Environmental response to the early Toarcian carbon cycle and climate perturbations in the northeastern part of the West Tethys shelf
Environmental response to the early Toarcian carbon cycle and climate perturbations in the northeastern part of the West Tethys shelf
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西特提斯陆架东北部托阿尔期早期碳循环和气候扰动的环境响应
DOI：
10.1016/j.gr.2018.03.013
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发表时间：
2018
影响因子：
6.1
通讯作者：
Lorenz
中科院分区：
文献类型：
--
作者：
Ruebsam;Wolfgang;Müller;Tamás;Kovács;János;Pálfy;József;Schwark;Lorenz
早陶拉纪（早侏罗世；~183 Ma）气候和碳循环扰动伴随着陶拉纪海洋缺氧事件（T-OAE）期间沥青沉积物的广泛堆积。在特提斯大陆架西北部，有机碳积累在欧洲陆表盆地系统（EEBS）的水动力受限区域尤为普遍，在形成延伸到光带的含氧水期间达到顶峰。在邻近的西特提斯陆架东北部（NE-WTS），靠近较深且通风较好的北特提斯陆架，富含有机质的地层沉积仅限于空间范围有限的坳陷。虽然有大量的研究工作涉及EEBS的沥青地层，但在开阔的特提斯附近地区的环境条件演变和有机质聚集的驱动因素却很少受到关注。在这里，我们研究了在T-OAE期间沉积的NE-WTS的地层约束良好，异常富含有机质的沉积物演替。有机和同位素地球化学调查提供了对特提斯附近T-OAE时期环境条件演化和动态的深入了解。本研究取样的沉积岩来自地表露头，其矿物成分经历了与气候有关的变化。特别是硫化物（主要是黄铁矿）发生了明显的变化，导致硫的损失接近定量。干酪根和沥青组分受风化作用影响较小，具有较强的古环境信号。新的数据表明，有机碳的积累是对环境条件变化的直接反应，这也导致了早期托阿利亚期碳循环的扰动。随着富含12c的碳多次注入地球的海洋-大气系统，有机碳埋藏的增加是逐步发生的。藻类高产和随后硫酸盐还原菌的有机物分解导致富h2s水扩展到光区，促进了绿藻科的生长。氮同位素值的稳定增加证明了在扩大的氧最小带中反硝化作用加剧。由此导致的生物可利用氮有效性的下降，加上恶劣的环境条件，促进了蓝藻的增殖，这表明2α -甲基-藿烷的丰度增加。富氧水的形成与淡水驱动的盐度分层无关。有机地球化学盐度指标（甲基化铬）证明了正常的海洋盐度，支持特提斯水团的强烈影响。这项研究提高了我们对特提斯附近环境对早期托瓦西亚气候和碳循环扰动的环境响应的认识。我们证明，光区泛白是T-OAE的一个共同和特别广泛的特征，并不局限于流体动力学受限的EEBS。
Early Toarcian (Early Jurassic; ~183 Ma) climate and carbon cycle perturbations were accompanied by widespread accumulation of bituminous sediments, formed during the Toarcian Oceanic Anoxic Event (T-OAE). On the northwestern Tethyan shelf, organic carbon accumulation was particularly widespread in hydrodynamically restricted regions of the European Epicontinental Basin System (EEBS) where it peaked during the formation of euxinic waters extending into the photic zone. In the adjacent northeastern West Tethys shelf (NE-WTS), an area proximal to the deeper and better ventilated NW Tethys, deposition of strata enriched in organic matter was restricted to depressions of limited spatial extent. While numerous works have addressed the bituminous strata from the EEBS, evolution of environmental conditions and drivers of organic matter accumulation in areas proximal to the open Tethys have received much less attention.Here, we investigated a stratigraphically well-constrained, exceptionally organic matter-rich sediment succession from the NE-WTS deposited during the T-OAE. Organic and isotope geochemical investigations provided insights into the evolution and dynamics of environmental conditions during the T-OAE in a setting proximal to the Tethys.The sedimentary rocks sampled for this study originated from a surface outcrop that experienced weathering-related alteration of its mineral constituents. In particular, sulfides (mainly pyrite) were significantly altered, resulting in a near-quantitative loss of sulfur. In contrast, kerogen as well as bitumen fractions have not been significantly affected by weathering processes and carry a robust paleoenvironmental signal.The new data show that organic carbon accumulation occurred as a direct response to changing environmental conditions that also led to the early Toarcian carbon cycle perturbation. Increase in organic carbon burial occurred in a stepwise manner, following multiple injections of12C-enriched carbon into the Earth's ocean-atmosphere system. High algal productivity and the subsequent organic matter decomposition by sulfate reducing bacteria led to an expansion of H2S-rich waters into the photic zone, which promoted the growth ofChlorobiaceae. A steady increase in nitrogen isotope values testified to intensified denitrification in an expanded oxygen minimum zone. The resulting decline in the availability of bio-utilizable nitrogen in combination with harsh environmental conditions promoted the proliferation of cyanobacteria as indicated by increasing abundances of 2α‑methyl‑hopanes. Formation of euxinic waters in the NE-WTS was not associated with a freshwater driven salinity stratification. Organic geochemical salinity indicators (methylated chromanes) attest to normal marine salinity, supporting a strong influence of Tethyan water masses.This study enhances our knowledge on the environmental response towards the early Toarcian climate and carbon cycle perturbations in a setting proximal to the Tethys. We demonstrate that photic zone euxinia was a common and particularly widespread feature of the T-OAE and has not been confined to the hydrodynamically restricted EEBS.
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影响因子：
5.3
作者：
Hermoso, Michael;Minoletti, Fabrice;Jenkyns, Hugh C.
通讯作者：
Jenkyns, Hugh C.
影响因子：
4.6
作者：
Them TR;Gill BC;Selby D;Gröcke DR;Friedman RM;Owens JD
通讯作者：
Owens JD
影响因子：
5.3
作者：
Izumi, Kentaro;Kemp, David B.;Inui, Mutsuko
通讯作者：
Inui, Mutsuko
影响因子：
4.3
作者：
Hermoso, M.;Minoletti, F.;Pellenard, P.
通讯作者：
Pellenard, P.
无脊椎动物化石图集
影响因子：
4.9
作者：
G. Sælen;P. Doyle;M. Talbot
通讯作者：
M. Talbot