川西北地区下寒武统龙王庙组构造-沉积演化特征

Characteristics of tectonic-sedimentary evolution of the Lower Cambrian Longwangmiao Formation in the northwestern Sichuan Basin

在前人研究的基础上,根据野外剖面、钻井岩心、显微薄片、扫描电镜及测井等资料,对川西北地区下寒武统龙王庙组构造-沉积演化特征进行综合研究。结果表明:研究区总体为一套台地相碳酸盐岩沉积,岩性以泥-粉晶白云岩、泥晶白云岩为主。在纵向上,自下而上可将龙王庙组划分为3段,且发育多期次海进-海退沉积旋回,并由海向陆缓慢过渡;横向上,研究区自西向东以发育混积潮坪相和局限台地相为主。在晚震旦世克拉通内裂陷“两隆夹一凹”的沉积格局、川中古隆起及沧浪铺组沉积期构造挤压活动的影响下,逐渐形成西北高、东南低的古地貌格局,在继承沧浪铺组陆源滨岸沉积体系的基础上,使得龙王庙组最终形成了以“潮坪+台内滩”这种特殊的构造-沉积格局。

Analyses of field profiles,well drilling cores,thin sections,scanning electron microscope and logging data are carried out in order to study the tectonic-sedimentary evolution characteristics of the Lower Cambrian Longwangmiao Formation in northwest Sichuan.The results show that the study area as a whole is a set of platform facies carbonate deposits composed of mainly argillaceous-powder dolomite and micrite dolomite.Comparison of drilling cores of Longwangmiao Formation reveals that the Longwangmiao Formation can divide into three sections from the bottom to the top,with development of multiple transgression and regression sedimentary cycles and with slow transition from sea to land.In the horizontal direction,the study area mainly develops mixed tidal flat facies and limited platform facies from west to east.It is considered that the sedimentary framework of two uplifts sandwiched with one depression in the late Sinian craton rifting,the middle Sichuan uplift and the tectonic compression activity in the Canglangpu sedimentary period bring about the paleogeomorphic pattern of high in the northwest and low in the southeast.Based on inheriting the continental source shoreline sedimentary system of Canglangpu Formation,the Longwangmiao Formation finally formed a special structural-sedimentary pattern of“tidal flat+inner platform beach”.