Paleozoic Midu region Sedimentary geochemistry and palaeoenvironment analysis

Title: Paleozoic Midu region Sedimentary geochemistry and palaeoenvironment analysis
　　Author: Cai stable
　　Degree-granting unit: Kunming University of Science
　　Keywords: Midu region;; Late Paleozoic;; sedimentary geochemistry;; paleoenvironmental analysis
　　Summary:
　　In this paper, China Geological Survey Bureau "Midu, clouds region 1:50000 regional geological minerals survey project" basis, through the geological survey, select Midu Late Paleozoic Devonian - Permian strata in the study. Development of a large study area, the more continuous late Paleozoic strata, these strata of rocks with different combinations, formed in Neodymium Magnets different sedimentary facies. Therefore, this paper selected the Late Paleozoic Dali Midu two representative cross-section, the macro state produced from the wild, rock composition and depositional environment in terms of Midu Late Paleozoic Devonian - Permian strata were compared with the system research; micro sedimentary rocks carried out major elements, trace elements, REE geochemistry, geochemical methods attempt to use the system to further reveal the history of the study area in this period and ancient sedimentary geochemistry and the ancient marine environment climate changes. After nearly two years of geological survey and comprehensive study, the results show that:
　　1 of Dali Midu Late Paleozoic Devonian - Permian strata of the lithologic characteristics of the vertical and horizontal comparison study, and the spatial distribution of lithology groups do a certain amount of analysis, This comprehensive study of the area lithofacies paleogeography have some reference.
　　2 In previous studies, based on the lithology of each group combined with other features that the Devonian system - under the system of Permian marine deposits are in each group. Devonian area music groups in the system should be the lotus shallow shelf facies; Devonian system - the system should be deep-sea long village with education - second deep-sea sediments, water bodies appear gradually shallowing upward variation, phase transition to the platform sedimentary environment; Carboniferous group is well under low-energy cross-system carbonate platform facies; Carboniferous on the system - long trap water under the EC Permian group is still the platform margin shoal facies; Permian in the system Yang is still open platform with a new group - Taiwan basin phase as the main driving force to strengthen with the water, and gradually evolved into high-energy platform margin shoal environment. Devonian System - Permian in the overall system is characterized by changes in water depth: deep → shallow → second deep → shallow water.
　　3 In this paper, the various strata of Late Paleozoic major elements, trace elements, REE geochemistry of sedimentary analysis, summarize, sum up. The results showed that:
　　① Devonian Lotus Music Group - the vast majority of the Permian Formation of new samples positive m values ​​and B / Ga are all areas of marine deposits, Devonian - Permian marine strata were deposited;
　　② Ni / Co ratio is the reaction of oxygen with the good old geochemical indicators. Lotus Music Group Devonian Ni / Co ratio of the majority of <5, an average of 4.9 part of oxygen-rich environment; long education Devonian village Ni / Co ratio of total> 5, an average of 5.74 is oxygen-poor environment; Carboniferous horizontal wells group Ni / Co than most> 5, an average of 5.22 is still oxygen-poor environment; Permo-Carboniferous group of cross-well Ni / Co than most> 5, an average of 5.22 is still oxygen-poor environment; Carboniferous water long Trap Group - new group of Permian Yang Ni / Co majority of <5, an average of 3.79 is oxygen-rich environment; Therefore, Devonian - Permian ancient oxygen relative to the overall variation of oxygen-poor → show → second oxygen-rich oxygen variation.
　　③ the various strata of the ancient sea water salinity calculations, Devonian music group Ancient Lotus salinity range between 8.60 ‰ ~ 13.67 ‰, an average of 11.75 ‰, the salinity of brackish water environment; Devonian Department of http://www.everbeenmagnet.com/en/products/110-sintered-neodymium-magnets Education long-range village paleosalinity 2.50 ‰ ~ 8.29 ‰ in between, most of the samples S> 3% o, an average of 4.64 ‰, this time for the whole salinity brackish water environment; lower Carboniferous ancient group of cross-well system salinity range of 0.46 ‰ ~ 3.12 ‰ with an average of 1.67 ‰, S <3 ‰, Early Carboniferous low salinity. Carboniferous - Permian water long trap set - the Carboniferous system in the new group of ancient sun salinity range between 0.03 ‰ ~ 4.46 ‰, the majority of the sample S <3% o, an average of 2.25% o, described from the Late Carboniferous world - the ancient Permian ocean salinity has remained at a low level, may be related to continental margin into the river. The results show that the ancient sea water salinity brackish water environment experienced decreasing salinity changes in the process.
　　④ various historical periods of the ancient environment of the climate characteristics of the use of constant element index ω (MgO) / ω (CaO) to discriminate, obtained in the study area late Paleozoic Devonian - Permian climate change in the overall trend is changed from hot and dry climate warm and humid climate;
　　4 long study area Devonian village education development a large number of gray - black thin-bedded chert, chert laminae level of development. In this paper, chert samples analyzed the causes discussed. Chert samples of the study area has a constant element of Al / (Al + Fe + Mn) value of 0.24 to 0.56, the standard falls within the hydrothermal cherts, and generally with high Si02 low TiO2, MgO, Al2O3, and ΣREE content characteristics, the North American shale-normalized REE distribution patterns of flat, and possessed δCe <1 and negative anomalies δEu> 1 is unusual, light rare earth elements enrichment. Siliceous rocks in the study area shows a clear hot water sedimentary origin attributes, while adding terrigenous components.
　　5 study area Al2O3 / (Al2O3 + Fe2O3) -Fe2O3/TiO2 diagrams and Al2O3 / (A12O3 + Fe2O3) -La/Ce illustrate the region's sedimentary rocks formed in the ocean basins and continental margin tectonic setting between, the sea split Valley stretch, chert formed by submarine hydrothermal effects.
　　Degree Year: 2010