A STRATIGRAPHIC UNCONFORMITY SURFACE BETWEEN THE NEOGENE AND THE PALEOGENE IN THE JIYANG DEPRESSION,BOHAI BAY BASIN, EASTERN CHINA:GEOLOGIC CHARACTERISTICS, FORMATIONPROCESS AND GEODYNAMIC ORIGIN

摘要

Regional stratigraphic unconformity surfaces are commonly observed in both orogenic beltsand sedimentary basins. They have superficially simple features, but in fact contain abundant geo-logic and geodynamic in formation on basin evolution, which was rarely systematically studied.Based on the elaborate research on geologic characteristics of the stratigraphic unconformity sur-face between the Neogene and the Paleogene in the Jiyang depression, Bohai Bay basin, EasternChina, this paper reconstructed its formation process and paleotopography in the late Oligocene. ltis the most interesting that this stratigraphic uncon formity surface represents the transiton of theJiyang depression evolution from rifting extension to thermal down-warping and also implies an u-plift process during the transition. This paper thought it worthy to study the origin of thisstratigraphic uncohformity surface and its relation to the stage transition of basin evolution. ThenpossibIe influences of regional stress field and deep dynamic process variations on the stratigraphicunconforrnity surface formation were anaIyzed. The stratigraphic unconformity surface betweenthe Neogene and the Paleogene in the Jiyang depression should be the direct result of extremestretching of llthosphere and diapirism of hot upper mantle, which can also possibly explain the co-incidence of the unconformity surface formation with the stage transition of basin evolution. Fur-thermore. the influences of the stratigraphic unconformity surface formation on oil and gas accu-mulation, the erosion amount calculation, and the elaborate time structure recorded by thestratigraphic unconformity surface were discussed.