Research On Sedimentary System Of Early Cretaceous In Liupanshan Basin And Surrounding Areas

The paper, that studied the outcrops and core, the original sedimentary structures, lithology, geochemical index, provenance characteristics and combined with logging and seismic facies, have redefined of the stratigraphic division and correlation in the research area. From point, line to surface, protraying the single well sedimentary facies histograms, typical profile histogram, well profile comparison chart and even sand flat sedimentary facies distribution of maps, conducting the sedimentary facies distribution research and provenance analysis, and exploring the source area. Researching and classification of depositional systems and sedimentary facies and sand body distribution characteristics.The Cretaceous in the study area only develop the Liupanshan group. From the old to new the Stratigraphic is divided into five groups:Sanqiao formation, Heshangpu formation, Liwaxia formation, Madongshan formation and Naijiahe formation. The thickness is developed and up to more than 3000 meters. The Liupanshan group lithology and sedimentary facies are mainly developed alluvial fan facies conglomerate, and transition to the delta facies sandstone, finally to lacustrine argillaceous limestone. Sedimentary evolution between the three continuous development, and the underlying and overlying strata were angular unconformity.Through the study of the main characteristics of basic rock, the ancient flow analysis and gravels in the research area. It is considered that the study area is mainly controlled by the three direction that are the southwest, the northwest and the northeast areas. Presumably the southwestern provenances are from Qilian-Qinling orogenic belt, the northwestern provenances are from the north Qilian massif, and the northeastern provenances are from the Huabei platform.we identified that the early Cretaceous research area is classified into four kinds of sedimentary system, they are alluvial fan sedimentary system, river sedimentary system, the braided fluvial delta sedimentary system and lake sedimentary system.The study area in the deposition period of Sanqiao group is mainly alluvial fan sedimentation. In Madongshan formation sedimentary period is mainly fluvial sediments.At Liwaxia formation sedimentary period has evolved into a braid river delta and shore shallow lake facies. The lakes developed to its peak in Madongshan formation sedimentary period, with shore shallow lake facies and semi deep lake facies sediments. Naijiahe formation sedimentary period is deposited on the decline of lakes, shrinking lake area, with semi-deep lake deposits, parts of the area have evolved into the semi deep lake deep lake facies and salinization lacustrine deposition.