Potential effects of the Emeishan large igneous province on Capitanian marine anoxia in the Upper Yangtze region

IF 4 1区 地球科学 Q1 GEOGRAPHY, PHYSICAL
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Abstract

The widespread Capitanian (late Guadalupian) marine anoxia/euxinia has long been regarded as a key driver of the end-Guadalupian (middle Permian) biotic crisis. However, the cause of this marine anoxia is debated, particularly regarding the influence of the Emeishan large igneous province (ELIP). To investigate the contribution of the ELIP to marine anoxia and the possible causal mechanisms, we undertook a conodont biostratigraphic and geochemical study of the middle Permian Maokou Formation in a platform-to-trough transect in the Upper Yangtze region, South China. Our results show that the depositional facies of the Maokou Formation changed from a carbonate ramp to an intra-platform trough within the Jinogondolella (J.) altudaensis zone in the northwestern Yangtze region, which can be attributed to the initial activity of the ELIP. Mantle-derived Sr inputs in the initial and main stages of the ELIP led to two decreases in 87Sr/86Sr during the Capitanian, in the J. shannoniJ. altudaensis and J. prexuanhanensisJ. xuanhanensis zones. The elevated 87Sr/86Sr values during the late Capitanian may have been due to enhanced continental weathering caused by rapid climate warming in response to subaerial eruptions of the ELIP. The deep-water anoxia–euxinia expanded during the middle Capitanian, as indicated by increased MoEF/UEF and V/(V + Ni) values, along with the disappearance of burrows and appearance of small pyrite framboids in the J. altudaensis zone in the Cheng 20 well. However, shallow-water anoxia occurred during the late Capitanian (i.e., J. prexuanhanensisJ. xuanhanensis zone), as evidenced by positive Ce anomalies and losses of aerobic benthic species in the Erya section. Importantly, marine anoxia and negative δ13Ccarb excursions occurred synchronously, but earlier in deep water than in shallow water, potentially indicating an expansion of the oxygen minimum zone (OMZ). The deep-water anoxia corresponded to a decrease in 87Sr/86Sr ratios and the appearance of an intra-platform trough in the J. altudaensis zone, whereas the shallow-water anoxia in the late Capitanian coincided with elevated 87Sr/86Sr ratios. This suggests that the initial activity of the ELIP promoted the development of the OMZ in deep waters during the middle Capitanian, while the subaerial eruptions of the ELIP drove climate warming that led to the expansion of the OMZ into shallow-water platforms during the late Capitanian.

峨眉山大型火成岩带对长江上游地区摩天岭海洋缺氧的潜在影响
长期以来,大范围的卡皮坦期(瓜达卢派晚期)海洋缺氧/缺氧现象一直被认为是瓜达卢派末期(二叠纪中期)生物危机的主要驱动因素。然而,关于海洋缺氧的原因,尤其是峨眉山大型火成岩带(ELIP)的影响,一直存在争议。为了研究峨眉山大火成岩带对海洋缺氧的影响以及可能的成因机制,我们对华南上长江地区中二叠统茅口组的平台-槽断面进行了锥齿类生物地层学和地球化学研究。研究结果表明,茅口地层的沉积面貌由碳酸盐岩斜坡转变为长江西北部金刚岭(J. altudaensis)带内的平台内槽,这可归因于ELIP的初始活动。ELIP初期和主要阶段来自地幔的Sr输入导致87Sr/86Sr在盖层期间的两次下降,分别发生在J. shannoni-J.altudaensis区和J. prexuanhanensis-J.xuanhanensis区。卡皮坦纪晚期的87Sr/86Sr值升高可能是由于ELIP的亚航空喷发导致气候迅速变暖,从而引起大陆风化加剧。深水缺氧-缺氧期在卡皮坦纪中期扩大,这表现在MoEF/UEF和V/(V+Ni)值的增加,以及Cheng 20井J. altudaensis区洞穴的消失和小型黄铁矿框架体的出现。然而,浅水缺氧发生在晚期卡皮坦时期(即J. prexuanhanensis-J. xuanhanensis区),Erya剖面的正Ce异常和好氧性底栖生物物种的消失证明了这一点。重要的是,海洋缺氧和 δ13Ccarb 负偏移同步发生,但深水区比浅水区发生得早,这可能表明最低含氧区(OMZ)扩大了。深水缺氧与 J. altudaensis 区 87Sr/86Sr 比值下降和平台内槽出现相对应,而 Capitanian 晚期浅水缺氧与 87Sr/86Sr 比值升高相吻合。这表明,在卡皮坦中期,ELIP的初始活动促进了深水OMZ的发展,而在卡皮坦晚期,ELIP的海下喷发推动了气候变暖,导致OMZ扩展到浅水平台。
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来源期刊
Global and Planetary Change
Global and Planetary Change 地学天文-地球科学综合
CiteScore
7.40
自引率
10.30%
发文量
226
审稿时长
63 days
期刊介绍: The objective of the journal Global and Planetary Change is to provide a multi-disciplinary overview of the processes taking place in the Earth System and involved in planetary change over time. The journal focuses on records of the past and current state of the earth system, and future scenarios , and their link to global environmental change. Regional or process-oriented studies are welcome if they discuss global implications. Topics include, but are not limited to, changes in the dynamics and composition of the atmosphere, oceans and cryosphere, as well as climate change, sea level variation, observations/modelling of Earth processes from deep to (near-)surface and their coupling, global ecology, biogeography and the resilience/thresholds in ecosystems. Key criteria for the consideration of manuscripts are (a) the relevance for the global scientific community and/or (b) the wider implications for global scale problems, preferably combined with (c) having a significance beyond a single discipline. A clear focus on key processes associated with planetary scale change is strongly encouraged. Manuscripts can be submitted as either research contributions or as a review article. Every effort should be made towards the presentation of research outcomes in an understandable way for a broad readership.
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