鄂尔多斯盆地南部地区延长组深水沉积构造特征及地质意义

Deep-water Sedimentary Structures of Yanchang Formation in Southern Ordos Basin and the Geological Significance

鄂尔多斯盆地南部地区上三叠统延长组长7段发育有典型的重力流沉积。对野外露头剖面进行大量调查研究,发现研究区重力流沉积发育丰富的沉积构造,底层面构造、软沉积变形构造是主要的两种类型。这种深水沉积构造组合能够很好地揭示研究区广泛发育的一定坡度背景下深水重力流沉积体系。滑移-滑塌沉积、砂质碎屑流沉积、浊流沉积是研究区发育最为广泛的深水重力流沉积类型,滑移-滑塌及软沉积变形构造为触发机制沉积响应,底层面构造为砂质碎屑流沉积及浊流沉积响应。综合分析研究区地层发育的大量凝灰岩夹层、深水泥岩中发育的植物碎屑、深水砂岩中发育的大量浅黄色泥砾等沉积特征,认为地震、火山喷发及季节性洪水为研究区深水重力流沉积最有利的触发因素。

The Chang7 member of Yanchang Formation in the southern margin of Ordos Basin develops typical gravity flow deposits. It is found that the gravity flow deposits develop various sedimentary structures in the field investigation on field outcrops,mainly including bottom layer structures,soft-sediment deformation structures.These deep-water sedimentary structure combinations can well reveal that deep-water gravity flow deposits are widely developed under the background of slope breaks in the study area. Slip-slump deposits,sandy debris flow deposits and turbidite deposits are the most widely developed types of deep-water gravity flow deposits in the study area. Slip-slump structures and soft-sediment deformation structures are the sedimentary response of trig-gering mechanism,while bottom layer structures are the sedimentary response of sandy debris flow deposits and turbidite deposits. After the comprehensive analysis of characteristics of a large number of tuff interlayers,plant debris developed in deep-water mudstone,a large number of light yellow mud gravel developed in deep-water sandstone and other sedimentary characteristics of the formation in the study area,it is inferred that the earthquake,volcanic eruption and seasonal floods are the most advantageous triggering factors of deep-water gravity flow deposits in the study area.