Carbon, Oxygen And Strontium Isotope Stratigraphy Of The Permian In Tongjiang Region, Sichuan

Isotope stratigraphy has became a important part of Chemistry Stratigraphy. Stable isotopes can be used not only for the stratigraphic division and correlation, and stable isotopic composition of ancient marine carbonate have great significance to the study of major global geological events, such as ancient sea-level changes, volcanic activity, biotic extinction and ancient climate changes. There have less information of carbon, oxygen and strontium isotopes of the Yangtze block, and the studies of carbon, oxygen and strontium isotopes of Permian marine carbonates are not systematic. By means of isotope stratigraphy of the section in Tongjiang Region, which has the typical characteristics of Permian carbonate rocks in Yangtze block, the carbon, oxygen and strontium isotope composition and evolution of the Yangtze block have been revealed, and their geological significance have been discussed.Guided by stratigraphy, isotope geochemistry and isotope stratigraphy theory, and based on detailed measurement of field profile and carbon, oxygen and strontium isotope data obtained by isotopic experimental analysis, the evolution of carbon, oxygen and strontium isotope in study area are revealed, combined with the global evolution curve of carbon and strontium isotope, study area and the global Permian geological background, the significance of global correlation of carbon and strontium isotopic and their characteristics responses to global geological events are discussed, and attempt to calibrate the ages of the marine carbonate strata using strontium isotope stratigraphy.The Permian carbon isotope evolution curve of the study area shows mainly positive excursion, and negative excursion occurred at Maokou-Wujiaping formation boundary, Middle-upper Changing Age and Late Changxing Age. The Permian strontium isotope evolution curve shows an overall downward trend with the minimum value of the Mid Wujiaping Age, and started rising sharply until the Latest Permian. The Permian carbon and strontium isotope evolution curve of study area are similar to global Permian carbon and strontium isotope evolution curve, which explained that global geological events are the mostly dominative factors for the isotopic composition of seawater, and both carbon and strontium isotopic composition are globally correlative.The isotopic data of study area have a good response to the major global geological events:Sea-level changes frequently in Permian such as the transgression in the beginning of Early Permian, the regression in the end of Early Permian, a new transgression in the beginning of Late Permian, the short-term regression in Middle-upper Changing Age and following the large-scale transgression in the Latest Permian. In addition to these sea-level events, there occurred the biological extinction event near the Permian-Triassic boundary which is the greatest mass extinction in Phanerozoic and large-scale volcanic event in Late Permian in study area. The evolutional curve of carbon isotopic of study area is quite consistent with sea-level curve, indicating that there is a positive correlation between carbon isotopic and sea level change. The intense negative deviation of carbon isotopic evolutional curve occurred near Permian-Triassic boundary was caused by mass extinction of lives. The evolutional curve of strontium isotopic of study area and the sea-level curve shows generally opposite, indicating that there is a negative correlation between strontium isotopic and sea level change. The negative deviation of strontium isotopic evolutional curve in Late Permian was caused by mantle-derived strontium produced by volcanic activity.According to the principle of strontium isotope stratigraphy and the strontium isotope-age database, the ages of several stratigraphic boundaries of Permian are calibrated and the dating results shows that most dating results were consistent with the international standard chronostratigraphic timescale that only individual result in errors.