川西前陆盆地侏罗系沉积体系变迁及演化模式

川西前陆盆地侏罗系整体气候炎热、干旱,受板块差异挤压的影响,周围山体继承性隆升,前渊坳陷不断发生迁移。构造作用控制物源区迁移,进一步分配了不同时期沉积体系的展布。通过大量野外露头、测-录井、岩心和分析化验资料,阐明了川西前陆盆地物源特征及沉积体系变迁,以塔里木盆地北缘现代沉积为启示,建立了川西前陆盆地沉积演化模式。结果表明:①这一时期,研究区主要发育2种类型沉积体系,分别为早侏罗世的冲积扇-河流-正常三角洲-湖泊沉积体系和中-晚侏罗世的冲积扇-河流-浅水三角洲-湖泊沉积体系;②早侏罗世,前陆盆地的前渊坳陷位于米仓山山前,短轴方向的龙门山主体是研究区的主要物源区;中侏罗世,前陆盆地的前渊坳陷转移到大巴山山前,长轴方向的大巴山和短轴方向龙门山主体共同为研究区供源;晚侏罗世,前陆盆地的前渊坳陷再次转移到龙门山北段山前,长轴方向的龙门山北段和短轴方向龙门山主体共同为研究区供源;③证实了"长轴短轴共存,近源远源汇砂"的物源分布特征,建立了2种川西侏罗纪前陆盆地沉积演化模式,分别为早侏罗世的再生前陆盆地大盆深湖模式和中-晚侏罗世的再生前陆盆地大盆小湖模式。

Jurassic sedimentary system transition and evolution model in Western Sichuan Foreland Basin

During Jurassic sedimentary period, the climate of Western Sichuan Foreland Basin was hot and arid. Influenced by differential squeezing of the plates, surrounding mountains uplifted successively, and foredeep depression migrated continuously. Tectonism was able to control the migration of provenance area, further determining the distribution of sedimentary system in different periods. Based on a large number of field outcrop, logging, core and assay data, this study illustrates the provenance characteristics and sedimentary system transition of Western Sichuan Foreland Basin. Meanwhile, the sedimentary evolution model of Western Sichuan Foreland Basin is established by gaining enlightenment from the modern sedimentation on the northern margin of Tarim Basin. The results show that:(1) in this period, two types of sedimentary systems were primarily developed in the study area, i.e., Early Jurassic alluvial fan-fluvio-normal delta-lake sedimentary system and Mid-Late Jurassic alluvial fan-fluvio-shallow delta-lake sedimentary system. (2) In the Early Jurassic, the foredeep depression of Foreland Basin was located in front of Micang mountain, where Longmen mountain massif in the short axis acted as the main provenance area; in the Middle Jurassic, the foredeep depression of Foreland Basin migrated to the front of Daba mountain, where Daba mountain in the long axis and Longmen mountain massif in the short axis were major provenance areas of the study area; in the Late Jurassic, the foredeep depression of Foreland Basin migrated to the front of the northern segment of Longmen mountain again, where the northern segment of Longmen mountain in the long axis and Longmen mountain massif in the short axis were major provenance areas of the study area. (3) The provenance distribution characteristics, i. e., "coexistence of long axis and short axis, sand convergence of near source and far source", were confirmed. On this basis, this study establishes two Jurassic sedimentary evolution models of Western Sichuan Foreland Basin, i. e., large basin-deep lake model in the Early Jurassic rejuvenated foreland basin and large basin-small lake model in the Mid-Late Jurassic rejuvenated foreland basin.