川中—川南过渡带雷口坡组台内滩组合特征

Structural characteristics of intra-platform shoal in the Leikoupo Formation(T_2) in the transitional zone of the central and southern Sichuan Basin

以四川盆地川中—川南过渡带中三叠统雷口坡组主力产层雷11亚段海相碳酸盐岩为研究对象,通过对钻井、录井、测井及岩心等大量资料的综合分析,研究台内滩结构特征、分布规律及其主控因素。研究区雷11亚段台内滩岩石类型主要包括亮晶鲕粒灰岩、残余鲕粒云岩,亮晶砂屑灰岩、残余砂屑云岩和亮晶砂屑云岩,亮晶生屑灰岩、残余生屑云岩及其过渡类型等,它们分别是构成鲕滩、砂屑滩、生屑滩的主要岩石类型。台内滩垂向上以发育向上变浅的沉积序列为特征,包括滩基、滩核和滩盖3个沉积单元;横向上具有明显的3分性,可分为滩核、滩缘、灰质滩间海3个微相。海平面升降变化引起的海水深度和水动力条件变化控制滩体的发育特征与叠置样式;隆坳分异的古地貌决定台内滩体的差异分布和横向组合特征。

Through comprehensive research on drilling, logging and core data of T2111 sub-member, which is the major pay of the Leikoupo Formation in the transitional zone of the central and southern Sichuan Basin, the structural characteristics, distribution regularity and its major controlling factors of intra-platform shoal are studied. The major rocks of intra-platform shoal in T2111 sub-member include oosparite, residual oolitic dolostone, sparrenite, residual doloarenite and sparry doloarenite, sparry bioclastic limestone and residual bioclastic dolostone, which constitute oolitic shoal, arene shoal and bioclastic shoal. The intra-platform shoal is characterized vertically by shallowing-upward sequences, and consists of three sedimentary units, namely bank base, bank core and bank cover. Besides, three microfacies can be distinguished laterally, bank core, bank edge and interbank sea. The variation of water depth and hydrodynamic conditions caused by sea level change control the characteristics and superposed pattern of shoal body. Meanwhile, the palaeogeomorphology with alternating uplifts and depressions defines the differential distribution and lateral combination pattern of intra-platform shoal body.