The Late Ordovician mass extinction (LOME, ca. 445 Ma; Hirnantian stage) is the second most severe biological crisis of the entire Phanerozoic. The LOME has been subdivided into two pulses (intervals), at the beginning and the ending of the Hirnantian glaciation, the LOMEI-1 and LOMEI-2, respectively. Although most studies suggest a rapid cooling and/or oceanic euxinia as major causes for this mass extinction, the driver of these environmental changes is still debated. As other Phanerozoic’s mass extinctions, extensive volcanism may have been the potential trigger of the Hirnantian glaciation. Indirect evidence of intense volcanism comes from Hg geochemistry: peaks of Hg concentrations have been found before and during the LOME, and have all been attributed to global volcanism in origin. Here, we present high-resolution mercury (Hg) profiles in three study sections, from a shelf to slope transect, on the Yangtze Shelf Sea (South China) to address the origin of Hg anomalies across the Ordovician–Silurian (O–S) boundary. The results show Hg anomaly enrichments in the middle Katian, late Katian, the LOMEI-1 at the beginning of the Hirnantian glaciation, the LOMEI-2 in the late Hirnantian glaciation, and late Rhuddanian. The Hg anomaly enrichments during the middle–late Katian and late Rhuddanian would probably reflect a volcanic origin. We find two different controls on the recorded Hg anomalies during the extinction time: i.e., primarily volcanism for the Hg anomaly at the LOMEI-1 and euxinia for the Hg anomaly at the LOMEI-2. Expansion of euxinia at the LOMEI-1 would have been probably enhanced by volcanic fertilization via weathering of volcanic deposits during the Middle and late Katian, and combined with euxinia at the LOMEI-2 to finally be responsible for the two pulses of the LOME.
The Late Ordovician mass extinction (LOME) is the second largest mass extinction of the Phanerozoic1,2, and has been linked to the Hirnantian glaciation2. The LOME is subdivided into two intervals (LOMEI-1 and LOMEI-2) which occurred at the onset and the end of the Hirnantian glaciation, respectively2,3,4,5. The LOME is marked by the disappearance of ~ 85% marine species2,6,7 or ~ 53% of marine genera8. Massive environmental changes were coeval with the LOME, such as rapid global cooling (Hirnantian glaciation) corresponding to expansion of ice sheets on the Gondwana supercontinent9,10,11,12, and expanded anoxia and/or euxinia in ocean4,13,14,15,16,17.
In the geologic record, mass extinction events and global climate changes are often associated to the emplacement of a large igneous province (LIP; e.g., Ref.18), but no LIP basalts have been found in the LOME interval, although a Suordakh LIP was postulated19 mainly based on the evidence of the poorly aged-constrained Suordakh dolerite eruption within the Katian20. Volcanic activity during the LOME has been indirectly inferred by coeval mercury (Hg) peaks found in sedimentary successions (e.g., middle Katian, upper Katian, LOMEI-1 at uppermost Katian and LOMEI-2 in upper Hirnantian) at Wangjiawan (in South China)21, Monitor Range (Laurentia)22, drillhole XY5 (South China) and Vinini Creek (Laurentia)23, and peri-Baltic region24.
Sedimentary Hg has been increasingly used as a tracer for volcanic activity during mass extinction events (e.g., ref.25). Volcanism is the primary sources of atmosphere Hg before the Anthropocene26 and, given its short residence time in the atmosphere, gaseous volcanic Hg is easily transported and deposited in different depositional environments globally25,27. Therefore, sedimentary Hg can be used as a proxy for volcanism25,28,29,30,31. However, increases of Hg deposition in different depositional setting can be also linked to other (local) factors, such as increase of riverine Hg transport to marine settings32, massive oxidation of terrestrial organic matter16,31, and development of euxinic conditions33. Hence, a peak of Hg concentration in the sedimentary record does not unequivocally indicate massive coeval volcanic activity.
In this study, we present new Hg concentration data across the Ordovician–Silurian boundary from three sections at Shuanghe, Qiliao and Tianba on the Yangtze Shelf Sea in South China4,14. Combined with previous data on redox conditions and climate changes from the same outcropped sections4, these Hg data are used to explore Hg deposition during the LOME in the study area, shedding new light on the origin of the Hg peaks coeval to the biological and environmental changes.
During the Ordovician–Silurian transition, the Yangtze Platform (South China Block) was located near the equator34 (Fig. 1). After the middle Katian, it gradually evolved into a siliciclastic-dominated shelf basin, called the Yangtze Shelf Sea4,35. The shale strata, which include the Late Ordovician Wufeng Formation and early Silurian Lungmachi Formation, or Wufeng-Lungmachi Shale, deposited on the shelf with deepening northwards to the Panthalassic Ocean4,36,37. The bottom black shale interval of Wufeng-Lungmachi Shale in South China corresponds to typical, organic-rich shales (hot shale, i.e., more radioactive shale)7,38. Owing to the glaciation, a rapid sea level drop occurred during the Hirnantian. Paleo-water-depth in the Yangtze Shelf Sea during this glaciation was likely about 40–100 meters37. The Kuanyinchiao Bed at the top of the Wufeng Formation was formed during this glaciation time (Fig. 2), and contains characteristic cold water Hirnantian fauna. The marine carbonate Kuanyinchiao Bed is widely distributed, and has a conformity contact with the underlying Wufeng Formation in the study area. High-resolution graptolite zones have been previously identified in South China39, providing a solid biostratigraphic framework and allowing correlation with other Ordovician–Silurian boundary sections around the world7.
From the Late Ordovician to early Silurian, volcanic ash layers deposited are extensively reported, especially in North America40 and South China41,42,43. In North America, over 100 volcanic ash layers dominantly occurred in pre-late Katian stage40. There were two pulses of volcanic ash layers deposited in South China in the Late Ordovician and early Silurian42. The first pulse occurred in late Katian stage41,42,44 and the second pulse erupted around the boundary between the Rhuddanian stage and the Aeronian stage (ca. 440.8 Ma)42,45.
Materials and methods
Fresh rock samples were collected from three sections (Shuanghe, Qiliao and Tianba sections) that were deposited from proximal to distal areas on the Yangtze Shelf Sea, South China (Fig. 1). For each section, high-resolution graptolite zones have been previously defined4. Previous studies have reported, from the same rock samples, TOC contents, C-isotopes, Fe-speciation, major elements and trace elements concentrations4,12,46. In this study, we measured Hg concentration and TS content of all samples, and the TOC content of 6 new samples.
Hg concentration was measured using a Lumex RA-915 M mercury analyzer with pyrolyzer PYRO-915 + at State Key Laboratory of Biogeology and Envionmental Geology, China University of Geosciences. An aliquot of ~ 50 mg of powdered sample was weighed in a glass boat and was heated in the pyrolyzer at 700 °C. Volatilized Hg concentration was quantified via atomic absorption spectrometry. A soil standard (GSD-17a; Hg = 120 ± 10) was used to calibrate the instrument. Repeated measurements of the standard at the start of each run and throughout the analysis sequence indicate reproducibility was generally better than 10% for Hg concentrations.
For the measurement of TOC content, sample powders (2 g) were decarbonated with HCl (10% vol/vol) prior to TOC analyses on a LECO CS-230 analyzer. TS was measured directly by bulk sample. Analytical precision was generally better than 5% and 8% for TOC, and TS contents, respectively. Hg concentrations have been normalized for TOC and TS contents25,33.
At Shuanghe section, Hg concentrations range from 5 to 161 ppb (average is 61 ppb) (Table 1). Background Hg concentration is ~ 50 ppb. Higher Hg concentrations are found at the base of the lower Katian Wufeng Formation, in the upper Katian, LOMEI-1 (end-Katian), LOMEI-2 (Hirnantian), and in the upper Rhuddanian (Fig. 2). At Qiliao section, Hg concentrations range from 27 to 600 ppb (average is 245 ppb) (Table 1). Background Hg concentration is ~ 80 ppb. Higher Hg concentrations occur at LOMEI-1, LOMEI-2, and in the upper Rhuddanian (Fig. 2). At Tianba section, Hg concentrations range from 8 to 498 ppb (average is 130 ppb) (Table 1). Background Hg concentration is ~ 45 ppb. Hg spikes occur in the upper Katian, LOMEI-1, LOMEI-2, and upper Rhuddanian (Fig. 2).
At Shuanghe, TOC contents range from 0.1 to 8.8% (average is 3.8%)4,14 (Table 1). Higher TOC values occur at base of the early Katian Wufeng Formation, LOMEI-1, and LOMEI-2 (Fig. 2). At Qiliao, TOC contents range from 2.6 to 14% (average is 6.0%)4 (Table 1). Higher TOC values occur at LOMEI-1 and LOMEI-2 (Fig. 2). At Tianba, TOC contents range from 0.1 to 16% (average is 3.8%) (Table 1). TOC increases at base of the lower Katian Wufeng Formation, LOMEI-1, and LOMEI-2, respectively (Fig. 2).
At Shuanghe, TS contents range from 0.1 to 4.0% (average is 1.3%) (Table 1). TS increases at base of the low-Katian Wufeng Formation, in the upper Katian, and at LOMEI-1 and LOMEI-2 (Fig. 2). At Qiliao, TS contents range from 0.1 to 5.6% (average is 1.3%) (Table 1). Higher TS occurs at LOME-1 and LOME-2 (Fig. 2). At Tianba, TS contents range from 0.1 to 0.5% (average is 0.16%) (Table 1). TS is higher in lower Katian Linxiang Formation, and at LOMEI-1 and LOMEI-2 (Fig. 2).
At Shuanghe, peaks of Hg/TOC occur in the middle Katian at the base of the Wufeng Formation (from ~ 20 to ~ 80 ppb/wt.%), end-Katian LOMEI-1 (from ~ 10 to 30 ppb/wt.%) and late-Hirnantian LOMEI-2 horizons (from ~ 18 to ~ 60 ppb/wt.%) (Fig. 2). At Qiliao, peaks of Hg/TOC occur at LOMEI-1 (~ 20 to ~ 50 ppb/wt.%), LOMEI-2 (from ~ 40 to ~ 65 ppb/wt.%), and in the upper Rhuddanian (from ~ 50 to ~ 100 ppb/wt.%) (Fig. 2). At Tianba, peaks of Hg/TOC occur in the middle-Katian Linxiang Formation (from ~ 30 to ~ 280 ppb/wt.%), in the upper Katian (from ~ 30 to ~ 140 ppb/wt.%), and at LOMEI-1 (from ~ 40 to ~ 220 ppb/wt.%) (Fig. 2).
At Shuanghe, peaks of Hg/TS occur at the middle-Katian Linxiang Formation (from ~ 40 to ~ 150 ppb/wt.%), upper Katian, LOMEI-1 (from ~ 40 to ~ 120 ppb/wt.%) and LOMEI-2 horizons (from ~ 40 to ~ 150 ppb/wt.%) (Fig. 2). At Qiliao, peaks of Hg/TS occur in upper Katian (from ~ 1000 to ~ 3000 ppb/wt.%), at the LOMEI-1 (from ~ 250 to ~ 1200 ppb/wt.%), and in the upper Rhuddanian (from ~ 200 to ~ 3200 ppb/wt.%). At Tianba, peaks of Hg/TS occur in the upper Katian (from ~ 70 to ~ 2400 ppb/wt.%), LOMEI-1 horizon (from ~ 700 to ~ 5200 ppb/wt.%), LOMEI-2 horizon (from ~ 1700 to ~ 3500 ppb/wt.%), and in the upper Rhuddanian (from ~ 1800 to ~ 7000 ppb/wt.%) (Fig. 2).
Hg host and digenesis
Hg concentrations in sediments are controlled mainly by local depositional environment, primary volcanic loading, and post depositional diagenesis47. In general, Hg is mainly associated with organic matter under “normal” conditions and with sulfide only under strong euxinic conditions28,47,48. Hg/TOC or Hg/TS ratios are then used to assess the excess input of Hg besides of the sources from Hg-TOC complexes or HgS33,48,49.
Cross-plots between TOC and Hg (Fig. 3) show that Hg concentrations have no correlation with TOC contents under euxinic environments but have positive correlation (R2 is 0.5 to 0.73, Qiaoliao and Tianba sections) or weak correlation (R2 = 0.18, Shuanghe section) with TOC contents under non-euxinic environments. It suggests that organic matter is an important host of Hg in these marine sedimentary rocks owing to the association between Hg and organic matter and the reactive Hg organic complexes50. Cross-plots between TS and Hg (Fig. 3) show strong correlation (R2 = 0.81, Qiaoliao section) to no correlation (R2 is less than 0.31, Shuanghe and Tianba sections) under euxinic environments, but show no correlation under non-euxinic environments. This suggests that sulfide is not a host of Hg under non-euxinic conditions but may be a host of Hg during euxinic intervals48.
Normalization of Hg concentrations to TOC and TS can reflect Hg anomalies. Hg/TOC ratios could be inflated because of diagenetic degradation of organic matter, which lowers TOC content22, or due to analytical uncertainty for TOC < 0.2%51. Therefore, high Hg/TOC ratios in the upper Linxiang Formation of the middle Katian at Shuanghe and Tianba (Table 1) do not indicate true positive Hg anomalies, but are linked to very low TOC values (< 0.1%), and are not plotted in Fig. 2. However, the high Hg/TOC ratios in the lowermost Wufeng Formation are associated with TOC contents higher than 0.2%, suggesting true Hg positive anomalies in the middle Katian at Shaunghe and Tianba. In addition, all other recorded high Hg/TOC ratios are associated with TOC > 2.0%22.
A diagenetic effect is excluded because of the well-preserved conditions of primary laminated shale4,14. In addition, organic-carbon isotope data record the global positive excursion of the glacial interval in the Hirnantian stage, also suggesting a primary chemostratigraphic signal preserved in the sample containing matured organic matter52. These analyses point to no or weak diagenetic effect on our geochemical data across the O–S boundary.
Hg enrichment pattern across the Ordovician–Silurian transition
We correlate the Hg/TOC and Hg/TS curves across the Ordovician–Silurian boundary in the three study sections, with the published Hg curves elsewhere (Fig. 4). These Hg anomalies all correspond to Hg concentration peak and peaks of Hg/TOC and/or Hg/TS ratios, indicating increase of Hg input. Two Hg positive anomalies occur in the middle and late Katian, three anomalies occur at LOMEI-1, LOMEI-2 and Late Rhuddanian, respectively (Fig. 4). Elsewhere, one Hg positive anomaly had also been found in late Katian from a drill hole XY5 in South China23,52 and Monitor Range in North America22. Two Hg positive anomalies at LOMEI-1 and LOMEI-2 had also been found in many locations such as Wangjiawan, Dingjiapo21, XY5 drill hole52 in South China and Monitor Range section in North America22. In other locations in South China, Hg positive anomalies were found in the early Rhuddanian48. Hg positive anomalies in Poland in the middle Katian, LOMEI-1, and LOMEI-2 were reported, respectively24. Besides, Hg positive anomalies at LOMEI-2 and in the Rhuddanian were reported in Scotland53. Overall, the Hg anomaly in the middle Katian in our study sections can be correlated with those in other location in South China52, Monitor Range in U.S.22, and in Poland24. The Hg anomalies in the upper Katian and at LOMEI-1 in our study section can be correlated with those in other locations in South China21,52, Monitor Range in U.S.22, and Poland24. The Hg positive anomaly at LOMEI-2 in our study sections can be correlated with those in other locations in South China21,52, Monitor Range in U.S.22, Poland24, and Scotland53. The Hg positive anomaly in the upper Rhuddanian in our study sections can be correlated with those in Scotland53 and other location in South China48.
Origin of the Hg anomalies in the study sections
The positive Hg anomalies (i.e., peaks of Hg/TOC and/or Hg/TS) in the middle and late Katian are associated with relative high TOC and TS contents at Shuanghe and Qiliao sections, indicating that this upper Katian Hg enrichment was not related to higher TOC or sulfide fluxes and reflect an enhanced Hg loading into the basins, supporting their interpretation as genuine Hg positive anomalies21,22,24,52. Abundant ash beds in the middle and upper Katian in South China42,43,44,54 (Fig. 2) and several ash beds in middle Katian in Poland24 have been found. Considering the regional/global signal of Hg anomaly in the middle and late Katian mentioned above, the inferred volcanism in South China or a ‘LIP’ in the middle-late Katian20,40,55 may contribute to the two positive Hg anomalies in the middle and late Katian in this study sections and other locations21,22,23, and large mass-independent sulfur isotope anomalies52. In other words, the Hg positive anomalies in the middle and late Katian suggest a volcanic increasing Hg loading during this time.
High Hg/TOC or Hg/TS ratios at the LOMEI-1 at the end-Katian in the three study sections are associated with relatively high TOC or TS contents, and high Hg concentrations, also suggesting higher Hg loading into the basins. The Hg spike at the LOMEI-2 at Shuanghe was associated with high TOC contents, invariable Hg/TOC ratios & TS contents, and high Hg/TS ratios, indicating that this Hg enrichment at Shuanghe was linked to higher TOC fluxes. Meanwhile, the Hg spike at the LOMEI-2 at Qiliao was associated with high TS contents, invariable Hg/TS ratios, relatively high TOC contents and Hg/TOC ratios (Fig. 2), suggesting that Hg enrichment at Qiliao might be related to local sulfide deposition. Sulfide-carrier Hg anomaly was also reported by previous study with coarse resolution across the LOME interval48. Hg profile at Tianba does not show any positive anomaly at the LOMEI-2, but the good covariation of Hg-TOC (Fig. 3e) suggests organic matter carrier of Hg during this time.
Overall, Hg positive anomaly at LOMEI-1 record higher loading of Hg into the basin, while an increase of Hg drawdown at LOMEI-2 due to more reducing conditions4 or increase of organic matter deposition in the late Hirnantian (Fig. 2). Higher Hg fluxes in the basins at LOMEI-1 could be related to different factors, as an increase of volcanic activity or enhanced continental weathering56,57. Considering the relatively low continental weathering indicated by chemical index alteration (CIA) values4 and the sporadical occurrence of ash beds in South China42,46 (Fig. 2), the abrupt Hg (and Hg/TOC) anomalies at LOMEI-1 would be of volcanic origin as suggested by previous published works in South China and U.S.21,22,23,24. However, intermittent or weak euxinia also developed during the LOMEI-14 with high Hg/TOC or Hg/TS ratios, relatively high TOC or TS contents in the three study sections, suggesting Hg enrichment during this time would be partially related to euxinic condition in water column.
The relatively high Hg concentration in the upper Rhuddanian is associated with non-euxinic conditions, relatively low TOC or TS contents, but relatively high Hg/TOC and Hg/TS ratios in this study. The abrupt increasing of Hg/TOC, or Hg/TS ratios coincides with invariable or small decreasing TOC or TS, excluding an inflation of too low TS and TOC contents. These probably suggest a genuine Hg positive anomaly and extra environmental loading related to volcanism or weathering56,57. This anomaly is associated with abrupt occurrence of frequent ash beds42 in Fig. 2 and relatively low weathering of CIA evidence10, pointing to a volcanic origin of increasing Hg loading. Previous study53 has also suggested that this anomaly in the Scotland derived from increased Hg flux rather than sequestration by anoxia/euxinia. These may indicate global Hg loading by volcanism during the late Rhuddanian.
Implications for the mass extinction
The interpretation of two different controls on the recorded Hg anomalies, i.e., a mixed origin of volcanism and euxinia for the Hg anomaly at the LOMEI-1 and a redox control on the Hg anomaly at the LOMEI-2, shed new lights on the Late Ordovician extinction mechanism. The middle-Katian Hg positive anomaly was temporally coincided with the middle-Katian genus richness drop58. The inferred volcanic-origin (although lack of solid volcanic lithology evidences) of Hg positive anomaly in the middle Katian in this study may suggest significant climatic effect triggered by volcanism on the initial of long-term mass extinction from middle Katian to late Hirnantian58,59.
The most distinct Hg anomaly and volcanism reported by previous studies are in the Late Katian and at LOMEI-1 (at end-Katian) (Fig. 4). As shown in Fig. 2, intensity of volcanic activity estimated by distribution and thickness of volcanic ash layers gradually decreased from the middle Katian to end-Katian. However, long-term weathering of volcanic deposits would enhance the nutrient input to ocean and thus result in large amount of organic matter burial and the consumption of CO2 in the atmosphere via biological pump59,60,61. Increasing burial rates of organic matter would gradually contribute to expansion of euxinia in bottom water4, finally driving the LOMEI-1. Additionally, Hg toxic effect could also have contributed to this extinction process57.
As shown by our data, the development of euxinic conditions at the LOMEI-2 was not related to volcanism (Fig. 2), but to the large amount of organic matter burial resulted from increased availability of nutrients either input from exposed continental shelves or recycled from organic matter degradation4. However, at the LOMEI-2, high organic carbon burial mentioned above created euxinic conditions in bottom water, accumulating Hg and killing the survivors such as conodonts, Hirnantia fauna (cool water brachiopod fauna)5 after LOMEI-1.
We present herein five Hg anomaly enrichments across the Ordovician–Silurian boundary, i.e., two anomalies in the middle and late Katian, three anomalies at LOMEI-1 (end-Katian), LOMEI-2 (late Hirnantian), and one spike in the late Rhuddanian of South China, respectively. All these Hg anomalies in the Late Ordovician and early Silurian were global or at least regional based on the global Hg chemostratigraphy correlation. The Hg positive anomalies in the middle–late Katian and in the late Rhuddanian were probably caused by primary volcanic loading. Our data suggest that during the mass extinction interval, the Hg positive anomalies at LOMEI-1 and LOMEI-2 have been controlled by different factors: i.e., volcanism probably caused the Hg anomaly at the LOMEI-1, and the development of strong euxinic conditions increased Hg drawdown at the LOMEI-2. Volcanism during the Middle and late Katian would probably enhance the expansion of euxinia at the end of Katian by long-term weathering of volcanic deposits, and was finally responsible for the LOMEI-1. Furthermore, there was no or weak volcanic loading of Hg during the LOMEI-2. Hg enrichment during this time was related to euxinic condition in water column, suggesting that the LOMEI-2 was linked to euxinia.
Sepkoski, J. J. J. Patterns of Phanerozoic extinction: a perspective from global data bases. In Global Events and Event Stratigraphy in the Phanerozoic (ed. Walliser, O. H.) 35–51 (Springer, 1996).
Sheehan, P. M. The Late Ordovician mass extinction. Ann. Rev. Earth Planet. Sci. 29, 331–364 (2001).
Harper, D. A. T., Hammarlund, E. U. & Rasmussen, C. M. Ø. End Ordovician extinctions: A coincidence of causes. Gondwana Res. 25, 1294–1307 (2014).
Zou, C. et al. Ocean euxinia and climate change ‘double whammy’ drove the Late Ordovician mass extinction. Geology 46, 535–538 (2018).
Rong, J. Y. et al. The latest Ordovician Hirnantian brachiopod faunas: New global insights. Earth-Sci. Rev. 208, 103280 (2020).
Jablonski, D. Extinctions: A paleontological perspective. Science 253, 754–757 (1991).
Melchin, M. J., Mitchelll, C. E., Holmden, C. & Štorch, P. Environmental changes in the Late Ordovician–early Silurian: Review and new insights from black shales and nitrogen isotopes. Geol. Soc. Am. Bull. 125, 1635–1670 (2013).
Fan, J. et al. A high-resolution summary of Cambrian to Early Triassic marine invertebrate biodiversity. Science 367(6475), 272–277 (2020).
Vandenbroucke, T. R. A. et al. Polar front shift and atmospheric CO2 during the glacial maximum of the Early Paleozoic Icehouse. Proc. Natl. Acad. Sci. USA 107, 14983–14986 (2010).
Yan, D., Chen, D., Wang, Q. & Wang, J. Large-scale climatic fluctuations in the latest Ordovician on the Yangtze block, south China. Geology 38, 599–602 (2010).
Finnegan, S. et al. The magnitude and duration of Late Ordovician-Early Silurian glaciation. Science 331, 903–906 (2011).
Saupe, E. E. et al. Extinction intensity during Ordovician and Cenozoic glaciations explained by cooling and palaeogeography. Nat. Geosci. 13, 65–70 (2020).
Hammarlund, E. U. et al. A sulfidic driver for the end-Ordovician mass extinction. Earth Planet. Sci. Lett. 331–332, 128–139 (2012).
Zou, C. N., Qiu, Z., Wei, H. Y., Dong, D. Z. & Lu, B. Euxinia caused the Late Ordovician extinction: Evidence from pyrite morphology and pyritic sulfur isotopic composition in the Yangtze area, South China. Palaeogeogr. Palaeoclim. Palaeoecol. 511, 1–11 (2018).
Bartlett, R. et al. Abrupt global-ocean anoxia during the Late Ordovician-Early Silurian detected using uranium isotopes of marine carbonates. Proc. Natl Acad. Sci. USA 115, 5896–5901 (2018).
Corso, D. et al. Permo-Triassic boundary carbon and mercury cycling linked to terrestrial ecosystem collapse. Nat. Commun. 11, 2962 (2020).
Phol, A. et al. Vertical decoupling in Late Ordovician anoxia due to reorganization of ocean circulation. Nat. Geosci 14, 868–873 (2021).
Bond, D. P. G. & Grasby, S. E. On the causes of mass extinctions. Palaeogeogr. Palaeoclimatol. Palaeoecol. 478, 3–29 (2017).
Ernst, E. R. & Youbi, N. How Large Igneous Provinces affect global climate, sometimes cause mass extinctions, and represent natural markers in the geological record. Palaeogeogr. Palaeoclimatol. Palaeoecol 478, 30–52 (2017).
Khudoley, K. A. et al. Early Paleozoic mafic magmatic events on the eastern margin of the Siberian Craton. Lithos 174, 44–56 (2013).
Gong, Q. et al. Mercury spikes suggest volcanic driver of the Ordovician-Silurian mass extinction. Sci. Rep. 7, 5304 (2017).
Jones, D. S., Martini, A. M., Fike, D. A. & Kaiho, K. A volcanic trigger for the Late Ordovician mass extinction? Mercury data from south China and Laurentia. Geology 45, 631–634 (2017).
Hu, D. et al. Major volcanic eruptions linked to the Late Ordovician mass extinction: Evidence from mercury enrichment and Hg isotopes. Glob. Planet. Chang. 196, 103374 (2021).
Smolarek-Lach, J., Marynowski, L., Trela, W. & Wignall, P. B. Mercury spikes indicate a volcanic trigger for the Late Ordovician mass extinction event: An example from a deep shelf of the peri-Baltic region. Sci. Rep. 9, 3139 (2019).
Grasby, S. E. et al. Mercury as a proxy for volcanic emissions in the geologic record. Earth-Sci. Rev. 196, 102880 (2019).
Selin, N. E. Global biogeochemical cycling of mercury: A review. Annu. Rev. Environ. Res. 34, 43–63 (2009).
Percival, L. M. E. et al. Globally enhanced mercury deposition during the end-Pliensbachian extinction and Toarcian OAE: A link to the Karoo-Ferrar Large Igneous Province. Earth Planet. Sci. Lett. 428, 267–280 (2015).
Sanei, H., Grasby, S. E. & Beauchamp, B. Latest Permian mercury anomalies. Geology 40, 63–66 (2012).
Sial, A. N. et al. Mercury as a proxy for volcanic activity during extreme environmental turnover: The Cretaceous-Paleogene transition. Palaeogeogr. Palaeoclimatol. Palaeoecol. 387, 153–164 (2013).
Font, E. et al. Mercury anomaly, Deccan volcanism, and the end-Cretaceous mass extinction. Geology 44, 171–174 (2016).
Grasby, S. E. et al. Isotopic signatures of mercury contamination in latest Permian oceans. Geology 45, 55–58 (2017).
Them, T. R. II. et al. Terrestrial sources as the primary delivery mechanism of mercury to the oceans across the Toarcian Oceanic Anoxic Event (Early Jurassic). Earth Planet. Sci. Lett. 507, 62–72 (2019).
Shen, J. et al. Sedimentary host phases of mercury (Hg) and implications for use of Hg as a volcanic proxy. Earth Planet. Sci. Lett. 543, 116333 (2020).
Torsvik, T. H. & Cocks, L. R. Gondwana from top to base in space and time. Gondwana Res. 24, 999–1030 (2013).
Wang, X. Ordovician tectonic-paleogeography in South China and chrono- and bio-stratigraphic division and correlation. Earth Sci. Front. 23, 253–267 (2016).
Chen, X., Rong, J. Y., Li, Y. & Boucot, A. J. Facies patterns and geography of the Yangtze region, South China, through the Ordovician and Silurian transition. Palaeogeogr, Palaeoclimatol, Palaeoecol. 204, 353–372 (2004).
Rong, J. Y. & Huang, B. An indicator of the onset of the End Ordovician mass extinction in South China: The Manosia brachiopod assemblage and its diachronous distribution. Acta Geol. Sin. 93(3), 509–527 (2019).
Lüning, S. et al. Lower Silurian ‘hot shales’ in North Africa and Arabia: Regional distribution and depositional model. Earth-Sci. Rev. 49, 121–200 (2000).
Chen, X. et al. The global boundary stratotype section and point (GSSP) for the base of the Hirnantian Stage (the uppermost of the Ordovician System). Episodes 29, 183–196 (2006).
Huff, W. D. Ordovician K-bentonites: Issues in interpreting and correlating ancient tephras. Quat. Int. 178, 276–287 (2008).
Su, W. et al. K-bentonite, black-shale and flysch successions at the Ordovician-Silurian transition, South China: Possible sedimentary responses to the accretion of Cathaysia to the Yangtze Block and its implications for the evolution of Gondwana. Gondwana Res. 15, 111–130 (2009).
Qiu, Z. & Zou, C. Unconventional petroleum sedimentology: Connotation and prospect. Acta Sediment. Sin. 38, 1–29 (2020).
Qiu, Z. & Zou, C. Controlling factors on the formation and distribution of “sweet-spot areas” of marine gas shales in South China and a preliminary discussion on unconventional petroleum sedimentology. J. Asian Earth Sci. 194, 103989 (2020).
Du, X. et al. Was the volcanism during the Ordovician-Silurian transition in South China actually global in extent?: Evidence from the distribution of volcanic ash beds in black shales. Mar. Petrol. Geol. 123, 104721 (2021).
Wang, Y. et al. Developmental characteristics and geological significance of the bentonite in the Upper Ordovician Wufeng-Lower Silurian Longmaxi Formation in eastern Sichuan Basin, SW China. Petrol. Explor. Dev. 46, 653–665 (2019).
Qiu, Z. et al. Controlling factors on organic matter accumulation of marine gas shale across the Ordovician-Silurian transition in South China: Constraints from trace-element geochemistry. J. Earth. Sci. 32, 887–900 (2021).
Bergquist, B. A. Mercury, volcanism, and mass extinctions. Proc. Natl. Acad. Sci. USA 114, 8675–8677 (2017).
Shen, J. et al. Mercury in marine Ordovician/Silurian boundary sections of South China is sulfide-hosted and non-volcanic in origin. Earth Planet. Sci. Lett. 511, 130–140 (2019).
Fitzgerald, W. F., Lamborg, C. H. & Hammerschmidt, C. R. Marine biogeochemical cycling of mercury. Chem. Rev. 107, 641–662 (2017).
Fitzgerald, W. F. & Lamborg, C. H. In Treatise on Geochemistry 2nd edn (eds Holland, H. & Turekian, K.) 91–129 (Elsevier, 2014).
Grasby, S. E. et al. Mercury deposition through the Permo-triassic biotic crisis. Chem. Geol. 351, 209–216 (2013).
Hu, D. et al. Large mass independent sulphur isotope anomalies link stratospheric volcanism to the Late Ordovician mass extinction. Nat. Commun. 11, 2297 (2020).
Bond, D. P. G. & Grasby, S. E. Late Ordovician mass extinction caused by volcanism, warming, and anoxia, not cooling and glaciation. Geology 48, 777–781 (2020).
Qiu, Z. et al. Discussion of the relationship between volcanic ash layers and organic enrichment of black shale: A case study of the Wufeng-Longmaxi gas shales in the Sichuan Basin. Acta Sediment. Sin. 37, 1296–1308 (2019).
Lefebvre, V., Servais, T., François, L. & Averbuch, O. Did a Katian large igneous province trigger the Late Ordovician glaciation? A hypothesis tested with a car-bon cycle model. Palaeogeogr, Palaeoclimatol. Palaeoecol. 296, 310–319 (2010).
Richardson, J. B. et al. Mercury sourcing and sequestration in weathering profiles at six Critical Zone Observatories. Glob. Biogeo. Cycl. 32, 1542–1555 (2018).
Grasby, S. E. et al. Toxic mercury pulses into late Permian terrestrial and marine environments. Geology 48, 830–833 (2020).
Rasmussen, C. M. Ø., Kröger, B., Nielsen, M. L. & Colmenar, J. Cascading trend of early Paleozoic marine radiations paused by Late Ordovician extinctions. Proc. Natl. Acad. Sci. U.S.A. 116, 7207–7213 (2019).
Tao, H., Qiu, Z., Lu, B., Liu, Y. & Qiu, J. Volcanic activities triggered the first global cooling event in the Phanerozoic. J. Asian Earth Sci. 194, 104074 (2020).
Shen, J. et al. Improved efficiency of the biological pump as a trigger for the Late Ordovician glaciation. Nat. Geosci. 11, 510–514 (2018).
Longman, J. et al. Volcanic nutrient supply initiated Late Ordovician climate change and extinctions. Nat. Geosci 14, 924–929 (2021).
This work was financially supported by the National Natural Science Foundation of China (Grants 41888101 and 41602119) and Science and Technology Major Projects of PetroChina (2021yjcq02 and 2021DJ2001).
The authors declare no competing interests.
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Qiu, Z., Wei, H., Tian, L. et al. Different controls on the Hg spikes linked the two pulses of the Late Ordovician mass extinction in South China. Sci Rep 12, 5195 (2022). https://doi.org/10.1038/s41598-022-08941-3