Research On Geochemical Characteristics And Sedimentary Environments Of Black Shales In The Eastern Guizhou

Early Cambrian black shales, widely spreading in the southern China, are the mainly ore-bearing strata of many large and super large metallic or nonmetallic deposits and have been regarded as activity textbooks recording a large number of geological events of this time as well. Therefore, studying on the black shales in the southern China has become a hot topic of disscussion recently, and many scholars have paid much attention to the black shales spreading in the southern China including western Hunan province and northern Guizhou province, however, eastern Guizhou province is rarely studied. So, the research regarding the black shales in the east Guizhou province has important theoretical significance and practical value.The major object of this paper is discussing the temperature and pressure conditions about the formation of black shale, material sources, fluid sources and depositional environment according to sedimentology and geochemical characteristics.Through detailed field geological survey, profile measurements of the black rocks in eastern Guizhou as well as previous research results, the formation of black shales' lithofacy palaeogeography environment can be deduced, which is slope-basin area and gradually evolved into-far waterfront near the west coast.Using the X-ray fluorescence spectrometry, atomic absorption spectrometry, ICP-MS and chemical analysis, the quantities of major elements, rare earth and other trace elements in black shales are determined. Among them, Ba, Mo, Pb, Zn, Sc, As and other trace elements are relatively rich in black shales, the total content of rare earth in black shales is 100.84-252.00×10-6, the ratio between light rare earth and heavy rare earth is high. The content of vanadium in black shales is regular with the valence of vanadium specifically, the content of vanadium in black shales increases accomply with the increase content of high valence vanadium, and vice versa.An conclusion is reached that black shales are formed at the temperature between 30℃to 250℃according to the analysis of Eu anomalies as well as the conclusion of inclusion temperature and oxygen isotope. On the basis of element ration of the black, it is presumed that black shales are formed in the environment which is anoxic and on the shallow seabed about 200m; combining with the elements, and diagenetic material information to draw water sediments, terrestrial material and biological function, the main source of fluid is marine jet hot stream composed with infiltrationed marine water. And on this basis we proposed the diagenetic environment and mechanism of black shales.