Characteristics and formation condition of gravity flow developing in low-lying slope zone of Dongying delta in Jiyang Depression

Key words:  low-lying slope zone of large delta  gravity flow  debris flow  identification mark  Dongying Sag

Abstract:

The latest deep-water gravity current theory was used to subdivide the type of the gravity flow developed in the low-lying slope zone of large delta, and the discerning standards were established; and then the controlling factors of the distribution were discussed. The results show that a series of gravity flows can be developed in the low-lying slope zone of the large delta. The sand body formation however is not determined by one certain flow state, but always by several flow states including plastomer, debris flow and turbidite. They transform in order and have different lithofacies associations. According to the different longitudinal sequential patterns, the gravity flow could be divided into four types, which include the slide sand, the slump sand, the debris flow sand and turbidite. By comparative analysis of sedimentary structure characters, grain size characters, logging face and seismic face, the sand type could be identified. The controlling factors of the formation and distribution of gravity flow which developed in the low-lying slope zone of large delta include ancient material source, ancient sedimentary slope angle, contemporaneous fault and depositional base-level cycle. Ample material source is the material base for the development of gravity flow, and different types of sands could transform in order when the slope has suitable sedimentary angle. The decreasing plate of codeposition fault is the favorable development area, and the depositional base-level cycle controls the longitudinal distribution of the gravity flow sands.