The Study On The Depositional System Characteristic Of Upper Paleozoic In The ZiZhou-QingJian Region

Applied with outcrop observation,core description and other geophysical basic data, the theories of sedimentary facies and geology are applied, Stratum division ,the source of clast, sedimentary facies types, the distribution of sedimentary facies and sand body are studied in this thesis. Sedimentary system developed in Upper Paleozoic are deeply studied.By the above research ,the following important innovations are obtained:According to the sign layer, the character of lithology and electromotive curve, sedimentary cycle, consulting the practice of exploration and exploitation, the lithology stratigraphy are divided, the characteristic of strata are discussed,respectively. Viewpoint and method of high resolution sequence stratigraphy are firstly applied in study area, and high resolution sequence stratigraphy are divided ,and are compared with traditional strata division.On the basis of the background of areal geology and the distributing of diverse sedimentaty system analyzing, combined with the variety of light and heavy mineral association, the origin of clast composing of sandstone are analysed when Upper Paleozoic are deposited ,the result shows that they are origined in low grade metamorphic crystal fundus in north of the Ordos Basin.It is held that Paleozoic stratum is composed of five sedimentary system by outcrop, well core,logging facies,including braided delta, meandering delta, lacustrine and so on. The sedimentary system can be further divided into following microfacies: barrier island - lagoon in Ben-xi formation, tidal level ground and shallow marin shelf in Tai-yuan formation, normal delta front in Shan₂³ Shan₁¹ and braided river-controled delta front in He₈^2He₈¹, and the two types of delta system are both shallow mesa delta system with high constructive, charactered by subaqueous distributary channel being highly developed,while, bayou bam being not well developed.therefore,the sandy body of subaqueous distributary channel ,not only the framework sandstone of delta front subfacies ,but also the main sandstone for gas accumulation in study area.Microelement testing shows that the water in paleoenvironment mainly is freshwater,but is influenced by seawater at long intervals.On the basis of these described above, the characteristic of depositional system and sandy body in space are discussed. Besides,depositional model of delta system are constructed and depositional evolvement are analysed by the author.After gas accumulation and favorable sandstone influence factors are discussed. According to the distributing of sandy body , top conformation and the practice of exploration and exploitation in study area, favorable region in the main aim segment are forecasted.