The Devonian–Carboniferous (D–C) transition coincides with the Hangenberg Crisis, carbon isotope anomalies, and the enhanced preservation of organic matter associated with marine redox fluctuations. The proposed driving factors for the biotic extinction include variations in the eustatic sea level, paleoclimate fluctuation, climatic conditions, redox conditions, and the configuration of ocean basins. To investigate this phenomenon and obtain information on the paleo-ocean environment of different depositional facies, we studied a shallow-water carbonate section developed in the periplatform slope facies on the southern margin of South China, which includes a well-preserved succession spanning the D–C boundary. The integrated chemostratigraphic trends reveal distinct excursions in the isotopic compositions of bulk nitrogen, carbonate carbon, organic carbon, and total sulfur. A distinct negative δ¹⁵N excursion (~−3.1‰) is recorded throughout the Middle Si. praesulcata Zone and the Upper Si. praesulcata Zone, when the Hangenberg mass extinction occurred. We attribute the nitrogen cycle anomaly to enhanced microbial nitrogen fixation, which was likely a consequence of intensified seawater anoxia associated with increased denitrification, as well as upwelling of anoxic ammonium-bearing waters. Negative excursions in the δ¹³C_carb and δ¹³C_org values were identified in the Middle Si. praesulcata Zone and likely resulted from intense deep ocean upwelling that amplified nutrient fluxes and delivered ¹³C-depleted anoxic water masses. Decreased δ³⁴S values during the Middle Si. praesulcata Zone suggests an increasing contribution of water-column sulfate reduction under euxinic conditions. Contributions of organic matter produced by anaerobic metabolisms to the deposition of shallow carbonate in the Upper Si. praesulcata Zone is recorded by the nadir of δ¹³C_org values associated with maximal △¹³C. The integrated δ¹⁵N-δ¹³C-δ³⁴S data suggest that significant ocean-redox variation was recorded in South China during the D–C transition; and that this prominent fluctuation was likely associated with intense upwelling of deep anoxic waters. The temporal synchrony between the development of euxinia/anoxia and the Hangenberg Event indicates that the redox oscillation was a key factor triggering manifestations of the biodiversity crisis.

中文翻译：

---

华南泥盆纪-石炭纪过渡期间环境变化的同位素证据及其对生物危机的影响

泥盆纪-石炭纪（D-C）转变与汉根堡危机、碳同位素异常以及与海洋氧化还原波动相关的有机质保存增强相一致。生物灭绝的驱动因素包括海平面变化、古气候波动、气候条件、氧化还原条件和洋盆结构。为了研究这一现象并获取不同沉积相的古海洋环境信息，我们对华南南缘台地斜坡相发育的浅水碳酸盐岩剖面进行了研究，其中包括保存完好的跨越D的层序。 –C 边界。综合化学地层趋势揭示了本体氮、碳酸盐碳、有机碳和总硫的同位素组成的明显变化。在整个中硅区域记录了明显的负 δ ^{15 N 偏移（~−3.1‰）} 。praesulcata地带和上硅区。普拉埃苏卡塔区，汉根堡大灭绝发生时。我们将氮循环异常归因于微生物固氮作用增强，这可能是与反硝化作用增强相关的海水缺氧加剧以及缺氧含铵水域上升的结果。在中 Si 中发现了δ ¹³ C _carb和 δ ¹³ C _org值的负偏移。praesulcata区域，可能是由于强烈的深海上升流造成的，这种上升流放大了营养物通量并输送了¹³ C 贫乏的缺氧水团。中 Si 期间δ ³⁴ S 值降低。praesulcata区域表明，在环境条件下，水柱硫酸盐还原的贡献越来越大。厌氧代谢产生的有机物对上硅浅层碳酸盐沉积的贡献。praesulcata区是通过与最大 △ ^{13 C 相关的 δ 13} C _org值的最低点记录的。整合的 δ ¹⁵ N-δ ¹³ C-δ ³⁴ S 数据表明，在 D– 期间，华南地区记录了显着的海洋氧化还原变化。 C 过渡；这种显着的波动可能与深层缺氧水域的强烈上升有关。真氧/缺氧的发展与汉根堡事件之间的时间同步性表明，氧化还原振荡是引发生物多样性危机表现的关键因素。