Provenance analysis of Oligocene sediments in western Qaidam Basin

Provenance analysis is of great significance in determining the sediment source,parent rock properties,sediment transport distance,and even sedimentation and tectonic evolution of the whole basin.Heavy mineral assemblages,light mineral assemblages,REE distribution pattern and palaeocurrent direction were systemically analyzed in this paper.Six main provenances in the Oligocene period of western Qaidam Basin were determined,i.e.,eastern Altun provenance,western Altun provenance,Aral provenance,Tomorlog provenance,Qimantag-Dongqaishan provenance,and Wanxi-Gansen provenance.Provenance characteristics significantly control sediment characteristics.The sediment transport distance from western Altun provenance was short.Pyroclasts supply was evidently controlled by seasonal floods,so it was very unstable and always developed near-source steep type fan delta and near-shore subaqueous fan sediments.Sediments from the rest of the provenance were transported for a long distance,with the maximum transport distance being about 190 Km;pyroclasts supply was stable,and thus developed braided delta sediments of far-source mild slope type.Due to the influences of several provenances,the sedimentary characteristics were obviously different.