The Major Flooding Period’s Sedimentary System Of Latepaleozoic In Zhongwei Area And Adjacent Regions

Zhongwei area and circumference regions is surrounded by the Alxan block,North China plate and north Qilian. Stratigraphic classification in study area isdifferent from North China plate because of regional tectonic and global change of sealevel. During the Carboniferous, the sea level changes frequently in this area, so that itdeposits the offshore facies and coal bed. Therefore, we mainly study the depositionalsystem during major flooding period, which will has great significant promoting inpredicting the coal, oil and gas resources.The study area is bounded by Yongdeng and Jingyuan to the north of Wuda andQilian Mountain, from Jingtai and Dongqing Lake area to107°E. On the basis oftheories of Sedimentology, Historical Geology, Paleontology, Petrology, LithofaciesPaleogeography and the investigation of filed sections and analysis of sedimentaryfacies, Combined with previous studies, the following fruitful results have beenachieved:(1)The research of main lithology of Zhongwei area and circumference regions havebeen conducted by outcrop observation and thin slice identification, and sandstone,conglomerate, mud, shale, siltstone, limestone, gypsum, dolomite, coal arerecognized as main types. and sandstone, mud, shale，siltstone, limestone, aremain rock in the carboniferous, sandstone, conglomerate, siltstone are main rockin the Devonian system and Permian.(2)According to the lithology, strata thickness, depositional fabric, sedimentarystructure, sedimentary cycle etc. A detailed sedimentary facies division for latePaleozoic in research area have been made and6sedimentary system and14sedimentary subfacies, and several sedimentary micro facies have been identified.Six sedimentary systems are River sedimentary system, lake sedimentary system,delta sedimentary system, the barrier-tidal flat-lagoon sedimentary system,carbonate platform sedimentary system, shallow sea sedimentary system;14 sedimentary subfacies include Braided river subfacies, Meandering river subfacies,Lakeshore subfacies, Shallow lake subfacies, delta subfacies, tidal flat,barrier island phase, lagoon subfacies, estuarine subfacies, openplatform subfacies, restricted platform subfacies, shallow-sea subfacies.(3)Under the analysis of facies sequence configuration,12sections’sedimentary cyclehave been divided. The number of cycle in different section is not the samebecause of the difference of strata integrity.(4)Through the research of Upper Paleozoic in research area, the difference betweenresearch area and the central and eastern regions of Erdos have become clear. Theresearch area seawater did not be connected with the North China seawater untilTaiyuan period because of middle palaeohigh, In the late period of Carboniferous,the research area seawater conjoined with North China seawater in Otog Bannerand Otog Front Banner. In the early period of early Permian, the research areaseawater conjoined with North China seawater to expand epicontinental sea.(5)According to contrast of32sections, and combined with previous studies, UpperPaleozoic sedimentary facies and sedimentary facies mode chart have beenelaborated by mapping in the major flooding period.