Characteristics and evolution of lacustrine turbidite of Chang-7 Member of Yanchang Formation in northern Shaanxi

Lacustrine turbidite of Chang-7 Member in the studied area consists of siltstone and fine sandstone with respect to grain size,which is feldspathic lithic sandstone,syrosem arkose and arkose with respect to mineral constitution affected by provenance. There are such apparent signatures as lithology,sedimentary structure,sedimentary sequence and well logs,to recognize turbidite. During the paleogeographic evolution of Chang-7 Member,lake basin and deep lake are both at their maximum extent during Chang-73 stage,resulting in the deposition of Zhangjiatan shale with widespread extent and of turbidite with fragmental-like. Deep lake line is gradually moving toward lake center and turbidite sand bodies are gradually turning better with better lateral continuity,connectivity and more thickness,from stages of Chang-73,Chang-72 and Chang-71 ,which can be favorable reservoir in deep-water.