Abstract In this paper we study the Lilang Super Group in the Spiti area, Indian Himalaya to understand environmental changes in the aftermath of the end-Permian mass extinction. We focus on the Mikin and Kaga Formations, which span the Induan to Ladinian stages of the Lower and Middle Triassic. These strata formed on the southern mid-palaeolatitude margin of East Gondwana and are interpreted as condensed, mixed carbonate – siliciclastic ramp deposits that deepened distally. Carbon isotope ratios of carbonate (δ13Ccarb) show an increase from −2.6 to 0‰ from the Griesbachian substage to the Dienerian-Smithian transition, followed by a negative shift to −3‰ in the Smithian substage and a large positive excursion from −3.0 to 3.5‰ across the Smithian-Spathian boundary. A short negative shift to −1.0‰ occurred in the early Spathian substage, and is followed by a positive trend from ~−1.0 to 1.0‰ in the Middle Triassic, with several minor excursions occurring during the Aegean substage. Carbon isotope ratios of total organic carbon (δ13Corg) co-vary with δ13Ccarb, suggesting that both proxies represent the original isotopic signatures. Sedimentary and palaeontological evidence, as well as trace metal geochemistry (Mo/Al ratio), indicate anoxic conditions developed from the late Griesbachian to the Dienerian substages, and dysoxic to probably fully oxic conditions from the late Dienerian substage onward. Anoxic conditions only very briefly reoccurred in the late Smithian substage. Ti/Ca and Zr/Al ratios suggest a consistently high terrestrial input in the first three substages of the Early Triassic, followed by a decrease across the Smithian–Spathian boundary. Thus, in the Spiti area, the positive δ13Ccarb excursion across the Smithian–Spathian boundary is recorded in generally well‑oxygenated sediments and coincides with a decrease in terrestrial input. While evidence for enhanced weathering is lacking, observations are strongly at odds with studies postulating eutrophication as a universal kill mechanism for the Smithian–Spathian crisis. The strata in the Spiti area contain an Early Triassic gap in phosphorite deposition indicating a ~ 5 Myr waning of coastal upwelling in an otherwise persistent (>100 Myr) upwelling zone of the East Gondwana margin. The phosphorite gap suggests low P availability, low rates of organic matter degradation, and a reduction in nutrient exchange between deep and surface water masses. Altogether, the phosphorite gap, the paucity of sessile and filtering fauna in oxygenated waters, and low organic carbon burial rates indicate a collapse in marine productivity in the aftermath of the end-Permian mass extinction.

中文翻译：

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印度喜马拉雅山脉 Spiti 中下三叠世海洋系列的综合生物化学地层学：对早三叠世营养危机的影响

摘要 在本文中，我们研究了印度喜马拉雅山脉 Spiti 地区的 Lilang Super Group，以了解二叠纪末大灭绝后的环境变化。我们关注跨越下三叠纪和中三叠统的 Induan 到 Ladinian 阶段的 Mikin 和 Kaga 组。这些地层形成于东冈瓦纳古纬度中南部边缘，被解释为向远端加深的浓缩碳酸盐-硅质碎屑斜坡沉积物。碳酸盐的碳同位素比 (δ13Ccarb) 从 Griesbachian 亚级到 Dienerian-Smithian 过渡从 -2.6 增加到 0‰，然后在 Smithian 亚级负移至 -3‰ 和从 -3.0 到 -3.0 的大正偏移3.5‰ 跨越史密森-斯帕特边界。在早期的 Spathian 亚阶段发生了短暂的负移至 -1.0‰，紧随其后的是在中三叠世从 ~-1.0 到 1.0‰ 的积极趋势，在爱琴海亚阶段发生了几次小幅偏移。总有机碳 (δ13Corg) 的碳同位素比率与 δ13Ccarb 共变，这表明这两个代表都代表了原始同位素特征。沉积和古生物学证据以及微量金属地球化学（Mo/Al 比）表明，从晚 Griesbachian 到 Dienerian 亚阶段发展为缺氧条件，从晚 Dienerian 亚阶段开始，缺氧到可能完全有氧条件。缺氧条件仅在晚期史密斯亚阶段非常短暂地再次发生。Ti/Ca 和 Zr/Al 比率表明，在早三叠世的前三个亚阶段中，陆地输入始终很高，随后在史密斯 - 斯帕斯阶边界处下降。因此，在斯皮蒂地区，δ13​​Ccarb 穿过史密斯-斯帕斯边界的正偏移记录在一般充氧良好的沉积物中，与陆地输入的减少相吻合。虽然缺乏风化作用增强的证据，但观察结果与假设富营养化是史密斯-斯帕西亚危机的普遍杀伤机制的研究存在强烈分歧。Spiti 地区的地层在磷矿沉积中包含一个早三叠世间隙，表明在东冈瓦纳大陆边缘的其他持续（>100 Myr）上升流带中，沿海上升流减弱了约 5 Myr。磷矿间隙表明磷的可用性低，有机物降解率低，以及深层和地表水团之间的养分交换减少。总之，磷矿间隙，含氧水域中无柄和过滤动物群的缺乏，