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Mercury evidence for pulsed volcanism during the end- mass extinction

Lawrence M. E. Percivala,1,2, Micha Ruhla, Stephen P. Hesselbob, Hugh C. Jenkynsa, Tamsin A. Mathera, and Jessica H. Whitesidec

aDepartment of Earth Sciences, University of Oxford, Oxford OX1 3AN, United Kingdom; bCamborne School of Mines and Environment and Sustainability Institute, University of Exeter, Penryn TR10 9FE, United Kingdom; and cOcean and Earth Science, National Oceanography Centre Southampton, University of Southampton, Southampton SO14 3ZH, United Kingdom

Edited by Edward A. Boyle, Massachusetts Institute of Technology, Cambridge, MA, and approved May 19, 2017 (received for review April 3, 2017) The Central Atlantic Magmatic Province (CAMP) has long been records (Fig. 1A and refs. 12 and 14). The apparent episodic em- proposed as having a causal relationship with the end-Triassic placement of CAMP basalts over several hundred kiloyears, at least extinction event (∼201.5 Ma). In North America and northern in and North America, is a key feature of this LIP. Africa, CAMP is preserved as multiple basaltic units interbedded The oldest known CAMP basalts are the lower Moroccan unit with uppermost Triassic to lowermost sediments. How- [termed the Lower Formation in the High Atlas and the Tasguint ever, it has been unclear whether this apparent pulsing was a local Formation in the Argana basin (17, 18)]. This unit is overlain by feature, or if pulses in the intensity of CAMP volcanism charac- two further Moroccan basalt units: the Middle and Upper for- terized the emplacement of the province as a whole. Here, six mations in the High Atlas [the former named the Alemzi For- geographically widespread Triassic–Jurassic records, representing mation in Argana (17, 18)]. For clarity, the High Atlas names are varied paleoenvironments, are analyzed for mercury (Hg) concen- used henceforth in this study. These three basalt groups are trations and Hg/total organic carbon (Hg/TOC) ratios. Volcanism is interbedded with sedimentary deposits. A fourth extrusive unit, a major source of mercury to the modern environment. Clear in- the Recurrent Formation, is locally preserved higher in the creases in Hg and Hg/TOC are observed at the end-Triassic extinc- Moroccan sequence, with much thicker sediments between it and tion horizon, confirming that a volcanically induced global Hg the Upper Formation (Fig. 2B and refs. 14, 17, and 19). These cycle perturbation occurred at that time. The established correla- four basalt units are defined and correlated on the basis of distinct tion between the extinction horizon and lowest CAMP basalts igneous geochemistry. Based on geochemical correlation with allows this sedimentary Hg excursion to be stratigraphically tied to a specific flood basalt unit, strengthening the case for volcanic North American CAMP units, which are temporally constrained by astrochronological and radioisotopic geochronology, the Hg as the driver of sedimentary Hg/TOC spikes. Additional Hg/TOC – peaks are also documented between the extinction horizon and Moroccan Lower Upper formations are thought to have erupted the Triassic–Jurassic boundary (separated by ∼200 ky), supporting in quick succession, with several hundred kiloyears then passing pulsatory intensity of CAMP volcanism across the entire province before the eruption of the Recurrent Formation (2, 14). At least three major CAMP units are documented in North

and providing direct evidence for episodic volatile release during EARTH, ATMOSPHERIC,

the initial stages of CAMP emplacement. Pulsatory volcanism, and America: the Orange Mountain, Preakness, and Hook Mountain AND PLANETARY SCIENCES associated perturbations in the ocean–atmosphere system, likely basalts in the Newark Basin (20), with time-equivalent basalts had profound implications for the rate and magnitude of the end- known from other North American basins. The Orange Moun- Triassic mass extinction and subsequent biotic recovery. tain Basalt overlies thin, usually lacustrine, sediments deposited above the extinction horizon, and is thought to have been mercury | end-Triassic extinction | Central Atlantic Magmatic Province Significance he end of the Triassic Period was marked by a major mass Textinction event (∼201.5 Ma; e.g., refs. 1 and 2), one of the The end of the Triassic Period (∼201.5 million years ago) wit- five largest environmental perturbations of the Phanerozoic Eon. nessed one of the largest mass extinctions of animal life known Significantly increased extinction rates of marine fauna, and major from Earth history. This extinction is suggested to have coin- turnovers in terrestrial vegetation and vertebrate groups, have been cided with and been caused by one of the largest known epi- well documented (e.g., refs. 3–8). The end-Triassic mass extinction sodes of volcanic activity in Earth’s history. This study examines predated the onset of the Jurassic by ∼100 ky to 200 ky, as defined mercury concentrations of sediments from around the world by the first occurrence of the Jurassic ammonite species Psiloceras that record this extinction. Mercury is emitted in gaseous form spelae (9). The sedimentary record of the extinction correlates with during volcanism, and subsequently deposited in sediments. alarge(upto6‰) negative excursion in organic carbon isotopes We find numerous pulsed elevations of mercury concentrations 13 in end-Triassic sediments. These peaks show that the mass ex- (δ Corg:Fig.1A), indicative of a severe carbon cycle perturbation coincident with the biotic crisis (e.g., refs. 10–13). Moroccan strata tinction coincided with large-scale, episodic, volcanism. Such that record this global carbon cycle perturbation are transected by episodic volcanism likely perturbed the global environment over the lowest documented flows of the Central Atlantic Magmatic a long period of time and strongly delayed ecological recovery. Province (CAMP). Consequently, the end-Triassic extinction has Author contributions: L.M.E.P. performed research; L.M.E.P., M.R., and J.H.W. analyzed been postulated as precisely coincident with the onset of known data; L.M.E.P., M.R., S.P.H., H.C.J., T.A.M., and J.H.W. wrote the paper; and M.R., S.P.H., CAMP volcanism (e.g., refs. 2, 12, 14, and 15). and J.H.W. provided rock samples. CAMP represents the most aerially expansive continental Large The authors declare no conflict of interest. Igneous Province (LIP) known on Earth, consisting of volumetri- This article is a PNAS Direct Submission. × 6 2 cally large-scale flood basalt sequences covering at least 7 10 km 1To whom correspondence should be addressed. Email: [email protected]. across four continents and both hemispheres (Fig. 2A and ref. 16). 2 Present address: Institute of Earth Sciences, Géopolis, University of Lausanne, CH-1015 In North America and Morocco, CAMP basalts are interbedded Lausanne, Switzerland. with continental sediments, which have precise temporal constraints This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10. and are stratigraphically well correlated with marine sedimentary 1073/pnas.1705378114/-/DCSupplemental.

www.pnas.org/cgi/doi/10.1073/pnas.1705378114 PNAS | July 25, 2017 | vol. 114 | no. 30 | 7929–7934 Downloaded by guest on September 26, 2021 AB

Fig. 1. (A) Stratigraphic correlation of the end-Triassic extinction with the Moroccan Lower Formation CAMP basalt. Argana lithology, carbon isotope, and

paleomagnetic data are from ref. 14. Newark lithology and pCO2 data are from ref. 22; paleomagnetic and astrochronological data are from ref. 48; carbon isotope data are from ref. 12; and trilete spore data are from ref. 49. St Audries Bay lithology and astrochronology are from refs. 42 and 50; biostratigraphy and carbon isotope data are from refs. 10 and 50; trilete spore data are from ref. 51; and paleomagnetic data are from refs. 52 and 53. Stratigraphic cor- relation of CAMP units between Argana, Newark, and St Audries Bay is based on refs. 12 and 42. Kuhjoch biostratigraphy, lithology, and carbon isotope data are from ref. 11. The end-Triassic extinction horizon (marked as ETE) and Triassic–Jurassic boundary (marked as TJB) are also shown. (B) Example of Hg/TOC dataset from this study (Kuhjoch, Fig. 3) is shown to stratigraphically correlate with the lowest CAMP basalt unit that intersects the end-Triassic extinction horizon at Argana. See SI Appendix, Fig. S2 for a full stratigraphic correlation of end-Triassic records.

extruded 14 ky to 20 ky after that event (2, 14, 21). Radioisotopic emplacement (22). However, the effect of local processes, such as dating has demonstrated that the Preakness Basalt and Hook diagenesis, on this record cannot be ruled out. Reconstructions of Mountain Basalt were emplaced 270 ky and 620 ky later, re- pCO2 based on stomatal indices (albeit at low temporal resolu- spectively (2). The Newark Basin Orange Mountain and Hook tion) show no such pulsing during the Triassic–Jurassic transition Mountain basalts have been geochemically established as equiv- (6, 23). Nor is there yet evidence of episodic CO2 increases as- alent to the Moroccan Middle and Recurrent formations, re- sociated with the early Moroccan CAMP pulses (CAMP pulses 1, spectively (14); the Preakness Basalt has no known Moroccan 3, and 4 in Fig. 2B) that were extruded coincident with, and in the counterpart (2, 14). Consequently, North American and Moroccan immediate aftermath of, the extinction event. records suggest that CAMP was emplaced in at least three major Here, the volatile emissions and ocean−atmosphere impact of pulses of basalt extrusion over ∼700 ky, with the products of the CAMP volcanism is investigated by analysis of sedimentary first major pulse further divisible into at least three or four mercury (Hg) concentrations across multiple Triassic–Jurassic geochemically and stratigraphically distinct units. Thus, a total of at sedimentary archives. Volcanism is known to be a major natural least six CAMP units are documented in Morocco/North America source of Hg, emitting it as a trace volcanic gas (24). Gaseous (Fig. 2B), which were relatively close to one another at the end of elemental Hg has a typical atmospheric residence time of 0.5 y to the Triassic Period. However, more geographically dispersed 2 y (25), allowing the element to be globally distributed before CAMP basalts are also known from southern Europe, Brazil, and being drawn down and eventually deposited in sediments. Several elsewhere in western Africa, with potentially different temporal Phanerozoic events have previously been linked to approximately relationships with the end-Triassic extinction and the dated CAMP coeval LIPs through documented increases in sedimentary Hg flows (16). Therefore, it is not clear whether the intensity of CAMP concentrations, including the end-Permian and end- volcanism was pulsatory across the entire province, or whether the extinctions and Oceanic Anoxic Event (e.g., refs. 26–29). apparent pulsing recorded in North America and Morocco was a Importantly, sedimentary drawdown of Hg is typically achieved local feature of the much larger-scale LIP. via organic matter (30, 31), although sulphides and clays may Proxy records of volcanic volatiles can aid in reconstructing the also play a role (32–34). Consequently, sedimentary Hg con- history of CAMP volcanism and its effects. Analyses of pedogenic centrations are typically normalized against total organic carbon carbonates suggest increases in atmospheric pCO2 following em- (TOC) to account for the effect on Hg drawdown by changes in placement of each of the Newark CAMP basalts (CAMP pulses 3, organic matter deposition rates when looking for evidence of an 5, and 6 in Fig. 2B), supporting a pattern of globally incremental elevated supply of Hg to the environment (26).

7930 | www.pnas.org/cgi/doi/10.1073/pnas.1705378114 Percival et al. Downloaded by guest on September 26, 2021 AB variety of marine and nonmarine paleoenvironments (Fig. 2A): St Audries Bay (United Kingdom: restricted shallow marine), END-TRIASSIC WORLD CAMP BASALT STRATIGRAPHY Kuhjoch (Austria: open shallow marine), Arroyo Malo (Argentina: (Ma) back-arc shallow marine), Astartekløft (Greenland: fluviodeltaic), 200.9 Recurrent Formation/ 6 6: Hook Mountain Basalt Partridge Island (Canada: lacustrine), and Igounane (Morocco:

201.0 evaporitic–lacustrine). See SI Appendix, Study Areas and Methodol- D ogies for details on all of the studied sections, and see SI Appendix, A B 201.1 G Fig. S2 for a full correlation among all of the above sections and F E 201.2 other end-Triassic records. N. America composite Morocco

5 5: Preakness Basalt/ 201.3 Hickory Grove Basalt (5A) Results and Discussion 5A Hg as a Recorder of CAMP Volcanism. Clear excursions in Hg/TOC 201.4 Upper Formation/ 4: York Haven Intrusive ratios and/or Hg concentrations are observed at five of the six 201.5 4 Middle Formation (Alemzi Fm.)/ C 3 3: studied locations (St Audries Bay, Kuhjoch, Arroyo Malo, Astar- 2 Orange Mountain Basalt CAMP ETE 1 2: North Mountain Basalt tekløft, and Partridge Island). The onsets of these excursions are 201.6 1: Lower Formation (Tasguint Fm.) stratigraphically coincident with the globally observed δ13C negative Sediments deposited between basalt units excursion that marks the extinction horizon (Fig. 3). Four sections also record additional peaks in Hg/TOC above that level. Crucially, Fig. 2. (A) Paleogeographic reconstruction of the end-Triassic world, with at all sites where Hg has been normalized to TOC, the Hg/TOC the modern continents overlain. The locations of the six studied sections are indicated (A, St Audries Bay, United Kingdom; B, Kuhjoch, Austria; C, Arroyo peaks result from elevated Hg concentrations rather than decreased Malo, Argentina; D, Astartekløft, Greenland; E, Partridge Island, Canada; and TOC content (see SI Appendix,Fig.S4). For Partridge Island and F, Igounane, Morocco). The New York Canyon section in Nevada (G; note Igounane sediments, Hg/TOC ratios were deemed unreliable due to different color) studied by ref. 35, and CAMP are also shown (based on the very low TOC content (typically below analytical uncertainty) in figure 1 from refs. 2 and 12). (B) Summarized composite stratigraphy of sedimentary samples. Consequently, Hg signals at these two loca- Moroccan and North American CAMP basalts, following the stratigraphic tions are presented without normalization to TOC. The Hg trends relationships and ages (in million years) from refs. 2 and 14. The Hickory generated in this study are also compared, in Fig. 3, with the existing Grove Basalt is included with the Preakness, due to their geochemical simi- New York Canyon record (35), which appears to have a subtly larity. The age of the end-Triassic extinction (ETE) is also indicated. different trend in sedimentary Hg/TOC increase, potentially resulting from atmospheric or local sedimentological processes. In addition to interrogating the pulsatory history of CAMP The observed peaks in sedimentary Hg and Hg/TOC strongly suggest that a perturbation to the global Hg cycle took place volatile emissions, Hg analysis of uppermost Triassic sediments – also provides a unique opportunity to test the assumption that during the Triassic Jurassic transition, beginning coincidentally Hg-enriched sediments were deposited precisely coincident with with the end-Triassic extinction. The absence of a recorded Hg the eruption of LIP basalts. There are excellent age constraints perturbation in sediments at Igounane is interpreted to result on numerous end-Triassic records (including those containing from their deposition being below the oldest known CAMP flows (thus at a time preceding the onset of CAMP basalt extrusion). A CAMP basalts), and the precise correlation between the end- EARTH, ATMOSPHERIC, lack of change in terrestrial spores from Argana sediments below AND PLANETARY SCIENCES Triassic extinction horizon and lowest Moroccan CAMP basalt the CAMP basalts further suggests that these sediments were (the Lower Formation) is well established. Such temporal con- deposited before the end-Triassic extinction (14), and thus be- straints may allow some Hg/TOC peaks in uppermost Triassic fore the onset of CAMP volcanism. sediments to be directly correlated with specific CAMP basalt The correlation between Hg excursions and the extinction units. This direct association between Hg/TOC excursions and horizon in the other five studied records is strongly suggestive of specific basalt flows has not been possible for other events due to a perturbation to the global Hg cycle at that time. Variations in the poor preservation, or limited stratigraphic control relative to marine redox during the extinction may have influenced the the sedimentary record, of many LIPs. – marine Hg cycle, but the records at both Kuhjoch and Arroyo A recent study on the Triassic Jurassic boundary section at Malo do not show a consistent stratigraphic correlation between New York Canyon (Nevada) showed an abrupt increase in Hg the observed Hg/TOC peaks and lithological or geochemical concentrations and Hg/TOC ratios correlated with the negative evidence for redox changes (ref. 37 and this study). Additionally, δ13 excursion in Corg that marks the end-Triassic extinction ho- the Hg excursions preserved in the terrestrial records from rizon (35). These Hg excursions were attributed to volcanic Astartekløft and Partridge Island could not have been caused by processes operating during the emplacement of CAMP. Here, changes in the oceanic Hg inventory. Consequently, an atmo- the New York Canyon results are greatly expanded by analyzing spheric Hg perturbation is the most plausible cause. six further sedimentary records from around the world, to test The Hg perturbation also coincided with the established onset whether the end-Triassic Hg perturbation was a global phe- of an increase in atmospheric pCO2, based on Hg/TOC and nomenon. The possibility of multiple episodic peaks in sedi- stomatal density records from Astartekløft (23) (SI Appendix, mentary Hg is also investigated, to examine whether the Figs. S2 and S5). This correlation suggests a geologically simul- documented pulsatory nature of CAMP emplacement occurred taneous increase in atmospheric Hg and CO2, plausibly origi- province-wide or was limited to specific areas of the LIP. The nating from magmatic degassing during CAMP emplacement. synchrony of any Hg excursions with respect to the earliest Emissions of both gases could also result from thermogenic gas CAMP flows is also assessed using the established stratigraphic release from kerogen in subsurface organic-rich sediments in- correlation between the end-Triassic extinction horizon and the truded by (CAMP-associated) sills. Thermogenic emissions have stratigraphically lowest known CAMP basalts. been previously suggested as a key contributor to LIP atmo- spheric perturbations (e.g., refs. 38 and 39). Thermogenic vola- Study Areas 13 tiles also explain the observed negative excursion in δ Corg at End-Triassic records of both marine and terrestrial environ- the extinction horizon more satisfactorily than magmatic carbon ments are known from a number of locations around the world emissions (40). However, peaks in Hg/TOC stratigraphically (figure 1 in ref. 36). In this study, the Hg records from six geo- above the extinction horizon are not marked by distinct negative 13 graphically widespread sections are presented, representing a excursions in δ Corg. Consequently, there is less evidence for

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AE FG

Fig. 3. Comparison of Hg/TOC data from St Audries Bay, Kuhjoch, Arroyo Malo, Astartekløft, and New York Canyon (35), and Hg data from Partridge Island and Iguonane (where TOC contents were below error). Letters next to locations refer to letters on the map in Fig. 2A. Carbon isotope data, biostratigraphy (ammonite first appearance), lithology, and magnetostratigraphy are also shown to allow stratigraphic correlation of the end-Triassic extinction (ETE) horizon and Triassic–Jurassic boundary (TJB). Lithological data are from St Audries Bay (10), Kuhjoch (11), Arroyo Malo (54), Astartekløft (10), Partridge Island (this study; shown in figure), Argana (14), Igouane (this study; shown in figure), and New York Canyon (35). Carbon isotope and biostratigraphic data are from St Audries Bay (10, 50), Kuhjoch (11), Arroyo Malo (ref. 54 and this study), Astartekløft (10), Partridge Island (this study), Argana (14), and New York Canyon (35). Line M indicates the magnetostratigraphic correlation, below the extinction horizon, between St Audries Bay, Partridge Island, Argana, and Igounane. The gray shading illustrates the stratigraphic gap between line M and line ETE. Magnetostratigraphic data are from St Audries Bay (52, 53), Partridge Island (55), 13 and Argana (14). Note, for Astartekløft, the expanded horizontal scale, and the gaps in data due to sand beds with negligible TOC. Full δ Corg, Hg, TOC, and Hg/TOC data for each individual section are reported in SI Appendix, Table S3 and Fig. S4.

these later Hg perturbations resulting from thermogenic emis- North America and Morocco (17–20). However, these litholog- sions, and magmatic Hg emissions are a more probable cause. ical records only prove an apparent pulsing of CAMP basalts in Additional evidence for a volcanic origin of the perturbation specific locations of what is a much larger-scale province. Epi- to the global Hg cycle during the end-Triassic extinction comes sodic volcanism across the entire extent of CAMP has been from the established correlation between the lowest known CAMP inferred from pedogenic carbonate pCO2 reconstructions (22), but flow (the Lower Formation in the High Atlas) and the extinction these concretionary carbonates can be impacted by local (diage- horizon. This correlation allows the Hg/TOC increase at the ex- netic) processes. The observed pulsatory signal of Hg perturba- tinction horizon to be precisely stratigraphically matched with that tions in multiple, globally distributed, sedimentary records across particular unit of CAMP (Fig. 1B; see also SI Appendix,Fig.S2 the Triassic–Jurassic transition provides independent evidence and refs. 14 and 15). Consequently, it is highly likely that volcanic that the intensity of CAMP volcanism, and likely CAMP em- Hg associated with this lowest CAMP flow contributed to the placement, occurred in a noncontinuous manner. global Hg perturbation during the end-Triassic extinction. The Although the Hg records shown in Fig. 3 do show excursions in ability to stratigraphically correlate an Hg excursion directly with Hg/TOC in Jurassic strata and support the continuation of CAMP an individual CAMP basalt flow greatly strengthens the use of this volcanism into the Jurassic, most of the Hg/TOC peaks are do- element as a proxy for volcanism. cumented between the end-Triassic extinction horizon and the – The Pulsatory Release of Magmatic Volatiles. In addition to the Hg Triassic Jurassic boundary. The data (Fig. 3) suggest that at least excursion at the extinction horizon, four sections record distinct two, and possibly three, major volcanic episodes occurred between peaks in sedimentary Hg/TOC higher up in the stratigraphy. the extinction and the beginning of the Jurassic (as defined by These higher peaks are most clearly distinct at Kuhjoch and ammonite biostratigraphy). This interval is estimated as lasting only Arroyo Malo, but may also be recorded at New York Canyon 100kyto200kybasedonU–Pb geochronology and astrochronol- and St Audries Bay (Fig. 3). Pulsatory CAMP volcanism has ogy (e.g., refs. 1, 2, 41, and 42). Ar–Ar and U–Pb geochronology been inferred from the stratigraphic record of CAMP basalts in suggests that the three oldest Moroccan basalt units (the Lower,

7932 | www.pnas.org/cgi/doi/10.1073/pnas.1705378114 Percival et al. Downloaded by guest on September 26, 2021 Middle, and Upper formations: units 1, 3, and 4 in Fig. 2B)andthe from the emplacement of CAMP and the associated large-scale first of the major North American CAMP pulses (units 2–4inFig. emission of magmatic volatiles, and potentially thermogenic 2B) were likely all emplaced during this interval (2, 14, 17). It is volatiles from intruded country rock (including Hg). The ap- possible that the observed three pulses in Hg/TOC observed in pearance of a global Hg excursion at the end-Triassic extinc- strata between the extinction horizon and the Triassic–Jurassic tion horizon and multiple Hg/TOC peaks between it and the boundary may directly relate to atmospheric volatile release from Triassic–Jurassic boundary is further evidence that pulses in the thefirstthreeCAMPbasaltunitsintheMoroccanArganaBasin, intensity of CAMP volcanism (and associated volatile release) and their North American equivalents. However, further correlative were not limited to North America and Morocco but were rep- work is needed to confirm such a hypothesis. The later North resentative of the entire province. The direct correlation between American CAMP basalts, and the Moroccan Recurrent Formation the oldest preserved flows of CAMP and the end-Triassic extinc- (units 5 and 6, Fig. 2B), were emplaced 300 ky to 600 ky after the tion horizon allows the earliest pulse of elevated Hg in the sedi- extinction (refs. 2, 14, and 21 and references therein). Thus, the mentary record of this time to be linked directly with these basalts. – Hg/TOC peaks between the extinction horizon and the Triassic This correlation supports a volcanic origin for the increased Hg Jurassic boundary cannot be related to these later flows. abundances and represents a unique tie between a globally ob- The observed record of multiple pulses in Hg/TOC is direct served mercury excursion and a specific basalt unit from a LIP. evidence that volatile release associated with CAMP volcanism The recording of multiple Hg/TOC excursions between the ex- was also pulsatory, likely including episodic emissions of carbon, tinction horizon and the Triassic–Jurassic boundary highlights that sulfur, and Hg. Moreover, pulsatory emissions are shown to have the initial stages of CAMP emplacement were marked by multiple occurred throughout the first 100 ky to 200 ky immediately fol- episodes of volcanic volatile release. Repeated volcanically driven lowing the end-Triassic extinction, in addition to the docu- perturbations of the ocean−atmosphere system in the 100 ky to mented later pulses of volcanic emissions (22). Consequently, the 200 ky during and immediately following the end-Triassic extinc- large increase in atmospheric pCO during the extinction event 2 tion may have had important implications for the biospheric im- may have arisen as a series of episodic carbon cycle perturbations pact of CAMP. to the atmosphere (and subsequently the ocean). Pulsatory – perturbations of the ocean atmosphere system caused by epi- Methods sodic volcanic events (and release of volatiles) associated with CAMP may explain the documented prolonged period of eco- Hg analysis was undertaken on the RA-915 Portable Mercury Analyzer with PYRO- 915 Pyrolyzer (Lumex) at the University of Oxford (26). Where previous TOC system deterioration and delayed recovery of benthic fauna – determinations were not available, new data were measured using either a during the emplacement of CAMP (35, 43 45). Strohlein Coulomat 702 (46) or Rock-Eval VI (47) at the University of Oxford. The 13 δ Corg analyses were performed on decarbonated Arroyo Malo samples (pre- Conclusions pared at the University of Oxford) with a Thermo Scientific Flash 2000 HT Ele- Investigation of the global history of CAMP volatile emissions is mental Analyzer coupled to a Thermo Scientific MAT253 isotope ratio mass important for understanding the development of this igneous spectrometer via a Conflo IV open split interface at the Stable Isotope Laboratory province and its potential environmental impact. This study at the Open University. For full method details, see SI Appendix, Study Areas demonstrates that the Hg cycle was perturbed on a global scale and Methodologies. during the Triassic–Jurassic transition. Hg excursions are recorded EARTH, ATMOSPHERIC,

in five of the six sections studied; the one section with no record ACKNOWLEDGMENTS. We greatly appreciate the two anonymous reviewers AND PLANETARY SCIENCES for their reviews, which much improved this manuscript. We gratefully of Hg enrichment was likely deposited before the onset of acknowledge Alberto Riccardi, Susana Damborenea, and Miguel Manceñido CAMP volcanism. The onset of Hg enrichment occurred syn- for their assistance in collecting material from Arroyo Malo, Argentina; Paul chronously across the globe, coincident with the end-Triassic Olsen for assistance in collecting samples from Igounane, Morocco; and John extinction and associated global carbon cycle perturbation. The Farmer and the University of Edinburgh for provision of geochemical stan- presence of Hg/TOC excursions in sedimentary records of ter- dards. We acknowledge Natural Environment Research Council Grant NE/ G01700X/1 (to T.A.M.) and PhD studentship NE/L501530/1 (to L.M.E.P.), Shell restrial and marine paleoenvironments, across both hemispheres, International Exploration and Production Inc., a Niels Stensen Foundation indicates that atmospheric mercury concentrations likely increased Research grant (to M.R.), the US National Science Foundation Grants EAR substantially. This atmospheric perturbation probably resulted 0801138 and EAR 1349650 (to J.H.W.), and the Leverhulme Trust for funding.

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