鄂尔多斯盆地徐庄组碳酸盐岩风暴沉积发育特征及其地质意义

摘要

The tempestites which developed in the Cambrian Xuzhuang Formation in Ordos Basin mainly ineludes many sedimentary structures,such as erosional base,storm flow-generated gravelstones,hummocky and swaley cross-stratification.Sedimentary structure in different conditions can form different storm sedimentary sequences.The ideal storm sedimentary sequence includes five units,from bottom to top,which are composed of A-erosional base and conglomerates representing the deposition of storm peaks and decay period,B-graded bedding with grain-size decreasing upward when storm weakened,C-parallel lamination,D-hummocky cross-stratification representing fluid property changes from density flow to tractive current in storm attenuation period,E-mudstone with horizontal bedding and micrite limestone forming in storm rest period.Based on outcrop observation in the field,there are five types of depositional sequence.Different types of depositional sequence have different sedimentary characteristics and different sedimentary environments.The carbonate tempestites in Cambrian Xuzhuang Formation have important significances in evolution of palaeoblocks and restoration of ancient latitudes,and in research of Ordos Basin palaeogeography.%鄂尔多斯盆地寒武系徐庄组发育碳酸盐岩风暴沉积现象.风暴沉积主要包括侵蚀底面、风暴砾屑层、丘状和洼状层理等沉积构造.沉积构造在不同的条件下会形成不同的沉积序列,理想的沉积序列包括5个沉积单元,从下到上依次为:A侵蚀底面及砾屑段,代表风暴高峰期和衰减期的沉积作用,底面有突变的底界及特殊的沉积构造;B粒序段,为风暴减弱时沉积物从下向上变细的层段;C平行纹层段;D丘状纹层段,为风暴衰减期流体性质逐渐由密度流变为牵引流时形成的产物;E水平层理泥岩和泥晶灰岩段,为风暴停息期晴天条件下的产物.经野外考察发现研究区共可识别出5种不同类型的沉积序列组合,每种序列组合有不同的沉积特点,代表的沉积环境也不同.研究区寒武系徐庄组碳酸盐岩风暴沉积的发现和研究,对于古板块演化与古纬度恢复、鄂尔多斯盆地古地理研究具有重要的意义.