浅谈深水块体搬运复合体的结构、成因分类以及识别方法

A Brief Introduction to Deep-Water Mass-Transport Complexes:Structures,Genetic Classifications and Identification Methods

全球普遍发育的块体搬运复合体是深水地层的重要组成单元,广泛分布在大陆边缘和陆相湖盆中。系统认识块体搬运复合体有助于拓展深水油气勘探领域和评价海底工程地质风险。典型的块体搬运复合体由头部拉张区、体部滑移区和趾部挤压区3个部分组成,三者在顺坡搬运过程中,存在由头部到趾部依次演变的关系。基于沉积物搬运过程和不同阶段流体性质,将块体搬运复合体分为滑动岩、滑塌岩和碎屑岩3类,分别对应搬运过程的弹性形变、弹性和塑性形变以及塑性形变阶段。块体搬运复合体在三维地震平面图通常可根据其沉积物的流动方向(顺坡方向)依次识别出头部陡崖、体部滑塌褶皱和趾部挤压脊等构造单元,剖面上以弱—中振幅反射和丘状—长条状外形为特征,具有不规则顶底界面。测井上块体搬运复合体具有顶底界面突变的曲线响应。露头上块体搬运复合体通常具有一种或多种沉积构造,比如块状构造、滑塌褶皱和泥质撕裂屑等。块体搬运复合体与浊积岩的主要区别在于块体搬运复合体整体以"冻结式"搬运沉积,具有"长条形—似扇形"的斜坡组合形态,垂向上沉积厚度大,无明显粒序分异特征,地层倾角常大于浊积岩沉积地层。

Mass-Transport Complexes(MTCs)are important components of deep-water systems,and widely distributed in continental margins and lake basins.Understanding MTCs is helpful for expanding the targets of deep-water hydrocarbon exploration and for evaluating geological risks of subsea engineering.Typical MTCs consist of three parts:the head tension area,body slip area,and toe compression area.During the transportation of MTCs,these three domains come into being successively.MTCs can be classified into three types:slide rock,slump rock,and debris rock,based on the sediment transport process and fluid properties,and they respectively correspond to elastic deformation,elastic and plastic deformation and plastic deformation stages.In 3D seismic plan,according to the direction of sediment flow(the slope direction),some depositional elements of MTCs,such as head cliffs,body folds,and toe squeeze ridges,can be clearly identified in proper order,and in seismic profiles MTCs are characterized by weak-medium amplitude reflections,mound-like shapes,and irregular top/bottom interfaces.In conventional log data,MTCs are commonly responded as abrupt shifts at their top/bottom interfaces.In outcrop data,MTCs have several kinds of sedimentary structures,such as massive textures,sliding folds,and mud lumps.Compared with turbidites,MTCs have many distinct characteristics.For example,MTCs are deposited from sediments transported through a"frozen"manner and have an"elongate-fan-like"slope morphology,a relative large thickness.Furthermore,MTCs can be characterized by no obvious features of grading differentiation and relatively large stratigraphic dips.