The Redox Significance Of Depositional Pyrite Morphology In Enshi Area, Hubei Province

During the Guadalupian–Lopingian(G–L) transition, the tectonic activity, geomagnetic polarity, oceanic redox conditions and sea level all ocured great changes. In the biological world, shallow benthic organisms also occured a great changge during this period. A part of larger benthic organisms became extinct, formed an independent mass extinction event. This mass extinction was mainly related to the Emeishan mantle plume basalt eruption, oceanic anoxic which deteriorated the environment and a falling of the global sea level. However, the final causes of this mass exitnction are not clear. As one of the main factor of this extinction, the oceanic redox research is weakness. Oceanic anoxic usually was one of the straightforward factors of the biological death. The oceanic anoxic deteriorated the ecological environment of the bottom of the seabed and increased the living environment presure of the benthic organisms, it caused the extinction. However, researches on the oceanic redox about G-L bountary was rare and weak. In this paper, we use the framboidal pyrite morphology and size distribution as marine redox index to analyze the marine redox of the Middle-Upper Permian system boundary(G-L boundary) in order to explored the causes of the extinction and the pyrite deposits.The studies have shown that Maokou Formation was a dysoxic-oxic environment, Gufeng Formation sedimentary period was an anoxic-sulfured environment, Wangpo shales of the lower part of the Wujiaping Formation was an anoxic-sulfured environment, Wangpo shales of the upper part of the Wujiaping Formation was a dysoxic-oxic environment, Xiayao limestone of the upper part of the Wujiaping Formation was a poor oxygen environment. The Gufeng Formation was last stage of the Guadalupian, it corresponded typical benthic organisms disappeared period during the Guadalupian period, that aslo was consistent with the time of the mass extinction, it explain that the anoxic-sulfured environment has a causal relationship with the extinction. A long period of the anoxic, the sulfured environment was occured intermittently, that caused a great threat to the survival environment of the benthic organisms.Under the background of global sea level falling, thus occured the extinction event at the end of the Guadalupian period.