北黄海盆地东部坳陷下白垩统层序地层及沉积演化OA北大核心CSTPCD

The Lower Cretaceous of the Eastern Depression in the North Yellow Sea Basin is a favorable reservoir for hydrocarbon exploration.However,scarce studies on its fine stratigraphic delineation and sedimentary evolution have restricted the deep understanding of the prospect of hydrocarbon exploration in the eastern depression.Through the core observation,logging and recording analyses,and well-seismic calibration in the eastern depression,it is concluded that the Lower Cretaceous mainly developed 3 third-order sequences,K1SQ1,K1SQ2,and K1SQ3 in bottom-up order.Only 2 third-order sequences,K1SQ1 and K1SQ2,are visible in the drilling,and the descending half-circle of the K1SQ2 sequence is always incomplete,with only the ascending half-cycle of the sequence remaining.The K1SQ1 was in the period of faulting extension,and the vertical lithological sequence exhibited a complete depositional cycle with progradation-retrogradation.In the early stage,there were fluvial phases which developed at mainly the basin margins,the fan-delta phases were in the southern rift zone of the basin,and the braided river-delta phase was in the northern slow-slope zone.Due to the uprising of the lake level,mudstone-dominated lake deposits were developed in the middle and late stages.In the advanced stage,small-scale braided river delta deposits developed in the northern slow-slope zone.The K1SQ2 was in the period of stabilized rupture,which inherited the depositional characteristics of the K1SQ1 period and contracted slightly.The K1SQ3 was in the period of faulting abortion,which was characterized by the development of a large area of fluvial phase deposits.