The Study On Event Deposits Of The Interval 6 Of Yanchang Formation In Ningxian-Qingyang Area

The article was based on the latest achievements home and abroad and guided theoretically by sedimentology, geochemistry, and geophysics. Combined with the geologic background of the area, the paper analyse on the provanace of Chang-6 formation, sedimentary system and pattern of turbidites, Event Deposits.The conclusions are as follows:In order to ascertain the provanace of Chang-6 formation in Ningxian-Qingyang region,and reveal the distribution of sedimentary system,this article,On base of analysis assay,make use of Dikinson t riplot of sandstone clastic composition for in distinguishing tectonic setting.The types of the parent rocks and directions of sediment supply are discussed on the basis of clastic, heavy mineral assemblages, sandstone distribution and classification with debris during the deposition of the Chang-6 formation.The results of research in this study have disclosed that, the tectonic setting of Chang-6 formation is a complex orogenic belt and the principal sources of detritus lay to the west,southwest and south,and the northeast is the mixed provanace area in Ningxian-Qingyang region.Based on the information concluded from the field outcrop,well cores, logging data and palaeontologic marker,Comprehensively analyzing sedimentary systems.There are lacustrine deposits,delta deposits and turbidites deposits in the depositional period of interval 6 of study area,but have extensive turbidites. The basin is wider in the north and steeper in the south,steeper in the west and wider in the east of Ordos Basin.There exist deepwater steep-slope braided delta front and turbidite deposits in study area.The mainly reservoirs are delta front sandbodies and Semi-deep lake turbidite sandbodies.The turbidites in Ordos Basin have the typical turbidity current characteristics. The research of turbidites indicates that they are low-density flow in lacustrine facies and the collapse of braided river delta front in the south-west parts of the basin.The provenance analysis of turbidite indicates that the deposits of turbidite had mainly originated.With all this in mind,The developmental pattern of turbidites was set up.According to petrolgical characteristics of tuff interbed, the paper discusses the properties and distributions of tuff. And through the research on geochemisty of tuff interbed。Based on the research of the distribution feature of high resistance mudstone and effective hydrocarbon source rocks,combine with sedimentary facies,lithofacies palaeogeography framework and seismic profile of Member 7-6 of Yanchang Formation. These kinds of depositional events were regional and local,combining with many factors such as climate which making essential contribution to the oil reservoir of Yanchang Formation.The paper discuss the contact,difference and the relationship with hydrocarbon accumulation on turbidity current event, volcanic event , hypoxic event.