The Division And Comparison Of The Carboniferous System In The Kexi-Liushugou Area, Western Junggar

This dissertation is object on the sedimentary stratum of Carboniferous System in the Kexi-Liushugou area of Western Junggar, Xinjiang. Studying the features of strata in our researching area synthetically, including lithofacies, rock association, organic fossil analysis and contact relationship between the stratum and structural form differences. Through the several years of our research, gained the achievement as follows:1. The clastic rock with Carboniferous Xibeikulasi Formation and Baogutu Formation in the Kexi-Liushugou area of Western Junggar, is different from each other, and have macroexamination regional extension stability and regional correlation. They are belongs to two different rock-stratigraphicunits.2. The Xibeikulasi Formation is no barrier seacoast (main littoral or terrigenous sea basin deposit) coarse clastic deposit, the major lithology of which are conglomerate, bearing gravel coarse sand, and sandstone; Baogutuzu Formation is deep-sea facies microclastic rock, with volcanic rock, limerock partings or banding, and radiolarian silicalite in some area, which consists siltstone, siliceous siltstone,silicalite and so on.3. The terrigenous supply of Xibeikulasi formation is sufficient. It develops coarse-grained gravel-bearing sandstone, scouring erosion surface, convolute bedding and other primary sedimentary structures. The gravels have obviously orientable arrangement. The above show that the Xibeikulasi formation formed under a non-barrier coast sendiment environment (dominated by onshore sedimentary system) with strong hydrodynamic force.Relative to the overlying coarse fragment sandstone of Xibeikulasi formation, the Baogutu formation is composed of normal cycle formed by fine sandstone-siltstone-siliceous siltstone, with getting better and higher of the psephicity, sorting and maturity. The Baogutu formation developed under wave base of lower regime is a suit of abyssal fine-clastic sediment formation.4. The Xibeikulasi Formation aboved-mentioned unconformity on the Baogutu Formation, they contact directly between which there is no indication of fault; the lithology of both sides of contact, the occurrence is different; and basal conglomerate spread on the unconformity interfaces. The unconformity indicates one big important tectonic event happened, represents the tectonic setting transition from one sedimentary cycle finished and a new one happened. These suggest that folding mountain-building movement occurred after the Baogutu formation sedimentary, and then the Xibeikulasi formation begin to deposit. The corals Lithostrotionella cf. shimeri, Multithecopora which was discovered from the limestone gravel at the bottom of Xibeikulasi formation can be contrast with the fossil assemblage of Baogutu formation, and the lithologic character of limestone gravel is same with the limestone of Baogutu formation. During our 1:50000 regional geological and mianeral survey, the lithologic deposit record only occurred in the Baogutu Formation. It can be sure that the gravel must come from the Baogutu formation. So that, the chronogensis of the Xibeikulasi formation and the Baogutu formation is understood without further explanation.5. The significantly different fold-shapes between Xibeikulasi formation and Baogutu formation show that they are products of different deformation domain, tectonic stress field and dynamics system. The strong compression deformation of Baogutu formation is related to aforesaid folding mountain-building movement, and after Xibeikulasi formation forming, Baogutu formation experience superimposed folding again.6. LA-ICP-MS dating technique is used to determine the zircons from Baogutu formation, and yielded zircon U-Pb age of 346±12Ma (MSWD=1.14,95% confidence). The data is consistent with the SHRIMP age of 328.6±1.8Ma of volcanic rock in the Baobei gold deposit, Western Junggar. With the relevant data synthesized, the Baogutu formation was considered to form in the Early Caiboniferous.7. According to the biology fossil, discordant contact relationship, and correlating the regional researching, the Carboniferous system in the Kexi-Liushugou area is divided into the Late Carboniferous Xibeikulasi Formation and the Early Carboniferous Baogutu Formation. The result affords important basis for building correct regional stratigraphic sequence and correlation, and it is great significant for recoverying paleosedimentary basin in the area, discriminating features of crustal moving, rebuilding the Late Paleozoic era geologic history of the central Asia.