Origin and depositional model of deep-water lacustrine sandstone deposits in the 7th and 6th members of the Yanchang Formation(Late Triassic), Binchang area, Ordos Basin, China

Sandstones attributed to different lacustrine sediment gravity flows are present in the 7th and 6th members of the Yanchang Formation in the Ordos Basin,China. These differences in their origins led to different sandstone distributions which control the scale and connectivity of oil and gas reservoirs. Numerous cores and outcrops were analysed to understand the origins of these sandstones. The main origin of these sandstones was analysed by statistical methods, and well logging data were used to study their vertical and horizontal distributions.Results show that the sandstones in the study area accumulated via sandy debris flows, turbidity currents and slumping, and sandy debris flows predominate. The sandstone associated with a single event is characteristically small in scale and exhibits poor lateral continuity. However, as a result of multiple events that stacked gravity flow-related sandstones atop one another, sandstones are extensive overall, as illustrated in the cross section and isopach maps. Finally, a depositional model was developed in which sandy debris flows predominated and various other types of small-scale gravity flows occurredfrequently, resulting in extensive deposition of sand bodies across a large area.