浅议沉积学中的流体问题

An overview of hydromechanics in sedimentology

笔者从流体的角度,对近年来有关流体沉积问题的研究成果进行整理、总结、归纳和诠释。从沉积学的角度总体上可将流体分为牵引流、过渡流和重力流3大类:其中牵引流是研究的基础,可进一步分为单向流、双向流和振荡流3种基本类型以及叠置流、复合流和叠加流3种复合类型,可按照流体力学的相关方法展开研究;过渡流和重力流沉积研究的关键在于各种重力流类型之间(浊流、液化沉积物流、颗粒流和碎屑流)及其和牵引流之间的相互转化。流体的沉积机制可分为垂直降落沉积(静水)、底床阻碍沉积(牵引流)和能量减弱沉积(重力流)3大类,各种流体的交互作用最终可形成丘状(洼状)交错层理的水动力条件。通过综述可以发现,从流体角度进行沉积学研究尽管困难,但仍然可行,特别是对于复杂水动力条件下的沉积学研究具有一定的意义。

The reported and published research works on fluid deposition in recent years have been reviewed,summarized,concluded and explained in this article from the viewpoint of sedimentary flow.Sedimentary flow can be classified into traction flow,conversional flow and gravity flow based on sedimentology perspective.Among these,traction flow is the foundation of the sedimentary study,which can be further divided into three elementary types(unidirectional flow,bi-directional flow and oscillatory flow)and three compound types(overlay flow,combined flow and superposition flow),which can be further studied using hydromechanics method.The key to the study of conversional flow and gravity flow deposition is the mutual transitions between traction flow and gravity flow,as well as different gravity flow types,such as turbidite current,fluidized sediment flow,grain flow and debris flow.The sedimentary mechanics of flow could be classified into three types which include vertical settling deposition(static water),bed blocking deposition(traction flow)and energy weakening deposition(gravity flow),the interactions of different flow types could finally form the hydrodynamic conditions of hummocky(swaley)cross-bedding.This overview suggests that studying sedimentology from a fluid perspective is feasible in spite of many difficulties,and has an important significance especially in complex hydrodynamic conditions.