The Research On The Sedimentary Palaeogeograph And Basin Analysis Of Cretaceous In Wu Langai Basin

With sedimentology, stratigraphy, paleogeographic and sedimentary basin analysis theory as the guide, comprehensive outcrops and drill logging data, combined with the regional geological survey report, mineral reports and predecessor's researches, taking stratigraphy, sedimentology and structurology for multidisciplinary usion analysis, this paper sumed up the lithofacies-paleogeographic and basin analysis results of lower Cretaceous Bayanhua group in Wu Langai Basin.Based on the precursors researches and our previous work, divided the Wu Langai Basin into five secondary depression, Gao Lihan, Wu Lite, Ba Qibei, Ba Yanhushuo and Bai yinhua, further more, this paper summarized and compared the stratum of the Ba Yanhua group.Through the measured sections and observed sections in field, drilling and logging data, researched the lithofacies types, sedimentary structure, section structure features of lower Cretaceous Bayanhua group in Wu Langai Basin, the results show that there are three sedimentary facies could be identified in this area, classified as alluvial fan facies, lakes phase, sublacustrine fan facies, detailed characteristics description of the various kinds of sedimentary facies also be writed in this paper. Further, the overall Bayanhua group belong to lake sediment system, reflects the lower Cretaceous in Wu Langai Basin experienced longitudinal evolutionary sequences like sublacustrine fan of deep lake - shallow lake - alluvial fan sedimentary.On the basis of the basin formation and sedimentary system analysis, using the principle of sequence stratigraphy, divided lower Cretaceous Bayanhua group into two groups. According to the stratigraphic sequences characteristic and the stratigraphic framework figure found that the formation in Wu Langai Basin experienced process as twice sedimentary cycles of trangressive system tract and regressive system tract, twice maximal flooding surface, three sequence boundaries. Deposition area is whole in lakes deposition system, and it can be further divided into swamp,shallow lake sand bars,sheet sandstone,bay phase,beach dam,lake tidal flat.Based on the predecessor's research achievement, combining the sedimentary system, stratum and stratigraphic framework in this research, according to topic research task and purpose and former geological data, research degree, using point (single outcrop or singlewell) - line (united Wells profile) - plane (lithofacies - paleogeographic diagram) graphic method, constructively, taking coal seam as isochronal geological-mass (in k1b2 section), located optimal descision k1b2 - k1b4 (k1b1 not dozen wear) for mapping unit, programing paleogeographic map of lower Cretaceous Bayanhua group in Wu Langai Basin. The results show that in the central region of Wu Langai Basin in early cretaceous, there are three deep lakes where are widely distributed dark mudstone, gradually modify to transition phase to the north as marked by celadon mudstone, with gentle terrain slope. Contrary, side slope is increased relief in the south, developed shallow lakes which were rolling north east, paralleling with the basin margin. Between the shallow lakes is belonged to binhu region, extend to the south and north were ancient land erosion areas.Relyed on the analysis results of the basin, the internal development with Wu Langai basin tectonic style combining analysis research. We think Wu Langai basin evolution and the controlling factor has the following features: the tectonic, Wu Langai basin covers the Paleozoic above with He GenShan suture zone, center of basin axis, suggesting that ancient basic superposition of basin development base structure plays an important control function. In Indian teams northwest - south east period to the main squeeze, and formed in north China region, thick crust surface appear magnificent plateau namely ancient plateau, Wu Langai basin is located in the northern of Mesozoic early plateau. Late Jurassic, along with the collapse of north China plateau, basin mainly into the stretch deformation, especially evolutionary stages, is stretching deformation of the cretaceous rush. According to the regional geological data and drilling material, ulam early basin cover basin into because faulted basin, control is a series of normal faults, we have in the west margin found several are faults. Late downwarped basin evolution, stratigraphic dip into sedimentary basin, and slow to peripheral expansion overburden, cause basin exceed the boundary faults common suffered previously covered.Based on basin analysis, the study combine Wu Langai basin with its internal and developmental tectonic stycle. we think that there are following features aboat wu lan gai basin and its governing factor: on the tectonic, wu lan gai basin cover above paleozoic He Genshan suture zone ,the center of basin is coincide with suture zone axis,it suggest that age-old base structure plays an important control function in the development of basin. In indosinian ,the directon of major squeezing is north west - south east,and thickened crust is formed in north China region ,grandiose plateau whose name is North China paleoplateau turns up in the earth's surface , wu lan gai basin is located in the north rim of the Mesozoic early plateau.In late Jurassic epoch,basin enter into Evolutionary stages of give full priority to stretching deformation, especially, the Cretaceous period is the fastigium of stretching deformation.according to areal geology and well drilling data, break is the cause of formation of wu lan gai early basin.a series of normal fault control the development of basin, we have found several normal fault in the west margin of basin.later stage of basin evolution change over to downwarpingregion,and stratigraphic dip slow down,basin deposition expand and override toward persphery,it lead to boundary faults of early basin suffered cover.