下扬子区印支期后构造演化与有利勘探区预测

通过恢复下扬子区白垩纪末期与古近纪末期的剥蚀厚度及分析印支不整合面Tg0的最大埋深,结合古地温条件得出下扬子区中生界、古生界均发生过晚期生烃和成藏。白垩纪末期,黄桥、句容和无为地区最大剥蚀厚度分别为1 000m、1 500 m和800 m。古近纪末期,黄桥地区最大剥蚀厚度约450 m,句容和无为地区无剥蚀。在3.3℃/100 m～4℃/100 m的古地温梯度下,白垩纪末期,无为地区约70%面积的二叠系—下三叠统烃源岩埋深达到2 000～4 000 m,进入生油阶段,但未进入生气阶段;句容地区二叠系—下三叠统烃源岩几乎全部进入生油阶段,次凹区进入了4 000 m以下的生气阶段;黄桥地区约70%面积的二叠系—下三叠统烃源岩进入生油阶段,主要位于北部深凹区和西部次凹区,凹陷深处烃源岩进入生气阶段。印支不整合面Tg0自白垩纪末期油气生成以来的多个古鼻凸轴线指示了油气运移路径、方向和聚集区,从喜山期至今的迁移变化指示了有利勘探区。

Tectonic Evolution and Prediction of Favorable Prospecting Area after the Indosinian Stage in Lower Yangtze Region

By recovery of erosion thickness of the latest Cretaceous and the latest Paleogene and the analysis of the maximum depth of Indosinian unconformity Tg0,it is suggested that the Paleozoic-Mesozoic hydrocarbon source rock have occurred late hydrocarbon generation and accumulation.In the latest Cretaceous,the largest erosion thicknesses of Huangqiao,Jurong and Wuwei areas are 1,000 m,1,500 m and 800 m.In the latest Paleogene,the largest erosion thickness of Huangqiao area is about 450 m,but Jurong and Wuwei areas are not denuded.Under the paleo-geothermal gradient of 3.3 ℃/100 m to 4 ℃/100 m,in the latest Cretaceous,the depths of about 70% Permian-Lower Triassic hydrocarbon source rocks are 2,000 m to 4,000 m and have entered the oil generation stage under the gas generation stage in Wuwei area;Almost all the Permian-Lower Triassic hydrocarbon source rocks have entered the oil generation stage in Jurong area,and its sub-sag region with depth below 4,000 m entering the gas generation stage;In Huangqiao area,about 70% Permian-Lower Triassic source rocks reach the oil generation stage,mainly in northern deep depression and western sub-depression,and its deep parts have entered the gas generation stage.Many ancient nose uplift axises in Indosinian unconformity Tg0 since the latest Cretaceous hydrocarbon generation indicate the hydrocarbon migration paths,directions and accumulation areas,and their changes from Himalayan to the present indicate favorable prospecting areas.