四川盆地东部须家河组物源—沉积格局与古地理演化

Provenance-sedimentary Pattern and Paleogeographic Evolution of the Xujiahe Formation in the Eastern Sichuan Basin

四川盆地东部须家河组是重要的油气勘探层系,但该时期区域内盆山耦合关系制约下物源—沉积格局的时空配置缺乏宏观认识制约了进一步的勘探与开发。在钻井和野外露头观察及二维地震测线资料的基础上,结合古水流、重矿物组合、稀土元素及碎屑锆石特征,系统开展了川东地区须家河组物源体系研究,阐明沉积体系的时空配置与盆山耦合关系,建立了周缘构造活动控制下的古地理演化过程。须家河组沉积时期共划分出北部米仓—大巴山构造带、东部江南—雪峰构造带、南部黔中古陆3个物源体系。主要为陆相碎屑岩沉积,发育辫状河三角洲—湖泊沉积体系。三角洲沉积体系在各时期均有发育,湖泊沉积体系主要发育在须三段中部地区,须五段迁移至西部。晚三叠世,扬子与华北板块俯冲发生碰撞造山运动,同时与华夏地块持续作用,使盆地北部米仓—大巴山构造带隆升且供源逐渐增强,江南—雪峰构造带持续供源。须三期米仓—大巴山构造带逐渐开始活动但供源较为局限,江南—雪峰造山带已广泛隆升接受剥蚀,沉积中心位于中部大竹和邻水等地。须四期—须五期构造作用加剧使得周缘物源区发生强烈隆升,盆内为多物源沉积,沉积中心较须三期向西迁移至广安和合川一带。须六期扬子地块持续向北俯冲,使米仓—大巴山构造带保持抬升并出露基底遭受剥蚀,砂体逐渐填平补齐,沉积中心相较于须四期—须五期继续向西迁移至潼南地区。重建川东地区须家河组沉积时期周缘构造带控制下的古地理演化对于该地区油气勘探具有重要的指导意义。

The Xujiahe Formation in the eastern Sichuan Basin is an important oil and gas exploration layer.However,the lack of macroscopic understanding of the temporal and spatial configuration of the provenance sedimentary pattern under the constraints of the basin-mountain coupling relationship has restricted further exploration and development.On the basis of drilling and field outcrop observation and two-dimensional seismic line data,combined with the characteristics of paleocurrent,heavy mineral assemblage,rare earth elements and detrital zircon,the paleogeographic evolution process under the control of peripheral tectonic activities was established.Three provenance systems were divided:the Micang-Dabashan tectonic belt,the Jiangnan-Xuefeng tectonic belt,and the Qianzhong ancient land.It is mainly continental clastic rock deposition and develops braided river delta-lake sedimentary system.The delta sedimentary system was developed in each period,and the lake sedimentary system was mainly developed in the middle area of the T3X3,and migrated to the west in the T3X5.In the late Triassic,the subduction of the Yangtze plate and the North China plate collided with the orogenic movement,which also interact with the Cathaysia block,so that the Micang-Dabashan tectonic belt uplifted and the supply gradually increased,and the Jiangnan-Xuefeng tectonic belt continued to supply.During the T3X3 period,the Micang-Dabashan tectonic belt gradually began to be active but its supply was limited.The Jiangnan-Xuefeng orogenic belt was widely uplifted and eroded.The sedimentary center was located in the central Dazhu and Linshui.During the T3X4-T3X5,the intensification of tectonic action caused the strong uplift of the surrounding provenance area.It was a multi-provenance deposit.The sedimentary center migrated westward to Guang'an and Hechuan areas.During the T3X6,the Yangtze block continued to subduct northward,so that the Micang-Dabashan tectonic belt remained uplifted and the exposed basement was eroded.The sand bodies were gradually filled up.The sedimentary center continued to migrate westward to Tongnan area.The reconstruction of the paleogeographic evolution under the control of the peripheral tectonic belt of the Xujiahe Formation provides important practical guiding significance for oil and gas exploration.