Abstract The early Bajocian event was characterized by a protracted, ca. 4 Myr-long positive carbon isotope excursion that has been recognized in both marine and continental records. It is concomitant with a marine eutrophication event that led to regional demises of the neritic carbonate factory, as well as floral and faunal turnovers. The ultimate cause and modality of this event remains uncertain. In this study, we present a high-resolution, biostratigraphically calibrated, bulk organic matter carbon isotope dataset derived from the marine sedimentary record of the Central High Atlas Basin in Morocco and spanning the upper Aalenian–lower upper Bajocian. Within the context of the overall lower Bajocian positive carbon isotope excursion, this curve displays a complex trend of subordinated positive and negative shifts, which can be correlated to the high-resolution bulk carbonate carbon isotope record of southeastern France and southern Spain. The presence of a similar complex shape in these carbon isotope records over a large paleogeographic area highlights that the carbon cycle perturbation associated with the early Bajocian event was more intricate than previously depicted. Using the difference in carbon isotope fractionation between the carbonate and organic matter records as a first-order tracer of atmospheric pCO2 variations implies that the late early Bajocian was characterized by two interludes (late Propinquans and late Humphriesianum chronozones) of low greenhouse gas concentrations. This inference is supported by high-resolution paleotemperature and global sea-level records, suggesting the transient development of polar ice caps during the Middle Jurassic.

中文翻译：

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早期 Bajocian 事件期间全球碳循环的瞬态和长期变化：侏罗纪凉爽气候事件的证据

摘要 早期的 Bajocian 事件的特点是旷日持久，约。4 Myr-long 正碳同位素偏移已在海洋和大陆记录中得到认可。它伴随着海洋富营养化事件，导致浅海碳酸盐工厂的区域性消亡，以及花卉和动物群的更替。这一事件的最终原因和方式仍不确定。在这项研究中，我们提出了一个高分辨率的、生物地层校准的、大块有机物质碳同位素数据集，该数据集来自摩洛哥中部高阿特拉斯盆地的海洋沉积记录，跨越上阿伦阶 - 下巴约西亚阶。在整体较低的 Bajocian 正碳同位素偏移的背景下，该曲线显示出从属正负偏移的复杂趋势，这可以与法国东南部和西班牙南部的高分辨率块状碳酸盐碳同位素记录相关联。在大面积古地理区域的这些碳同位素记录中存在类似的复杂形状，这突出表明与早期 Bajocian 事件相关的碳循环扰动比之前描述的更复杂。使用碳酸盐和有机质记录之间碳同位素分馏的差异作为大气 pCO2 变化的一级示踪剂意味着晚早巴约阶的特征是两个低温室气体浓度的穿插（晚 Propinquas 和晚 Humphriesianum chronozones）。这一推论得到高分辨率古温度和全球海平面记录的支持，