Depositional systems and evolution of the Upper Carboniferous Huanglong Formation in the eastern Sichuan Basin

New research on basic geology has been done for Upper Carboniferous carbonate lithologic gas pools in the Huanglong Formation in the eastern Sichuan Basin. Based on the development characteristics of terrigenous clastic deposit and the development location of suspending gravels with some psephicity, the transgression direction and tidal depositional system distribution are deduced. It is believed that, two transgression channels were developed in southeast of Yunyang and northwest of Dazhou in the area, two tidal-flat depositional systems in Chongqing-Wanzhou and southeast of Dazhou respectively were formed, and a suit of complete type-I sequence composed of lowstand systems tract (C2h1), transgressive systems tract (C2h2) and early highstand systems tract (C2h3) was developed. Sedimentary microfacies features of each member of the Huanglong Formation were delineated finely. In the middle stage of late Carboniferous, transgressive systems tract was developed in eastern Sichuan, where shallow shoal and algal dolomite-flat microfacies were developed, which are favorable for the development of carbonate lithologic traps. In contrast, in the early and late stages of late Carboniferous, lowstand systems tract and highstand systems tract were developed, respectively, where shallow shoal microfacies were poorly developed, which limited the large scale development of carbonate lithologic traps.

摘要：以川东上石炭统黄龙组碳酸盐岩岩性地层气藏为目标，开展新一轮系统基础地质研究。根据陆源碎屑沉积发育特点与悬浮且具有一定磨圆度砾石的发育位置推断海侵方向与潮汐沉积体系分布，认为上石炭统黄龙组发育云阳东南部与达州西北部两个海侵通道，并形成了重庆—万州与达州东南部两个潮坪沉积体系，发育了一套由低水位体系域（C2h1）—海进体系域（C2h2）—早期高水位体系域（C2h3）组成的较完整的I型层序。精细刻画黄龙组各段沉积微相分布特征，川东晚石炭世中期为海进体系域发育期，浅滩与藻云坪微相较发育，有利于碳酸盐岩岩性圈闭的形成；晚石炭世早期与晚期分别为低位体系域与高位体系域发育期，其浅滩沉积微相发育局限，不利于碳酸盐岩岩性圈闭的规模形成。图7参17