大别造山带北缘中-上侏罗统园筒山组沉积学研究

Sedimentary characteristics of Middle-Upper Jurassic Yuantongshan Formation on northern margin of Dabie orogenic belt

位于大别造山带北缘的安徽肥西地区,侏罗-白垩系地层发育,其中,中-上侏罗统园筒山组厚约1 170 m,主要为细粒碎屑岩;根据Miall的岩相分类,园筒山组有13种岩相,主要为Fl、Fm、Fr、Fsm、Sp、Sr、Ss、Sl,少量的是P、Frc、Sm、St和Sh;识别出5种主要沉积相,分别为点沙坝、洪泛平原、决口扇、滨湖和浅湖沉积;自下而上,园筒山组经历了从曲流河沉积—滨-浅湖沉积—曲流河沉积体系的演变,河流类型为高弯度细粒曲流河,属于冲积扇前端的冲积平原环境,这也揭示了在中-晚侏罗世,大别造山带作为物源区处于比较遥远的位置,同时也属于构造宁静阶段。

The Jurassic-Cretaceous stratum develops in Feixi area of Anhui Province,the north margin of the Dabie orogenic belt,where Middle-Upper Jurassic Yuantongshan Formation is about 1 170 m thick and mostly composed of fine detrital rocks.Based on Miall＇s classification of petrofacies,thirteen types of petrofacies are determined,which includes mainly Fl,Fm,Fr,Fsm,Sp,Sr,Ss and Sl,secondarily P,Frc,Sm,St and Sh,and five types of sedimentary facies are discriminated,which is comprised of point bar,floodplain,crevasse splay,shore and shallow lacustrine respectively.The deposit of Yuantongshan Formation goes through a bottom-up change from meandering deposit through shore-shallow lacustrine to meandering deposit system.The stream is a kind of fine highly bending meandering river,and it belongs to alluvial plain environment on the front of alluvial fans.It also reveals that Dabie orogenic belt as the source area of Yuantongshan Formation was in a far distant place and under stable tectonic setting in Middle-Late Jurassic.