华东地区二叠纪层序地层分析

THE PERMIAN SEQUENCE STRATIGRAPHY IN EASTERN CHINA

华东地区二叠纪地层甚为发育,分布广泛,生物化石丰富,研究程度较高,不仅生物地层研究颇详,同时近几年来在沉积学及岩相古地理方面也做过较多工作,这些均为层序地层研究和划分创造了有利条件。前几年,我们在安徽、江苏、福建、江西、浙江等地实测和详细观察了23条剖面(图1),在详细研究地层、沉积学、沉积相的基础上,试图对研究区二叠纪层序地层作一探讨。一、二叠纪层序地层划分本区二叠纪沉积盆地介于华夏古陆与鲁东古陆之间,为一克拉通盆地,比较稳定。盆地内发育北东向坳陷与隆起以及同沉积断裂。栖霞期和吴家坪期甚为稳定,岩性岩相单一,厚度变化不大。在茅口期和长兴期,盆地发生分异。

The Permian strata are well developed, widespread and contain abundant fossils in eastern China. They can be divided into A, B and c sequences. Sequences A and B correspond to the Early Permian Qixia and Maokou Formations, respectively, while Sequence C to the Late Permian Wujiaping and Changxing Formations. Sequences A and C represent typeⅠsequence, the lower boundary of which is referred to as typeⅠunconformity. Sequence B represents type∏sequence, the lower boundary of which is referred to as typeⅡunconformity. The depositional duration of Sequence A is about 5 Ma, while Sequenceb B and C about 10 Ma. The lowstand systems tract consists mainly of the coal-bearing series which are assigned to the coastal plain and lower deltaic plain deposits. The condensed sections are composed of radiolarian siliceous rocks, siliceous mudstones and carbon-bearing mudstones, 3 to 15 meters thick, which contain ammonites and brachiopods and represent the starved sediments deposited during maximum rates of sea-level rises. On the carbonate platform, the highstand systems tract is dominated by the aggradational deposits which are composed of light grey grainstones and bioclastic micritic limestones, whereas on the coastal plain, occur the progradatianal deposits which belong to the deltaic coal-bearing series with great thickness. Syndepositional fault activites are closely related with regional sea-level changes, and thus interpreted as the important controlling factors on the coal-bearing series which constitute the highstand systems tract with great thickness.