Abstract:

Geological characteristics in southwest of the East China Sea Basindiffer greatly from those of other parts:1.It was marine environment before the Neogene;2.The faults are distributed in echelon pattern;3.Regional uplift in the end of the Eocene resulted in sedimental lacunaeand erosion for about 15-20 million years in the west part of the area.This article firstly proposed the existance of positive inverted struc-tures.The main proofs are:1.There is a“basin”shape basement beneath the positive invertedstructures;2.Seismic reflection is“dune”shape;3.Sediments of great thickness spread under the structures;4.The fault texture on top of the structures is “flower”shape;5.The faults usually do not cut the basement;6.The upper parts of the structures are generally eroded;7.Formations beneath the structures have abnormal high-pressure;8.Low vilocity.The existance of wrench faults,plastic formations,seesaw motion andhorizontal compression are considered to be the formation factors of thiskind of structures.It has been proved by well drilling in both Bohai and the South ChinaSea that high-pressure mudstones beneath the structures are the most favour-able source rocks.Thus,the structures under which there are plasticformations are favourable places for the enrichment of hydrocarbon in the East China Sea Basin.