Progress of shallow-water delta research and a case study of continental lake basin

By summarizing the research progress of shallow water delta and combining with the study of shallow delta of the Yanchang Formation in Ordos Basin, this paper discussed the sedimentary characteristics of the shallow water delta. The results indicate that the basic conditions for development of shallow water delta include stable tectonic setting, large basin area, low relief of paleotopography, frequent changes of lake level, shallow water and abundant provenance supply. In general, shallow water delta deposition lacks the traditional characteristics of three-tier structure. There are differences between different types of shallow water delta sedimentary bodies. For example, shallow braided river delta features in coarse grained sediments, strong water energy, incomplete vertical facies sequence, and poor preservation of mouth bar. In contrast, mouth bar is common in shallow water meandering river delta. The case study of continental lake basin shows that the Yanchang Formation of Ordos Basin developed shallow water braided delta and shallow water meandering delta, which are characterized by small area of delta plain and widespread delta front zone. Its width-depth ratio of channel is large, the sediments are coarse, and it is common to find multiple superimposed erosion surfaces and large trough-shaped, wedge-shaped cross-bedding in plain distributary channel deposits. Delta front can extend more than one hundred kilometers and underwater distributary channels are characterized by lateral branches and bifurcate and vertical intermittent fining upwards rhythm. Moreover, the space-time evolution of shallow water delta sedimentary system in the study area is also discussed. ©, 2015, Oil and Gas Geology. All right reserved.