川北—川东地区中二叠世晚期地层划分新认识及地质意义

四川盆地中二叠统茅口组具有良好的勘探前景，但目前对川北—川东地区茅口晚期地层划分及相关地质认识存在不足。基于120口井的测井资料分析，并结合3条野外剖面的实测情况，重新识别了川北—川东地区茅口组与吴家坪组界面，进一步明确了茅口晚期沉积格局。取得以下3点认识:（1）自然伽马能谱测井可以有效识别茅口组上部硅质沉积物和吴家坪组底部泥页岩，依据新的地层划分方案，茅口组LHST2段（茅二a亚段—茅三段）尖灭线向东大幅推移至开县附近。（2）构造沉降控制了茅口晚期地层向东减薄和沉积演化。（3）茅口晚期沉积相由碳酸盐岩均斜缓坡相逐渐变为远端变陡缓坡相，最终演化为弱镶边台地相；远端变陡缓坡相控制了茅口组白云岩和硅质沉积物形成，弱镶边台地相控制了茅口组川北台缘带形成。 

Geological significance of late Mid-Permian stratigraphy in northern and eastern Sichuan Basin,SW China

The Mid-Permian Maokou Formation in the Sichuan Basin shows good petroleum prospectivity.However,knowledge of the stratigraphy in the northern and eastern Sichuan Basin during the late Maokou period are still unclear.The interface between the Maokou and Wujiaping formations was re-identified,and the sedimentary pattern in the study area during the late Maokou period was clarified based on the logging data from 120 wells combined with the measured data of three field profiles.The results suggest the following.(1)Natural gamma-ray spectral logging can effectively identify the siliceous sediments at the top of Maokou Formation and the mud shale at the bottom of Wujiaping Formation.According to a new stratigraphic division,the erosional edge on LHST2 section of Maokou Formation moved eastward to the Kaixian area.(2)Tectonic subsidence controlled the eastward thinning and the sedimentary evolution in the late Maokou period.(3)The sedimentary evolution in the late Maokou period was from the homoclinal carbonate ramp facies to the distal steepening ramp facies,and then to the weak rimmed platform facies.Distal steepening ramp facies controlled the formation of dolomite and siliceous sediments,while the weak rimmed platform facies controlled the formation of the platform margin.