四川盆地须家河组地层划分方案讨论

DISCUSSION ON THE CORRELATION OF THE XUJIAHE FORMATION IN SICHUAN BASIN

从晚三叠世盆地演化阶段划分和物源方向分析出发,认为晚三叠世处于巴颜喀拉海控大陆边缘盆地向受控于龙门山推覆抬升的川西前陆盆地的转化时期,其间重要的盆地转换界面就是须三、须四段之间的安县运动界面。在对南北向和东西向钻井、露头剖面的区域地层进行详细划分对比基础上,认为须下盆的须二、须三段地层主要发育在川西地区中北段,并以鸭子河地区最为发育,往南因受安县运动影响,须三段地层遭受剥蚀,从北往南逐渐减薄缺失,在大邑构造减薄,在平落坝缺失须三段,造成须二段与须四段不整合接触。从川西地区往东须二段、须三段也逐渐变薄,在川中地区缺失。川中、川南和川东地区的须家河组与川西地区须上盆即须四段、须五段地层相当。

According to the basin evolution and tion of the lateTriassic sedimentary sources, we believe that the late Triassic is represents an interval during which the continental margin basin controlled by Bayankala sea switched to a West Sichuan foreland basin controlled by Longmen Mountains which was napping and uplifting. The transition is represented by the Anxian tectonic movement between the third and fourth members of the Xujiahe Formation. On the basis of drilling data, outcrop observation, and stratigraphic correlation,we think that the second and third members of the Xujiahe Formation are mainly developed in the north part of the West Sichuan Basin,as typified by the Yazihe area. Affected by the Anxian Tectonic Movement,the third member of the Xujiahe Formation was eroded in the southern part of the basin; the thickness of this member gradually decreases from the north to the Dayi structure in the south,and it is completely missing in the Pingluoba structure where the second member is in direct contact with the fourth member of the Xujiahe Formation. The second and third members of the Xujiahe Formation thin eastward from the western Sichuan Basin,and is missing in the middle Sichuan Basin. The Xujiahe Formation which in the middle, south and east parts of Sichuan Basin are equivalent to the fourth and fifth members of the Xujiahe Formation in the western Sichuan Basin.