An open ocean record of the Toarcian oceanic anoxic event
An open ocean record of the Toarcian oceanic anoxic event
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DOI：
10.5194/se-2-245-2011
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发表时间：
2011-01-01
期刊：
影响因子：
3.4
通讯作者：
Schwark, L.
中科院分区：
文献类型：
--
作者：
Groecke, D. R.;Hori, R. S.;Schwark, L.
海洋缺氧事件是中生代以海洋富含有机质沉积物（黑色页岩）的广泛分布和全球碳循环的显著扰动为特征的时间间隔。这些扰动在沉积物中被全球记录为碳同位素偏移，而与岩性和沉积环境无关。在早期Toarcian，黑色页岩沉积在泛古陆的表陆和陆缘陆棚，这些沉积岩与一个明显的（约200年）。7千分之一）负（有机）碳同位素偏移（CIE），这被认为是全球碳循环中的重大扰动的结果。因此，下托阿西期被认为是一次海洋缺氧事件（T-OAE）。如果T-OAE确实是一个全球性的事件，这一事件的同位素表达应该被发现超越epi和陆缘盘古大陆的地方。为了解决这一问题，分析了沉积在开阔的泛地中海的日本下托阿西期富含有机质的硅质岩的有机质碳同位素组成（δ C-13（org））。结果表明，在三角洲C-13（org）中存在一个主要的负偏移（>千分之六），根据放射虫生物地层学，这与潘盖世陆表和陆缘地层中已知的下托阿西期负CIE相关。一个较小的负偏移在三角洲C-13（org）（约。千分之二）被认为是较低的研究继承。在目前的生物地层学分辨率范围内，这种漂移可能代表了欧洲大陆表陆继承中记录的靠近Pliensbachian/Toarcian边界的漂移。这些结果表明，结合其他先前发表的数据集，这些早侏罗世碳循环扰动影响了全球活跃的可交换碳循环库（深海，浅海，大气）。
Oceanic anoxic events were time intervals in the Mesozoic characterized by widespread distribution of marine organic matter-rich sediments (black shales) and significant perturbations in the global carbon cycle. These perturbations are globally recorded in sediments as carbon isotope excursions irrespective of lithology and depositional environment. During the early Toarcian, black shales were deposited on the epi- and pericontinental shelves of Pangaea, and these sedimentary rocks are associated with a pronounced (ca. 7 parts per thousand) negative (organic) carbon isotope excursion (CIE) which is thought to be the result of a major perturbation in the global carbon cycle. For this reason, the lower Toarcian is thought to represent an oceanic anoxic event (the T-OAE). If the T-OAE was indeed a global event, an isotopic expression of this event should be found beyond the epi- and pericontinental Pangaean localities. To address this issue, the carbon isotope composition of organic matter (delta C-13(org)) of lower Toarcian organic matter-rich cherts from Japan, deposited in the open Panthalassa Ocean, was analysed. The results show the presence of a major (>6 parts per thousand) negative excursion in delta C-13(org) that, based on radiolarian biostratigraphy, is a correlative of the lower Toarcian negative CIE known from Pangaean epi- and pericontinental strata. A smaller negative excursion in delta C-13(org) (ca. 2 parts per thousand) is recognized lower in the studied succession. This excursion may, within the current biostratigraphic resolution, represent the excursion recorded in European epi-continental successions close to the Pliensbachian/Toarcian boundary. These results from the open ocean realm suggest, in conjunction with other previously published datasets, that these Early Jurassic carbon cycle perturbations affected the active global reservoirs of the exchangeable carbon cycle (deep marine, shallow marine, atmospheric).