Stepwise atmospheric carbon-isotope excursion during the Toarcian Oceanic Anoxic Event (Early Jurassic, Polish Basin)
Stepwise atmospheric carbon-isotope excursion during the Toarcian Oceanic Anoxic Event (Early Jurassic, Polish Basin)
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DOI：
10.1016/j.epsl.2010.11.021
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发表时间：
2011-01-03
影响因子：
5.3
通讯作者：
Pienkowski, Grzegorz
中科院分区：
文献类型：
--
作者：
Hesselbo, Stephen P.;Pienkowski, Grzegorz
在中生代（250-64 Ma）约0.5 Myr的区间内，发生了严重的环境变化，包括高海面温度和极低的海水氧含量。这些海洋缺氧事件（oae）与对碳循环的严重干扰同时发生。早侏罗世的碳同位素异常标志着Toarcian Oceanic缺氧事件（T-OAE）发生于-182 Ma，在海相剖面上表现为一系列朝向较轻值的戏剧性步骤。在此，我们提供了来自波兰盆地的陆相有机质（植物碎屑分离物）的新的碳同位素数据，这些有机物是通过晚普林恩巴赫-中托瓦良期海岸和边缘海洋演替收集的，该盆地是一个内陆气候和海平面变化记录良好的环境。结果表明，木本有机质中向轻碳同位素值的转变，以及大气中二氧化碳的转变，同样发生在主要步骤中。这里的步骤与从海洋有机物中发现的步骤相关联，它们以前被归因于100 kyr的气候偏心率强迫。研究结果为气态水合物中同位素轻碳在轨道和气候控制下以一系列快速爆发的方式释放到海洋-大气系统提供了强有力的支持。此外，可以证明碳同位素步骤与海岸线运动之间的联系。负偏移的个别峰值大多与指示海平面上升的相（洪水面）有关。然而，与此同时，推断出的更高的大气二氧化碳含量可能导致降雨和温度增加，导致风化和侵蚀加速，从而增加沉积物供应、进积和退积，导致同位素变化与推断的海平面变化之间存在一些不匹配。亲水植物群大孢子丰度的增加和高岭石的显著增加与负同位素偏移的整体发展一致。综合数据表明，每个100 kyr周期的碳同位素值都具有日益剧烈的古气候变化特征，最终达到极端炎热和潮湿的条件，与最终最负碳同位素偏移的峰值同时发生。化学地层对比可以非常精确地确定波兰盆地晚普林恩巴赫-中托瓦西亚海岸和边缘海相沉积演替的年代。(C) 2010 Elsevier B.V.版权所有
During the Mesozoic (250-64 Ma) intervals of about 0.5 Myr were subject to severe environmental changes, including high sea-surface temperature and very low oxygen content of marine water. These Oceanic Anoxic Events, or OAEs, occurred simultaneously with profound disturbance to the carbon cycle. The carbon-isotope anomaly in the Early Jurassic that marks the Toarcian Oceanic Anoxic Event (T-OAE) at -182 Ma is characterized in marine sections by a series of dramatic steps towards lighter values. Herein we present new carbon-isotope data from terrestrial organic matter (phytoclast separates), collected through a Late Pliensbachian-Middle Toarcian coastal and marginal marine succession in the Polish Basin, a setting where hinterland climate and sea-level change are well recorded. The results show that the shift to light carbon-isotope values in the woody organic matter, and therefore also in atmospheric carbon dioxide, similarly occurred in major steps. The steps are here correlated with those identified from marine organic matter, where they have previously been attributed to 100 kyr eccentricity forcing of climate. The results provide strong support for orbitally and climatically controlled release of isotopically light carbon from gas hydrates into the ocean-atmosphere system in a series of rapid bursts. Additionally, a link between the carbon-isotope steps and shoreline movements can be demonstrated. Individual peaks of the negative excursion are mostly associated with facies indicative of sea-level rise (flooding surfaces). However, at the same time inferred higher atmospheric carbon-dioxide content may be expected to have resulted in increased rainfall and temperature, leading to accelerated weathering and erosion, and consequently increased sediment supply, progradation and regression, causing some mismatches between isotope shifts and inferred sea-level changes. Enhanced abundance of megaspores derived from hydrophilic plant groups, and marked increase in kaolinite, are coincident with the overall development of the negative isotope excursion. The combined data suggest that each 100-kyr cycle in carbon-isotope values was characterized by increasingly severe palaeoclimatic change, culminating in extremely hot and humid conditions co-incident with the peak of the final most negative carbon-isotope excursion. The chemostratigraphic correlation allows very precise dating of the Late Pliensbachian-Middle Toarcian coastal and marginal marine sedimentary succession in the Polish Basin. (C) 2010 Elsevier B.V. All rights reserved.