7 / 2021-04-01 14:56:19

季节性古气候变化影响的浅水三角洲分流河道砂体沉积构型

Keyword: shallow water delta; distributary channel; sandstone architecture; paleoclimate; Songliao basin

Sedimentary architecture of shallow water deltaic distributary channels influenced by seasonal variation of paleoclimate: a case study from the Cretaceous Yaojia Formation in the southern Songliao Basin, NE China

Using modern analog, field outcrops, geochemical test, and subsurface geological data from shallow-water delta deposits of the Cretaceous Yaojia Formation in the southern Songliao Basin, this study investigates the controlling mechanism of seasonal variation of paleoclimate conditions on the architecture of sand bodies in shallow water deltaic deposits. Controlled by seasonal variation of paleoclimate, the sedimentary process of the shallow water delta was affected by the high variation of sediment discharge during flood period and drought period. The sedimentary process differed greatly in different period. In flood period, the shallow water delta was controlled by high sediment discharge, major distributary channels and crevasse distributary channels were developed in delta plain. Terminal distributary channels and mouth bar deposits were produced by the flood-generated hyperpycnal flows. The sedimentary structures in distributary channels were formed in upper flow regime. In drought period, the sediment discharge decreased, the major distributary channels became main discharge paths. The deposits in crevasse distributary channels exposed and reddish sandstones were formed. The mud deposits in delta plain exposed and turned to red bed in the semi-arid climate. The dual-stage sedimentary model of shallow water delta is established based on the deposition process of the shallow water delta in the Yaojia Formation. This study gives further interpretation about the response regime of shallow water deltaic sandstones, to seasonal variation of paleoclimate, and provides basis for exploration and development of shallow-water deltaic hydrocarbon reservoirs.

This study was supported by the National Natural Science Foundation of China (Grant No.41902122), the Open Foundation of Top Disciplines in Yangtze University (Grant No.2019KFJJ0818014), and the Postdoctoral Innovation Post of Hubei Province (Grant No. 9621000813). 

Keyword: shallow water delta; distributary channel; sandstone architecture; paleoclimate; Songliao basin



季节性古气候变化影响的浅水三角洲分流河道砂体沉积构型

本文选取松辽盆地南部白垩系姚家组浅水三角洲沉积为研究对象，应用现代沉积、野外露头,地球化学分析测试和地下地质资料探索古气候季节性变化对浅水三角洲分流河道沉积构型的控制作用。本文研究发现受控于古气候季节性变化，姚家组浅水三角洲具有明显的洪水期和枯水期，沉积过程具有阶段性，在不同的阶段沉积机制具有明显差异。在洪水期，浅水三角洲沉积供给量大，浅水三角洲处于推进阶段，三角洲平原主干分流河道、决口分流河道同时发育，三角洲前缘末端分流河道和河口坝在洪水成因的异重流体作用下形成。三角洲分流河道内部发育高流态沉积单元，缺乏大型的交错层理沉积构造。在枯水期，沉积供给量减小，主干分流河道仍然是沉积物供给的主要通道，决口分流河道内水位明显降低，发育特殊的红层砂体。枯水期湖岸线后退，沉积物供给量低，三角洲平原大部分地区暴露在半干旱炎热的气候中，形成红层沉积。姚家组浅水三角洲在形成和发育阶段，经历了以上两个阶段的不同沉积作用，形成了特殊的古气候季节性变化主控的双阶段沉积模式。本研究进一步解释了分流河道砂体构型对古气候季节性变化的响应机制，也可以为浅水三角洲油气储层高效勘探开发提供理论依据。

关键词：浅水三角洲；分流河道；砂体构型；古气候；松辽盆地