Osmium isotope evidence for two pulses of increased continental weathering linked to Early Jurassic volcanism and climate change
Osmium isotope evidence for two pulses of increased continental weathering linked to Early Jurassic volcanism and climate change
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DOI：
10.1130/g37997.1
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发表时间：
2016-09
期刊：
影响因子：
5.8
通讯作者：
L. Percival;A. Cohen;M. Davies;A. Dickson;S. Hesselbo;H. Jenkyns;M. Leng;T. Mather;M. Storm-
中科院分区：
文献类型：
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作者：
L. Percival;A. Cohen;M. Davies;A. Dickson;S. Hesselbo;H. Jenkyns;M. Leng;T. Mather;M. Storm-
大火成岩省（LIPs）被认为通过增加大气CO2水平引起了许多环境突变事件，随后通过增强的大陆风化作用和有机质的埋藏而减少了CO2，从而减轻了环境突变。本文使用一套新的地球化学指标研究了两次这样的环境变化时期的沉积记录，即托瓦西亚海洋缺氧事件（T-OAE）和之前的Pliensbachian-Toarcian事件（plto）（两者都可能与Karoo-Ferrar LIP有关）。比较了威尔士卡迪根湾盆地Llanbedr农场Mochras岩心样品中锇同位素（187Os/188Os）记录与汞（Hg）和碳同位素（δ13C）记录的地层变化。通过钼/铀富集趋势分析，证实了这些沉积岩记录了开阔海相环境，表明这些样品的Os同位素记录反映了全球海洋的同位素组成。Os同位素数据包括首次跨越Pl-To边界的结果，当海水187Os/188Os从~ 0.40增加到~ 0.53时，此外还有新的数据显示在T-OAE期间187Os/188Os升高（从~ 0.42增加到~ 0.68）。1870 / 188o的增加都与负碳同位素漂移和汞浓度增加有关，支持陆地火山作用、风化作用和气候之间的相互作用，这些相互作用在驱动这些不同的全球环境变化事件中起着重要作用。这些观察结果还表明，卡鲁-费拉LIP对环境的影响不仅限于T-OAE。
Large igneous provinces (LIPs) are proposed to have caused a number of episodes of abrupt environmental change by increasing atmospheric CO2 levels, which were subsequently alleviated by drawdown of CO2 via enhanced continental weathering and burial of organic matter. Here the sedimentary records of two such episodes of environmental change, the Toarcian oceanic anoxic event (T-OAE) and preceding Pliensbachian–Toarcian (Pl-To) event (both possibly linked to the Karoo-Ferrar LIP), are investigated using a new suite of geochemical proxies that have not been previously compared. Stratigraphic variations in osmium isotope (187Os/188Os) records are compared with those of mercury (Hg) and carbon isotopes (δ13C) in samples from the Mochras core, Llanbedr Farm, Cardigan Bay Basin, Wales. These sedimentary rocks are confirmed as recording an open-marine setting by analysis of molybdenum/ uranium enrichment trends, indicating that the Os isotope record in these samples reflects the isotopic composition of the global ocean. The Os isotope data include the first results across the Pl-To boundary, when seawater 187Os/188Os increased from ∼0.40 to ∼0.53, in addition to new data that show elevated 187Os/188Os (from ∼0.42 to ∼0.68) during the T-OAE. Both increases in 187Os/188Os correlate with negative carbon isotope excursions and increased mercury concentrations, supporting an interplay between terrestrial volcanism, weathering, and climate that was instrumental in driving these distinct episodes of global environmental change. These observations also indicate that the environmental impact of the Karoo-Ferrar LIP was not limited solely to the T-OAE.