Characteristics of a sublacustrine fan in a half-graben rift lake basin and its petroleum prospects: Case study on the second member of the Tenggeer Formation, Saihantala Sag, Erlian Basin

Analysis has been carried out on the petrology, context and structure of sublacustrine fan sand bodies in the second member of the Tenggeer Formation. The sublacustrine fans are well developed, and are characterized by the Bouma sequence resulting from typical turbidite deposition and the presence of AAA and ABABAB sequences of non-typical turbidite systems. The depositional textures feature grain distributions typical of turbidite deposits and contain abundant turbidite deposit structures. The sublacustrine fans mainly develop in the lower part of the fault slope break formed by syn-sedimentary faulting in the fan delta front of the gentle slope in the sag and in the troughs in front of offshore subsea fan deposits in the down-thrown areas at boundary of the basin, controlled by an abrupt slope change. The formation of the sublacustrine fan is closely related to the long period of syn-sedimentary faulting activities, and the scale is controlled by the fault activity, slope gradient of palaeogeomorphology and the sediment supply. The sublacustrine fan sand bodies are adjacent to source rocks, and easily form lithologic traps and are favorable for petroleum migration and accumulation, which is significant for the petroleum prospecting in this area.