The Study On The Division And Comparison Of Carboniferous System In The Baogutu Area, Western Junggar

This dissertation is object on the sedimentary stratum of Carboniferous System in theBaogutu area of Western Junggar, Xinjiang. Studying the features of strata in our researchingarea synthetically, including lithofacies, rock association, organic fossil analysis and contactrelationship between the stratum and structural form differences. Through the several years ofour research, gained the achievement as follows:1. The clastic rock with Carboniferous Baogutu, Xibeikulasi and ChengjisihanshanFormation in the Baogutu area of Western Junggar, is different from each other, and havemacroexamination regional extension stability and regional correlation. They are belongs todifferent rock-stratigraphicunits.The Baogutu Formation is mainly containing many extremely thin pyroclastic rock,which is formed in345.6~328.4Ma, that belong to Visean stage. The Xibeikulasi Formation isno barrier seacoast（main littoral or terrigenous sea basin deposit）coarse clastic deposit, themajor lithology of which are conglometrate, bearing gravel coarse sand, and sandstone,formed in the Serpukhovian. The volcanic rock and shallow shelf facies are important parts ofChengjisihanshan Formation. The coral and wrist fossils(Choristites sp.and Pseudotimania sp.)discovered in the limestone layers and the zircons U-Pb isotopic dating for319.0Ma,313.6Maand312Ma, which is the further evidence for the strata formation age. indicates that the age ofChengjisihanshan Formation is from the Bashkirian to Moscow stage in Late Carboniferous.According to rock association, contact relationship and datas of the age, the correct regionalstratigraphic sequence was established as: The Baogutu Formation of Visean,(conformity)Xibeikulasi Formation of Lower Carboniferous Serpukhovian and the ChengjisihanshanFormation aboved-mentioned unconformity on the others, that from Bashkirian to Moscowstage in Late Carboniferous.2. The Baogutu formation is composed of normal cycle formed by finesandstone-siltstone-siliceous siltstone, with getting better and higher of the psephicity, sortingand maturity. The Baogutu formation developed under wave base of lower regime is a suit ofabyssal fine-clastic sediment formation.The terrigenous supply of Xibeikulasi formation is sufficient. It develops coarse-grainedgravel-bearing sandstone, scouring erosion surface, convolute bedding and other primarysedimentary structures. The gravels have obviously orientable arrangement. The above showthat the Xibeikulasi formation formed under a non-barrier coast sendiment environment (dominated by onshore sedimentary system) with strong hydrodynamic force. There have lotsof retain a complete magmatic origin detrital zircons and zircon age distribution range of322~359Ma characteristics indicate the sediment source for early carboniferous source in anactive continental margin environment. The Chengjisihanshan Formation is formed in theshallow water deposition as the volcanic rock elimination.As the material mentioned from this article is pointing the sedimentary environment inthe carboniferous as: Early carboniferous, regressive (deep sea-bathyal facies to shallow seafacies)-fold orogenic(one big important tectonic event happened)-water further the latecarboniferous to the filling (volcanic development and activity).3. According to the characteristics of rock type, lithology contrast diagram and columnarcontrast figure analysis in the study area distribution shows: the volcanic rocks and volcanicclastic rock content increased obviously to NE and the sedimentary clastic particle size issmaller, reducing trend. So the northeast of the reaseach area is much closer to the volcanicarc area than the sorthweast.4. To discuss the ancient tectonic environment. the Carboniferous can be divided intotwo stages. One is from extension of the collision diapauses to closure of remant ocean andthe other is from intracontinental collision and post-collision collapse in early Carboniferousto intra-plate deformation stage in late Carboniferous.