长岭断陷龙凤山次凹营城组重力流成因类型及沉积特征

以松辽盆地长岭断陷南部龙凤山次凹下白垩统营城组重力流沉积为研究对象,运用钻井取心资料,分析沉积物结构构造特征、搬运沉降方式及搬运介质流变学特征的差异,对不同古地貌单元下重力流类型、岩相组合特征及成因机制进行研究。结果表明:龙凤山次凹下白垩统营城组沉积时期主要分为东北洼陷带、西南断槽带和东南斜坡带3类古地貌单元,坡度自西向东逐渐变陡,西南断槽带中同沉积断裂活动所形成的断槽为研究区重要的输砂通道,为重力流砂体长距离搬运提供有利条件;凤山次凹营城组主要发育泥质密度流、低密度浊流、高密度浊流、泥质碎屑流和砂质碎屑流5种重力流类型;根据其触发机制和相序特征分为洪水型重力流岩相组合和滑塌型重力流岩相组合;洪水型重力流具有洪水涨水期(低密度浊流—碎屑流)、洪峰期(碎屑流—高密度浊流)、退水期(低密度浊流—泥质密度流)的重力流演化过程;滑塌型重力流发育滑动滑塌转化为砂质碎屑流、高密度浊流、低密度浊流和泥质密度流的重力流演化过程;西南断槽带受洪水作用的影响,碎屑物质沿断槽进入湖盆,形成扇三角洲相,扇三角洲前缘坡折带处滑塌形成湖底扇相,东南斜坡带受构造活动的影响,碎屑物质滑塌进入半深湖—深湖环境,形成近岸水下扇相。
The gravity flow in the Yingcheng Formation of the Longfengshan subsag was studied in this research. Based on the differences on the sediment composition structure, transportation-sedimentation mode and fluid rheological characteristics, we made full use of core, well logging, seismic explanation and other data, and carried out a study on the lithfacies types, lithofacies association characteristic and genetic mechanisms of gravity flow. The results are as follows. During the sedimentation of the Yingcheng Formation, the Longfengshan subsag can be divided into three tectonic-paleogeomorphology units, which are southwestern fault-slope zone, southeastern steep slope zone and northern depression belt. The paleogeomorphology steepens gradually from west to east. Faulted troughs formed by synsedimentary faulting are the main sand transporting channel. There are five gravity flow types developed in the Longfengshan subsag, including mud-only turbidite, low density turbidite, high density turbidite, glutenite debris flow and muddy debris flow. According to characteristics in triggering mechanisms and sedimentary facies sequences, the lithofacies association can be divided into two types, the gravity flow caused by slumping and the gravity flow caused by flooding. The whole flood process can be divided into three stage, including water-rising stage (low density turbidity flow-debris flow), flood peak stage (debris flow-high density turbidity flow), and water-recession stage (low density turbidity flow-muddy flow). The slumping process can be divided into four stages, including sliding, sandy debris flow, high density turbidity flow, and low density turbidity flow and muddy flow. The sedimentary characteristics of different tectonic-paleogeomorphology in gravity flow have been established. In the southwestern fault-slope zone, affected by flooding, terrigenous debris are transported along the faulted troughs into lacustrine and fan delta developed. Because of the development of slope break belt, the sublacustrine fan is developed by slumping of the fan