The present study reviews the main geochemical, sedimentological, and paleontological events associated with one of the largest perturbations in the Phanerozoic carbon cycle, the Mid-Ludfordian Carbon Isotope Excursion (MLCIE), which is globally documented in late Silurian marine successions. Climate changes associated with the MLCIE are not yet well documented in contrast to most other Silurian CIEs. We report seawater surface temperature changes across the entire MLCIE using δ¹⁸O_apatite records of conodonts originating from different regions located in temperate as well as tropical paleolatitudes. Significant positive δ¹⁸O_apatite excursions (up to 3.8‰) measured in temperate-water areas of the Prague Basin and Carnic Alps (peri-Gondwana) as well as in the tropical areas of Baltica (Laurussia) and Australia (Gondwana) provide evidence for significant global cooling during the MLCIE. The marked cooling of sea surface temperatures, coupled with a significant eustatic sea-level fall recorded on all corresponding paleocontinents, point to a major glaciation in polar and subpolar Gondwana which is denominated here as the “Mid-Ludfordian Glaciation”. The onset of rapid cooling in the Prague Basin (peri-Gondwana) is preceded by the deposition of shales enriched in redox-sensitive trace metals suggesting that anoxic/euxinic waters expanded on the deeper carbonate shelf just before the MLCIE. The coincidence of culmination of the anoxic event (named here as the Siluricus Ocean Anoxic Event) with the Lau/Kozlowskii extinction events is documented for the first time outside of the Laurussian epeiric basins. Widespread oxygen-deficient conditions are interpreted to have been stressful to shelfal ecosystems and may have been a major cause of the extinctions. The mid-Ludfordian glacio-eustatic sea-level fall caused a reduction of shelf habitats culminating in a lower faunal diversity and a change in the structure of faunal communities. The observed positive δ¹⁸O_apatite excursion is tightly coupled to δ¹³C and δ³⁴S anomalies documented from temperate (peri-Gondwana) as well as tropical (Laurussia) paleolatitudes. The δ¹⁸O_apatite data complete the Silurian seawater temperature curve and show evidence that one of the largest positive carbon isotope anomalies (MLCIE) of the Phanerozoic was preceded by a widespread anoxic event and tightly linked with a climate cooling event as documented as well for most other Silurian CIEs.

本研究回顾了与显生宙碳循环中最大扰动之一、中路德福碳同位素偏移 (MLCIE) 相关的主要地球化学、沉积学和古生物事件，该事件在晚志留纪海洋演替中被全球记录。与大多数其他志留纪 CIE 相比，与 MLCIE 相关的气候变化尚未得到很好的记录。我们使用源自温带和热带古纬度不同地区的牙形石的δ ¹⁸ O_磷灰石记录报告整个 MLCIE 的海水表面温度变化。δ ¹⁸ O_磷灰石显着阳性在布拉格盆地和卡尔尼克阿尔卑斯山（冈瓦纳周边）的温带水域以及波罗的海（劳俄罗斯）和澳大利亚（冈瓦纳）的热带地区测量的偏移（高达 3.8‰）提供了证据表明在MLCIE。海面温度显着降低，加上所有相应古大陆记录到的海平面显着下降，表明极地和亚极地冈瓦纳大陆存在主要冰川作用，这里称为“中路德福冰川”。在布拉格盆地（冈瓦纳盆地周边）开始快速冷却之前，富含氧化还原敏感痕量金属的页岩沉积表明缺氧/富氧水在 MLCIE 之前在更深的碳酸盐架上膨胀。缺氧事件（此处称为 Siluricus 海洋缺氧事件）与 Lau/Kozlowskii 灭绝事件的高潮的巧合首次在劳鲁士表层盆地之外被记录。普遍的缺氧条件被解释为对陆架生态系统造成压力，并且可能是灭绝的主要原因。中期 Ludfordian 冰川 - eustatic 海平面下降导致大陆架栖息地减少，最终导致动物群多样性降低和动物群落结构发生变化。观察到的正δ 中期 Ludfordian 冰川 - eustatic 海平面下降导致大陆架栖息地减少，最终导致动物群多样性降低和动物群落结构发生变化。观察到的正δ 中期 Ludfordian 冰川 - eustatic 海平面下降导致大陆架栖息地减少，最终导致动物群多样性降低和动物群落结构发生变化。观察到的正δ¹⁸ O_磷灰石偏移与 δ ¹³ C 和 δ ³⁴ S 异常密切相关，这些异常记录来自温带（冈瓦纳周围）和热带（劳鲁士）古纬度。δ ¹⁸ O_磷灰石数据完善了志留纪海水温度曲线，并显示出显生宙最大的正碳同位素异常 (MLCIE) 之一之前发生了广泛的缺氧事件，并与气候变冷事件密切相关，正如所记录的那样大多数其他志留纪 CIE。