Geochemical Characteristics And Sedimentary Source Analysis Of Black Shale Series Of Lower Cambrian Of The HuiLi-HuiZe-Dongchuan

Early Cambrian black shales, which are located in southern China, are the mainly strata bearing many large and super large metallic and nonmetallic deposits.Theformation of this shale is associated with global hypoxia events and have beenregarded as important reproducible sedimentary facies, representing an environmental upheaval.Lower Cambrian black rock series widely developed well in Huili, Huidong, Huize and Dongchuan area of southwestern margin of the Yangtze block.Therefore, itis of great theoretical and practical significance to study the formation of this lower Cambrian black shale, which is regarded as the indicator of mineralization and environment.This paper focuses on the sedimentary environment, material source and tectonic setting of source region of lower Cambrian black rock series, the characteristics of main and trace elements and rare earth elements are studied by the means of systematic sample of Yuhucun, Qiongzhusi and Canglangpu black rock series,according to sedimentology and geochemistry. Comprehensive analysis of regional ancient geography background and profile sedimentary characteristics indicate that marine transgression and sea-level rise occured during Early Cambrian, causing hypoxia event. The environment of that time is ittoral-neritic sea to bathyal region.To the early Late Cambrian, marine regression event happened, the sea level began to fall and water power have strengthened, indicating that the characteristics of environment was similar with foreshore and backshore. The n(V)/n(V+Ni), n(Ni)/n(Co), n(U)/n(Th) andδU features suggest that this area was under the anoxic reducing environment at that time and also the transition environment between hot water and normal deposition. The NASC Normalized REE patterns show that the total amount of rare earth elements is higher. An obvious differentiation between light and heavy REE is observed and Eu showed a negative anomaly, indicating that the sediments of this area are from the upper crust and mixed by a certain amount of hot water sediments. Study on combination and ratio characteristics of the main and trace elements and REEs indicate that the sediments are mainly terrigenous materials, supplemented by exhalative sedimentation and affected by a large number of biological sedimentation.The natures of source rocks are similar with andesite, dacite and sedimentary rocks.The tectonic setting of source is mainly continental arc and active continental margin with mixed sources.On the basis of above research, with combination of U-Pb dating analysis, the source of this black shales is from Kangdian old land located on the southwestern of the study area.