Features and sedimentary evolution of high-frequency sequence in continental lacustrine rift basin: Example of the lower Shahejie member 3 in Jiyang Depression，Bohai Bay Basin

Peng Li; Wu Yiming; Lian Zhanggui; Peng Peng; Wang Jian; Su Zhou; Yi Zhenli

doi:10.11743/ogg20190409

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Features and sedimentary evolution of high-frequency sequence in continental lacustrine rift basin: Example of the lower Shahejie member 3 in Jiyang Depression，Bohai Bay Basin
Vol. 40, Issue 4, Pages: 789-798(2019)
Online First：28 August 2019，

Published：2019
DOI： 10.11743/ogg20190409
稿件说明：

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DOI：

Peng Li, Wu Yiming, Lian Zhanggui, et al. Features and sedimentary evolution of high-frequency sequence in continental lacustrine rift basin: Example of the lower Shahejie member 3 in Jiyang Depression，Bohai Bay Basin[J]. 2019, 40(4): 789-798. DOI： 10.11743/ogg20190409.

摘要

岩相及其组合有规律地分布于层序地层格架内。通过岩心观察和样品测试数据综合分析，基于T（湖进）-R（湖退）层序划分方法，系统分析了渤海湾盆地济阳坳陷古近系沙三下亚段陆相断陷湖盆关键层序界面特征、变化形式、构成样式及分布模式，总结出沙三下亚段的沉积层序演化模式。研究结果表明：①沙三下亚段关键层序界面类型主要有区域性的最大湖泛面和层序界面；②层序变化形式主要有向上变浅的R半旋回、向上变深的T半旋回和稳定旋回3种，层序单元构成可归为3种类型，分别为快升慢降型、慢升快降型和均一型；③沙三下亚段为一完整的三级层序，可划分为4个四级层序，对应早期湖进体系域（早期LTST）、晚期湖进体系域（晚期LTST）、早期湖退体系域（早期LRST）和晚期湖退体系域（晚期LRST），四级层序和划分的五级层序单元具有全区的可对比性和完整性；④济阳坳陷沙三下亚段湖平面在总体快升慢降的背景下，主要经历4个变化阶段——早期LTST的快速上升阶段、晚期LTST的缓慢上升阶段、早期LRST的缓慢下降阶段及晚期LRST的下降阶段。层序演化过程中，构造沉降、沉积物供给和气候条件等因素在不同阶段所起的作用不同，从而造成层序格架内岩相及其组合分布的差异。

Abstract

Lithofacies along with its assemblages is distributed regularly within the sequence stratigraphic framework.Based on T(transgression)-R(regression) sequence division features

variations

architectures and distribution patterns of the key sequential interfaces have been analyzed systematically in fault continental lacustrine basin in the lower part of the third member of the Paleogene Shahejie Formation(Es

) in Jiyang Depression

Bohai Bay Basin

by core observation and sample test data.And the evolution pattern of sedimentary sequences in Es

has been summarized furtherly.The results show that ① the major types of key sequential interfaces in Es

are the regional maximum flooding surface(MFS) and sequence interface.② Three variations of sequences are identified

namely the shallowing-upward R-shaped semi-cycle

deepening-upward T-shaped semi-cycle and stable cycle.While the sequence units can be reduced to three types

namely the type characterized by fast rise but slow drop

the type characterized by slow rise but fast drop

and the type characterized by constant variation.③ As an integrated third-order sequence

the Es

can be sub-divided into four forth-order sequences

that is

the early lacustrine transgressive system tract(early LTST)

late lacustrine transgressive system tract(late LTST)

early lacustrine regressive system tract(early LRST) and late lacustrine regressive system tract(late LRST).These forth-order sequences together with the sub-divided fifth-order sequence units feature comparability and integrity. ④ The lake level of the Es

in Jiyang Depression generally fluctuates in a fast-rise-but-slow-fall pattern

and the fluctuation can be classified into four stages:the fast-rise stage during the early LTST

the slow-rise stage during the late LTST

the slow-fall stage during the early LRST

and the fall stage during the late LRST.In the process of sequence evolution

factors

such as tectonic subsidence

sediment supply and climate conditions

play specific roles in different stages

resulting in differential distribution of lithofacies and their assemblages within the sequence stratigraphic framework.