Filling Process And Evolutionary Model Of Sedimentary Sequence In Middle-upper Yangtze Cratonic Basin

With the guidance of modern sedimentology, sequence stratigraphy, paleontology, petroleum geology, structural geology and the theories of plate tectonics and activity , in accordance with the general idea of"tectonic-controlled basin→basin-controlled sequence and facies→sequence and facies -controlled reservoiring elements", and based on the tectonic-sequence (second-order sequence) that indicates the overall characteristics of basin, the sequence stratigraphy (third-order sequence) that indicates the filling framework of basin is taken as the research unit. Meanwhile, the sequence configuration, superimposed modes (above fourth-order sequence) and the distribution pattern of facies belts are taken as the research objects, besides that some combined methods including drilling, exposure and profile observations, classification and correlation of stratigraphy and sequence stratigraphy, assay data analysis and geophysical data interpretation are used. Accordingly, the filling process of sedimentary sequence of Middle-Upper Yangtze cratonic basins are analyzed, besides that the sedimentary and evolutionary modes are built, and the development characteristics, distribution pattern and controlling factors of accumulation factors of filling framework of sequence are discussed. The main new achievements are as follows:1. According to the previous results and the personality traits of the middle-upper Yangtze cratonic basins,the three-levels classification scheme of cratonic basin is proposed. It means that theⅠlevel basin classification is classified according to the plate tectonic position, theⅡlevel classification according to the dynamic origin of basin, and theⅢlevel detailed classification according to the building types of sequence deposition. And the evolution process of Middle-upper Yangtze cratonic during Sinian to middle Triassic period is divided into four stages that are the Sinian to the early Ordovician early(PhaseⅠ), the late early Ordovician to Silurian(PhaseⅡ),the Devonian to Carboniferous(PhaseⅢ) and the Permian to middle Triassic(PhaseⅣ).2. With the guidance of tectonic stratigraphic paleogeographic, and according to the compiling method of advantaged sedimentary facies, also based on the previous research achievements, the tectonic sequence paleogeographic maps were revised with new materials and understanding, on which the distribution features of hydrocarbon accumulation material, such as the main source rocks, reservoir, reef-beach and anointed halite, etc. were strengthened. Analyzed that on transverse distribution the sedimentary domain of middle-upper Yangtze included two parts that were intercratonic basin and pericrationic basin. On Vertical distribution, taking DouYun movement as dividing line during Caledonian stage, prior to it the overall paleogeographic outlook were west high and east low with the main sedimentary system of gently platform,and after it the overall paleogeographic outlook were segmented and restircted shelf sedimentary system by tectonic uplifling of central Sichuan uplify,central Guizhou uplift and Xuefeng uplift and so on. During Hercynian stage, the overall paleogeographic outlook were central high and edge low as a result of most regions uplifted and rim crack trapped and accept deposits where seawater gradually invaded from the edge to the internal in middle-upper Yangze craton. And the main sedimentary environment were shelf- platform- basin system that was controlled by the factors of deep faults, sea-level changes and paleogeomorphology etc. To the Triassic period, this evolutionary stages of marine craton basin were over due to the Anxian movement, in the meanwhile entered into the new evolutionary stages of continental foreland basin and downwarped basin.3.According to analyze the spatial and temporal variation characteristics of the stratigraphic structure, systems tracts superposition style and sedimentary facies distribution, the filling evolution process of tectonic stratigraphic and its control factors are brought to light.The opinions are that various control factors including basal tectonic characteristics, tectonic movement and deep fault, ancient uplift, paleogeographic background, relative sea-level changes, ancient climate and ancient latitude, and regional tectonic characteristics, etc. controlled the stratigraphy development by the influence of the filling conditions of sequence,such as paleogeographic background, sedimentary environment, provenance properties, sequence configuration and superposition style and so on. So the controlling function of various factors change in different times or different areas which leads to the differences of the filling process of tectonic sequence4. Based on the analysis of the process and characteristics of sedimentary filling about several typical craton basins in different evolutionary stages of the researched areas,which include the carbonate rock type of intracratonic rift basin, clastic rock type intracratonic sag basin, carbonate rock type cratonic margin rift basin and the intracratonic rift to sag basin. Conclusion is that the sequence filling, evolution and control factors of the different types of basins at the same period and the same type basin at different times are significantly different.5. Based on various consideration about basin evolutionary stages, sedimentary structure, sedimentary filling characteristic and the stratigraphic development control factors, the sedimentary evolution of the middle-upper Yangtze cratonic basins during Sinian to middle Triassic can be divided into two sedimentary cycles and a total of seven sedimentary stages.And its comprehensive depositional pattern about each sedimentary evolution stage are established. Furthermore, the differences of the sedimentary evolution model of the middle-upper Yangtze cratonic basins were comprehensive compared on the aspects of characteristics, evolution process, control factors and petroleum geological significance, etc6.After launched the researches of the major hydrocarbon accumulation elements,such as hydrocarbon generating material,storing material and sealing material, reef - beach geological body and gypsum rock,and the analysis of the development characteristic, distribution and control factors in the sequence stratigraphic framework of the middle-upper Yangtze cratonic basins, views are as folloes. (1)The aggregation and distribution of hydrocarbon substances in the sequence framework of middle-upper Yangtze during Sinian to Paleozonic were controled by tectonic setting, basin properties, paleoclimate, paleogeography and depositional environment and other factors,and have a close relationship with sea level rise caused by a variety of factors, and always accumulated and distributed in low-energy anoxic environment. On vertical distribution,multiple sets of source rocks developed and selectively concentrated developed in the transgressive systems tract and the middle-lower sedimentary cycle. On transverse distribution , marine hydrocarbon source rocks differently preserved in stratigraphic framework of various regions. The high quality source rocks mainly distributed from eastern Sichuan to western Hubei,northern Guangxi to southern Guizhou and the large areas of Sichuan basin.(2)High-energy depositional environment, karst area,favorable diagenetic environment and the combined effects of Structure in the sequence framework were the master conditions of the forming of high quality reservoirs. Reservoir development has obvious consistency with high water system tract in the second cycles of global sea level; Meanwhile, the third cycles of transgression in the level 2 sea-level cycles were beneficial to the development of regional reservoir. And the late regression cycles were conducive to the development of ancient carbonate karst reservoir. While the initial to early transgressive cycles were conducive to the carbonate reservoirs of platform edge, or the offshore beach within platform.(3)The controlling factors of reef-beach reservoir are divided into the developmental control factors of reef-beach formation and the reservoir physical properties that are respectively control the macro- reservoir distribution and the micro-reservoir properties. According to analysis found that the beach in Canglangpuan stage of early Cambrian are mainly distributed in BaoKang regions, northern Yangtze and distuibuted in a vast area from Yongshan, Yunnan to Jinsha,Guizhou,and Pengshui,Eastern Sichuan to Yichang,Hubei. In addition, the reef-beach combination from Changxing group to the jialing group in the northeast of sichuan are mainly as zonal distributed in the platform edge. And the inner platform shoals are also relatively development.(4)The gypsum as a special geological rock that its development and distribution were influenced by many factors, such as sea-level changes, sedimentary environment, climate, deposition rate,settling velocity and post-tectonic, etc. According to the block function from strong to weak, the distribution rules are as follows:①The lower - middle Triassic gypsum rocks are most widely distributed in the vast areas of Sichuan basin,and from DangYang to ChenHu region,Hebei Province;②The lower - middle Cambrian gypsum rocks are mainly distributed in the southwestern sichuan basin to northwest guizhou and southeast sichuan as well;③Sealing layer in the Dengying group of the upper Sinian are mainly distributed in the southwest Sichuan to northwest guizhou;④The evaporation rocks of the lower Carboniferous are sporadically distributed,and only mainly in the central Hunan.