藏南地区关键层位地层柱状图

藏南地区的古近系海相地层发育较好，含丰富的有孔虫和其他海相生物化石。基于对西特提斯域内（主要为地中海地区）大有孔虫分类学和地层学的研究，西方学者们在1998年建立了古新统—始新统大有孔虫生物地层。与位于东特提斯域内西藏相比，地中海地区古新世的大有孔虫发育相对较差。因而，基于西特提斯大有孔虫建立的生物地层精度较低。本次研究对藏南古汝地区下古近系碳酸盐岩沉积地层进行详细的剖面测量和高密度样品采集，在大有孔虫分类学研究的基础上，补充、完善藏南地区大有孔虫生物地层；在生物地层学的基础上，结合碳同位素地层建立高分辨率的年代地层格架。
本次研究共实测7条剖面，剖面位置处于东经89°11′~89°13′，北纬28°3′~28°7′之间；高程范围为4643~5380 m。经实验室内岩石薄片观察，对所测地层时代进行了初步判断。P2剖面为覆于晚白垩系地层之上的灰岩层序，代表了研究区最早古新世的沉积；P1剖面为一套下古新统巨厚灰岩沉积；E2剖面为古新统顶部，接近古新统/始新统界线；E1、E3、E3s和E4剖面的时代大致为始新世早期；E4剖面顶部的灰绿色泥灰岩和红色泥页岩代表了研究区最晚的海相地层。
我们计划对这些剖面中的有孔虫进行详细的分类学和地层学研究，建立高分辨率的大有孔虫生物地层；同时，我们还要分析大有孔虫组分和丰度上的变化，进一步探讨大有孔虫在早古近纪的演化过程。对于剖面中的砂岩地层，我们要进行碎屑锆石U-Pb同位素分析，所获得的年龄与生物地层学数据相互印证，并进一步探讨印度—欧亚大陆碰撞影响下的古地理演化过程。

The Paleogene marine strata in southern Tibet are well-developed and contain abundant foraminifera and other marine fossil organisms. Based on taxonomic and stratigraphic studies of larger benthic foraminifera in the Western Tethys Domain (mainly the Mediterranean region), Western scholars established the Paleocene-Eocene larger benthic foraminiferal biostratigraphy in 1998. Compared with Tibet in the Eastern Tethys Domain, the Paleocene larger benthic foraminifera in the Mediterranean region are relatively poorly developed. Consequently, the biostratigraphy established based on Western Tethyan larger benthic foraminifera has low resolution. This study conducted detailed section measurements and high-density sampling on the lower Paleogene carbonate sedimentary strata in the Guru area of southern Tibet. Based on taxonomic research of larger benthic foraminifera, we supplemented and improved the larger benthic foraminiferal biostratigraphy in southern Tibet; on the basis of biostratigraphy, we established a high-resolution chronostratigraphic framework combined with carbon isotope stratigraphy.

A total of 7 measured sections were included in this study, located between 89°11′–89°13′ E longitude and 28°3′–28°7′ N latitude, with an elevation range of 4643–5380 m. Through laboratory thin section observation, a preliminary judgment was made on the age of the measured strata. Section P2 is a limestone sequence overlying the Upper Cretaceous strata, representing the earliest Paleocene deposits in the study area; Section P1 is a set of thick lower Paleocene limestone deposits; Section E2 is at the top of the Paleocene, close to the Paleocene/Eocene boundary; Sections E1, E3, E3s, and E4 are roughly of early Eocene age; the gray-green marl and red mud shale at the top of Section E4 represent the youngest marine strata in the study area.

We plan to conduct detailed taxonomic and stratigraphic studies of foraminifera in these sections to establish a high-resolution larger benthic foraminiferal biostratigraphy; meanwhile, we will analyze the changes in the composition and abundance of larger benthic foraminifera to further explore the evolutionary process of larger benthic foraminifera during the early Paleogene. For the sandstone strata in the sections, we will perform detrital zircon U-Pb isotopic analysis, and the obtained ages will mutually corroborate the biostratigraphic data to further discuss the paleogeographic evolution under the influence of the India-Eurasia collision.