南海西南部主要盆地碳酸盐岩层序地层学解释

THE INTERPRETATION OF CARBONATE SEQUENCE STRATIGRAPHY IN THE SOUTHWESTERN REGION OF SOUTH CHINA SEA

本文以碳酸盐岩层序地层学理论为基础,应用地震勘探研究成果和有关的钻探资料,具体分析了南海南部主要沉积盆地中碳酸盐岩的沉积背景、沉积相带、层序类型和沉积体系域。确认本区的碳酸盐岩沉积层序均由低水位体系域、海侵体系域和高水位体系域组成。在沉积相带和体系域之间存在一定的相互关系,两者还与特定的岩性、岩相组合相对应。本项研究为南沙海域碳酸盐岩的油气勘探提供了依据,也可望能促进层序地层学理论更为深入地应用到南海油气勘探活动中。

The southwestern region of South China Sea cantains carbonate platform and bank deposits which are mainly mid-late Miocene and show large thickness at the southern and southeastern parts of Wan' an Besin and the western part of Zengmu Basin. Based on the carbonate sequence stratigraphy, the deposi- tional setting and the resultant facies distribution of the carbonate platform/bank have been outlined and the system tracts and lithology of the marine carbonate deposition are also discussed in the paper. Two carbonate sequences are distinguished in mid-Miocene and late-Miocene deposites. These se- quences are all bounded below by a large-scale type I sequence boundary and above by other type boundary. Each sequence consists of highstand system-tract, lowstand system-tract and transgressive sys- tem tract. The highstand system-tract can be subdivided into two types here, keep-up and catch-up. Ihe keep-up is interpreted to represent a relatively rapid rate of accumulation that is able to keep pace with periodic rise in relative sea level. The keep-up platform is characterized by grain-rich, mud-poor lithofa- cies. The catch-up which displays a sigmoid depositional profile is interpreted to represent a relative slow rate of accumulation that is characterized by micrite-rich lithofacies. The lowstand system-tract de- posited during sea-level lowstand can be divided into allochthonous debris derived from erosion of the slope front and aulochthonous carbonate wedges deposited on the upper slope. The transgressive system- tract which displays a onlap depositional profile is characterized by mud-rich, grain-poor lithofacies and almost occures at the lower slop basin floor.