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![Early Triassic paleogeography (ca. 250 Ma) of (A) the world (adapted from Ron Blakey, http://jan.ucc.nau.edu/∼rcb7/) and (B) the South China craton (Yin et al., 2014). Red rectangle in A shows location of inset map B. Black triangles (outlined in white) in B represent present study sections (SS-Shangsi; GX-Ganxi; CH-Chaohu). Number of ash beds from conodont Clarkina changxingensis to Isarcicella isarcica zones is shown by red (8), yellow (5-7), purple (3-4), black (1-2), and open (0) symbols (note: Site numbers are given in the Supplemental Material [see footnote 1]). In panel A, red numbers represent previous mercury studies, as shown in Figure 2, including 43 (Zal; Sial et al., 2020), 66 (Buchanan Lake [BL]; Sanei et al., 2012), 67 (Festningen [F]; Grasby et al., 2015), and 70 (Gujo-Hachiman [GH]; Shen et al., 2019a). C-Cathaysia Oldland; K-Kangdian uplift; PTO-Paleo-Tethys Ocean; NTO-Neo-Tethys Ocean; NPJ-Nanpanjiang.](profile/Jun-Shen-20/publication/346934020/figure/fig1/AS:967398400200704@1607657160298/Early-Triassic-paleogeography-ca-250-Ma-of-A-the-world-adapted-from-Ron-Blakey.png)
Early Triassic paleogeography (ca. 250 Ma) of (A) the world (adapted from Ron Blakey, http://jan.ucc.nau.edu/∼rcb7/) and (B) the South China craton (Yin et al., 2014). Red rectangle in A shows location of inset map B. Black triangles (outlined in white) in B represent present study sections (SS-Shangsi; GX-Ganxi; CH-Chaohu). Number of ash beds from conodont Clarkina changxingensis to Isarcicella isarcica zones is shown by red (8), yellow (5-7), purple (3-4), black (1-2), and open (0) symbols (note: Site numbers are given in the Supplemental Material [see footnote 1]). In panel A, red numbers represent previous mercury studies, as shown in Figure 2, including 43 (Zal; Sial et al., 2020), 66 (Buchanan Lake [BL]; Sanei et al., 2012), 67 (Festningen [F]; Grasby et al., 2015), and 70 (Gujo-Hachiman [GH]; Shen et al., 2019a). C-Cathaysia Oldland; K-Kangdian uplift; PTO-Paleo-Tethys Ocean; NTO-Neo-Tethys Ocean; NPJ-Nanpanjiang.
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Enhanced regional subduction-related volcanism in the South China craton concurrent with Siberian Traps large igneous province magmatism was a likely contributor to major biotic and environmental stresses associated with the Permian-Triassic boundary (ca. 252 Ma) mass extinction. However, the timing, intensity, and duration of this regional volcani...
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... the Permian-Triassic transition, the South China craton was a small (∼3 × 10 6 km 2 ) near-equatorial microcontinent in the eastern part of the Paleo-Tethys Ocean (Fig. 1A). The three study sections were located on its northwestern margin (an upwelling zone; Fig. 1B) and represent shallow shelf (Ganxi) to deep shelf/ basin (Shangsi and Chaohu) environments. The study sections accumulated sediment throughout the PTB transition despite a eustatic regression at the end of the Permian (e.g., as recorded by ...
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... the Permian-Triassic transition, the South China craton was a small (∼3 × 10 6 km 2 ) near-equatorial microcontinent in the eastern part of the Paleo-Tethys Ocean (Fig. 1A). The three study sections were located on its northwestern margin (an upwelling zone; Fig. 1B) and represent shallow shelf (Ganxi) to deep shelf/ basin (Shangsi and Chaohu) environments. The study sections accumulated sediment throughout the PTB transition despite a eustatic regression at the end of the Permian (e.g., as recorded by absence of the conodont Clarkina meishanensis zone in shallow-water sections; Yin et al., 2014). ...
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... and (3) similar patterns of Hg/ TOC variation were observed in all three study sections, despite differences in environmental setting (i.e., Ganxi = shallow shelf, Shangsi and Chaohu = deep shelf/basin) and geographic location (>1000 km separation). These considerations support a regional control on Hg inputs to the sediment during ME1 to ME3 (Fig. ...
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... First, these events are not documented in any section outside of the Tethys region (Fig. 2). Second, the Upper Permian across the South China craton contains many ash beds, demonstrating frequent volcanic activity at a regional scale ( Yin et al., 1992). These ash beds increase in number and thickness to the south and southwest (paleocoordinates; Fig. 1; Yin et al., 1992), favoring a subduction-zone volcanic arc along the South China craton-Indochina plate boundary as their source. Third, the chemical compositions (i.e., trace elements and hafnium isotopes) of syndepositional magmatic zircons from these ash beds demonstrate a felsic to intermediate source, consistent with ...
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... hafnium isotopes) of syndepositional magmatic zircons from these ash beds demonstrate a felsic to intermediate source, consistent with subduction-zone rather than flood-basalt volcanism ( Gao et al., 2013;He et al., 2014). Regional volcanism may have also contributed Hg to ME4, although this spike is found in almost all PTB sections globally ( Fig. 2; Shen et al., 2019a), demonstrating that it was not primarily related to plate-margin volcanism in the PaleoTethys region. Rather, ME4 records the second stage of STLIP eruptions, which has been linked to combustion of organic-rich sediments in the West Siberian Coal Field (Burgess et al., 2017), ...
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... volcanism may have also contributed Hg to ME4, although this spike is found in almost all PTB sections globally ( Fig. 2; Shen et al., 2019a), demonstrating that it was not primarily related to plate-margin volcanism in the PaleoTethys region. Rather, ME4 records the second stage of STLIP eruptions, which has been linked to combustion of organic-rich sediments in the West Siberian Coal Field (Burgess et al., 2017), ...
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Anomalous mercury (Hg) contents recorded near the Permian-Triassic boundary (PTB) are often linked to Siberian Traps Large Igneous Province (STLIP) volcanism and the Permian-Triassic boundary mass extinction (PTBME). However, mounting evidence indicates that the relation between STLIP volcanism and Hg “anomalies” is not straightforward. This study...
The long-term effects of the Central Atlantic Magmatic Province, a large igneous province connected to the end-Triassic mass-extinction (201.5 Ma), remain largely elusive. Here, we document the persistence of volcanic-induced mercury (Hg) pollution and its effects on the biosphere for ~1.3 million years after the extinction event. In sediments reco...
Anomalous mercury (Hg) contents recorded near the Permian-Triassic boundary (PTB) are often linked to Siberian Traps Large Igneous Province (STLIP) volcanism and the Permian-Triassic boundary mass extinction (PTBME). However, mounting evidence indicates that the relation between STLIP volcanism and Hg “anomalies” is not straightforward. This study...
The driving forces, kill and recovery mechanisms for the end-Permian mass extinction (EPME), the largest Phanerozoic biological crisis, are under debate. Sedimentary records of mercury enrichment and mercury isotopes have suggested the impact of volcanism on the EPME, yet the causes of mercury enrichment and isotope variations remain controversial....
The latest Permian mass extinction (LPME) was triggered bymagmatism of the
Siberian Traps Large Igneous Province (STLIP), which left an extensive record
of sedimentary Hg anomalies at Northern Hemisphere and tropical sites. Here,
we present Hg records from terrestrial sites in southern Pangea, nearly antipodal
to contemporaneous STLIP activity, pro...
Citations
... Latitudinal diachroneity of the terrestrial EPME Previous work has shown that the marine ecosystem collapse was brief and globally synchronous and was embedded in a long-term interval of global environmental degradation. The onset of the main marine extinction has been constrained to the Clarkina meishanensis and equivalent conodont zones (40)(41)(42)(43), which was calibrated to 251.945 ± 0.033 Ma ago at the Meishan GSSP (3) (table S4), 251.984 ± 0.031 (44) or 251.939 ± 0.031 Ma ago (4) at the extended Penglaitan section, and 251.939 ± 0.031 Ma ago at the Dongpan section (44) in South China. ...
... The emplacement of the SLIP has been the most widely hypothesized trigger of the terrestrial and marine EPME since the early 1990s due to their temporal coincidence (3,5). However, sediments related to felsic volcanism developed extensively along the convergent margins of southern Pangea and around the Tethyan Ocean during the Permian-Triassic transition (21,43,(75)(76)(77) (Fig. 1), introducing another possible stressor for the EPME. Mercury spikes during this interval have been reported globally and are thought to be derived from the SLIP (6), but they are not correlative between different sections based on the high-resolution geochronologic framework presented here, which could be generated from different stages of the SLIP or affected by local sedimentological processes (Fig. 5). ...
The end-Permian mass extinction was the most severe ecological event during the Phanerozoic and has long been presumed contemporaneous across terrestrial and marine realms with global environmental deterioration triggered by the Siberian Traps Large Igneous Province. We present high-precision zircon U-Pb geochronology by the chemical abrasion–isotope dilution–thermal ionization mass spectrometry technique on tuffs from terrestrial to transitional coastal settings in Southwest China, which reveals a protracted collapse of the Cathaysian rainforest beginning after the onset of the end-Permian marine extinction. Integrated with high-resolution geochronology from coeval successions, our results suggest that the terrestrial extinction occurred diachronously with latitude, beginning at high latitudes during the late Changhsingian and progressing to the tropics by the early Induan, spanning a duration of nearly 1 million years. This latitudinal age gradient may have been related to variations in surface warming with more degraded environmental conditions at higher latitudes contributing to higher extinction rates.
... Given the common use of Hg as a proxy for volcanism within Mesozoic sediments (Sanei et al., 2012;Sial et al., 2013;Thibodeau et al., 2016;Grasby et al., 2019;Keller et al., 2020;Shen et al., 2020a), it has been heavily used as a tool to understand the triggering mechanism for the perturbation in the carbon cycle during the TOAE (Percival et al., 2015;Fantasia et al., 2018aFantasia et al., , 2019Font et al., 2022). The KF-LIP is commonly invoked as the primary source of Hg and trigger for the onset of the TOAE ). ...
... Based on this Δ 199 Hg trend, they interpreted their Griesbachian Hg/TOC excursion as having resulted from terrestrial Hg input due to elevated Early Triassic continental weathering. Recently, J. Shen et al. (2021) reported several Hg enrichment intervals predating the PTBME (named ME1-ME3), as well as one interval coeval with the PTBME (ME4), from three marine sections in South China. These authors reported the same pattern of decreasing Δ 199 Hg values from the Changhsingian to Griesbachian. ...
... Owing to the paucity of U-Pb zircon ages for deep-water sections from which Hg anomalies have been reported in South China, it is difficult to confidently correlate our recorded Hg anomalies with those reported for other localities in the Tethys region. However, the E1 anomaly recorded from the studied successions together with ME2 and ME3 episodes of J. Shen et al. (2021), indicate that Hg anomalies preceding the PTB extinction are recorded in both shallow and deep-marine settings in South China. In contrast, the E2 Griesbachian Hg anomaly is not recorded from any shallow-water marine section nor deep-water sections in South China, except for deep-water sections in the Nanpanjiang Basin (e.g., Xinmin, Kejiao; Figure 9). ...
... This is evident from the older and well-known Emeishan LIP , the occurrence of P-T volcanic rocks especially in southwest South China (Gao et al., 2013), the abundant volcanic ash layers within P-T marine sedimentary successions, shown to be genetically distinct from STLIP rocks (Gao et al., 2013;He et al., 2014;Yang et al., 2012), as well as Changhsingian Hg/TOC anomalies restricted to the Tethys region (J. Shen et al., 2021;this study). In addition, regional arc volcanism has been linked to notably decreased carbonate and biogenic silica production, as well as decreased water column oxygenation in South China (J. ...
Anomalous mercury (Hg) contents recorded near the Permian-Triassic boundary (PTB) are often linked to Siberian Traps Large Igneous Province (STLIP) volcanism and the Permian-Triassic boundary mass extinction (PTBME). However, mounting evidence indicates that the relation between STLIP volcanism and Hg “anomalies” is not straightforward. This study focuses on the timing and provenance of volcanic fluxes around the PTBME in South China. We constrain carbon isotope (δ13C) and Hg concentration and isotope records by utilizing high-precision U-Pb zircon ages from two expanded deep-water marine sections spanning the Late Permian to Early Triassic in the Nanpanjiang Basin. Results reveal two episodes of Hg enrichment. The oldest episode predates the onset of a large negative δ13C excursion, which is documented to be older than 252.07 ± 0.130 Ma. The second episode occurred between 251.822 ± 0.060 and 251.589 ± 0.062 Ma, coinciding with the nadir of the δ13C excursion. Volcanic ash geochemistry and Hg isotope compositions suggest that mercury was mainly sourced from subduction-related volcanic arc magmatism in the Tethys region, which peaked between 251.668 ± 0.079 and 251.589 ± 0.052 Ma. These results are compatible with suggestions that regional arc volcanism contributed to the causes of the PTBME in South China and provide evidence that Hg anomalies close to the PTB are not a reliable stratigraphic marker for the PTB extinction event. This study demonstrates that relations between volcanism, environmental perturbations and mass extinction during the Permian-Triassic transition are better resolved with the aid of high-precision U-Pb zircon ages.
... Our results suggest that several different types of regional volcanic activities could have been responsible for the basal middle Tournaisian biotic turnover. In recent years, many authors emphasized the influence of enhanced regional subduction-related arc-volcanism as a potential trigger of biotic crises during the end-Ordovician (Yang et al., 2019), Frasnian-Famennian (Racki et al., 2018b;Racki, 2020;Zhao et al., 2022a), end-Devonian (Kalvoda et al., 2019;Rakociński et al., 2021b), and end-Permian (Shen et al., 2021). However, to better constrain the influence of volcanic activity during the LASE, additional Hg isotopic data are needed. ...
... The short-lived spike of Hg and Hg/TOC was coincident with a sharp δ 13 C minimum 27,28 . Many sections also show a negative shift of Δ 199 Hg by~0.1‰ at or post-EPME relative to the Late Permian background levels before the extinction [24][25][26][29][30][31][32][33] (Supplementary Figs. 1-4; Supplementary Table 1). ...
... Previous studies often assumed the enhanced Hg enrichment and the negative shift of Δ 199 Hg were synchronous across the EPME and interpreted them as the result of increased atmospheric Hg deposition from volcanic emission, and/or of massive terrestrial Hg input to oceans from biomass burning and soil erosion, which are often also linked to volcanism [24][25][26][29][30][31][32][33] . Such interpretations follow because mantle-sourced volcanic Hg typically has circum-zero Δ 199 Hg values 34,35 , and modern terrestrial vegetation and soil typically have negative Δ 199 Hg values 23 , both of which are lower than background values of pre-EPME marine sediments (0.1-0.2‰) (Supplementary Table 1). ...
... This result does not exclude the contribution of soil erosion to the Hg enrichment and negative shift of Δ 199 Hg, especially for the shallow marine Meishan section. Instead, it suggests that soil erosion alone (as proposed by most previous studies [24][25][26][29][30][31][32][33] cannot account for the full extent of the Δ 199 Hg negative shift during the main EPME interval as shown in the model Run #2, and additional Hg MIF in seawater caused by PZE is required for this shift. ...
The driving forces, kill and recovery mechanisms for the end-Permian mass extinction (EPME), the largest Phanerozoic biological crisis, are under debate. Sedimentary records of mercury enrichment and mercury isotopes have suggested the impact of volcanism on the EPME, yet the causes of mercury enrichment and isotope variations remain controversial. Here, we model mercury isotope variations across the EPME to quantitatively assess the effects of volcanism, terrestrial erosion and photic zone euxinia (PZE, toxic, sulfide-rich conditions). Our numerical model shows that while large-scale volcanism remains the main driver of widespread mercury enrichment, the negative shifts of Δ¹⁹⁹Hg isotope signature across the EPME cannot be fully explained by volcanism or terrestrial erosion as proposed before, but require additional fractionation by marine mercury photoreduction under enhanced PZE conditions. Thus our model provides further evidence for widespread and prolonged PZE as a key kill mechanism for both the EPME and the impeded recovery afterward.
... This Hg could transport globally in the atmosphere and subsequently deposits into land and ocean systems, resulting in anomalous high Hg concentrations in global soil and marine sediments . Mercury is hosted in sediments in multiple phases, including organic matter, sulfides, and clay minerals Shen et al., 2020). Recent studies suggest that anomalously high Hg to total organic carbon (Hg/TOC) ratios can be a useful proxy for tracing large volcanism in geological history Shen et al., 2020), although studies also suggest that the depositional environments may play a critical role in Hg accumulation in sediments rather than input sources (Shen et al., 2022;Xue et al., 2022). ...
... Mercury is hosted in sediments in multiple phases, including organic matter, sulfides, and clay minerals Shen et al., 2020). Recent studies suggest that anomalously high Hg to total organic carbon (Hg/TOC) ratios can be a useful proxy for tracing large volcanism in geological history Shen et al., 2020), although studies also suggest that the depositional environments may play a critical role in Hg accumulation in sediments rather than input sources (Shen et al., 2022;Xue et al., 2022). Besides, caution must be paid to weathered rocks because Hg may be lost during silicate weathering (Charbonnier et al., 2020;Park et al., 2022). ...
... Possible host phases of Hg in sediments include organic matter, sulfides, and clay minerals (Krupp, 1988;Grasby et al., 2019;Shen et al., 2019Shen et al., , 2020. Mercury has a strong affinity to the organic matter in normal sediments Shen et al., 2020), however recent studies have suggested that sulfides (e.g., pyrite) can be another important host of Hg in sulfidic water conditions (Shen et al., 2019(Shen et al., , 2022. ...
... Heterogeneity of Siberian Traps activity concerning the magnitude of eruptions and emplacement style (e.g., intrusive vs. eruptive) has been introduced as a potential explanation for highintensity events at decadal to centennial time scales 3,10,11 . Given the difficulty in elucidating a decadal-to centennial-scale volcanic history from the volcanic rock relics in Siberia, various direct or indirect chemical tracers (e.g., Hg) have been introduced to track LIP activity [12][13][14][15] . Some of these studies suggest that the strong volcanic activity at the end-Permian was pulsatile 16 , and that for both marine and terrestrial extinctions to occur, the destruction of terrestrial ecosystems had to take place first [17][18][19] . ...
The exact drivers for the end-Permian mass extinction (EPME) remain controversial. Here we focus on a ~10,000 yr record from the marine type section
at Meishan, China, preceding and covering the onset of the EPME. Analyses of
polyaromatic hydrocarbons at sampling intervals representing 1.5–6.3 yr
reveal recurrent pulses of wildfires in the terrestrial realm. Massive input
pulses of soil-derived organic matter and clastic materials into the oceans are
indicated by patterns of C2-dibenzofuran, C30 hopane and aluminum. Importantly, in the ~2,000 years preceding the main phase of the EPME, we observe a
clearly defined sequence of wildfires, soil weathering, and euxinia provoked by
the fertilization of the marine environment with soil-derived nutrients. Euxinia
is indicated by sulfur and iron concentrations. Our study suggests that, in
South China, centennial scale processes led to a collapse of the terrestrial
ecosystem ~300 yr (120–480 yr; ± 2 s.d.) before the onset of the EPME and that
this collapse induced euxinic conditions in the ocean, ultimately resulting in
the demise of marine ecosystems.
... As mentioned above, volcanic Hg derived from primitive mantle mostly has near zero Δ 199 Hg (Sun, Streets, et al., 2016;Zambardi et al., 2009). Two major mechanisms were proposed to interpret the deviation of odd-MIF: a positive shift of Δ 199 Hg was generally considered to be related to the loading of atmospheric Hg that underwent photoreduction into oceans (Deng et al., 2020;Grasby et al., 2017;Shen et al., 2019;Sial et al., 2020Sial et al., , 2021Wang et al., 2018), while a negative shift Δ 199 Hg indicated input through enhanced soil erosion and terrestrial biomass burning Shen et al., 2019Shen et al., , 2021Wang et al., 2018;Zhao et al., 2022). ...
The oceans, serving as some of the most extensive reservoirs of mercury (Hg) on Earth, play an essential role in the global Hg biogeochemical circulation, as a sink for atmospheric deposits and surface runoff while simultaneously emitting Hg to the atmosphere. Clarifying the mechanisms during cycling of Hg in marine ecosystems is a crucial segment in elucidating global Hg behavior and assessing its risks to wildlife and humans. The stable Hg isotope technique has emerged as a powerful tool for identifying potential sources and certain processes of Hg. Herein, the research advances in marine Hg biogeochemical cycling were reviewed from an isotopic tracing perspective, including sources of marine Hg, isotopic fingerprints across various marine media, and applications of Hg isotopes in pathways, transport, and transformation mechanisms associated with marine environments. The knowledge gaps and challenges were further discussed in the development of ultratrace level and species-specific isotopic analytical methods, the isotope fractionation mechanisms in reactions and processes, and the integration of multiple approaches and cross disciplines. These future studies would advance our understanding of Hg behavior in oceanic environments, its authentic function, and interactions with other ecosystems in the global Hg cycle, and evaluate its response to environmental changes.
... Mercury contents and isotope ratios in sediments have been widely used to trace and evaluate the record of volcanism in geological history, and to determine Hg source(s) and evaluate Hg's transport mechanisms in the Earth system (e.g., Sanei et al., 2012;Grasby et al., 2019;Shen et al., 2020a;Percival et al., 2021;Yager et al., 2021;Shen et al., 2022a). Volcanism and wildfires are the main causes of abnormal mercury enrichment anomalies in strata (Shen et al., 2020a(Shen et al., , 2020bShen et al., 2022). Volcanism can not only release Hg directly into the atmosphere, but can also lead to abnormal Hg accumulation in sediments through magma heating of organic-rich sediments (e.g., Shen et al., 2020b;Shen et al., 2022). ...
... Volcanism and wildfires are the main causes of abnormal mercury enrichment anomalies in strata (Shen et al., 2020a(Shen et al., , 2020bShen et al., 2022). Volcanism can not only release Hg directly into the atmosphere, but can also lead to abnormal Hg accumulation in sediments through magma heating of organic-rich sediments (e.g., Shen et al., 2020b;Shen et al., 2022). Meanwhile, burning (caused by wildfire) of surface organic matter and soil erosion can also cause Hg enrichment anomalies (Blum et al., 2014;Thibodeau et al., 2016;Shen et al., 2020b;Shen et al., 2022), because the majority (>90%) of Hg in terrestrial systems resides in soils and is associated with organic matter (e.g., Shen et al., 2020b;Shen et al., 2022). ...
... Volcanism can not only release Hg directly into the atmosphere, but can also lead to abnormal Hg accumulation in sediments through magma heating of organic-rich sediments (e.g., Shen et al., 2020b;Shen et al., 2022). Meanwhile, burning (caused by wildfire) of surface organic matter and soil erosion can also cause Hg enrichment anomalies (Blum et al., 2014;Thibodeau et al., 2016;Shen et al., 2020b;Shen et al., 2022), because the majority (>90%) of Hg in terrestrial systems resides in soils and is associated with organic matter (e.g., Shen et al., 2020b;Shen et al., 2022). Photochemically-induced Hg mass independent fractionation (MIF) can effectively trace the source and pathway of Hg in various environments (Blum et al., 2014;Sun et al., 2020;Shen et al., 2020b). ...
The deep-time geological record can provide insights into the processes and mechanisms of glacier retreat. Ice sheets of the Late Paleozoic Ice Age (LPIA) collapsed extensively during the early Artinskian (early Permian) approximately 290 million years ago through massive glacial melting that was associated with dramatic increases in global temperature, atmospheric pCO2, sea level, and resulted in profound changes in terrestrial plant distribution and diversity. A hypothesized mode of this extensively glacial melting is multiple large-scale volcanic events, but the causes and effects have not yet been clearly established because of the lack of detailed coeval records of volcanism and environmental changes. Here, we present a record of these events from an Artinskian terrestrial succession in the Liujiang Coalfield, North China. Our new Usingle bondPb zircon dating, high-resolution chemostratigraphy, and kerogen maceral data reveal that environmental changes (carbon cycle perturbation, wildfire, and continental weathering) in the region were intricately linked with the large-scale volcanism associated with the Tarim-II, Panjal and Choiyoi volcanic provinces. Our study shows that hypothesized volcanism and wildfire raised temperatures by releasing greenhouse gases, while the ensuing warming led to ice sheet melting, the release of terrestrial Hg and C and resulting Hg and C cycle anomalies.
... Recently, Hg anomalies have been widely used as tracers of massive volcanism in the sedimentary record (Sanei et al. 2012;Percival et al. 2017;Racki et al. 2018b;Jones et al. 2019;Rakociński et al. 2021aRakociński et al. , 2022Shen et al. 2021). This is because volcanic eruptions and submarine volcanic and hydrothermal activities are the main natural sources of mercury in recent and ancient environments, and are reflected by Hg spikes in sedimentary rocks (e.g. ...
... McKenzie et al. 2016;Lu et al. 2021) and other biotic crises, such as the Ordovician-Silurian(Yang et al. 2019), end-Frasnian(Racki, 2020), end-Devonian(Rakociński et al. 2021b) and end-Permian(Shen et al. 2021). ...
The mid-Tournaisian black radiolarian cherts of the Lydiennes Formation are exposed in deep-shelf successions of the Puech de la Suque and Col des Tribes sections of the Mont Peyroux Nappe area in the Montagne Noire, southern France. This interval represents the mid-Tournaisian anoxic event that is also termed the Lower Alum Shale Event. This event is associated with a global marine transgression that was characterized by increased productivity and drastic facies changes from pelagic carbonate sedimentation to the widespread deposition of black organic-rich siliceous shales and radiolarites in many parts of the world. In the present study, high-resolution inorganic geochemistry and framboidal pyrite analyses were employed to decipher changes in depositional conditions during the mid-Tournaisian anoxic event in the Montagne Noire. The results show that the total organic carbon contents of sediments associated with the Lower Alum Shale Event vary from 0.09 to 1.9 wt %. These low to moderate total organic carbon contents, high U/Th, low Corg/P and intermediate V/Cr ratios, enrichment in redox-sensitive trace elements, such as U, Mo and V, as well as varying sizes of pyrite framboids, indicate periodic dysoxic to anoxic bottom-water conditions during deposition of the studied sediments. Anomalous Hg spikes (>500 ppb) are also reported in the mid-Tournaisian deep-water marine succession of the Montagne Noire in the present study, which confirm a possible influence of increased regional volcanic activity during this environmental turnover.
