Sedimentary characteristics and processes of the Paleogene Dainan Formation in the Gaoyou Depression, North Jiangsu Basin, eastern China

In this paper,the type,vertical evolution,and distribution pattern of sedimentary facies of the Paleogene Dainan Formation in the Gaoyou Depression of the North Jiangsu Basin are studied in detail.Results show that fan delta,delta,nearshore subaqueous fan,and lacustrine facies developed during the Dainan Formation period and their distribution pattern was mainly controlled by tectonics and paleogeography.The fan delta and nearshore subaqueous fan facies predominantly occur in the southern steep slope region where fault-induced subsidence is thought to have created substantial accommodation,whereas the delta facies are distributed on the northern gentle slope which is thought to have experienced less subsidence.Finally,the lacustrine facies is shown to have developed in the center of the depression,as well as on the flanks of the fan delta,delta,and nearshore subaqueous fan facies.Vertically,the Dainan Formation represents an integrated transgressiveregressive cycle,with the E2d1being the transgressive sequence and the E2d2being the regressive sequence.This distribution model of sedimentary facies plays an important role in predicting favorable reservoir belts for the Dainan Formation in the Gaoyou Depression and similar areas.In the Gaoyou Depression,sandstones of the subaqueous distributary channels in the fan delta and the subaqueous branch channels in the delta are characterized by physical properties favorable for reservoir formation.

Numerical simulation of the detachment dynamics in North China Basin

Refering to geological evidences and recent Lincheng-Julu deep seismic reflection profile in the west-central part of North China Basin, it is concluded preliminarily that a low angle detachment structure may exist in the central part of North China depression. Numerical method is used to simulate the influence of hot mantle intrusive bodies to Cenozoic basin tectonic movements. Numerical simulations show that,① The intrusion of hot mantle material has led to an extensional stress state in the upper crust in central North China depression. As time increasing, the extensional stress state changed slightly in the upper crust and was in keeping with the normal faulting tectonics in the upper crust in depression area. ② In Cenozoic era, under the effects of magmatic intrusion and the resistance of Taihang Mountain, the weak zone produced by the Mesozoic thrust faulting would become a detachment structure.③ With the elapse of time, the horizontal compressive stress gradually concentrated in the median crust, and the concentration of stress may generate strike-slip earthquakes in the median crust above the intrusive body.

Carboniferous–Permian marine transgressions in the Jiyang Depression

In recent years, great attention has been paid to oil and gas exploration in the Carboniferous-Permian strata of the Bohaiwan basin, especially the Carboniferous-Permian marine transgression, using data from drilling, outcrops and carbonate acid-insoluble residue experiments together with the tectonic evo- lutionary history of the peripheral orogenic zones of the North China plate and the Tan-Lu fault zones. The .＇;tudy concludes that marine transgressions took place on six occasions during Carboniferous-Perm- ian time in the Jiyang Depression. The marine transgressions were concentrated in the Late Carbonifer- ous： two marine transgressions occurred in the early Late Carboniferous, and the scale of the first was smaller and the time was shorter than those of the second. The other four marine transgressions hap- pened in the late Late Carboniferous, the first and the fourth of which were larger in scale and longer in time than the second and the third. The seawater came from the Jiaobei area, the eastward part of the Qinling-Dabie residual sea basin, and invaded progressively as a planar flow from south to north and from east to west. These findings have great significance for thorough analysis of the sedimentary characteristics and evolution of the Carboniferous-Permian strata in the livang Denression.

Weathered and Volcanic Provenance-Sedimentary System and Its Influence on Reservoir Quality in the East of the Eastern Depression, the North Yellow Sea Basin

Seismic stratigraphy, core logging and the data from cores are used to identify the development and evolution of the east provenance-sedimentary system and to analyze its influence on the quality of reservoirs in the eastern depression of the North Yellow Sea Basin. The eastern provenance-sedimentary system is a fan delta （delta） and subaqueous fan sedimentary system with volcanic provenance. Its evolution is closely related to internal uplift and coeval volcanic activity. During faulting and volcanic activity, an internal uplift gradually formed and the eastern provenance-sedimentary system began to develop. Clastic materials from the weathered uplift and volcanic activity were the main sources of sediment and were deposited in the Middle Jurassic to the Early Cretaceous. A subaqueous fan sedimentary system developed in the Middle Jurassic, a deltaic to subaqueous fan sedimentary system developed in the Late Jurassic, and a fan delta to subaqueous fan sedimentary system developed in the Early Cretaceous. The volcaniclastic detritus was mainly composed of acidic materials with a small amount of intermediate materials. The reservoir in the eastern sedimentary system is a type of tight sandstone with ultra-low porosity and very low permeability due to the influence of volcanism and diagenesis. The reservoir quality is worse than those of the northern and the western sedimentary systems. However, the high volume of volcanic materials and deep-marine sedimentary conditions resulted in good-quality hydrocarbon source rocks that ensures the exploration potential in the eastern sedimentary system reservoir.