银根-额济纳旗盆地恩格尔乌苏一带二叠系腕足类动物群及其意义

Permian Brachiopod Faunas from Engeerwusu Area in Yingen-Ejin Banner Basin and Its Significance

恩格尔乌苏处于哈萨克斯坦板块、塔里木板块与华北板块的结合部位,发育恩格尔乌苏断裂。恩格尔乌苏断裂的性质和带内地层特征受到广大地质学家的关注。前人认为在恩格尔乌苏断裂带,地层主要是上石炭统阿木山组,形成构造混杂带,发育蛇绿混杂岩,是塔里木板块和华北板块的分界。笔者在恩格尔乌苏北海尔汗剖面发现了腕足类动物群,该动物群属冷水和暖水混生的"哲斯动物群"。据此,把前人认为是阿木山组中段的地层重新厘定为下-中二叠统双堡塘组。双堡塘组沉积环境为裂谷环境下的三角洲-滨岸相,不是洋盆环境,暗示在早-中二叠世恩格尔乌苏断裂不是华北板块与塔里木板块的缝合带。

Engeerwusu is located at the junction of the Kazakhstan,Tarim and North China plates,and the Engeerwusu Fault was previously considered to be the boundary between the Tarim and North China plates.The strata outcropped in this area were assigned to the Late Carboniferous Amushan Formation.The Engeerwusu Fault zone,along which the Amushan Formation is exposed,has been considered as a tectonic melange zone,or a ophiolitic melange zone.A brachiopod fauna composed by both warm-water and cold-water elements is found from the Haierhan section in the north part of Engeerwusu and this fauna is similar to the Zhesi fauna in taxonomy composition.Accordingly,the strata previously thought as the Amushan Formation are redetermined and assigned to be the Early-Middle Permian Shuangbaotang Formation in this study,and are considered to deposited in the delta-onshore facies under rift valley environment.It indicates that no oceanic basin existed during the Late Paleozoic（Early-Middle Permian） along the Engeerwusu that is between North China and Tarim plates.Therefore,the Engeerwusu Fault zone is not a suture zone between Tarim and North China plates during the Early-Middle Permian,based on the data of sedimentary and palaeontology.