Analysis of Sediment Provenance of Chang8 Group of Yanchang Formationin Yanchi-Dingbian Area of Ordos Basin

In the west part of Ordos basin,the sedimentary characteristics of Chang-8 formation in Yanchi-Dingbian area vary a lot.However,the provenance and depositional system are not well studied,having an unfavorable effect on further exploration.In order to verify the provenance and depositional system distribution,we analyze the characteristics of the mother rocks in the source by studying the mineral composition,heavy mineral,debris and geochemical characteristics.The results indicate that there is an obvious partition in both detrital component and heavy mineral.Integrating the debris distribution and rare-earth element features,we conclude that this area is mainly controlled by provenance from three major directions:northwest,north,and northeast,among which the provenance from the northwest and the north are the most primary ones.Palaeo-provenance match well with the depositional system in space,thus radically determines the depositional system pattern of the Chang-8(Member 6 of Yanchang Formation) and distribution of sand body,which contribute a lot to oil migration and accumulation.