中国海相烃源岩发育控制因素

Development constraints of marine source rocks in China.

烃源岩的形成取决于生烃母质生物的生存环境和有机质良好的保存条件,这两大因素从根本上来说又取决于生物繁殖时和埋藏时的古气候、古洋流、古构造及古环境等各要素的良好匹配。海相高有机质丰度烃源岩的形成与大气中的中等含氧量、干热的气候、冰期-冰后期之交的气温快速转暖、冰川迅速融化所导致的海平面快速上升等密切相关。大洋环流的形成和演变也是控制海相高有机质丰度烃源岩形成的主要因素,上升洋流富磷、富硅、富铁族元素等营养盐和富绿硫细菌极大地促进了有机质生产力、埋藏率的激增。通过研究,建立了中国华南和塔里木盆地寒武系上升洋流分布模式、塔里木盆地上奥陶统良里塔格组台缘斜坡灰泥丘相源岩形成时的反气旋洋流分布模式。研究发现,优质烃源岩仅发育于被动大陆边缘背景下的裂谷、克拉通内裂谷、克拉通内坳陷盆地和克拉通边缘坳陷盆地。欠补偿盆地、蒸发潟湖、台缘斜坡(灰泥丘)和半闭塞—闭塞欠补偿海湾,是高丰度烃源岩发育的有利环境;低的无机物输入和低的沉积速率,有利于高有机质丰度烃源岩形成;呈斜坡的海底地貌,有利于烃源岩形成。

The formation of source rocks is largely dependent on the nature of organisms from which kerogen is derived and the preservation conditions of organic matter, which are fundamentally dependent on a favourable combination of various elements in which organisms live and are subsequently buried. These elements include climate, oceanic currents, structure and environmental conditions. The formation of marine organic-rich source rocks is closely related to the oxygen content in the atmosphere, xerothermic climate, and the rapid rise of sea level caused by a rapid increase of temperatures and melting of glaciers, between a glacial age and a postglacial age. The formation and evolution of oceanic currents are considered as another important factor that controls the formation of marine organic-rich source rocks. The upwelling of waters rich in green-sulfur bacteria and elements, such as phosphorus, silicon and ferrous compounds, can greatly accelerate the productivity and burial rate of organic matter. A distribution model of the Cambrian upwelling in South China and Tarim Basin and a distribution model of anticyclone oceanic currents during the formation of the lime-mud mound source rock on the mesa-marginal slope of the Upper Ordovician Lianglitage Formation in Tarim Basin are proposed. These studies show that high-quality source rocks can develop only in rift valleys in passive continental margin, intracratonic rift valleys, intracratonic sag basins and sag basins at the cratonic margin. In addition, a favorable environment for the development of organic-rich source rocks also includes undereompensation basins, evaporire lagoons, mesa-marginal slopes （lime-mud mound） and semi-blocked or blocked undercompensation bays. Moreover, a low input of inorganic matter and a low depositional rate are of great advantage to the formation of organic-rich source rocks, and the slope seabed landform favors the formation of source rocks.