The Late Triassic was a particularly turbulent interval of the geologic past, marked by repeated paleoenvironmental instability culminating in the end-Triassic mass extinction (ETME). These episodes of disturbance are associated with enhanced volcanism, harbinger of the eventual break-up of Pangea. As evidenced by geochemical signals in the marine carbon isotope record, these events were often significant enough to disrupt the global carbon cycle. However, the duration and extent of ETME-associated disturbances leading up to the Triassic/Jurassic boundary (TJB) remain contentious. The present study investigates eight stratigraphic sections from across British Columbia to create a comprehensive Panthalassan carbon isotope record spanning the Norian to early Hettangian. Three distinct negative excursions are observed: an excursion proximal to the Norian/Rhaetian boundary (NRB), another excursion within the Rhaetian, and a final excursion coinciding with the TJB. This is generally consistent with prior studies, but suggests there may be no clear distinction between the negative excursion associated with the NRB, and the oldest Rhaetian “precursor” excursion proposed to be associated with the TJB. Several of the excursions observed in the present study are too large in magnitude to plausibly reflect global ocean water chemistry (∼10 ‰ compared to the expected ∼3 ‰), indicating some local mechanism was amplifying these carbon isotope excursions. A potential explanation is increased organic carbon respiration in restricted marine environments, triggered during episodes of paleoenvironmental disturbance. Regardless, this evidence for repeated carbon isotope excursions supports paleontological data suggesting that the ETME is not a singular and geologically instantaneous event at the TJB, but is instead the amalgamation of several turnovers beginning as early as the NRB.

中文翻译：

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加拿大科迪勒拉山脉晚三叠世碳同位素异常：与 Norian/Rhaetian 边界和三叠纪末大灭绝事件相关的古环境扰动


晚三叠世是地质历史上一个特别动荡的时期，其特点是反复的古环境不稳定，最终导致三叠纪末大灭绝 （ETME）。这些扰动事件与火山活动的增强有关，预示着盘古大陆最终会解体。正如海洋碳同位素记录中的地球化学信号所证明的那样，这些事件通常足以破坏全球碳循环。然而，导致三叠纪/侏罗纪边界 （TJB） 的 ETME 相关扰动的持续时间和范围仍然存在争议。本研究调查了不列颠哥伦比亚省的八个地层剖面，以创建跨越诺里安到早 Hettangian 的全面 Panthalassan 碳同位素记录。观察到三种明显的负偏移：靠近 Norian/Rhaetian 边界 （NRB） 的偏移，Rhaetian 内部的另一次偏移，以及与 TJB 重合的最后一次偏移。这与以前的研究基本一致，但表明与 NRB 相关的负偏移与被认为与 TJB 相关的最古老的 Rhaetian“前体”偏移之间可能没有明确区别。本研究中观察到的几次偏移量级太大，无法合理地反映全球海水化学（∼10 ‰ 与预期的 ∼3 ‰ 相比），表明一些局部机制正在放大这些碳同位素偏移。一个可能的解释是在古环境干扰事件期间触发的受限海洋环境中有机碳呼吸增加。 无论如何，这些重复碳同位素偏移的证据支持古生物学数据，表明 ETME 不是 TJB 的一个单一的、地质上的瞬时事件，而是早在 NRB 就开始的几次周转的合并。