CONSPECTUS ON MESOZOIC BASINS IN BOHAI BAY PROVINCE

According to the remaining of Mesozoic strata and structural deformation on the basement rocks exposed beneath the Cenozoic basin in Bohai bay province, the Mesozoic basins can be divided into 5 periods of development. The first period was an intra-craton large depressional basin developed during the Early-Middle Triassic time. The second period during Late Triassic was a craton interior sag just developed on the southern Bohai Bay. The third period during Early-Middle Jurassic was a compress-flexing basin which developed within the core of the syncline deformed by Late Indosinian movement. The fourth period during Late Jurassic-Early Cretaceous was a rifting basin and the rifting center was on the western Bohai Bay province. The fifth period during Late Cretaceous was a post-rifting sag. As a response to Indosinian and Yanshanian movements, these basins were induced to inversion and erosion. The Early Indosinian movement formed some large-scale gentle foldings trending in east-west in Bohai Bay province , but the deformation during Late Indosinian movement was different from Western to Eastern Bohai Bay province. In the Western part the deformation was weak only EW-trending open folds occurred while in the Eastern part deformation was stronger but some NE folds and thrusts superposed on the EW folds. Some large-scale gentle folds trending in northeast direction developed during Early Yanshanian movement in Bohai Bay province and had resulted in deformation and inversion of Early-Middle Jurassic basin. Middle and Late Yanshanian movements had not caused any substantial foldings in the Jurassic and Cretaceous basins, however there are regional inversion uplifts in the Late Jurassic-Early Cretaceous basins and the Late Cretaceous basins. After Early-Middle Jurassic the tectonic regime had a fatal change from successive sag and compresso-flexing into the period of mainly rifting basin.