A mass extinction took place at the end of Guadalupian，seriously killing many species. For the causes of this extinction event，some researcher suggested that the marine anoxia was one of the major causes. However，there are few studies on this redox condition during the G-L transition period，lacking of direct evidence to support the relationship between ocean anoxia and mass extinction at the end of Guadalupian. Framboidal pyrite size distribution is one of the few reliable indicators of redox conditions of sedimentation water column. Since the microcrystal size is related with framboid pyrite size，its size distribution should be also a indicator of redox condition. In this paper，we study the microcrystal size distribution across the Maokou-Heshan Formations boundary in the Penglaitan section，so as to analyze the redox conditions of water column. The studied results show that the most microcrystallite size of Maokou and Heshan Formations range from 0.4 μm to 1.2 μm and has a narrow size variation，though some of the samples show a wider variation. At the Maokou Formation-Heshan Formation boundaries，the samples with a small size （average less than 0.7 μm） and a small the maximum size （average less than 1.2 μm） intermittently occurs，likely indicating euxinic to anoxic environment. The average size of most samples from Maokou and Heshan Formations ranges from 0.7 μm to 1.0 μm with a maximum value less than 3.3 μm，probably indicating the dysoxic to oxic environment. In the Penglaitan section，the euxinic to anoxic layers is coincided with the mass extinction level at the G-L boundary，indicating a causal link between. Marine anoxia is probability one of the main causes of the end Guadalupian mass extinction.
Wei Xuemei Wei Hengye Qiu Zhen Jiang Zengguang Baima Quzong. Framboidal microcryst size characteristics of pyrite and its redox significance across the G-L boundary in Penglaitan section，Laibin，Guangxi[J]. Chinese Journal of Geology, 2017, 52(1): 230-241.