鄂西—湘西地区震旦系灯影期岩相古地理与层控铅锌矿关系初探

Preliminary Approach on the Stratabound Lead—Zinc Deposits and Lithofacies Palaeogeographic Framework of the Dengyingxia Age, Sinian(Edicarian),in Western Hunan—Western Hubei Area

依据研究区震旦系十余条代表性剖面的沉积特征及其横向展布规律,并结合两种相变面和两种穿时性划分出的地层格架,应用等时面优势相成图方法编制了震旦系灯影期岩相古地理图。区内古地理格局具有东高西低、北浅南深(水深)的特点,沉积自南西向北东超覆,层位逐渐抬高、穿时;岩性、厚度、颜色和沉积相类型上的差异是统一沉积背景下沉积物相变、穿时的结果。灯影组以发育大套白云岩为特征,纵向上构成总体向上变浅的沉积相序列,同时反映了缓坡型碳酸盐岩台地的生长发育过程;空间上从北西至南东发育从潮坪、局限台地、浅滩、台地边缘斜坡到台地前缘盆地等沉积。岩相古地理对层控铅锌矿具有明显的控制作用,主要分布于台地边缘浅滩相与局限台地潮下过渡部位。

Based on field investigations, the sedimentary characteristics and horizontal correlation as well as two types of facies-changing surfaces and two types of diachronisms of the upper Sinian（Edicarian） for more than dozen main logged sections in the study area are comprehensively studied in this paper, all of them become the basis to establish the lithofacies palaeogeographic map of the Dengyingxia Ages of Sinian System in the light of dominant facies and in the way to make stratigraphic map. The feature of paleogeographical framework was that the southern formed in shallow water and the northern in deep water; the difference in lithology, color, grain type of the stratigraphic sediment-styles and the assemblages and the character of sediment-facies were all controlled by the sedimentary facies-changed and diachronism. Vertically, the stratigraphic succession from the dolomite of the Dengying Formation makes up of a larger scale upward- shoaling succession of sedimentary facies and demonstrates a growth process of the ramp carbonate platform. Horizontally, the principal lithofacies palaeogeographic units in the upper Yangtze region,i, e. carbonate tidal flat,subtidal facies of restricted platform and platform marginal facies as well as basin facies from the northern to the southern have been described. The stratabound lead-zinc deposits distributing between platform marginal facies and subtidal facies of restricted carbonate platform were dominated by the lithofacies palaeogeographic framework.