Abstract:

Geological surveys of the East China Sea began in 1974.Since then,the Bureau of Marine Geology,Ministry of Geology and Mineral Resources is in charge of the extensive geological and geophysical investigations on this sea area of 770,000 sq km.Up to now,plenty of useful information have been obtained.According to seismic spectrum and well logging data,the stratigraphic sec-tions of the East China Sea can be divided in descending order as follows:the Donghai Group(Q),the Shantan Formation(N₂),the Liulang Formation(N₁³),the Yuquan Formation(N₁²),the Longjing Formation(N₁¹),the Huagang Formation(E₃),the Pinghu Formation(E₂),the Paleocene and Upper Cre-taceous,etc.These sediments,which have a total thickness of 15,000m,consist predominantly of dark gray-greenish gray and light gray mudstones and sand-stones interbedded with conglomerates,carbonates and coal.The East China Sea includes following six tectonic elements(1st order):Zhemin uplift area,the East China Sea shelf basin,Diaoyudao uplift-foldedbelt,the East China Sea shelf foredeep,Okinawa trough basin and Ryukyu uplift-folded belt.The shelf basin can be divided into Fujiang,Zhedong,Taibei,Taixi depressions.The later three depressoins are subdivided into 14 sags(e.g.Xihu,Oujiang,Minjiang,Jilong)and arches(e.g.Hupijiao).Up to now,13 structural belts and more than 100 local structures(e.g.Longjing)have been located.The closed area of the local structure is generally more than 50 sq km,the largest one is up to 1,000 sq km.The East China Sea shelf basin,which has an area of 284,000 sq km,contains thick Meso-Cenozoic sediments,mostly deposited in marine,swamp and lacustrine environments,where there are abundant organic matters,many source rocks,shallower oil threshold depthes,good trap conditions and ade-quate timing.Commerial oil and gas have been tested from three horizons of Eocene,Oligocene and Miocene ages respectively in Pinghu and Longjing structures.The authors suggest that pressed anticlinal and buried-hill drapping anticlinal hydrocarbon pools are predominante in the basin,and other pools of stratigraphic,lithologic,reef and combination types could be also disco-vered there.