age of the Tibet-Tethys can provide direct and basic data for the explanation of the process of collision between India and Asia. The youngest marine strata are exposed in the Gamba-Tingri area of southern Tibet, which was a remnant marine basin during the late evolution of Tibet-Tethys. The study on this area may provide good information about the late evolutionary history and closing age of the Tibet-Tethys remnant sea.In this work, a great number of microfossils have been found and identified. Study on the microfossils (especially planktonic foraminifera) indicates: (1) the youngest marine bed in Tibet is represented by the top of the Sandstone-shale Member of the Zhepure Formation that occurs in the Zongpuxi Section of the Gamba area, and is of the early Late Eocene age. The age stands for the final closing of the Tibet-Tethys; (2) The age of the youngest marine bed in Gamba is correlative with, or more or less younger than that of the Tingri region. Both are referred to early Priabonian.