川东嘉陵江组-雷口坡组层序岩相古地理

The sequence-based lithofacies-paleogeography of Jialingjiang Formation and Leikoupo Formation in eastern Sichuan Basin,China

以层序岩相古地理编图思路为指导,对川东地区下三叠统嘉陵江组和中三叠统雷口坡组进行层序地层学和岩相古地理研究。嘉陵江组划分为2个三级层序(TSQ1,TSQ2),雷口坡组划分为1个三级层序(TSQ3)。以三级层序体系域或三级层序为编图单元,编制5张层序岩相古地理图:TSQ1的TST主要为开阔台地相灰岩沉积,HST为局限台地相膏岩、膏质白云岩、泥质白云岩等沉积,反映水体变浅、蒸发的古地理格局;TSQ2的TST同样为开阔台地相灰岩沉积,HST水体变浅,区内以沉积膏岩、白云质膏岩、泥质白云岩等为特征;受江南古陆隆升扩大影响,TSQ3发育不完整,缺失上部地层,由东往西,表现出由陆源碎屑岩到碳酸盐岩的沉积格局,沉积环境由有障壁海岸到局限台地的过渡。海平面的升降变化是层序发育、古地理演化的主要控制因素。

Based on the method of studies the sequence stratigraphy sequence-based lithofacies-paleogeography mapping, this paper and lithofacies-paleogeography of Lower Triassic Leikoupo Formation and Middle Triassic Jialingjiang Formation in eastern Sichuan Basin. The Jialingjiang Formation is divided into two sequences （TSQ1, TSQ2）, and the Leikoupo Formation into one sequence （TSQ3）. Taking the system tract or sequence as the mapping unit, 5 maps of sequence- based lithofacies paleogeography are drawn from Jialingjiang Formation to Leikoupo Formation in eastern Sichuan Basin. In TST of TSQ1 there mainly deposits limestone of open platform and in HST of TSQ1 there deposits in restricted platform facies gypsolith, gypsum-dolomite and pelitic-dolomite, showing the sea level falling and the evaporated environment in eastern Sichuan basin. In TST of TSQ2 there also deposits limestone of open platform. Then, with the water body shoaling, there deposits gypsolith, gypsum dolomite and pelitic-dolomite of restricted platform in HST of TSQ2. With the Jiangnan old land enlarging, TSQ3 is incomplete and the upper stratum is absent. From east to west, in TSQ3 there deposits clastic rock to the carbonate and the beach-barrier coast to restricted platform in sedimentary environment. The most important factor of controlling sequence filling and paleogeography evolvement is the sea level fluctuation.