THE PROVENANCE AND FEATURES OF DEPOSITIONAL SYSTEM IN THE YANCHANG FORMATION OF TRIASSIC IN SOUTHEAST AREA OF ORDOS BASIN

Provenance and features of depositional system of Yanchang Formation of Triassic in southeast margin of Ordos basin was analyzed through regional stratigraphic correlation,paleocurrent measurement,distribution and combination of light minerals and heavy minerals,and sedimentary facies.The results showed that the Luliang uplift which received the late Triassic basin sediments uplifted after Yanchang period and was not the Provenance of Yanchang Formation in the southeastern margin of Ordos basin.The paleocurrent revealed by Yanchang Formation in Yichuan-Fuxian in southeast margin of Ordos basin was northeast direction.Characteristics of mineral assemblage were similar to those in the north of Yan'an delta.Sedimentary debris content gradually reduced from Zhijing-Chuankou to Fuxian area,and the content of unstable mineral such as chlorite increased in sequence from the north,middle to the southwest of Fuxian delta,indicating that the provenance direction of Yanchang Formation in the southeastern margin of Ordos basin was northeast direction.In fact,the Fuxian delta was the eastern stretch of Yan'an delta,which developed platform delta front and sloping delta front of meandering river delta.The platform delta front mostly produced the truncated and completed underwater distributary channel sandstone body and the sloping delta front mostly induced the compound and overlap-type channel mouth bar sands.High quality reservoir mostly distributed in the truncated distributary channel and the overlap-type channel mouth bar sands.Determination of the features of depositional system was helpful to the development of further hydrocarbon exploration in the study area.