桂北下震旦统杂砾岩成因之探讨

A DISCUSSION ON THE ORIGIN OF THE LOWER SINIAN POLYCOMPONENT CONGLOMERATE IN NORTHERN GUANGXI

广西北部分布着下震旦统两套厚度大的杂砾岩系,即长安组与南沱组,均由含砾泥质岩、含砾砂岩及其夹一些砂。泥岩组成。过去认为与冰川作用有关,称之为“冰碛层”等等。近年来,人们对其成因有所争议。笔者借实习之机,在该区对南沱组杂砾岩系进行野外与室内研究,根据其岩性特征、砾石成分,砾石形态和表面特征,以及其夹层沉积特征和粒度分析结果,认为这套杂岩系不仅具有冰川作用的痕迹,而且还有正常海洋沉积性质,它是由大陆冰川携带碎屑入海消融后迅速堆积,受重力等因素形成的泥石流沉积物,属冰融泥石流沉积。

Two thick polycomponent conglomerate formations of Lower Sinian (ie, the chang an Formation and the Nantuo Formation) are distributed in Northern Guangxi. They are composed of gravel-bearing mudstone and gravel-bearing sandstone intercalatated with sandstone and mudstone, and were considered genetically related to glacier and known as 'tillite' and glacier-marine deposit' etc. in the past. In recent years, however, disagreements have arisen on their origin. The author conducted field and laboratory studies on the polycomponent conglomerate of the Nantuo Formation during his course of post-graduate. From the evidence of the lithology, the component, shape and surface features of the gravel, the depositional features of the intercalations, and the results of analysis, it can be seen that the polycomponent conglomerate formation not only shows traces of glacier, but also the characteristics of normal marine deposition. Based on this, the author balieves that it may have been debris flow deposits transported by land glacier and deposited in marine environment because of the melting of the glacier.