Sedimentary Characteristics and Environment of the Paleogene Nangqian Basin in Qinghai Province

Nangqian basin is a typical representative of the medium-mini-type Paleogene basins controlled by the local north-northwest-trending faults and distributing along the Jinsha-Red River belt in the northeastern margin of Qinghai-Tibet.Combined with the results of field geological investigation,and analysis and determination of samples,as well as the indoor comprehensive study,the paleoclimate characteristics,indications of sedimentary facies,the provenance,as well as depositional environment of Gonjo Formation in the Nangqian basin were systematically analyzed in the framework of basin evolution.It is concluded that the Gonjo Formation can be divided into a three-stage structure,and the depositional environment is an alluvial fan-river-lake-delta environment;the complex conglomerate gravel composition,the poorly sorted and rounded sandstone,and the fillings being the sub-angular shaped inequigranular grit,the calcite cement or the ferruginous cement indicate that the sedimentary environment is proximal and quickly accumulated,and the paleocurrent direction is versatile;the depositional environments belong to warm and moist-dry climate with strong evaporation.