Global geological processes that occurred during the Ordovician–Silurian transition (OST) were investigated exploring sections from the Argentine Precordillera (Cerro La Chilca, Baños de Talacasto and Villicum) which were deposited close to polar zones of Gondwana during the oldest Phanerozoic glaciation. C-N-Hg isotopes and redox-sensitive trace metal chemostratigraphy allowed to assess the relative importance of volcanism, glaciation, post-glacial sedimentation and extinction events during the OST. At Cerro La Chilca and Baños de Talacasto sections, Katian and early Hirnantian strata are missing. Hirnantian and Rhuddanian strata occur in the all three sections. At Cerro La Chilca, coeval positive δC shift, Hg spike and ΔHg ∼ 0 ‰ were recorded in the Sandbian Los Azules Formation, suggesting volcanic Hg loading. Coeval Hg/TOC spikes at the Baños de Talacasto and Villicum sections and ΔHg ∼ 0 ‰ in the late Hirnantian ( Zone) recorded the second pulse of the Late Ordovician mass extinction (LOME 2), for which volcanism was postulated as the cause of warming and anoxia. Another Hg/TOC spike in the early Rhuddanian at Baños de Talacasto and Villicum is coeval with slightly positive ΔHg values, an enrichment related, perhaps, to an enhanced continental runoff that followed the Late Ordovician glacial cycle (LOGC-3). At the Cerro La Chilca, positive δN values in the Sandbian suggest less intense water-column denitrification while negative nitrogen isotope values in the LOME 2 period indicate denitrifying conditions. At the Baños de Talacasto and Villicum sections, sea-level fluctuations and nitrogen upwelling helped shaping the δN pathway within the LOME 2 and early Rhuddanian intervals, with negative δN values attesting that conditions became less reducing closer to the OST. The odd-MIF Hg isotope pattern within the LOME 2 time interval was probably induced by coeval volcanism, glaciation and sea-level fall, and in the early Rhuddanian by deglaciation and sea-level rise.

中文翻译：

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阿根廷前记录勒拉奥陶纪-志留纪过渡期间的 C、N、Hg 同位素和元素化学地层学：对火山活动与灭绝之间联系的影响


研究人员对奥陶纪-志留纪过渡期间发生的全球地质过程进行了研究，探索了阿根廷 Precordillera（Cerro La Chilca、Baños de Talacasto 和 Villicum）的部分，这些部分在最古老的显生宙冰川时期沉积在冈瓦纳极地附近。 C-N-Hg 同位素和氧化还原敏感的痕量金属化学地层学可以评估 OST 期间火山活动、冰川作用、冰后沉积和灭绝事件的相对重要性。在 Cerro La Chilca 和 Baños de Talacasto 部分，Katian 和早期 Hirnantian 地层缺失。赫尔南阶和鲁丹阶地层均出现在这三个部分。在 Cerro La Chilca，Sandbian Los Azules 地层中记录到了同期的正 δ13C 位移、Hg 尖峰和 ΔHg ~ 0 ‰，表明存在火山汞负载。 Baños de Talacasto 和 Villicum 剖面的同时期 Hg/TOC 峰值以及赫南特晚期（带）的 ΔHg ~ 0 ‰ 记录了晚奥陶世大规模灭绝 (LOME 2) 的第二次脉冲，火山活动被认为是变暖的原因和缺氧。早鲁丹世巴尼奥斯德塔拉卡斯托和维利库姆的另一个 Hg/TOC 峰值与略微正的 ΔHg 值同时发生，这种富集可能与晚奥陶世冰川旋回（LOGC-3）之后大陆径流的增强有关。在 Cerro La Chilca，Sandbian 的正 δN 值表明水柱反硝化作用较弱，而 LOME 2 时期的负氮同位素值表明反硝化条件。在 Baños de Talacasto 和 Villicum 地段，海平面波动和氮上涌帮助塑造了 LOME 2 和鲁丹期早期的 δN 路径，负 δN 值证明接近 OST 时条件变得不那么减少。 LOME 2时间间隔内的奇数MIF汞同位素模式可能是由同时期的火山活动、冰川作用和海平面下降引起的，而在鲁丹纪早期则由冰消作用和海平面上升引起。