川北及川西北地区早寒武世物源及古地理响应OA

The Early Cambrian sedimentary successions in northern and northwestern Sichuan Basin record critical information on the differential evolution of multiple provenance systems along the northwestern margin of the Yangtze Block.This study focuses on Lower Cambrian outcrop sections in the Guangyuan-Beichuan area(northwestern Sichuan)and the Nanjiang-Wangcang area(northern Si-chuan).Through integrated sedimentological analyses including heavy mineral identification,lithic fragment composition statistics,cathodoluminescence(CL)imaging of detrital zircons,and palaeocurrent measurements,a systematic provenance tracing and palaeogeographic reconstruction were conducted.The results indicate that:(1)Three major source areas existed during the Early Cambrian in the study area-the Motianling,Pengguan,and Hannan provenances-which differ significantly in formation age,tectonic affinity,and parent rock lithology.(2)In northwestern Sichuan Basin,controlled by Palaeo-Tethyan subduction,the Motianling provenance continuously supplied felsic igneous and siliceous rock detritus,whereas the Pengguan provenance first emerged as a submarine high during the second member of the Qiongzhusi Formation and evolved into an exposed volcanic island arc by the Canglangpu stage,predominantly supplying mafic igneous(basaltic)detritus.(3)In northern Sichuan Basin,influenced by the Proto-Qinling Ocean,the Hannan provenance exhibited episodic evolution:during deposition of the Qiongzhusi Formation through the first member of the Canglangpu Formation(Xianfengdong Formation),it remained submerged and oolitic limestones developed in the northern Sichuan area;during the second member of the Canglangpu Formation(Yanwangbian Formation),it became subaerially exposed,forming alluvial fan-fan delta coarse clastic deposits.(4)By the late Canglangpu stage,all three source areas were exposed simultaneously,resulting in a palaeogeographic differentiation pattern characterized by sustained clastic infilling in northwestern Sichuan and a tripartite sedimentary response in northern Sichuan.This study provides new sedimentological evidence for multi-plate interactions along the northwestern margin of the Yangtze Block during the Early Cambrian.