Abstract:

The research and exploration of shallow delta have been paid much attention in recent years. A large shallow braided delta developed in Longdong Area of southwestern Ordos Basin. Based on some outcrop, core, logging, seismic data from Triassic Yanchang Formation in Ordos Basin, it is suggested that the geological setting of Ordos Basin is favorable for the formation of shallow braided delta during the period of Yanchang Formation. The shallow braided delta is characteristics of coarse grain size, many soft lithoclasts, low content and texture maturity, many cross beddings, normal cycles, many distributary channels, thick sandbodies, distal extension etc. During the sedimentation of the shallow braided delta in southwestern Ordos Basin, the sediment center was near to provenance, the width to depth ratio of the channel was big and shallow water sedimentary structures were developed. The development of the braided shallow delta was controlled by the tectonic activities and lake level changes and therefore, the shallow braided delta in southwestern Ordos Basin was formed in the form of small plain and large delta front.

Key words:  shallow braided delta, sedimentary model, Yanchang Formation, Longdong Area, Ordos Basin