Characteristics Of Sequence Stratigraphy And Plaeoenvironmental Evolution Of Lower Cambrian In Hunan, China

The study area is located at the middle of continents of South China block, Hunan Province, which crossed Yangtze and South China continental blocks. Lower Cambrian sediments, are well developed in Hunan, with the main sedimentary formations of black shale and carbonates in western and central Hunan, and a suit of greywacke and carbonaceous slate with different thickness rhythmic layers in southern area. Based on the systematic former research material about the lower Cambrian of the studied area, guided by the methods of sequence stratigraphy, lithofacies palaeogeography, sedimentology and chemostratigraphy, this thesis, though detailed observations and research field profiles, research the sequence stratigraphy and lithofacies palaeogeography of lower Cambrian of Hunan Province, clues on sedimentary facies analysis-sequence stratigraphic division-geochemical analysis-sea-level changes research-paleogeographic map maps. This draws primary conclusions and new fruits as follows:1. Based on the research and comparative analysis of many field profiles, the author detailed describes the petrological characteristics of the lower Cambrian in Hunan, and expounded the strata characteristics of each division, and puts forward the contrast scheme, then further clarify the rock combination characteristic, Stratigraphic sequence and the boundary and contact relationship between formations of the Lower Cambrian.2. We exploratory researched the chronology of the Cambrian bottom initial about the zircon in the tuff output the bottom of Niutitang Fm, and accurately determined the zircon SHRIMP dating of 5244±10Ma. The zircon dating is between the time trilobite first appearing and the age of the boundary of Cambrian and Sinian.3. Combined with comprehensive research of sedimentary facies marks such as lithologic characteristic, sedimentary structure, geochemical characteristics (Lord measured, trace, rare earth, C-0 isotopes), we summarized the sedimentary facies and its evolution mode. From the view of sequence stratigraphy, the Lower Cambrian in the study area constitutes a second-order sequence with about 32Ma, which can be further subdivided into six third-order sequences, corresponding six orderly transgression-regression cycles. As a global contrast strata, it's transgression development in the Meishucun stage and the regression development in the Qiongzhusi stage. Impacted by palaeosedimentary environment, the depositional systems tracts of the third-order sequences are formed by the vertical sequences of "the CS+HST" and "the TST (transgression system tract)+CS (condense section)+HST...