High temperature methane emissions from Large Igneous Provinces as contributors to late Permian mass extinctions
大规模火成岩省的高温甲烷排放是晚二叠纪大灭绝的贡献者

Received: 2 May 2022 收到：2022 年 5 月 2 日
Accepted: 1 November 2022
接受: 2022 年 11 月 1 日
Published online: 12 November 2022
发布于网上：2022 年 11 月 12 日
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Major mass extinction events during the last 500 Ma of Earth's history coincide with the eruptions of Large Igneous Provinces (LIPs) . They have been attributed to a combination of magmatic activities and greenhouse gas release . During the eruptions, massive quantities of greenhouse gases (e.g., and ) were emitted into the atmosphere, leading to rapid global warming, which then contributed to the widespread demise of both aquatic and terrestrial ecosystems . The Late Permian mass extinctions (LPME), the most severe biosphere crisis in Earth's history, eliminated more than of the Earth's species. Two independent extinction events during the LPME, the Guadalupian-Lopingian extinction (GLE) and the Permian-Triassic extinction (PTE), occurred within a fairly short period ( 10 Ma ), which, in timing, could be attributed to the eruption of the Emeishan Large Igneous Province (ELIP; -260 Ma) and Siberian Traps Large Igneous Province (STLIP; -252 Ma) respectively . High-resolution stratigraphy and paleo-biodiversity studies also support the strong correlation between the LPME and the LIPs . The links among the global carbon cycle, climate change, and mass extinctions have been recorded in the 5 to 8 per mil ( ) negative shift in stable carbon isotopes of both carbonate and organic carbon ( and ) through the .
地球历史上最后 500 百万年内发生的主要大规模灭绝事件与大型火成岩省(LIPs)的喷发 不谋而合。它们被归咎于火山活动和温室气体释放的结合 。在喷发期间,大量的温室气体(如 和 )被排放到大气中,导致全球急剧变暖,这又促进了水生和陆地生态系统的广泛衰落 。晚二叠世灭绝(LPME)是地球历史上最严重的生物圈危机,消灭了超过 的地球物种。LPME 期间的两次独立灭绝事件,即瓜达鲁佩-罗平城灭绝(GLE)和二叠纪-三叠纪灭绝(PTE),发生在一个相当短的时期(约 10 百万年),其时间上可归因于恩梅山大型火成岩省(ELIP;约 260 百万年前)和西伯利亚大陆板块大型火成岩省(STLIP;约 252 百万年前)的喷发 。高分辨率地层学和古生物多样性研究也支持 LPME 与 LIPs 之间的强相关性 。全球碳循环、气候变化和大规模灭绝之间的联系,在 5 到 8‰(< code8 >)的碳酸盐和有机碳( 和 )稳定碳同位素负偏移中有所记录 。

Although an association between global warming and the LPME has been widely accepted, temporal emission mechanisms of greenhouse gases are not entirely clear and remain a topic of discussion. The volcanism associated with the LPME triggered greenhouse gas outbursts and extreme climate changes , primarily due to from magma degassing, thermal metamorphism, and combustion of coal, carbonates, and shales . In contrast, released by volcanic intrusion into coal, destabilization of submarine and permafrost clathrates, and enhanced microbial methanogenesis is thought to have had a secondary effect . However, large quantities of solid bitumen (or termed as pyrobitumen), the by-product of the pyrolysis of oils into , can be found in areas within the ELIP and STLIP regions . This additional source of methane, generated underground by oil
尽管人们普遍接受全球变暖与晚泥盆纪大灭绝事件之间存在关联,但温室气体的时间排放机制并不完全清楚,仍然是一个讨论话题。与晚泥盆纪大灭绝事件相关的火山活动引发了温室气体喷发和极端气候变化,主要是由于来自岩浆脱气、热变质以及煤炭、碳酸盐和页岩燃烧的排放。相比之下,由于火山岩侵入煤层、海底和永冻层气凝物的破坏以及微生物甲烷生成的增强,这些因素被认为具有次要作用。然而,在伊利亚斯边缘岩浆省(ELIP)和西西伯利亚地幔柱(STLIP)地区,可以发现大量的固态沥青(或称为热沥青),这是油类热解产生的副产品。这种地下产生的额外甲烷来源,可能对晚泥盆纪大灭绝事件的气候变化产生了重要影响。

cracking and subsequently released into the atmosphere, may play a much more important role during the LPME interval than previously thought. is a potent greenhouse gas, and its global warming potential is approximately 28 times relative to for a 100-year time horizon without considering climate feedback (e.g., stratospheric ozone depletion .
在 LPME 时期内,裂缝及其后释放到大气中的 可能比之前认为的更加重要。 是一种强大的温室气体,其全球升温潜能在 100 年时间尺度上相当于 的约 28 倍,不考虑气候反馈(如平流层臭氧消耗 )。

Pyrolysis of paleo-oil and related emissions induced by the volcanic activity of both the ELIP and STLIP have been investigated previously based on petrological recordings and gas-venting pipes . It was suggested that carbon gases and and even halocarbons might have been released into the atmosphere through pipes in both Sichuan Basin, China and Tunguska Basin, Siberia during the Late Permian. Nevertheless, previous work was based on indirect evidence in the petrological recordings to infer the possibility of gas emissions. They did not quantify the extensiveness of the pyrolysis process and had insufficient evidence of its strong correlation with the LIPs. In this study, we focus on natural gases by combining clumped isotopes for methane and isotope tracers for noble gases together with basin modeling techniques, to investigate the link between volcanism and generated by large-scale oil cracking, and evaluate its impact on the LPME.
古油热解及与温拉斯-西伯利亚大火成岩省(ELIP)和锡尔特温拉斯大火成岩省(STLIP)火山活动相关的气体排放已基于岩石学记录和气体排放管进行过前期研究。已有研究建议,在中国四川盆地和俄罗斯西伯利亚通古斯盆地的晚二叠世期间,可能通过这些管道向大气中释放了二氧化碳、甲烷及卤代烃。然而,以前的工作仅依赖于岩石学记录中的间接证据来推测气体排放的可能性,未能量化热解过程的广泛性,也缺乏与大火成岩省密切相关的充分证据。在本研究中,我们通过结合甲烷团状同位素和贵金属气体同位素示踪剂以及盆地建模技术,重点研究天然气,探讨火山活动与由大规模油裂解产生的气体之间的联系,并评估其对晚二叠世大灭绝事件的影响。

The Sichuan Basin in the southwestern China is an ideal case study, because (a) it is located in the outer zone of the ELIP in the Upper Yangtze platform of South China continental block (Fig. 1a); (b) abnormal heating events induced by the ELIP have been identified in the basin and (c) widespread pyrobitumen and natural gas pools have been discovered within the Sinian-Cambrian dolostones in the basin, indicating that massive in-situ paleo-oils have been completely pyrolyzed into in its geological history . The ELIP is partly occupied by the Sichuan Basin and its magmas from the Emeishan mantle plume (EMP) have intruded through the Upper Yangtze sedimentary sequences (i.e., Precambrian to Silurian dolostones, marls, and shales) (Fig. 1a). Large basaltic eruptions, crustal melting, hydrothermal activity, and abnormal heating events occurred in the basin and may have initially covered from inner to outer zones . A thick succession of marine carbonates overlies the -800 Ma old basement, where a large-scale paleo-uplift (Leshan-Longnvsi) formed in the center of the basin and became a large petroleum system over the early Paleozoic (Fig. 1b). The sedimentary cover of the paleo-uplift includes Sinian-Ordovician marine carbonates, PermianTriassic carbonate-clastic rocks and Triassic-Quaternary clastic rocks (Fig. 1c). The Anyue gas field, with an area of , is located on the high point (Moxi-Gaoshiti Bulge) of the paleo-uplift with proven gas reserves of over one trillion cubic meters within the Sinian Dengying and Cambrian Longwangmiao Formations. The thick black shale of the Qiongzhusi Formation was deposited within the depression on the west of the high point. As the major source rocks (dominated by Type-I kerogen), the shale generated and expelled oils which migrated into the traps within the high points during the oil generation window from Ordovician to Devonia . Subsequently, the accumulated oils were pyrolyzed into pyrobitumen and methane gas, which were the most common fluids filling the pore space in the Sinian-Cambrian reservoirs . Geochemical evidence from pyrobitumen indicated that the gas pools were formed by in-situ thermal pyrolysis of paleo-oil pools .
四川盆地位于中国西南部,是一个理想的案例研究对象,原因如下:(a)它位于华南大陆块上扬子台地外缘的 ELIP 范围内(图 1a);(b)ELIP 导致的异常加热事件已在该盆地内被确认;(c)在该盆地的寒武系-震旦系白云岩内发现了广泛的热解沥青和天然气藏,表明大规模的古油藏在地质历史中已完全热解为干气。ELIP 部分占据了四川盆地,来自峨眉山地幔柱(EMP)的岩浆侵入了上扬子沉积序列(即震旦系-志留系的白云岩、泥灰岩和页岩)(图 1a)。该盆地发生了大规模玄武岩喷发、地壳熔融、热液活动和异常加热事件,可能从内至外范围内都有发生(图 1b、1c)。厚厚的海相碳酸盐覆盖在约 8 亿年的基底之上,在盆地中心形成了大规模的古隆起(乐山-龙门寺),成为古始生代大型含油气系统。这个古隆起的沉积覆盖包括震旦系-奥陶系的海相碳酸盐、二叠系-三叠系的碳酸盐-碎屑岩和三叠系-第四系的碎屛岩(图 1c)。安岳气田位于这一古隆起的高点(莫希-高石梯凸起)上,在震旦系灯影组和寒武系龙王庙组中证实有超过一万亿立方米的天然气储量。位于高点西部的凹陷中沉积了厚厚的黑色页岩,即穷珠寺组。 作为主要的源岩（主要由 I 型类酮组成），页岩在渥德维期至泥盆纪的油气生成窗口期内生成并排放了油品,这些油品迁移进入了高地陷穴。随后,积累的油品被热解转化为焦油质沥青和甲烷气,这些是塞宁-寒武系储层中最常见的充填孔隙空间的流体。来自焦油质沥青的地球化学证据表明,天然气藏是由古油藏原位热解成的。

Although previous studies have proposed that the formation of pyrobitumen within the strata may have been affected by occasional hydrothermal activity associated with the ELIP , their evidence is not sufficient to directly link the massive generation of oil-cracked within the ELIP to the EMP . It remains uncertain whether the ELIP could have acted as a widespread-impact "coking furnace" for promoting the massive generation of oil-cracked and pyrobitumen underground. Here, we examine 20 natural gas samples (dominantly ) collected from the Sinian-Cambrian dolostones in the Anyue gas field in the central Sichuan Basin within the outer zone of
尽管之前的研究提出了沉积层内焦油沥青的形成可能受到与埃尔利普有关的偶发性热液活动的影响,但其证据不足以直接将埃尔利普内大规模油裂解与 EMR 建立联系。目前仍不确定埃尔利普是否可能作为一个广泛影响的"焦炉",促进了地下大规模油裂解和焦油沥青的生成。这里,我们对四川盆地中部安岳气田晚前寒武纪-寒武纪白云岩中采集的 20 个天然气样品(主要为甲烷)进行了研究。
ELIP (Fig. 1b, c). We measure methane-clumped isotopes ( 9 samples) to obtain methane formation temperatures for investigation of the abnormal geothermal activity and determine noble gas isotopic compositions ( 11 samples) to understand the mantle influence on ELIP region. Furthermore, we conduct numerical simulation of basin evolution and hydrocarbon generation for the gas field to assist in constraining methane formation temperature and genesis (see Methods). This work quantifies the ELIP-induced generation within the reservoirs. The total volume of methane released into the atmosphere from the whole basin during the gas formation period is estimated as 1440 Gt .
埃利普(图 1b、c)。我们测量甲烷簇聚同位素(9 个样品),以获得甲烷形成温度,以调查异常地热活动,并确定贵重气体同位素组成(11 个样品),以了解地幔对埃利普地区的影响。此外,我们对流盆演化和油气生成进行数值模拟,以帮助约束甲烷形成温度和起源(见方法)。这项工作量化了埃利普引发的甲烷生成。在气体形成期间,整个盆地向大气释放的甲烷总体积估计为 1440 Gt。

The natural gas appears as a typical dry gas with a dryness index ) ranging from 583 to 3019. It contains ranging from to ranging from to ranging from undetectable to ranging from undetectable to ranging from undetectable to , and trace amounts of other gases (Supplementary Table 1). Methane shares similar values ranging from to and similar values ranging from to , while ethane shares similar values ranging from to (Supplementary Table 1). Low and content is likely related to minor thermochemical sulfate reduction (TSR) that took place in the reservoirs . Almost all gases from the Sinian and Cambrian reservoirs were generated from oil precursors accompanied with abundant pyrobitumen from 0.1 to over (average approximately . In addition to extremely high dryness index ( ), and values (much higher than and , respectively) also show that gases from the Sinian and Cambrian reservoirs have reached thermal equilibrium. They fall within the equilibrium thermogenic field defined by using and values (Supplementary Fig. 6a), indicating that there are no influences from biogenic or abiotic gases . Extremely high dryness index, a single in-situ gas source, and equilibrium conditions permit the use of the thermometer (defined by equation 4 in the Supplementary Information) for deriving formation temperatures of methane.
这种天然气是典型的干气,干燥指数(C1/(C2+C3))在 583 到 3019 之间。它含有从未检出到从未检出到从未检出到从未检出到从未检出的极微量其他气体(补充表 1)。甲烷的δ13C 值在-44.46‰到-41.73‰之间,δD 值在-207.8‰到-195.4‰之间,而乙烷的δ13C 值在-36.51‰到-33.99‰之间(补充表 1)。较低的硫酸盐还原(TSR)可能与储层中微量的热化学硫酸盐还原有关。来自寒武系和震旦系的几乎所有天然气都是由油前体物生成的,伴有从 0.1 到超过 2.5(平均约 1.8)的丰富热解沥青。除了极高的干燥指数之外,δ13C(CH4)和δ13C(C2H6)值(远高于δ13C(CO2)和δ13C(H2S)值)也表明寒武系和震旦系的天然气已达到热平衡。它们落在以δ13C(CH4)和δ13C(C2H6)定义的平衡热成因气体区域内(补充图 6a),表明没有生源气或无机气体的影响。极高的干燥指数、单一的就地气源以及平衡条件,使我们能够利用甲烷热力学温度计(补充信息中的公式 4)来推导形成温度。

values indicate methane formation temperatures in the samples vary from to (average of ), while the D-based temperature values of methane in samples vary from to (average of ) (Fig. 2b; Supplementary Table 2). These temperatures are significantly higher than the present reservoir temperatures and the peak temperatures of either TSR or oil-cracking (Fig. 2b; Supplementary Fig. 3). Also, they are significantly higher than the modeled reservoir temperatures (200- ) of the maximum burial during Late Cretaceous (Fig. 2a, b). In contrast, clumped methane isotope temperatures are closer to the highest trapping temperatures of the quartz inclusions that have been reported in the same gas reservoirs in the Anyue gas field , representing the invasion of deep-to-epizonogenic hydrothermal fluids corresponding to the ELIP, EMP (Fig. 2b). These generally higher temperatures derived from values indicate significant hydrothermal control in addition to the thermal effect associated with burial process.
在 中变化范围为 ),而 在 中变化范围为 )(图 2b;补充表 2)。这些温度明显高于当前的 以及 TSR 的峰值温度(图 2b;补充图 3)。此外,它们也显著高于在白垩纪晚期达到的 所模拟的储藏温度(图 2a,b)。相比之下,甲烷同位素温度与在安岳气田同样气藏中报告的石英包裹体的最高捕获温度 更为接近,代表了与 ELIP、EMP 相关的深部至准地壳热液流体侵入(图 2b)。这些从 导出的普遍较高温度表明,除了与埋藏过程相关的热效应之外,还存在显著的热液控制作用。

The interpretation of high-temperature methane formation in the Anyue gas field is supported by the gas compositions. Studies have shown that temperature differences can generate completely different end products especially in organic reactions . The kinetics of the oilcracking process has two distinct stages with significant difference in gas composition of methane and heavy hydrocarbon gases . The first stage is characterized by dominant production of
安岳气田高温甲烷形成的解释得到了气体组成的支持。研究表明,温度差异可以产生完全不同的最终产品,特别是在有机反应中。油裂解过程的动力学有两个明显的阶段,甲烷和重烃类气体的气体组成有很大差异。第一阶段以甲烷为主。

Fig. 1 | Tectonic and stratigraphic background of the study area and adjacent regions. a Map showing the geographic distribution of the Emeishan Large Igneous Province (ELIP) and Sichuan Basin in the Upper Yangtze platform, southwestern China . The administration boundaries in the map are originated from map products of National Geomatics Center of China (http://www.webmap.cn).
图 1 | 研究区域及相邻地区的构造和地层背景。a 显示四川盆地和峨眉山大火成岩省(ELIP)在扬子上扬子平台西南部地理分布的地图 。地图中的行政边界来自中国国家测绘地理信息局的地图产品(http://www.webmap.cn)。
b Tectonic setting of the study area and adjacent regions. The map of burial depth depicts the Cambrian bottom and constraints the boundary of Leshan-Longnvsi paleo-uplift . Nine gas samples for methane clumped isotope and noble gas analysis are indicated, samples not shown in the map are also collected from the same area in Sinian-Cambrian reservoirs. They are located on the Moxi-Gaoshiti Bulge as part of the Leshan-Longnvsi paleo-uplift, which is the center of the basin as well as the outer zone of ELIP. c Generalized stratigraphic column of the Sichuan Basin .
研究区域及邻近区域的构造背景。埋藏深度图描绘了寒武系底部,并限定了乐山-龙女寺古隆起 的边界。有九个天然气样品用于甲烷簇合同位素和贵重气体分析,未在地图上显示的样品也是从该区域的震旦系-寒武系储层收集的。它们位于莫希-高石梯脊为乐山-龙女寺古隆起的一部分,这既是盆地的中心,也是东川-理塘地幔柱的外围区域。c 四川盆地的概括性地层柱 。
Marine environments persisted in the basement from the Sinian to the Middle Triassic controlled by the Yangtze, Caledonian, and Hercynian movements, occurring unconformities of the Sinian-Cambrian by the deformation, the Devonian-Carboniferous by the late Paleozoic lifting, and the Permian-Triassic by the ELIP-induced dome and lifting . After the tectonic evolution during the middle Triassic, the terrestrial succession had become the main sedimentary facies until Late Cretaceous controlled by the Indosinian and Yanshannian movements . The Yanshannian-Himalayan lifting led to extensive absence of the Cenozoic in the basin . Symbols used in the figure include - Cambrian; O - Ordovician; C - Carboniferous; K - Cretaceous; E - Paleogene; N - Neogene; Q - Quaternary. wet gases and pyrobitumen, whereas the second stage is characterized by re-cracking of the wet gases to methane. This process leads to a progressive increasing dryness index of the gas . Kinetic modeling of the gases showed that the maximum yield of the gases was from to at geological heating rates from Ma to Ma and they were completely pyrolyzed into methane at a temperature of . Our methane generation model (Fig. 2 and also see Methods and Supplementary Fig. 3) which is based on the
从西尼亚纪到中三叠纪，受到扬子、加里东和赫西尼亚运动的控制，海洋环境一直存在于基底之中。其中出现了西尼亚-寒武的不整合面、泥盆纪-石炭纪的晚古生代抬升以及二叠纪-三叠纪的 ELIP 诱发的隆起和抬升。在中三叠纪的构造演化之后,陆地沉积相一直占主导地位,直到晚白垩纪,受印支运动和燕山运动的控制。燕山-喜马拉雅运动导致了该盆地在新生代缺失了大量地层。图中使用的符号包括:Ɔ-寒武纪;O-奥陶纪;C-石炭纪;K-白垩纪;E-古新世;N-新生代;Q-第四纪。第一阶段特征为湿性气体和热沥青,而第二阶段则以重新裂解湿性气体产生甲烷为特征,导致气体干燥指数逐步增加。气体动力学模拟显示,在地质加热速率为 x-y Ma、温度达到 z℃时,湿性气体产出达到最大,之后全部裂解成甲烷。图 2 及补充材料图 3 所示的甲烷生成模型基于上述结果。

Fig. 2 | History of geological evolution matches modeled geological temperatures. a The burial history and modeled reservoir temperatures and in the Anyue gas field, central Sichuan Basin recovered by model simulations on wellMX and well-GS (see Supplementary Fig. 1 and Supplementary Fig. 2). The reservoirs with dolomite diagenesis have allowed storage of the pre-existing oils and subsequent oil-cracked gases . The modeled temperatures correspond to the geological evolution history in the successive order of early cementation, surface dolomitization, syngenetic dissolution, meteoric karstification, burial dissolution, burial dolomite precipitation, hydrothermal invasion, and deepest burial dissolution .b Diagram of D-based temperatures ( -based T) vs. ratios. Dashed lines specify possible formation temperatures at which methane can be generated under different conditions . The error bars for D-based temperatures are dominantly derived from standard deviation for a constant offset against the stochastic distribution (see Supplementary Information). kinetic model and a geological heating rate of for the Sichuan basin indicates that such extremely dry gases in the Sinian-Cambrian reservoirs would require a formation temperature beyond . In contrast, the formation temperature at the maximum burial depth during Late Cretaceous had not exceeded (Fig. 2a, b). At this temperature, it was unlikely for the oils in the reservoirs to form such extremely dry gases. The gas products would have been characterized by high content of wet gases, which contradicts the gas compositions observed. Therefore, evidence from gas composition, kinetic modeling and the -based temperatures support the impact of the ELIP on the formation of methane in the Anyue gas field, by triggering abnormal heating and rapid oil cracking.
图 2 | 地质演化历史与模拟的地质温度相匹配。a 中央四川盆地安岳气田井 MX 和井 GS(参见补充图 1 和补充图 2)的埋藏史和模拟的储层温度。具有白云岩成岩作用的储层允许了先前存在的原油和随后的油裂解气的储存。模拟温度与地质演化历史的连续顺序相对应,包括早期胶结、表面白云岩化、共生溶解、大气溶蚀、埋藏溶解、埋藏白云岩沉淀、热液侵入和最深埋藏溶解。b δD 温度与δ13C 比率的关系图。虚线标示出不同条件下甲烷可生成的可能形成温度。δD 温度的误差主要源于针对随机分布的常数偏移的标准差(见补充信息)。四川盆地的动力学模型和地质加热速率表明,四川盆地寒武-震旦系储层中如此极干的气体需要形成温度超过 250°C。相比之下,在白垩纪晚期最大埋藏深度期间的形成温度未超过 180°C(图 2a,b)。在这种温度下,储层中的原油不太可能形成如此极干的气体。气体产品应该表现出高含量的湿气,这与观察到的气体组成不符。 因此,气体组成、动力学建模和基于 的温度证据支持 ELIP 对安岳气田甲烷形成的影响,通过引发异常加热和快速油裂化。

High-temperature methane formation in the Anyue gas field can also be supported by petrological evidence. Optical characteristics of pyrobitumen in the and reservoirs were observed to be similar to mesophase pitch, a liquid crystal material produced at high temperatures in a coking furnace, indicating that organic matter had been transferred to a graphite crystal. Honeycomb micropores, generally observed in carbon foams, appeared in the pyrobitumen , suggesting that the reservoirs had undergone a coking process by hydrothermal fluid invasion with rapid heating rather than gradual burial in the geothermal history. These anomalous temperatures suggest that methane generated in the Anyue gas field was mainly controlled by the invasion of hydrothermal fluids during the ELIP interval rather than the maximum burial at the Late Cretaceous, as such high temperatures in the region are only available during the ELIP period (Fig. 2). Further investigation on the mantle involvement is carried out by using noble gas tracers.
安岳气田的高温甲烷形成也可以通过岩石学证据得到支持。在 和