Sedimentary Geochemical Records For Emeishan LIP In Lekang Section And Its Relation To The Late Permian Mass Extinction

The late Permian mass extinction events are the most severe and sweeping events in the history of biotic evolution, and it has become an important and hot issue in the geologic community in the past decades. However, it has been long-term debated on the mechanism of the mass extinctions. Recently, more and more studies show that volcanic eruptions from LIPs may be closely associated with the synchronous mass extinction. In addition, the geochronological data also indicate that there can be coupling relationship between Emeishan LIP and the mass extinction in the late Permian. Whereas, whether the Emeishan LIP introduced directly the mass extinction in the late Permian has been still controversial. Based on the geochemical records of the sediment during the middle Permian to early Triassic, we can make some conclusions as following:1 , The sequence of sediment indicates that the basic volcano started to erupt in the early Wuchiapingian and voluminously occurred during the middle Wuchiapingian to middle Changhsingian, and then eliminated in the late Changhsingian. Meanwhile, the geochemistry characteristics of pyroclastic exhibit similarity to those of the high Ti basalt of Emeishan flood basalts. Combined with other geological information, we can conclude that the pyroclastic was the products of different faces of the Emeishan flood basalt, and is also an important constitution of the Emeishan LIP.2, The results of carbon isotope of the marine carbonate rocks for the Lekang section in Guizhou Province, western China, display different natures of evolution and can be divided into three different segments. The highly positive δ¹³C values ofthe marine carbonate rocks from the Maokouan Formation suggest a mild and blooming of biomass climate in that time. The extinction of biomass and the oxidation of the previously buried organism resulted in the drop of 8I3C values near the P2/P3. And most of the 8I3C values varying from 2%o to 4%o during the early Wuchiapingian, suggest the biomass at that time was less than that of Maokouan. The 813C values fall unceasingly and range from 0%o to 2%o during the middle Wuchiapingian and middle Changhsingian, which may be the result of the volcanism. Though the 513C values exhibit an ascending trend in the P/T, and appear the distinct excursion, it is parallel with the extinction of the P/T. The relatively low positive 8nC values in the early traissic indicate that the creatures began to slowly recover after the extinction.3, On the basis of the features of the sedimentary sequence in the region, together with their geochemical data and the similar affinity to the synchronous section in the ambient area, we propose that the late Permian mass extinction is not the direct result of the Emeishan LIP. Likely, the Emeishan LIP has an important and indirect effect on the two extinctions in the late Permian. Therefore, it is probable that the rapid, kilometer-scale crustal doming prior to the eruption of the Emeishan flood basalt and the descending of the global sea level induce the Guadalupian extinction. In combination with the fact that The P/T extinction occurred 2-5 Ma after the voluminous eruption of Emeishan flood basalt, we further assume that the following two factors: the accumulation of the environment deterioration related to large-scale eruption of the Emeishan LIP and the environment crisis related to the eruption of Siberia traps at the Permo-Triassic boundary, could jointly induce the great extinction at the Permo-Triassic boundary. Although these assumptions are still controversial at present, it is inconceivable that there is the closely coupling correlation between the Emeishan LIP geological consequences and synchronous mass extinction events.