Organic geochemistry of the early Toarcian oceanic anoxic event in Hawsker Bottoms, Yorkshire, England
Organic geochemistry of the early Toarcian oceanic anoxic event in Hawsker Bottoms, Yorkshire, England
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DOI：
10.1016/j.epsl.2013.12.033
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发表时间：
2014-03-15
影响因子：
5.3
通讯作者：
Summons, R. E.
中科院分区：
文献类型：
--
作者：
French, K. L.;Sepulveda, J.;Summons, R. E.
英国约克郡Hawsker Bottoms露头剖面的综合有机地球化学调查为了解Toarcian海洋缺氧事件（T-OAE;类似于183 Ma）的环境条件提供了新的见解。岩石评价和分子分析表明，该剖面均匀地位于早期油窗内。氢指数（HI），有机岩相学，多环芳烃（PAH）的分布，三环萜烷的比例标志着一个转变，以较低的相对丰度的陆源有机质提供给采样地点在发病的T-OAE和整个岩性过渡。与其他缺氧和灭绝的古代间隔，生物标志物指数的浮游植物群落结构并没有显示重大变化或异常值。沉积环境和氧化还原指标支持向更多的沉积物孔隙水的还原条件和发展的季节性分层水柱在T-OAE的转变。除了类胡萝卜素生物标志物的绿色硫细菌（GSB），我们报告的第一次出现的okenane，紫色硫细菌（PSB）的标志物，在海洋样品的年龄比类似的1.64 Ga。根据现代的观察，一个奥克烯烷的前体奥克烯酮的反渗透来源，将需要非常浅的透光带euxinia（PZE）和一个高度限制的沉积环境。然而，由于沿海的垂直混合，缺乏在现代海洋硫化物环境中，和建设的证据，在垫居住的Chromatiaceae的okenone生产的okenone生产的反渗透剂okenone生产，我们提出了一个沉积源作为替代。最后，我们报告了第一个平行的化合物特定的三角洲C-13记录在海洋和陆地来源的生物标志物在整个T-OAE。短链正构烷烃、无环类异戊二烯和长链正构烷烃的δ C-13记录都编码负碳同位素偏移（CIE），它们共同支持同位素轻碳的注入，影响了大气和海洋碳库。迄今为止，T-OAE的分子δ C-13记录显示负CIE，其与本体有机δ C-13偏移相比在幅度上较小。虽然多种机制可以解释这一观察，我们的分子，岩相学和岩石评价数据表明，陆源和海洋有机质的可变混合是一个重要因素，影响散装有机三角洲C-13记录的T-OAE。(C)2014爱思唯尔有限公司版权所有。
A comprehensive organic geochemical investigation of the Hawsker Bottoms outcrop section in Yorkshire, England has provided new insights about environmental conditions leading into and during the Toarcian oceanic anoxic event (T-OAE; similar to 183 Ma). Rock-Eval and molecular analyses demonstrate that the section is uniformly within the early oil window. Hydrogen index (HI), organic petrography, polycyclic aromatic hydrocarbon (PAH) distributions, and tricyclic terpane ratios mark a shift to a lower relative abundance of terrigenous organic matter supplied to the sampling locality during the onset of the T-OAE and across a lithological transition. Unlike other ancient intervals of anoxia and extinction, biomarker indices of planktonic community structure do not display major changes or anomalous values. Depositional environment and redox indicators support a shift towards more reducing conditions in the sediment porewaters and the development of a seasonally stratified water column during the T-OAE. In addition to carotenoid biomarkers for green sulfur bacteria (GSB), we report the first occurrence of okenane, a marker of purple sulfur bacteria (PSB), in marine samples younger than similar to 1.64 Ga. Based on modern observations, a planktonic source of okenane's precursor, okenone, would require extremely shallow photic zone euxinia (PZE) and a highly restricted depositional environment. However, due to coastal vertical mixing, the lack of planktonic okenone production in modern marine sulfidic environments, and building evidence of okenone production in mat-dwelling Chromatiaceae, we propose a sedimentary source of okenone as an alternative. Lastly, we report the first parallel compound-specific delta C-13 record in marine- and terrestrial-derived biomarkers across the T-OAE. The delta C-13 records of short-chain n-alkanes, acyclic isoprenoids, and long-chain n-alkanes all encode negative carbon isotope excursions (CIEs), and together, they support an injection of isotopically light carbon that impacted both the atmospheric and marine carbon reservoirs. To date, molecular delta C-13 records of the T-OAE display a negative CIE that is smaller in magnitude compared to the bulk organic delta C-13 excursion. Although multiple mechanisms could explain this observation, our molecular, petrographic, and Rock-Eval data suggest that variable mixing of terrigenous and marine organic matter is an important factor affecting the bulk organic delta C-13 records of the T-OAE. (C) 2014 Elsevier B.V. All rights reserved.