The Study On The Formation And Evolution Of Datong Cenozoie Down-faulted Basin

Datong Cenozoic downfaulted basin is located in the northern graben ofShanxi.It is an experienced multiphase tectonic movement and begandevelopment in the late Cenozoic.Author uses sedimentology and structuralgeology as theoretical guidance,and researched the surrounding mountain ofDatong basin in ancient-distribution of Mesozoic strata sedimentarycharacteristics and tectonic characteristics.In the base of all above research theauthor discusses the surrounding-mountain uplifting process of Datong basinand analyses sedimentary evolution characteristics of the Datong Cenozoicdownfaulted basin.According to what study above,it Mainly has the followingconclusion:1. Datong downfaulted basin formation of lower palaeozoic era in Zhou Linmountains include Cambrian, Ordovician, and in general,it is a set of stableepicontinental-sea carbonate.Basin mainly distributed in the basin on the eastside of Hunyuan, north east side of Henshan,Hanging Temple， west-sideErmaokou-Shentou area， and southwest NingWu syncline and north eastNiushiyao area,and can also be found in southeast of the basin inHengshan.There are the carboniferous-Permian, formations are mainlylocated in the west side of basin in Ermaokou of HuairenCounty-Louzigou-Houshimen-Yujing,and sporadic remaining can be found innorth-side of Hunyuan County、Guanwangpu、Liuguanzhuang、southwest ofNiushiyao and the northeast of Hengshan,and overall it is a set of sea and landinteraction environment mainland delta facies, fluvial facies sedimentary environment. Paleozoic strata can compare in the different parts of theMountainous areas around Datong Basin,which indicates Datong fault basinand the surrounding mountains accepted the Cambrian-Ordovician andCarboniferous Permian sedimentary.No Triassic strata distribution basinsurround the mountains. the Jurassic and Cretaceous strata only distributelimitedly the area of Datong basin2. Datong downfaulted basin and mountains areas stayed in a relativelystable period of construction in Paleozoic,then, Mesozoic entered the stage ofintense tectonic activity.Late Jurassic in NW-SE to the compressional stressfield and the surounding mountain of Datong basin occurred inversive thrustnappe, North East trending reverse faults and NW trending normal faultingtectonics of large-scale. The Cenozoic Datong Basin is characterized by theactive fault activity and the resurrection and reverse development of theMesozoic Yanshan fault during the extensional tectonic setting. The thecontrolling boundary faults of basin are transformed into normal fault, which isa step shaped to the direction of the basin. Tensile stress control of faultingresulted in block collapse, formed the northeast-southwest Datong downfaultedbasin.The contolling fault basin and basin fracture together control the formationto Datong Huairen sag, yellow beam depression uplift and the depression as themain secondary unit consisting of asymmetric half graben faulted basin,andcontroll the Cenozoic sedimentary basin, forming Huairen and Housuosedimentary center, the largest sedimentary thickness is1500m and3500mrespectively.3. Datong basin of Cenozoic sedimentary facies distribution is influencedby tectonic movement,horizontally from the loess hills to the lateral growthrelationship between basin has obvious heterogeneous characteristic at the sametime.In vertical, it is a regular periodic change.Since pliocene, basin of lakefacies model from bottom to top is lacustrine facies-alluvial fan and plain facies -lake facies-fan delta facies-alluvial fan and fluvial facies.It reflects the waterback-in-water back movement.4. The influence of the datong basin of Cenozoic tectonic activitiesreflected oscillation lifting process.Basin formation prior to uplift anddenudation area, affected by the Himalayan movement,and lacunae started fromEocene to Oligocene,The formation of Miocene of datong basin prototypestarted in the period of datong downfaulted basin initial chasmic.Sincepliocene,movement of basin-fracture began, with datong downfaulted basindeveloping into mature stage, and in Pliocene epoch,the basin sedimentarymainly filling-in,a quaternary drape type deposits.5. Datong downfaulted basin surrounding mountain uplift has experiencedthree stages as the followwing:(1) the overall uplift of Triassic period stage(250-205ma)/(2) intracontinental orogeny stage in Jurassic and Cretaceous(205-65ma)/(3) surrounding the Cenozoic basin, strong mountain uplift stage(65ma-present).6. Cenozoic basement strata of planing step of Shuozhou in Datongdownfaulted basin include Permian,Carboniferous,Ordovician and Cambriansystem.In the northeast region of Datong-Hunyuan,Cenozoic strata may includeJurassic and lower cretaceous strata, Yellow beam uplift area in Hu Jia Ling areaCenozoic basement strata underlying Fanshi basalt has upper Cretaceous strataand sections for Archean Fanshi basalt and lots of other Fanshi basalt underlyingstrata may in Paleozoic. The basement strata may have middle Paleozoic stratain the Cenozoic era, which has no deep drilling in the basin.