山西芮城水峪地区罗圈组海侵沉积物

Transgressive deposits from the Luoquan Formation in Shuiyu,Ruicheng,Shanxi

关键词:  新元古代冰川  罗圈组  芮城  水峪  鲕粒白云岩  海岸牵引流

Key words:  Neoproterozoic glaciation  Luoquan Formation  Ruicheng  Shuiyu  oolitic dolostone  coastal tractional current

摘要:

华北陆块南缘、西南缘广泛分布的罗圈组及其相应地层多被认为是新元古代末期冰川沉积。山西南部芮城水峪剖面位于华北南缘罗圈组出露范围的最北端,罗圈组受下伏蓟县系龙家园组白云岩风化面形态控制,横向岩性变化剧烈,分别由准原地堆积的风化角砾岩、紫红色含砾泥岩及一套特殊的"含砾砂质鲕粒白云岩"组成,均为温暖气候下海侵或海侵改造产物,与冰川作用无关。"含砾砂质鲕粒白云岩"在华北南缘罗圈组中尚属首次发现,具有明显的指相意义。该地区罗圈组海侵沉积物的存在,可能表明华北南缘罗圈组在各地区存在沉积环境乃至地层时代的巨大差异,不能简单以某一冰期的"冰碛岩"笼统看待。

Abstract:

The Luoquan Formation and its equivalents on the southern and southwestern margins of the North China landmass have long been interpreted as the latest Neoproterozoic glaciogenic deposits.In the Shuiyu region,Ruicheng,Shanxi,the Luoquan Formation shows a horizontal dramatic change due to the controls of the erosional surface of the underlying strata,and only consists of a succession of extraordinary "gravel-bearing sandy oolitic dolostones" containing parautochthonous gravels and intraclastics.Viewed from lithology,sedimentary textures and structures,and sedimentary facies,the authors in the present paper argue that the "oolitic dolostones" in the Luoquan Formation should be originated from the coastal tractional currents under the conditions of warm climates rather than from the glaciation.The first report of the "oolitic dolostones" has important implications for the recognition of the sedimentary environments of the Luoquan Formation.