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Unraveling short- and long-term carbon cycle variations during the Oceanic Anoxic Event 2 from the Paris Basin Chalk
Global and Planetary Change ( IF 3.9 ) Pub Date : 2020-03-01 , DOI: 10.1016/j.gloplacha.2020.103126
Slah Boulila , Guillaume Charbonnier , Jorge E. Spangenberg , Silvia Gardin , Bruno Galbrun , Justine Briard , Laurence Le Callonnec

Abstract The Oceanic Anoxic Event 2 (OAE2, ca. 94.6 Ma) is one of the major perturbations in the global carbon cycle during the Phanerozoic. Stable carbon isotopes (δ13C) from marine and continental sedimentary environments document this carbon cycle perturbation with a pronounced (> 2‰) positive carbon isotope excursion (CIE). Although the OAE2 stratigraphic interval has been intensively studied in terms of paleoceanography and paleoclimatology, several climatic and carbon cycle aspects are not yet well-understood. In particular, cyclic short-term Milankovitch-scale δ13C variations within the OAE2 and their potential implications for the global carbon cycle have been rarely addressed. Here, we present high-resolution (5 cm, ~2 kyr) δ13C data spanning the OAE2 from the Paris Basin Chalk (Poigny Craie-701 drill-core) to show high amplitude short-term δ13C oscillations, superimposed on the major CIE. Time-series analysis indicates that short-term oscillations are astronomically paced, with eccentricity cycles being the most prominent. Orbital forcing of δ13C variations is further supported by time-series analysis of the English Chalk (Eastbourne section). We suggest that orbitally paced carbon cycle oscillations were amplified by considerable emission of greenhouse gases from volcanism that caused the overall CIE. Astronomical calibration of the whole OAE2 (the perturbation and recovery phases) from the Poigny record provides a duration equivalent to eight to eight and a half short eccentricity cycles. Cyclostratigraphic correlations among several OAE2 key records indicate the same duration of the whole CIE. However, duration of the interval from the onset of CIE till the Cenomanian-Turonian boundary (CTB) is significantly different from one basin to another. In particular, a difference of almost two short eccentricity cycles is highlighted between the Anglo-Paris and Western Interior basins. According to cyclostratigraphic approach and correlations, the entry of W. devonense was at least 200 kyr later in the Western Interior Basin (WIB, USA) than in Europe. Key calcareous nannofossil biohorizons (e.g., Quadrum gartneri) are also stratigraphically upshifted in the WIB with respect to the European sections, hence concurring with the hypothesis of a younger CTB in the WIB. We ascribe such significant temporal offset to diachroneity of the CTB, which is likely the result of different, regional biotic responses to the global OAE2 paleoenvironmental perturbation.

中文翻译:

从巴黎盆地白垩揭示大洋缺氧事件 2 期间的短期和长期碳循环变化

摘要 大洋缺氧事件 2 (OAE2, ca. 94.6 Ma) 是显生宙全球碳循环的主要扰动之一。来自海洋和大陆沉积环境的稳定碳同位素 (δ13C) 记录了这种具有明显 (> 2‰) 正碳同位素偏移 (CIE) 的碳循环扰动。尽管在古海洋学和古气候学方面对 OAE2 地层区间进行了深入研究,但几个气候和碳循环方面尚未得到很好的理解。特别是,OAE2 中周期性的短期米兰科维奇尺度 δ13C 变化及其对全球碳循环的潜在影响很少得到解决。在这里,我们展示了高分辨率(5 cm,~2 kyr) 跨越巴黎盆地白垩(Poigny Craie-701 钻芯)的 OAE2 的 δ13C 数据,显示叠加在主要 CIE 上的高振幅短期 δ13C 振荡。时间序列分析表明,短期振荡是天文节拍的,其中离心周期最为突出。英国白垩(伊斯特本部分)的时间序列分析进一步支持了 δ13C 变化的轨道强迫。我们认为,导致整体 CIE 的火山活动产生的大量温室气体排放放大了轨道节奏的碳循环振荡。来自 Poigny 记录的整个 OAE2(扰动和恢复阶段)的天文校准提供了相当于八到八个半短偏心周期的持续时间。几个 OAE2 关键记录之间的旋回地层相关性表明整个 CIE 的持续时间相同。然而,从 CIE 开始到 Cenomanian-Turonian 边界(CTB)的间隔持续时间在不同盆地之间存在显着差异。特别是,在盎格鲁-巴黎盆地和西部内陆盆地之间突出了几乎两个短偏心率周期的差异。根据旋回地层学方法和相关性,西部内陆盆地(美国WIB)的W. devonense进入至少比欧洲晚200 kyr。相对于欧洲部分,WIB 中关键的钙质纳米化石生物地层(例如 Quadrum gartneri)在地层上也发生了上移,因此与 WIB 中更年轻的 CTB 的假设一致。我们将如此显着的时间偏移归因于 CTB 的历时性,
更新日期:2020-03-01
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