四川盆地东部上三叠统须家河组层序-古地理特征

摘要

Based on the Vail＇s theory from EXXEN Company,the Xujiahe formation of the Late Triassic were subdivided into 4 third-order sequences,corresponding respectively to the intervals of the member 1,member 2 to member 3,member 4 to member 5 and member 6 to member 7.The TST and HST in each sequence was taken as a mapping interval and,then,the palaeogeography was reconstructed.The paleogeographic units during the TST and HST of 4 sequences include fluvial plain,delta and shallow lake,in which the first two units constitute the basic framework in the area.The sediment provenances are mainly from the Jiangnan mountains in the southeast,follows by the Daba mountains in the north.In general,the fluvial plain is expanded westward by the tectonic impact.In the periods from the transgressive HST in the sequence I to one in sequence IV,the shallow lake is firstly narrowed,then expand with a westward migration.Coal is mainly formed in the interdistributary bays,pere-marsh and flood basin.%采用EXXON公司＂Vail＂学派的观点,将四川盆地东部须家河组划分为4个三级层序,其中层序1对应于须一段、层序2对应于须二段和须三段、层序3对应于须四段和须五段、层序4对应于须六段和须七段。以每个层序的湖侵及高位体系域为作图单元,进而展开古地理分析。4个层序湖侵及高位体系域期古地理单元主要有河流冲积平原、湖滨-三角洲、浅湖沉积环境,前两类古地理单元构成了基本骨架。物源区主要来自东南部江南山地,其次为北部大巴山山地。总体上,河流冲积平原古地理单元的分布规模受大地构造作用的影响向西不断扩大,在三级层序Ⅰ湖侵及高位体系域期至三级层序Ⅳ湖侵及高位体系域期间,浅湖区沉积范围先缩小、再扩大、再扩大且向西迁移。煤层主要发育在分流间湾、滨岸沼泽以及泛滥盆地。