Stud On Carbonate Petro;ogy, Sedimentology And Sedimentational Synchrony Of Late Cambrian In The North Part Of North China Platform

The north part of North China Platform is roughly the same as that of central to north Shanxi province,north Hebei province,BeiJing and Tianjin areas.Thls paper mainly deals with the upper Cambrian of this region.The upper Cambrian contains three formations(from bottom to top): Gushanzu Formation, Changshanzu Formation and Fengshanzu Formation.Dis- tributing evenly or changing homogeneously in the whole North China, these three formations are made up of stable carbonate SDS (Sedimentary Suits).The tectonic geological setting was quite stable.1, the main typies of carbonate rock contain:fragmental limestone, skeletal limeston,oolitic limestone,pellet limestone,micrite limestone, Calcisitite,stromatolithic limestone,bioherm limestone,dolomite and fragmental dolomite.2,the texture components are grains (intraclasts, oolites, skelets), nicrite matrix, sparite cement, remannent texture and crystallized texture3,there are many different kinds of sedimentary structures in thisregion, such as below, ripple marks, erosional structures, beddings (include horizontal lamination,palallel bedding,hummocky cross stra- tification and grain graded sequence),the structures displayed by di- fferent fragments arrangment (e. g".ridge-like" structure,imbricate structure, inverted" "structure et al), cutted bioherm structure, every kind of bio-generated structures and chemi-generated structures (include bird-eyes structure,stylolitic structure and hard,round struc- ture ).4,The calci-fragments and the cement's contents of CaO and Na20+K20+ A1203+Si02 are nagtive interrelated , i.e.,fragments and cement have high Na20+K20+A1203+Si02 velum and low CaO velum in proximality areas, while in distal area the Na20+K20+A1203+Si02 valums are much higher than the CaO .We cam also use those volums to distinguis the fragments' souce rocks from one another or generaly identify calcilutite's deposi- tional environments.Limeston contains higher Mn and Ba than dolomite. (?)ecause in limestone which riches in Ca,Ca is easy to be replaced by Mn, while dolomite contains more Ti than limestone.5,hased on a large amount of detail field and lab research works, (?) sedimentary facies have been divided, they are:a, basin (distal basin, proximal basin);b, basin temple,platform ramp;d,pletform edge sands; e,tidal fiat.Distinct depositional, patterns in these facies have been discussed respectively during fair weather arid storm weather conditions.6,four local sedimentary models have been established .They are: Hebei Qinhuangdao Shimenzhai Late Cambrian Sedimentary Model;Bei- jing Xishan Late Cambrian Sedimentary Model;Shanxi Linqiu Late Cambrian Sedimentary Model: Shanxi Kelan Late Cambrian Sedimentary Model.Finally a synthesized model have been got from these four local models-Late Cambring General Sedimentary Model in North Part of the North China Platform.7,after analying the four factors (tectonic activity, sediments supply, sea-level changes and climate condition),which control sedimentary cycles,and considering the (?)acts that sea-level changes and climate are the main factors in the research region, the author have divided five 3rd order sedimentary cycles in his 17 measured prufiles .Under the condition of stable tectonic geological setting and no sediments supply influence, corresponding cycle is or should be synchronous because the sea-level or depo- sitional water depth change(?),i.e. the cycles are consistent, espe- cially the linking lines of every cycles' apexes of maximum trans- gression, and the linking lines of every cycles' apexes of regresion. Three types of acurate lithofacies and paleogeographic maps have been drawn up .8,on the base of eyeles comparing, the author identified some conrresponding storm layers and have tried to draw another kind of lithofacies and paleogeographic map using one of the stom layers in almost all the research region.