一种特殊瘤状灰岩的成因研究

关于瘤状灰岩的成因主要有三种观点,其中一种认为与碳酸盐结核有关,另一种则认为是差异压实所为,再一种则认为是同沉积作用形成。然而,广西德保县都安下泥盆统达莲塘组发育的一种特殊的瘤状灰岩却因其产状貌似通常意义的砾状灰岩而使得人们将其误认为砾状灰岩。作者通过对这套“砾状灰岩”的沉积岩石学、生物化石、古构造等特征的研究,发现该“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同生和成岩碳酸盐结核,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 ),最后在印支期的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”实为瘤状灰岩,它代表的是闭塞、贫氧的 (台内洼槽 )沉积-成岩环境,是沉积成岩和构造等多种因素共同作用的产物。

Study on Origin of Special Nodular Limestone

There are three interpretations for the cause of formation of nodular limestones.The first interpretation is that they are the beds of carbonate concretions, the second is that they are the result of the differential compaction ,and the third is that they are formed by the sedimentation or the synsedimentary faulting.However, in the Da Liang Tang Formating of lower Devenian Series in Du-an,Debao county,Guangxi,a special nodular limestone is mistaken as a rudstone by some people,because the nodular limstone similar to the normal rudstones in its figure and mode of occurrence. The study on its petrology,paleontology,paleostructurs,etc., shows that the rudstone is not simply the beds of carbonate concretions, it was formed neither by the differential compaction nor by the sedimentation and synsedimentary faulting,and the fact is that lot of carbonate nodules were first formed in the poor-oxygen,closed flute facies of shelf platform;then,the differential compaction led to the extremely concave-convex of the bedding surface or the heterogeneity of the beds; finally,the nodules were turned and also transferred by the shearing ,flexural slip,flexural flow, process of the limb during forming the dome in the Indo-Chinese epoch, the "rudstone" we see today was produced. Hence,the "rudstone" in Du-an was realy the nodular limstone,and it was the result of sedimentationg,diagenesis and tectonism,etc,and it also shows a kind of sedimentary-diagenetic environment which was the poor-oxygen and closed flute of shelf platform.