Hydrothermal venting of greenhouse gases triggering Early Jurassic global warming
Hydrothermal venting of greenhouse gases triggering Early Jurassic global warming
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DOI：
10.1016/j.epsl.2007.02.013
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发表时间：
2007-04
影响因子：
5.3
通讯作者：
H. Svensen;S. Planke;L. Chevallier;A. Malthe‐Sørenssen;F. Corfu;B. Jamtveit
中科院分区：
文献类型：
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作者：
H. Svensen;S. Planke;L. Chevallier;A. Malthe‐Sørenssen;F. Corfu;B. Jamtveit
托阿尔期（早侏罗世）气候变化的特征是全球碳循环的重大扰动。这一事件持续了大约20万年，表现为全球变暖106 °C，海洋缺氧和海洋物种灭绝。然而，扰动和环境变化的触发机制存在着激烈的争论。在这里，我们提出的证据表明，在卡鲁盆地，南非的深层沉积水库的温室气体的快速形成和运输。岩浆岩床是在早侏罗世卡鲁大火成岩省形成的初始阶段侵位的，并对富含有机质的沉积寄主岩中轻元素的命运产生了深远的影响。有机碳总量和镜质组反射率数据表明，有机碳在加热过程中从围岩中损失。我们目前的数据，从一种新的类型的地质结构，角砾岩管道，植根于光环内的西卡鲁盆地的页岩。角砾岩筒是直径达150米的圆柱形结构，主要由角砾化和烘烤的黑色页岩组成。由于页岩变质过程中气体压力的积累，形成了数千个角砾岩管道，导致温室气体排放到Toarcian大气中。新的光环数据约束的质量平衡计算表明，高达1800亿吨的CO2形成的有机物质在西部卡鲁盆地。在侵入事件期间，整个盆地可能形成了大约15倍于此数量的CO2（27，400 Gt）。对与许多管道有关的岩床中锆石的U-Pb测年表明，岩浆侵位于1.825亿±0.4亿年前。这支持了侵入火山作用、气体排放和Toarcian全球变暖之间的因果关系。
The climate change in the Toarcian (Early Jurassic) was characterized by a major perturbation of the global carbon cycle. The event lasted for approximately 200,000 years and was manifested by a global warming of ∼6 °C, anoxic conditions in the oceans, and extinction of marine species. The triggering mechanisms for the perturbation and environmental change are however strongly debated. Here, we present evidence for a rapid formation and transport of greenhouse gases from the deep sedimentary reservoirs in the Karoo Basin, South Africa. Magmatic sills were emplaced during the initial stages of formation of the Early Jurassic Karoo Large Igneous Province, and had a profound influence on the fate of light elements in the organic-rich sedimentary host rocks. Total organic carbon contents and vitrinite reflectivity data from contact aureoles around the sills show that organic carbon was lost from the country rocks during heating. We present data from a new type of geological structures, termed breccia pipes, rooted in the aureoles within the shale of the Western Karoo Basin. The breccia pipes are cylindrical structures up to 150 meters in diameter and are mainly comprised of brecciated and baked black shale. Thousands of breccia pipes were formed due to gas pressure build-up during metamorphism of the shales, resulting in venting of greenhouse gases to the Toarcian atmosphere. Mass balance calculations constrained by new aureole data show that up to 1800 Gt of CO2was formed from organic material in the western Karoo Basin. About 15 times this amount of CO2(27,400 Gt) may have formed in the entire basin during the intrusive event. U–Pb dating of zircons from a sill related to many of the pipes demonstrates that the magma was emplaced 182.5±0.4 million years ago. This supports a causal relationship between the intrusive volcanism, the gas venting, and the Toarcian global warming.