The Lithological Features of Sublacustrine Fans and Significance to Hydrocarbon Exploration: A Case Study of the Chang 7 Interval of the Yanchang Formation, Southeastern Ordos Basin, North China

Table 1

The characteristics of log facies of different sedimentary facies in the study area.

Facies	Microfacies	Characteristics		Sedimentary structural	Lithology	Development position
		GR logging curve characteristics	Geometry
Sublacustrine fan	Main channel		Box shape, zigzag box shape	Tabular cross bedding, trough cross bedding, massive bedding, graded bedding	Thick-bedded massive sandstone	Near the boundary of deep lake, the area where the sublacustrine fan has just entered the deep lake
	Overflow deposit		Zigzag box shape	Horizontal bedding, ripple cross bedding	Thin interbed of fine sand and mud
	Branch channel		Zigzag box shape, bell-shaped shape	Tabular cross bedding, trough cross bedding, massive bedding, graded bedding	Medium to thin-bedded massive sandstone
	Interchannel		Zigzag shape	Ripple cross bedding, horizontal bedding, deformed bedding	Thin interbed of fine sand and mud
	Lobefringe		Zigzag shape	Ripple cross bedding, horizontal bedding	Sheet-like turbidite sandstones and deep lake mudstones	The area adjacent to the deep lake plain at the outermost margin of the sublacustrine fan
Deep lake	Deep lake plain		Zigzag shape	Horizontal bedding, rich in siderite, deep lake fossils	Mudstone and shale	Deep lake center