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Sedimentary Characteristics And Tectonic Implication Of Black Rock Series At The Turn Of Middle To Late Ordovician In Hunan-guangxi Area

Posted on:2017-03-16Degree:MasterType:Thesis
Country:ChinaCandidate:Y Y HeFull Text:PDF
GTID:2180330482484296Subject:Paleontology and stratigraphy
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Caledonian movement is one of the most important events during geological history in South China, with Ordovician period, which is the transition point, being the window for acquiring deep knowledge of it. Hunan-Guangxi area is located on the boundary of Yangtze and Cathaysia blocks, where Ordovician system is widely distributed with marked black siliceous rock series of middle-late Ordovician epochs in clastic rocks. In this dissertation, the importance of black rock series in early Paleozoic tectonic framework and basin evolution is discussed by exploring origin, sedimentary background together with temporal and spatial variation of the black rock series. Meanwhile, the overlying and underlying formation of the black rock series is researched in sedimentology, geochemistry and provenance analysis as the key strata.The black rock series of Yanxi Formation in the research area is mainly composed of cherts, siliceous slate, carbonaceous slate and silty slate with radiolarian fossils and graptolite fossils of Darriwilian stage of middle Ordovician epoch to early Sandbian stage of middle Ordovician epoch which could restrict its geological time. Vertically, the portion of siliceous rock rises and then decreases from bottom to the top. And horizontally, the portion and purity of siliceous rock reaches the top in the line of Chengbu-Yongzhou-Pingxiang, with more carbonaceous and argillaceous strata to south and north. The isopach map of relic strata of Yanxi Formation and its overlying and underlying strata show southward migration of accumulation center of the basin and clearer trend of northeastern distribution of thickness contours.Geochemistry characteristics of cherts indicate the bio-generic origin in normal marine environment with continental region sedimentary background. Terrigenous elastics increase first and then decrease vertically. The area of Chengbu- YongzhouPingxiang is the least affected area by terrigenous elastics with more affected areas to southeastern and northwestern parts respectively.Geochemical research of clastic rocks overlying and underlying Yanxi Formation shows the passive continental margin background of Ordovician of Hunan-Guangxi Area with quartziferous provenance including a small amount of felsic igneous rock and intermediate igneous rock source. After sedimentary of Yanxi Formation, there have been more and more active components. From the information of the detrital zircon, it could be concluded that provenance of Yangtze and Cathaysia both appear in the Ordovician of Hunan-Guangxi Area and after the sedimentary of Yanxi Formation provenance of Cathaysia rises, which shows more activity of Cathaysia and its rising.The Sedimentary of Yanxi Formation is the response to the process of foreland basin shaped by Caledonian movement in the area. Based on the research, the evolution phases of Ordovician basin include:the passive continental margin phase before the sedimentary of Yanxi Formation; the formation phase of foreland basin during the sedimentary of Yanxi Formation; and the development phase of foreland basin after the sedimentary of Yanxi Formation.
Keywords/Search Tags:Hunan-Guangxi Area, Ordovician, Yanxi Formation, Cherts, Foreland Basin
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