重力流主导的深水沉积特征及其模式——以共和盆地下三叠统为例
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本文为青海省地质勘查基金项目(编号2018317qjny005)、中国矿业大学(北京)越崎学者专项资金资助和国家科技重大专项(编号2017ZX05009- 002)联合资助的成果。


Sedimentary characteristics and depositional model of deep- water deposits dominated by gravity flow: A case study from the Lower Triassic in the Gonghe Basin
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    摘要:

    深水沉积具有良好的油气勘探前景,近年来已成为沉积学研究的前缘和油气工业界关注的焦点。以共和盆地下三叠统为例,通过野外剖面的详细观察描述,结合室内镜下薄片鉴定与粒度分析,对深水沉积类型、沉积特征、垂向组合、成因机制以及沉积模式进行系统研究。共和盆地早三叠世深水沉积类型主要有滑塌型深水重力流沉积、底流沉积以及深水悬浮沉积,其中滑塌型深水重力流沉积又可识别出滑塌沉积、砂质碎屑流沉积与浊流沉积三种类型。滑塌沉积常见以同沉积褶皱为代表的多种软沉积物变形构造;砂质碎屑流沉积以块状砂岩为主,内部可见砂质团块、泥砾或泥质撕裂屑,块状砂岩顶底与相邻岩层均为突变接触;浊流沉积普遍发育正粒序,可见不完整的鲍马序列,底面常见多种类型的底模构造;底流沉积发育多种牵引流沉积构造。研究区软沉积物变形构造类型丰富,其中滑塌层内的软沉积物变形构造主要在斜坡滑塌过程中形成;未发生滑塌层内的软沉积物变形构造主要因地震使沉积物发生液化作用及流体化作用而形成。在综合分析盆地构造背景、深水沉积分布规律、重力流触发机制的基础上,建立了共和盆地早三叠世滑塌型重力流主导的深水沉积模式。滑塌型重力流主要由地震以及火山事件触发,水道化的地区会形成大面积的海底扇沉积体系。底流作为深水环境中不可忽视的动力因素,往往会对重力流沉积进行后期改造而使其物性变好。深水悬浮沉积作为一种背景沉积,在重力流事件的间歇期成为主要的深水沉积物。研究显示内扇、中扇可作为致密砂岩油气的勘探区,外扇可进行页岩油气勘探。

    Abstract:

    Deep- water deposits have good prospects for hydrocarbon exploration, and have become the frontier of sedimentology and the focus of hydrocarbon industry in recent years. Based on detailed observation and description of outcrops, combined with the microscopic identification and grain size analysis of rock slices, the sedimentary types, sedimentary characteristics, vertical sequences, genetic mechanism and depositional model of the Early Triassic deep- water deposits in the Gonghe Basin were systematically studied. The Early Triassic deep- water deposits in the Gonghe Basin are mainly slumping deep- water gravity flow deposits,bottomcurrent deposits and deep- water suspension deposits, among which the slumping deep- water gravity flow deposits can be identified as slump deposits, sandy debrites and turbidites. Slump deposits are often characterized by a variety of soft- sediment deformation structures(SSDS) represented by synsedimentary folds. Sandy debrites are dominated by massive sandstones, with occasional sandy masses, muddy gravel or muddy debris inside. Massive sandstones are in abrupt contact with both overlying and underlying strata. Turbiditesare generally developed with graded bedding, showing incomplete Bouma sequence, and various types of bottom cast structures are common on the subface. Bottom current deposits are characterized by multiple tractive current sedimentary structures.There are abundant types of SSDS in the study area, in which the SSDS in slump beds are mainly formed in the process of slope failure, the SSDS in non- slump beds are mainly formed by liquefaction and fluidization of sediments caused by earthquakes. On the basis of comprehensive analysis of basin tectonic setting, distribution of deep- water deposits and triggering mechanism of gravity flow, the depositional model of the Early Triassic deep- water deposits dominated by slumping gravity flow in the Gonghe Basin was established.Slumping gravity flow is mainly triggered by earthquakes and volcanic events, and a widely distributed submarine fan depositional system is formed in the channelized zone. As the driving force that can not be ignored in deep- water environment, the bottomcurrent often reworks the gravity flow deposits to make their reservoir quality better.As the background deposits, deep- water suspension deposits become the dominant deep- water deposits during the intermittence of gravity flow events.The study shows that the inner and middle fans are favorable exploration areas for tight sandstone oil and gas, while the outer fan has the prospect of shale oil and gas exploration.

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引用本文

刘炳强,邵龙义,王伟超,黄献好,刘文进,张少林,张浩,鲁静.2020.重力流主导的深水沉积特征及其模式——以共和盆地下三叠统为例[J].地质学报,94(4):1106-1127.
LIU Bingqiang, SHAO Longyi, WANG Weichao, HUANG Xianhao, LIU Wenjin, ZHANG Shaolin, ZHANG Hao, LU Jing.2020. Sedimentary characteristics and depositional model of deep- water deposits dominated by gravity flow: A case study from the Lower Triassic in the Gonghe Basin[J]. Acta Geologica Sinica,94(4):1106-1127.

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  • 收稿日期:2019-04-28
  • 最后修改日期:2019-08-02
  • 录用日期:2019-08-08
  • 在线发布日期: 2019-10-21