漠河盆地西缘阿陵河砾岩层的形成时代及其地质意义

Geochronology and geological significance of the Alinghe conglomerate layer in the western margin of the Mohe Basin

一直以来,大兴安岭北部漠河盆地额木尔河群的地层自下而上划分为绣峰组、二十二站组、漠河组和开库康组。本次研究在漠河组之上发现一套复杂成分砾岩层,暂将其划分为阿陵河砾岩,为非正式填图单元。在详实的野外地质调研基础上,开展了层序地层学、沉积环境分析及阿陵河砾岩层中粗粒长石砂岩的碎屑锆石U-Pb测年研究。结果表明:阿陵河砾岩层整合于漠河组之上,是漠河盆地萎缩期潮湿—温暖气候条件下冲积扇相的沉积产物,物质来源主要来自盆地南部,其沉积时代应为晚侏罗世—早白垩世。漠河盆地从西向东,沉积时代变新,主体沉积时代由中侏罗世、晚侏罗世向早白垩世演化,与蒙古—鄂霍茨克洋自西向东闭合时代具有一致性。

It has been widely recognized by scholars for a long time that the Emuerhe Group in Mohe Basin in northern Great Xing’an Mountains, from bottom to top, consists of Xiufeng Formation,Ershierzhan Formation, Mohe Formation and Kaikukang Formation. A set of complex conglomerate layer has been identified recently on the Mohe Formation, which is temporarily named Alinghe conglomerate(informal mapping unit). In this paper, based on detailed field geological investigation, some studies on sequence stratigraphy, sedimentary environment and U-Pb dating of the detrital zircon of coarse-grained arkose in the Alinghe conglomerate layer.The results indicate that the Alinghe conglomerate is integrated on the Mohe Formation and is the sedimentary product of alluvial fan facies under humid and warm climate during the shrinking period of Mohe Basin. The material source was mainly from the south of the basin,and its sedimentary age should be Late Jurassic to Early Cretaceous. The sedimentary age of the Mohe Basin, from west to east, is determined from Middle Jurassic to Late Jurassic to Early Cretaceous, and the whole basin is updated from west to east, which is consistent with the closure of Mongolia Okhotsk Ocean from west to east.