陆相断陷湖盆滑塌型深水重力流沉积特征、识别标志及形成机制——来自海拉尔盆地东明凹陷明D2井全井段连续取心的证据

Sedimentary characteristics,identification mark and formation mechanism of the slumping deepwater gravity flow in fault lacustrine basin:a case study on the consecutive coring well of Ming D2 in Dongming sag,Hailaer Basin

通过对明D2井连续取心的观察分析,提出海拉尔盆地东明凹陷白垩系南屯组和大磨拐河组普遍发育滑塌型深水重力流沉积,其沉积构造丰富多样,特征明显。以沉积过程为基础,采用以Shanmugam为代表的简化划分方案,将滑塌型深水重力流分为滑动、滑塌、碎屑流和浊流4个过程,并对各过程和阶段的沉积特征进行了描述,总结了其主要识别标志,分析和探讨了其形成机理,认为滑塌型深水重力流的滑动、滑塌和碎屑流3个阶段主要为块体流搬运机制,浊流阶段沉积主要为牛顿流体或紊流机制。滑动阶段沉积以保留部分原始沉积构造(如砂泥互层和沉积旋回)、发育层内小型正断或逆断错断、较大角度的地层倾角为主要识别标志。滑塌阶段沉积以塑性变形为特点,以顶、底面均与暗色泥岩呈突变接触,内部发育大规模的同生软沉积变形构造(如包卷构造)为主要识别特征。碎屑流可以分为砂质碎屑流和泥质碎屑流;碎屑流沉积以宾汉流体为特征,整体冻结式沉积为特点,主要识别标志为砂岩顶、底面均与暗色泥岩突变接触,砂岩呈块状,可发育漂浮砾岩和泥岩撕裂屑等,在砂质碎屑流中还可发育逆粒序层理。以牛顿流体搬运的浊流沉积则以正递变层理为主要识别标志,底部与暗色泥岩呈突变接触,发育完整或不完整的鲍马序列为主要特征。

Through the observation and analysis of Well Ming D2,it is proposed that the slumping deepwater gravity flow sediments are widely developed with various sedimentary structures and obvious characteristics in Cretaceous Nantun Formation and Damoguaihe Formation in Dongming sag,Hailaer Basin.Based on sedimentary process,the simplified classification scheme represented by Shanmugam is used to divide the slumping deepwater gravity flow into four processes,i.e.,sliding,slumping,debris flow and turbidity current.Meanwhile,this paper describes the sedimentary characteristics in each stage of the process,summarizes the main identification marks,analyzes and discusses the formation mechanism.It is considered that the three stages of sliding,slumping and debris flow of the slumping deepwater gravity flow are dominated by the mass flow transport mechanism,and the sedimentation in the stage of turbidity current is mainly controlled by Newtonian fluid or turbulent flow mechanism.In the sliding stage,the partial reservation of primary sedimentary structure characteristics,such as sand-mud interbed and sedimentary cycle,is mainly identified by the development of small normal fault or reverse fault in internal layers,and large stratigraphic dip.The sediment in the slumping stage is mainly characterized and identified by plastic deformation with the top and bottom abruptly contacted with dark mudstone,as well as the large-scale internally-developed syndepositional soft-sediment deformation structures,such as convolute structure.The debris flow can be classified into sandy and muddy debris flows.The debris flow sediment is mainly marked by the Bingham fluid andoverall frozen sediment with the top and bottom of sandstone abruptly contacted with dark mudstone,massive sandstone as well as the favorable conditions for developing floating gravel and mudstone tearing clastics.In addition,the reverse graded bedding can be developed in the sandy debris flow.The turbidity sediment transported by Newtonian fluid is mainly indicated by normal grading bedding,the bottom abruptly contacted with dark mudstone,and the development of complete or incomplete Bouma sequence.