川西须家河组前陆盆地构造层序及沉积充填响应特征

川西坳陷在须家河组沉积期为典型的周缘前陆盆地,受幕式造山运动的控制,其构造层序具有"二元体系域"的特征,即强烈造山期体系域和构造宁静期体系域。构造运动不仅控制着前陆盆地的层序地层发育,也会分配层序内部的沉积物充填。基于Vail经典层序地层学理论,综合利用地震、测录井等资料,分析研究区内构造层序类型及主控因素,阐明不同构造层序内部的沉积充填响应特征。结果表明:须家河组在前陆盆地期(须二段—须五段)可以划分为2个构造层序,其中须二段和须四段为强烈造山期体系域,须三段和须五段为构造宁静期体系域;构造运动是控制研究区构造层序发育的主要因素;强烈造山期体系域以粗粒沉积为主,发育冲积扇—辫状河三角洲—湖泊沉积体系,构造宁静期体系域以细粒沉积为主,发育曲流河三角洲—滨浅湖沉积体系。

Tectono-stratigraphy and sedimentary infill characteristics of Xujiahe Formation in western Sichuan foreland basin

The tectono-stratigraphy in Xujiahe Formation is characterized by binary system tracts (tectonically active and tectonically stable) in western Sichuan depression, coincided with its episodic-orogenesis evolution phases as a peripheral foreland basin. Tectonic activity is suggested not just to control sequence stratigraphy development, but also to assign the sediment-infilling patterns within sequence successions. Based on Vail ''s sequence stratigraphy theory, integration of data from boreholes with seismic reflection allowed the analysis of tectono-stratigraphy types and their main controlling factors, as well as the illustration of sedimentary characteristics in or between orogeny episodes. The results show that Xujiahe Formation ''s sub-members (T_3x²-T_3x⁵) alternatively shift between the binary system tracts:T_3x² and T_3x⁴ belong to the tectonically active system tracts, while T_3x³ and T_3x^5are the tectonically stable ones. Tectonic activity controls tectono-stratigraphy development. Coarse grained deposition dominates in the tectonically active system tracts, as seen in alluvial fan-braided river delta-lacustrine facies which prevail in T_3x² and T_3x⁴; on the other hand fine grained sediments distribute widely in the tectonically stable system tracts, as evidenced by meandering river delta-lacustrine and swamp facies which predominate in T_3x³ and T_3x⁵.