Determining the style and provenance of magmatic activity during the Early Aptian Oceanic Anoxic Event (OAE 1a)
Determining the style and provenance of magmatic activity during the Early Aptian Oceanic Anoxic Event (OAE 1a)
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DOI：
10.1016/j.gloplacha.2021.103461
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发表时间：
2021-05
影响因子：
3.9
通讯作者：
L. Percival;L. R. Tedeschi;R. Creaser;C. Bottini;E. Erba;F. Giraud;H. Svensen;J. Savian;R. Trindade;R. Coccioni;F. Frontalini;L. Jovane;T. Mather;H. Jenkyns
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文献类型：
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作者：
L. Percival;L. R. Tedeschi;R. Creaser;C. Bottini;E. Erba;F. Giraud;H. Svensen;J. Savian;R. Trindade;R. Coccioni;F. Frontalini;L. Jovane;T. Mather;H. Jenkyns
大火成岩省（LIP）火山活动被认为是中生代几次重大气候和环境扰动的关键触发因素。大规模的碳排放与一个或两个从大Ontong-Java高原（G-OJP）的岩浆脱气和高北极LIP（HALIP）岩床的有机质丰富的沉积物的侵入已被广泛认为是早Aptian海洋Anoorthodonic事件（OAE 1a：~120 Ma）的触发器。然而，这两个LIP和相关的碳源在导致这场危机中的各自作用仍然存在争议。在这里，OAE 1a从太平洋，特提斯，北极和南大西洋领域的六个记录进行了调查，结合汞（Hg）浓度和锇（Os）同位素比值作为LIP活动的代理。与以前发表的数据集，结果表明全球一致的Os同位素证据LIP活动在OAE 1a，但地理上可变的地层汞的趋势。明确的汞富集，匹配Os同位素证据的LIP活动，并建议汞循环扰动OAE 1a的发病期间，记录在一个太平洋站点非常接近的G-OJP，但不是在北极，特提斯或大西洋的记录。这种模式突出了显着的G-OJP火山活动在OAE 1a的发病，并再次强调了有限的潜力，海底LIP喷发造成汞循环扰动，除了在非常接近源的地区。在北极（或太平洋以外的任何地方）的OAE 1a地层中没有明显的汞峰值，这并不支持当时强烈的HALIP活动，这表明G-OJP是OAE 1a开始时火山活动更活跃的LIP。因此，G-OJP排放的地幔碳更有可能发挥了重要作用，在启动OAE 1a比热挥发物与HALIP。一个短暂的脉冲HALIP相关的陆上喷发和/或产热挥发性排放物在早中期的OAE 1a，可能证明了更广泛的汞富集在地层从那个时候（包括在北极），可能延长了事件。然而，不能排除这些后来的汞流入的非火山原因。这些发现挑战了以前的建议，岩浆CO2排放LIPs是无法单独造成重大的碳循环扰动，并强调需要进一步调查，以确定是否高体积/侵位率的G-OJP（可能比其他LIPs大一个数量级）使其成为一个独特的情况下，站在与其他省份的热挥发物的作用可能更重要。
Large igneous province (LIP) volcanism has been proposed as a key trigger of several major climate and environmental perturbations during the Phanerozoic Aeon. Large-scale carbon emissions associated with one or both of magmatic degassing from the Greater Ontong-Java Plateau (G-OJP) and intrusion of organic-rich sediments by High Arctic LIP (HALIP) sills have been widely suggested as the trigger of the Early Aptian Oceanic Anoxic Event (OAE 1a: ~120 Ma). However, the respective roles of the two LIPs and associated carbon sources in causing this crisis remain debated. Here, six records of OAE 1a from the Pacific, Tethyan, Arctic, and South Atlantic realms are investigated, combining mercury (Hg) concentrations and osmium- (Os-) isotope ratios as proxies of LIP activity. Together with previously published datasets, the results indicate globally consistent Os-isotope evidence for LIP activity during OAE 1a, but geographically variable stratigraphic Hg trends. Clear mercury enrichments that match Os-isotope evidence of LIP activity, and suggest a Hg-cycle perturbation during the onset of OAE 1a, are documented at one Pacific site extremely proximal to the G-OJP, but not in Arctic, Tethyan or Atlantic records. This pattern highlights significant G-OJP volcanism during the onset of OAE 1a, and re-emphasises the limited potential for submarine LIP eruptions to cause Hg-cycle perturbations except in areas very proximal to source. The absence of clear Hg peaks in basal OAE 1a strata from the Arctic (or anywhere outside of the Pacific) does not support intense HALIP activity at that time, suggesting that the G-OJP was the more volcanically active LIP when OAE 1a commenced. Thus, G-OJP emissions of mantle carbon were more likely to have played a major role in initiating OAE 1a than thermogenic volatiles associated with the HALIP. A transient pulse of HALIP-related subaerial eruptions and/or thermogenic volatile emissions during the early–middle part of OAE 1a, potentially evidenced by more widespread Hg enrichments in strata from that time (including in the Arctic), might have prolonged the event. However, a non-volcanic cause of these later Hg influxes cannot be excluded. These findings challenge previous suggestions that magmatic CO2emissions from LIPs were incapable of causing major carbon-cycle perturbations alone, and highlight the need for further investigations to establish whether the high volume/emplacement rate of the G-OJP (potentially an order of magnitude greater than other LIPs) made it a unique case that stands in contrast to other provinces where the role of thermogenic volatiles was likely more crucial.