内蒙古西部额济纳旗及邻区上石炭统—下二叠统阿木山组的沉积特征和时代

Sedimentary characteristics and age of Amushan Formation in Ejin Banner and its adjacent areas,western Inner Mongolia

额济纳旗地区是阿木山组分布的最西端,产出于伸展背景下的裂谷环境,火山岩比较发育,从下到上可分为火山岩段、灰岩段和碎屑岩段。火山岩段和灰岩段产丰富的类化石,灰岩段下部产丰富的珊瑚化石。珊瑚化石的时代主要为晚石炭世,类从下到上分别属于Triticites组合和Pseudoschwagerina组合,从而确定阿木山组的3个岩性段之间以叠覆关系为主,地质时代为晚石炭世至早二叠世,其中火山岩段为晚石炭世小独山期或更早;灰岩段下部为小独山期,上部为紫松期;碎屑岩段为早二叠世紫松期或更晚一些至隆林期。

The westernmost end of the Amushan Formation is Ejin Banner area. The Amushan Formation was formed in an extended setting of rift, with abundant volcanic eruption. It comprises three units, namely volcanic rocks, limestone, and clastic rocks. Abundant fusulinids were found in units of volcanic rocks and limestone. In addition, abundant coral fossils indicating the age of Late Carbonifer- ous were found in the lower part of limestone. The fusulinids fi：om units of volcanic rocks and limestone of Amushan Formation be- long to fusuhnid Triticites and Pseudoschwagerina assemblages, suggesting that the Amushan Formation should be assigned to the Late Carboniferous-Early Permian period; in addition, the unit of volcanic rocks should be assigned to the Late Carboniferous Xiaodusha- nian stage or even earlier, the lower part ofhmestone unit to Xiaodu Shanian stage, the upper part of limestone unit to Zisongian stage and the clastic rocks unit to the Early Permian Zisongian stage or even to later Longlinian stage.