Reconstruction Of The Early Crataceous Basin And Its Evolution In Southwest Ordos

Ordos basin has developed during Mid-late Triassic and Early Cretaceous and has beenreformed since Late Cretaceous. It mainly possesses the characters of intra-craton and is aresidual basin with multi-stage and different reformation. So this paper taking LowerCrataceous of northwest Ordos basin as the study object, many kinds of disciplines are appliedsynthetically in this thesis, such as, stratigraphy, structural geology, sedimentology etc. On thebasis of the basic formation characteristics, the gravel fabric analysis, reconstruction of thedenuded thickness and the original thickness, combining with the analysis of structural settingduring basin's developing and the characteristics of later reformation, moreover, outside andinside study, area and major study, multi-datum, multi-method have been utilized at thereconstructed of Early Crataceous basin in southwest area.The reconstruction of strata's denuded thickness indicated that during Early Crataceous thebound of southwest basin was approximate Yellow River or beyond it at east, north boundaryof WeiHe basin and even farther south at south, LongXian-QianYang strip at southwest andoverlapping above obduction zone at west. Periphery highland and orogenic belt of southernand southwest were the main provenances. The WeiHe area was a transition belt ofbasin-and-range at that time. Nonmarine clastic rock sediment was developed at thefeebleness tensional setting of Early Crataceous. The prototype basin was a depression basinwith the characteristics of asymmetry and uneqilibrium shape of high in the east and south,low in the west and north. Depocenter and subsidence center was located at JingChuan-ZhenYuan region. The maximum thickness was about 1600 meters. After Early Crataceous,basin uplifted continuously, episodically and differently, which caused strong and unevenerosion, for example, the max erosion thickness in Mesozoic could be about 2000 meters nearYellow river in the east, brought the basin to present a entirely residual appearance.The gigantic sediment of Lower Crataceous impelled the hydrocarbon acting of sourcerocks in deep zone reaching peak and assembling and reservoiring cosmically. The strong erosion and reformation after Early Crataceous leaded the hydrocarbon acting slow doun orstasis and the further adjustment of oil and gas, which was disadvantage of reservoir'scontinuous forming, extending or preserving, at the same time exsolution and exhaustion ofoil and gas during the changing of temperature and pressure offseted the disadvantages partly,which was propitious to late reservoiring.The study of this thesis will help to develop the study recognition and the improvement ofanalytical methods of reformated basins, the achievements and conclusions will help toinstruct the evolution, the coupling of basin-and-range and the petroleum and gas explorationin the deep layers of southwest area in Ordos basin.