广西德保都安下泥盆统砾状灰岩成因研究

STUDY ON ORIGIN OF RUDSTONE FROM LOWER DEVONIAN SERIES IN DU-AN, DEBAO COUNTY, GUANGXI

广西德保县都安下泥盆统达莲塘组(相当塘丁组)的陆棚台内洼槽相碳酸盐岩地层中发育一套砾状灰岩。根据其岩石学、生物化石、古构造等特征分析,认为该砾状灰岩既不是沉积作用形成,也非同沉积构造作用形成,而是首先在闭塞的台内洼槽环境中形成大量的碳酸盐结核,然后差异压实作用导致地层表面强烈地凹凸不平或地层整体的不均匀性(致使强度降低),最后在穹隆形成过程中,由于翼部的剪切、弯滑、弯流作用,致使结核发生转动、移动而形成今天所见的砾状灰岩。因此都安砾状灰岩不能用作为包括斜坡在内的一些沉积环境(作用)的判别依据,它是多种因素共同作用的产物。

There is a set of rudstone in the Liantang Formation (equivalently Tangding Formation ) of lower Devonian Series in Du-an, Debao County, Guangxi. The rudstone is developed in the flute facies of shelf platform. Study on its petrology, palaeontology, palaeo-structures, etc. , shows that the rudstone is neither formed by the sedimentation nor by the synsedimentary structural process, but by the joint processes of many factors, i. e. , a lot of carbonate nodules were formed first in the closed flute facies of shelf platform; then,the differential compaction led to the concavo -convex of the bedding surface or the heterogeneity of the beds; the nodules were turned and also transferred by the shearing and flexural flow process of the limb during forming the dome, finally, the rudstone was produced. Hence, the rudstone in Du-an cannot be used as the evidence for sedimentary environment including continental slope.