塔里木盆地奥陶纪中晚期碳酸盐岩高精度碳同位素地层学研究

Ordovician is the key transition time in geological time, and marine paleoenvironment also change strongly during the time, however carbon isotope stratigraphy of marine carbonates can record these changes directly. Ordovicin marine carbonate rocks recorded seven obvious carbon excursion events: MDICE，GICE，HICE，Kope, Fairview，Waynesvill and Whitewater. Previous international studies on Ordovician carbon isotope mainly focused on Yangtz Block, however Tarim Block data are very rare. The seven carbon excursion events are various in different blocks in the world. In this study, we try to use many samples from outcrops, drilling cores and rock debris to obtain high-resolution carbon isotope curve, and to discriminate these carbon excursion events from the global records. Middle-late Ordovician carbonate rocks are importan reservoirs in Tarim Basin, so carbon isotope stratigraphy correlations underearth in drilling wells can helps to verify the accurate oil reservoir horizons.

奥陶纪是生物辐射的重要时期，该时期海洋的古环境也发生了强烈的波动，而海相碳酸盐岩的碳同位素地层可以直接记录这些波动。奥陶纪中晚期有7次显著的碳同位素漂移事件，即MDICE，GICE，HICE，Kope, Fairview，Waynesville和Whitewater等。之前国际上对中国奥陶纪海相碳同位素研究，基本集中在扬子板块，而塔里木板块的研究十分稀少。奥陶纪7次显著的碳同位素漂移事件，细节上在全球各板块之间表现有所差异。本次研究准备对塔里木板块奥陶纪中晚期的露头和井下剖面进行高密度采样与测试，在国际上首次取得该板块奥陶纪中晚期高精度碳同位素曲线，识别出该时期的碳同位素波动与全球事件的响应。塔里木板块奥陶纪中-晚期碳酸盐岩是重要的储层，高精度的碳同位素地层的划分，可以帮助进行井下碳酸盐岩地层划分，指示准确的含油气层位。

项目承担人通过对塔里木盆地奥陶纪中晚期的露头和井下剖面进行高密度采样与测试，取得该盆地奥陶纪中晚期高精度碳同位素曲线，识别出该时期的碳同位素波动与重要事件的响应，开展了该层位精细地层划分对比。塔里木板块奥陶纪中-晚期碳酸盐岩是油气赋存的重要储层，高精度的碳同位素地层的划分，为准确识别和对比含油气层提供了依据。此外，通过奥陶纪牙形石文献总结，将华北、华南及波罗的、北美等地奥陶系牙形石带进行细致对比，建立了塔里木盆地奥陶系台地到斜坡相区牙形石化石带序列及与华北、华南及波罗的、北美等地奥陶系牙形石化石带序列对比关系。同时对碳酸盐岩地层中夹杂的燧石团块进行微体化石的研究，从中发现了疑源类以及丝状蓝藻等有机壁微体化石，印证了碳酸盐岩碳同位素地层研究的可靠性，并解释了奥陶纪时期烃源岩的生物来源。