Provenance analysis of the Chang-6 pay sets of the Yanchang Formation in the west-central parts of the Ordos Basin

The types of the parent rocks and directions of sediment supply are discussed on the basis of the types and compositions of the sandstones,cathodoluinescence image of quartz,heavy mineral assemblages,sandstone distribution and palaeogeographic framework during the deposition of the Chang-6 pay sets of the Upper Triassic Yanchang Formation in the west-central parts of the Ordos Basin.The results of research in this study have disclosed that the parent rocks of the Yanchang Formation consist of acidic magmatic rocks,intermediateto low-grade metamorphic rocks and shallow- marine clastic rocks and carbonate rocks,and the principal sources of detritus lay to the northeast,northwest, west, southwest and south,especially the northeast and southwest. In these cases,there developed the deltaic depositional systems in Anbian in the northeast,Yanding in the northwest,Huanxian and Yanwu in the west;braided deltaic depositional systems in Zhenyuan in the southwest,and turbidite fan depositional systems in the Gucheng-Heshui region in the south.