Geochemical Variation Of Marine Carbonate Strata Along Rock Bedding Strike And Its Mechanism Simulation

Chemostratigraphy has presented that different sedimentary facies correspond to different geochemical features,even at the same age,which causes difficulties for global and inter-basin stratigraphic correlating.As we known,in a depositional system,diverse sedimentary environments deposit different sediments,and the facies develop horizontally too.Walther Law of Facies illustrates the relationship among facies in sequences and spaces,as well as strata diachronism between vertical and horizontal directions.This illustration provides a suggestion for defective correlating of various facies.Tieqiao section was selected for understanding stratigraphic correlation between the vertical and horizontal directions since it well exposed end-Guadalupian succession of continuous deposited marine carbonate,and GSSP of Guadalupian-Lopingian Boundary was defined in this section and Penglaitan section.This Guadalupian-Lopingian GSSP auxiliary section,well exposed and documented at Laibin,Guangxi,South China,was selected for its lateral tracing nearly 100m in distance.We selected 9 vertical sections measured by sequence classically and 3 horizontal profiles investigated along the bed strike for this research.Geochemical data of Tieqiao sections for lateral investigation was plotted into rectangular coordinate systems for contour maps.Chemostratigraphy of major elements and carbon isotope are well presented for depositional environment and provenance analysis of Tieqiao profiles.Their geochemical excursions,including contents of Ca,Fe and carbon isotope composition,has been drawn into related coordinate points and drawn as contour maps.These maps indicate that there are obvious differences of geochemical traits,even in one rock layer.A traceable rock bed may present different geochemical characteristics in different locations along the rock bed strike even in meters,so synchronous and environment correlation based on a bed needs more limited conditions.According to field measurements and laboratory sample analysis for element and isotope composition,rock samples at different locations on the same rock layer have different geochemical characteristics.However,the mechanism of this phenomenon remains unclear.Temperature is one of the important factors for physical-chemical condition,and it was well documented in the paleoenvironment evolution during geological history.Therefore,this paper applied an experiment to simulate the effects of different temperatures in same water system for early diagenesis effect of the carbon and oxygen isotopes composition of carbonates.The experiment was carried out with the proof machine of Paleopond which was designed and developed by our lab to simulate the deposition process of carbonate rocks.The carbonate samples was collected from the South China Sea and the water was from the Xuanwu Lake.The simulation results show that the temperature has a certain influence on their carbon and oxygen isotope composition of carbonate rocks samples.At low temperatures,the 813C value decreased with temperature increasing;at high temperatures,the ?13C value increased with temperature increasing.Oxygen isotope and formation temperature of carbonate rocks followed documented conclusions which has a roughly negative correlation with temperature.