【作者】 李兴鹏；

【导师】 李国彪；

【作者基本信息】 中国地质大学（北京） ， 古生物学与地层学， 2011， 硕士

【摘要】 古近纪为印度板块与亚洲板块碰撞、特提斯洋闭合的重要时期。西藏特提斯的消亡与青藏高原的形成是地球发展历史中的重大地质事件。本文选取西藏南部岗巴地区古近纪的经典剖面-宗浦剖面作为研究对象,利用生物地层学的方法进行探讨。本论文通过对宗浦剖面进行微体古生物(主要是底栖大有孔虫)地层学的精细研究,共鉴定出28属34种,对具体属种进行了详细的描述,并建立起该区古近纪有孔虫生物地层序列,把宗浦剖面划分为三个有孔虫化石组合带:Miscellanea–Lockhartia–Operculina组合带, Alveolina-Nummulites组合带, Orbitolites- Fascioites- Turborotalia组合带。并对古新世-始新世的界线(P/E)进行重新厘定,界线应当置于宗浦组与遮普惹组之间,即剖面第3层和第4层之间。以Miscellanea、Operculina两属分子和Lockhartia haimei Davies一属种的绝灭与Alveolina、Nummulites两属分子的大量出现为标志。此外,在岗巴宗浦剖面中的宗浦组与遮普惹组之间可见到一个明显的冲刷面,底部含底砾岩,夹粘土层,经研究这些底砾岩是遮普惹组下伏地层经剥蚀再沉积的产物。这可以作为此时海水突然变深及海底侵蚀或停积间断的证据,因此该界面是一海泛面,为平行不整合接触,无疑是古新世-始新世的天然界线。剖面的底栖大有孔虫在P/E界线附近呈现先灭绝、后复苏的演化特征,而界线上下岩性和沉积环境并未发生显著改变,联系在这一时期发生的全球增温事件(PETM事件),不难推断出致使出现这一现象的主要原因是PETM事件。根据P/E界线附近测得的碳氧同位素值分析,随着快到P/E界线δ13C出现负向偏移,最小峰值达到-8.5‰。其变化曲线与同一时期全球碳稳定同位素事件表现一致,进一步论证了P/E界线的位置;同时从地球化学的角度验证了PETM事件是造成该区底栖大有孔虫灭绝的主因。更多还原

【Abstract】 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.更多还原