华南瓜德鲁普世深水区氧化还原条件的演化及其对生物灭绝过程的影响

The Guadalupian mass extinction in the Permian mainly recorded the massive death of benthic invertebrates in shallow marine. The ultimate causes of this bio-crisis are still unclear. It may be related with problem that most of the previous studies were focused on the extinction lines instead of the process. For example, as a main kill-mechanism, most of the studies on marine anoxia were carried out in the middle-late Capitanian. However, the onset of the Guadalupian mass extinction was actually at the end of the Roadian (Early Guadalupian). The mass extinction process was long and prolonged. Therefore, we will carry out a project that makes a study on marine redox evolution during the entire Guadalupian and its impact on the mass extinction process. We choose the Gufeng Formation in the Pingdingshan section in Chaohu, and the Xiaolao section in Tongling Anhui Province in the northern Jiangnan Basin, and the Bancheng Formation in the Xiaodong section in Qinzhou, Guangxi Province in the southern Jiangnan Basin in South China as the study interval. The pyrite morphology and pyrite sulfur isotopic composition were used to analyze the redox evolution during the entire Guadalupian, and thus to discuss its impact on the mass extinction process. The mass extinction may be result of the enhanced environmental pressure caused by long-term dysoxic-anoxic conditions. The short-term anoxia and euxinia may be the last strike of the mass extinction process.

二叠纪瓜德鲁普世生物灭绝事件主要记录了浅海底栖无脊椎动物的大规模死亡. 造成该次生物危机的最终原因尚未清楚. 这或许与以往研究过多集中在灭绝线而不是灭绝过程有关. 例如作为主要灭绝机制的海洋缺氧的研究主要集中在卡匹敦中晚期. 而该次生物灭绝事件实际上从罗德末期（瓜德鲁普世早期）就已经开始，生物灭绝过程漫长而迟缓. 因而，本项目将对整个瓜德鲁普世海洋氧化还原条件演化及其对生物灭绝过程的影响进行研究. 选择华南地区江南盆地北部的安徽巢湖平顶山剖面和铜陵小涝剖面的孤峰组，以及盆地南部广西钦州小董剖面的板城组作为研究对象，利用黄铁矿形态与黄铁矿硫同位素结合的手段分析整个瓜德鲁普统氧化还原条件的变化，并探讨海洋氧化还原演化对生物灭绝过程的影响. 生物的灭绝有可能是海洋贫氧—缺氧的长期作用引起的生物生存和环境压力增大所致，短期的缺氧和硫化可能是生物灭绝过程的最后一击.

二叠纪瓜德鲁普世晚期发生了一次生物危机事件，称为瓜德鲁普统末生物大灭绝或卡匹敦中期生物大灭绝。该灭绝事件记录了曾经繁荣在温暖浅海海底的蜓类有孔虫、小型有孔虫、腕足、皱壁珊瑚等底栖无脊椎动物的大规模死亡。这个生物灭绝事件实际上是逐渐地选择性灭绝。该次生物危机事件的原因是否整个瓜德鲁普世长期环境恶化累加的结果？这是本项目要解决的主要问题。为此，项目针对下扬子地区瓜德鲁普统孤峰组展开古海洋氧化还原条件的调查。选择安徽巢湖平顶山剖面以及铜陵小涝剖面作为研究对象，主要进行黄铁矿形貌和黄铁矿硫同位素分析。结果表明，巢湖平顶山剖面代表的盆地水体在整个瓜德鲁普世主要以较为持续的硫化缺氧为主；小涝剖面代表的台地斜坡浅水环境主要以氧化贫氧为主，间歇性出现硫化缺氧环境。到了瓜德鲁普世晚期，台地斜坡浅水环境出现更加频繁的间歇性硫化缺氧事件。据此认为，台地斜坡浅水环境间歇性硫化事件可能是造成瓜德鲁普世生物主灭绝事件发生之前的生物多样性逐渐下降的原因；瓜德鲁普世晚期盆地缺氧硫化水体向浅水台地扩张、氧化还原界面的变浅导致浅水台地出现更加频繁的间歇性硫化缺氧事件，配合当时全球性的海退事件，引发了瓜德鲁普世末期生物大灭绝事件。