Midu Upper Paleozoic Sedimentary Geochemistry And Paleo-environmental Analysis

This paper is based on the "Midu,Xiangyun 1:5 million regional geology and mineral resources survey project" of China Geological Survey Bureau, Through the field investigation, select Midu regional Paleozoic Devonian-Permian strata to study. In the study area the Late Paleozoic strata was relatively large and continuou developed, they all have different rock strata combined, formed in different sedimentary facies. Therefore, in this thesis, Choose two representative The Late Paleozoic sections of Dali Midu, the macro aspects conducted Systemaly researc on the production from the wild state, rock composition and depositional environment, of the Midu Late Paleozoic Devonian-Permian strata; micro aspects conducted sedimentary rocks geochemistry researc of Constant element,Trace Elements and REE elements, Trying to use the system geochemical method further that ancient sedimentary geochemistry,the marine environment and ancient climate changof the study area in this history period. After nearly two years, field investigation and comprehensive study, made the following understanding:1. We make vertical and horizontal comparison study of Late Paleozoic Devonian-Permian lithologic characteristics of Midu Dali, Yunnan Province.And each group spatial distribution of lithology has done some analysis, which comprehensive study of lithofacies palaeogeography of the area has some reference.2. Based on previous studies, combined with the lithology combination group characteristics, We believe that the stratum between Mid-Devonian and Early-Permian was Marine deposit. The lianhuaqu stratum group of Mid-Devonian was Shallow shelf sediments; The changyucun stratum group of Middle to late Devonian was deep-sea sediments and the water lever gradually shallowed. Sedimentary environment transformed to Platform facies. The hengjing stratum group of ealy-Carboniferous was Carbonate Platform facie. Later stratum kept Platform margin shoal facies until shuichangjing stratum,which is belong to ealy Permian. Then the yangxin stratum of mid-Permian was Open platform and Basin facies yet. As the dynamic of water enhanced, it became high-energy platform margin shoal environment, From Mid-Devonian to Mid-Permian,the Water depth characteristics: shallow waterâ†'deep waterâ†'sub-shallow waterâ†'shallow water. 3. We analysis and summarized the various strata of Late Paleozoic and trace elements, REE geochemical characteristics of sedimentary. The results show that:â‘ The lianhuaqu Group Devonian-Permian formation in most samples Sr/Ba ratio of the overall performance of the marine sedimentary environment;â‘¡Ni/Co ratio is the reaction of oxygen with a good old geochemical indicators. Most of the lianhuaqu Group of Devonian Ni/Co ratio are under 5, an average of 4.9 are oxygen-rich environment;The changyuchun Devonian Ni/Co ratio of the overall >5, an average of 5.74 are poor oxygen environment; Carboniferous Horizontal Well Unit Ni/Co than most> 5, an average of 5.22 is still a poor oxygen environment; Carboniferous-Permian horizontal wells group Ni/Co ratio of the majority of> 5, the average is 5.â‘¢Each stratum of the ancient sea water salinity calculated results show that the ancient sea water salinity brackish water environment through the process of changeâ†'salt water environment;â‘£On the various historical periods of ancient climatic characteristics of the environment indicators using constant elementω(MgO)/ω(CaO) to discriminate, that the study of the Late Paleozoic, the general trend of climate is dry and hot climate becomes warm and humid climate;4. The changyuchun Devonian in the study area developed a large number of gray-like thin black chert, siliceous rock level laminar development. In this paper, cherts discussed the origin of the sample. Siliceous rocks in the study area has a constant element of Al/(Al+Fe+Mn) value of 0.24-0.56, fall within the standard hydrothermal chert, and generally have high SiO2 low TiO2, MgO, Al2O3, andΣREE content features, the North American shale standard flat rare earth distribution patterns, and possessedδCe<1 negative anomalies and 8Eu> a positive anomaly, LREE enrichment. Suggesting that the chert has obvious hydrothermal sedimentation properties, while a terrestrial component of the accession.5. We use the Al2O3/(Al2O3+Fe2O3)-Fe2O3/TiO2 diagram and Al2O3/(Al2O3+ Fe2O3)-La/Ce diagram to explain the study eara structure,which is formed between sea basin to the land border when the bottom of the sea drawing. Also the siliceous rock was impacted by the submarine hydrothermal.