Paleogene Biostratigraphy Of Foraminifera In Gamba Area, Southern Tibet

Paleogene is an important period when the Indian plate knocked against the Asian plate, and when Tethys closed. The demise of the Tibetan Tethys and the formation of the Tibetan Plateau are major geological events in the history of the Earth. This paper selects Gamba areas Paleogene classic profile in southern Tibet - Zongpu section as the research object, the use of biostratigraphy are discussed.This paper carried a meticulous study through Micropaleontology (mainly large benthic foraminifera) study of stratigraphy, 28 genera and 34 species are identified in all, the specific species were described in detail,in order to establish ancient Paleogene foraminifer stratigraphic sequence of this area , the Zongpu section were divided into three foraminiferal fossil Zone: Miscellanea–Lockhartia–Operculina Zone, Alveolina-Nummulites Zone, Orbitolites- Fascioites- Turborotalia Zone. And Paleocene-Eocene boundary (P/E) is re-determined, Boundary should be placed between in Zongpu Fm and Zhepure Fm, that section is between 3 layers and 4 layers. Extinction of the elements of Miscellanea, Operculina and Lockhartia haimei Davies and large numbers of Alveolina,Nummulites are marked. In addition, between Zongpu Fm and Zhepure Fm in Zongpu section ,Gamba can see an obvious erosion surface at the bottom with basal conglomerate, clay. After study the basal conglomerate is a product of the stratum under Zhepure Fm re-deposition by erosion. This can be evidence of at this time of seawater suddenly deep and submarine erosion or intermittent positive stop, so the interface is a flooding surface, is parallel to the unconformity, is undoubtedly a natural boundary of the Paleocene - Eocene.Large benthic foraminifera of the P/E boundary in the section is near extinction at first, after the evolution of the recovery, while the upper and lower boundaries of lithology and sedimentary environment did not change significantly, contact occurred during this period of global warming event ( PETM event), it is easy to infer the main reasons causing this phenomenon is the PETM event. According to P/E boundary of the value of the measured of carbon-oxygen isotope analysis, with the coming P/E boundaryδ13C negative to offset the minimum peak value of -8.5‰. The curve with the same period, the performance of the global carbon-oxygen isotope event the same, and further demonstrates the P/E boundary position; also verified from the geochemical point of view the area PETM event is caused by the main cause of extinction of large benthic foraminifera.