惠民凹陷西部沙四下亚段冲积扇沉积类型与成因分析

Types and genesis of the alluvial fans in the lower submember of the fourth member of the Shahejie Formation in the Huimin depression, Shandong

关键词:  惠民凹陷  泥石流扇  辫状河扇  地震相  沉积模式

Key words:  Huimin depression  debris flow fan  braided stream fan  seismic facies  sedimentary model

摘要:

本文在岩心观察和描述的基础上,结合地震、测井等资料及平面上砂体的分布形态,对惠民凹陷西部沙四下亚段的沉积特征及成因进行了研究。认为研究区沙四下亚段主要发育冲积扇沉积的泥石流扇和辫状河扇两种类型,共识别出了6种沉积微相。宁南断层和无南断层下降盘发育大面积的辫状河扇沉积。砂体垂直岸线分布,延伸距离较远。平面上分布呈扇形,沉积相带分异不明显,主要沉积微相为辫状河道、河道砂坝与河道间沉积。邻近齐广断层断崖处发育泥石流扇沉积,砂体不甚发育,与辫状河扇相比,该沉积类型砾岩富集,扇体规模较小。相带变化比较明显,主要沉积微相为泥石流沉积、河道沉积与漫流沉积。该沉积体系的形成主要受构造活动、古地貌、物源区性质与古气候等因素的影响,断裂活动是该沉积体系形成的决定性因素。

Abstract:

Two types of depositional systems are identified for the lower submember of the fourth member of the Shahejie Formation in the Huimin depression, Shandong, including the debris flow fan and braided stream fan. The braided stream fan deposits are well developed on the downthrown sides of the Ningnan fault and Wunan fault. In a planar view, they display the fan shape, and extend over a wide range of scale. The interchannel flood plain and crevasse splay deposits are less developed, and the sedimentary facies belts are less differentiated. The channel lag deposits and channel sandbar deposits are interpreted as the main sediment types. The debris flow fan deposits occur near the fault scarp of the Qiguang fault, and consist of the proximal fan, mid-fan and terminal fan subfacies. In comparison with the braided stream fan deposits, the debris flow fan deposits are characterized by the enrichment of conglomerate, smaller scales of fans, and sharp facies changes. The controlling factors for the formation of this type of depositional systems contain tectonism, palaeogeomorphology and palaeoclimates, especially active faulting.