凤县第四纪泥石流堆积物的显微结构构造

本文通过对陕西凤县晚更新世泥石流堆积体块状样薄片进行偏光显微镜观察,发现其具有独特的微观结构构造。文章对这些结构构造进行了形态特征描述和成因分析。认为,不同沉积相的微观结构构造的组合类型不同,因而可作为泥石流堆积体的重要沉积相特征之一。

MICROTEXTURES AND MICROSTRUCTURES IN THE DEBRIS FLOW SEDIMENTS AT BAO-LUE LINE

By observing the rock slice of the old mud-rock flow sediments at Bao Lue line with a polaring microscope, the author discovered some of their special textures and structures l.Microtextures 1) Supporting matrix texture This texture is composel of microcl astics which are some non-chemical deposits and less than 0.05mm in diameter these microclastics are cramcd among the fragme: nts. This is one kind of texture which belongs to high viscid and turbid sediments, ts. 2) Supporting clastic parlicles texture The big or relatively big fragments are in contact with each other at points, The microclastics are cramed only among this fragments, and their amount is small. This is a texture which is the result of a steady flow environment. 3) Sieve-like texture Its cheracteristics is that there are no or a few microclasties among fragment in the sediments. These fragments are not in contact with each other. This results from that the microclastics deposited earlier were carried away by following water flow. 2.Microstructures 1) Massive structure Its characsteristics are that the fragments have a disordered arrangement.This results from that the mass flow deposited quickly. 2) Local directional structure A few fragments are roughly directive in debris flow sediments. The fragments AB plane intersects the bedding plane with angle 50 to 30°. A few fragments were floated off by high viscosity mud fluid. Then they depo sited slowly when stoped. So this structure is formed in sediment. 3 ) Vertical directional structure A few strip of fragment insert in the sediment with angle 90° or more than 45°. This structure is deemed to be characstaristic structure of mass-flow deposit. 4 ) Ring and hemi-ring structure A few fine sands and silts encircle the relative big fragment with their a-axices and their a-axises parallel the configuration of fragmet.Eneircling when the fragment is encircled in full is called ring structure. When the fragment is encircled partly, it is called hemiring structure. Chief mechanism forming this structure is that a-axises of microclastic Parallel the configuration of fragment for reduction of resistance when they move around the fragment. 5 ) Flow linear structure The a-axises of a lot of fine sands and silts are parallel to the strik line of void detween two fragments. And the changes of their azimutbes follow the strik line of void. These fine fragments in fluid are floated and thea-axises are parallel the flow direction. When they deposit in the void spece, they keep this state in sediment. 6 ) Volution structure When a lot of fine sands and silts set around a centre and their a-axises link up each other this structure is formed. The mechanism is related to the high viscosity turbidity current. 7 ) Directional structure The AB planes of most fragments in general order.intersect the bedding plane with angle 5° to 30°. The cause of formation is relate to lower turbidity corrent or braided strea stream. 8) Bedding structure Bedding structure is formed by some laminaes, whose colour, granularity, ingredient are different from that of country rock. It is formed by action of water flow and low viscosity turbidity current. There are some composition of textures and structures of themselves in each sed imentary facis.This compositions are important characteristics of sedimentary facis in the old debris flow sediment.