四川宣汉立石河剖面二叠系岩石特征及沉积环境分析

Petrological Characteristics and Sedimentary Environment of the Permian of Lishihe Section in Xuanhan,Sichuan

基干剖面分析是岩相古地理研究的基础,对于油气资源潜力分析具有重要意义。四川宣汉立石河剖面二叠系自下而上发育栖霞组、茅口组、吴家坪组及长兴组,总厚度为732.24m。该剖面化石类型丰富,发育藻类-有孔虫-腕足类组合及海绵骨针组合。岩石类型多样,以石灰岩为主,含少量的白云岩、硅岩及粉砂岩。其中,眼球状石灰岩主要分布于茅口组底部,是沉积、成岩共同作用的结果;白云岩以云斑石灰岩中的云斑和层状白云岩产出,两者分别为埋藏白云化、混合白云化的产物;硅岩主要分布于茅口组上部及吴家坪组,为交代成因,其硅质来源于热水、玄武岩淋滤及上升流等。综合分析认为本区二叠系为缓坡型碳酸盐岩台地沉积,发育滨岸沼泽、局限台地、开阔台地及盆地边缘4种沉积环境,二叠纪经历了栖霞组-茅口组、吴家坪组-长兴组沉积期的2次海侵-海退旋回。石油地质条件分析结果表明,本区二叠系具备良好的烃源岩条件和储集条件。

As the basis for lithofacies paleogeography studies, the analysis of fundamental geological pro- files is of great significance to oil and gas resources potential assessment. The Lishihe section in Xuanhan, Sichuan consists of Qixia Formation, Maokou Formation, Wujiaping Formation and Changxing Formation upwardly with the total thickness of 732.24 m. Rich in fossil types, this section has both algae-foraminif- era-brachiopods fossil assemblage and the sponge spicules assemblage. The major rock type is limestone, with minor dolomites, cherts and siltstones. The eyeball-shaped limestone is mainly distributed in the bot- tom of Maokou Formation, as a product of both sedimentation and diagenesis. The dolomites are mainly found in the dolomite limestones formed by burial dolomitization and layered dolomites by mixed-water do- lomitization. The cherts are distributed majorly in the upper Maokou Formation and the whole Wujiaping Formation, which are metasomatic originated, while the silicon comes from hydrotherm, basalt leaching and upwelling. According to the facies indicators, the study area should be a ramp carbonate platform en- vironment in the Permian, and contains four types of sedimentary facies：coastal marsh, restricted plat- form, open platform and platform margin. The study area experienced two transgressive-regressive cycles in the Permian,one during the Qixia Formation to Maokou Formation depositional period, and the other in Wujiaping Formation to Changxing Formation period. Analysis on the petroleum geological conditions of this area shows that the Permian rocks can provide good source rocks and reservoirs.