非补偿陆相断陷盆地层序地层学研究——以廊固凹陷古近系为例

非补偿沉积表现为无明显的沉积间断面,单层暗色泥岩厚度大,分布范围广,沉积剖面以退积为特点。通过对廊固凹陷古近系基底地层、物源体系的研究,结合沉积物组合特点、沉积剖面序列和构造发育阶段特征,分析了非补偿沉积盆地的层序发育样式,总结了非补偿盆地层序边界发育特征,建立了层序地层格架,共划分了1个一级层序、3个二级层序、11个三级层序。研究了不同沉积、构造背景下各层序组内体系域的样式,将一个完整的层序划分为湖泊充填体系域、湖泊扩张体系域、湖泊稳定体系域及湖泊萎缩体系域(下降体系域)等4个阶段,使体系域的叠加与层序的演化相关联。建立了非补偿型陆相盆地有利体系域沉积模式,认为物源的演替是其主控因素,复杂的断裂系统仅是一种控制沉积作用的一种表象。

SEQUENCE STRATIGRAPHY OF NON-COMPENSATED,FAULT-CONTROLLED LAKE BASINS: A CASE STUDY OF THE PALEOGENE SYSTEM IN THE LANGGU DEPRESSION

Depositional successions in non-compensated lake basins are characterized by the lack of obvious discontinuous surfaces,great thickness of dark mudstone beds,wide spatial distribution,and the dominance of back-stepping sequences.As a case study,we investigated the Paleogene successions in the Langgu Depression and analyzed the basement structures,sediment supply system,sediment characterization,and tectonic settings,in order to understand the sequence boundary of a non-compensated depositional basin and to establish sequence stratigraphic framework of the Langgu Depression.The Paleogene successions in the Langgu Depression consist of one first-order sequence,three second-order sequences,and eleven third-order sequences.A typical sequence can be divided into four system tracts,including the lake infilling system tract,lake expansion system tract,lake stabilization system tract,and lake shrinkage system tract(or lake-level regressional system tract).Thus,the system tract stacking patterns are related to sequence development.This study provides a depositional model for system tract evolution in a non-compensated deposition basin,in which sediment supply played a key role controlling the stratal architecture.