藏南白垩纪中期大洋缺氧事件OAE1a的记录与成因研究

白垩纪中期OAE1a被认为是全球性大洋缺氧事件之一，期间全球古气候和古海洋条件发生了重大改变，对于认识古海洋演化和理解未来全球变化具有重要意义。目前，国际上缺乏对东特提斯洋OAE1a的研究，原因在于在东特提斯地区地层中没有找到该事件的地质记录。项目在前期研究，用菊石带和碳同位素曲线限定了西藏南部含OAE1a事件的海相地层，并在紧邻OAE1a的下伏地层发现了自生碳酸盐岩结核层，其形态、构造和碳同位素特征与甲烷释放成因的冷泉碳酸盐岩相似，预示着OAE1a之前东特提斯地区发生过甲烷释放事件。本项目拟通过地层学、沉积学、元素地球化学、同位素地球化学等多学科手段，确定OAE1a事件的精确地层位置，查明其沉积、地球化学等地质特征，恢复OAE1a期间东特提斯地区古海洋条件。结合该地区Aptian期地层中新发现的自生碳酸盐岩结的研究，查明OAE1a事件与甲烷释放事件之间的关系，探讨OAE1a形成机制。

The Early Aptian OAE1a is one of global anoxic events. The paleoclimatic and paleoceanographic conditions profoundly changed during the event. It provides a window to study the paleoceanography and an analogue for the future researches on global changes. The OAE1a in the eastern Tethys Ocean has not been studied it, because the sedimentary record was not found in in this area. Based on previous study of ammonites and carbon isotope curve, we found the stratigraphic record of OAE1a in Tethyan Himalaya tectonic zone. Furthermore, we found a limestone bed composed of authigenic carbonate concretions is immediately overlain by the OAE1a interval. The morphology, sturcture and the carbon isotope values are very similar to the methane-derived cool seep carbonates, which implies a large amount of methane were released to the ocean and atmosphere before the OAE1a. Based on the studies of stratigraphy, sedimentology, elementary geochemistry and isotope geochemistry, this project aims on: the stratigraphic and sedimentary characteristics of OAE1a in eastern Tethys, reconstruction of paleoceanogrphic conditions. By studying on the relationship between methane releasing and the OAE1a, the project will unravel the controlling factors to the formation of OAE1a.