SSP1.3

Large Igneous Provinces (LIPs) are accumulations of igneous rocks representing periods of intense volcanism in Earth’s history. The timing of the emplacement of many LIPs corresponds with global climatic perturbations and mass extinctions, leading to the hypothesis that their occurrence is implicated in these events. However, detailed investigations into these hypotheses are typically restricted to studies of individual events (e.g. the Siberian Traps emplacement at the Permian-Triassic boundary), and single forcing mechanisms (e.g. carbon emissions). As a result, it is often unclear what the overall impact of LIP emplacement was on climate in Earth’s history.

In this work, we present the results of the first integration of LIP degassing and weathering to a long-term model of global carbon cycling. We use the SCION climate-chemical model, which allows for both the addition of LIP degassing as a CO₂ forcing mechanism, and the introduction of LIPs as highly weatherable terranes on the Earth surface. In this way, we can estimate both the warming impact LIPs may have had on climate change in the past, through carbon degassing, but also the cooling effect they would have had, through enhanced silicate weathering. Our work shows the importance of LIP location on weathering rates, with those which are emplaced in the mid-latitudes having the biggest cooling impact.

Comparison of our reconstruction with previous estimates of Phanerozoic climates show that the inclusion of LIPs enhances model-data comparability. This is particularly clear in the late Triassic, and Cretaceous periods, where previous model reconstructions overestimated atmospheric CO₂ and global temperature. Our findings suggest LIP weathering is an important factor mitigating global climate change through the Phanerozoic.

How to cite: Longman, J. and Mills, B. J. W.: The role of Large Igneous Provinces in controlling long-term Phanerozoic climate change, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5403, https://doi.org/10.5194/egusphere-egu22-5403, 2022.

The End Triassic Extinction (ETE), one of the “big five” of the Phanerozoic, caused a severe loss of biodiversity both in the continental and in the marine realm. The ETE has been linked with enhanced volcanism of the Central Atlantic Magmatic Province (CAMP), which injected a large amount of CO₂ in the ocean-atmosphere system, triggering major paleoenvironmental perturbations including climate change, ocean acidification and marine anoxia.

In the marine realm, shallow-water benthic biocalcifiers of subtropical carbonate platforms were severely affected, with reef-building scleractinian corals and calcisponges, large megalodontid bivalves, involutinid benthic foraminifers and dasycladalean algae being among the most famous victims. In the classical localities of the Northern Calcareous Alps and Transdanubian Range, the ETE coincides with the demise of the Dachstein-type carbonate platform, which is generally sharply overlain by relatively deep-water facies of outer ramp to basinal environment. This stratigraphy has been interpreted as recording subaerial exposure of the carbonate platform, associated to a sea-level drop in the late Rhaetian that generated a hiatus of variable and generally poorly constrained duration, followed by drowning during transgression in the Early Jurassic.

A different stratigraphic evolution is recorded in some areas of the southern Tethyan margin (i.e., the southern Apennines and Sicily in southern Italy, Greece, the United Arab Emirates and Oman) where carbonate platform facies persist across the Triassic/Jurassic boundary. Stratigraphic sections in these areas are particularly significant to document the evolution of biodiversity of shallow-water benthic biocalcifiers across the ETE interval.

In this study we present new data on the stratigraphic distribution and changes in abundance of benthic foraminifers in two latest Triassic–earliest Jurassic carbonate platform sections of the southern Apennines (Italy) and Pelagonian domain (Greece). We document a decline in diversity and abundance of involutinid benthic foraminifers predating the extinction of several genera in the latest Rhaetian. Carbon isotope profiles of the studied sections show a complicated pattern of repetitive high-frequency negative excursions, seemingly related to local paleoenvironmental and/or early diagenetic features. However, by integrating bio- and carbon isotope stratigraphy we are able to correlate the studied sections with other persistent carbonate platform sections and with reference sections of the Lombardy Basin and of the Northern Calcareous Alps.

How to cite: Falzoni, F., Montanaro, A., Iannace, A., and Parente, M.: The record of the End Triassic Extinction in southern Tethyan carbonate platforms, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3986, https://doi.org/10.5194/egusphere-egu22-3986, 2022.

Massive release of volcanic gases into the ocean-atmosphere system during geologically short periods of time is often invoked as the main trigger of episodes of global paleoenvironmental perturbations, and a link has been proposed between some mass extinction events, OAEs and the activity of Large Igneous Provinces. However, establishing a precise correlation between sections where the volcanic deposits of LIPs are preserved and marine sections, which hold the key records of global biotic and paleoenvironmental changes, is not a trivial effort.  During the past 15 years, mercury concentration in sedimentary rocks has emerged as a useful proxy for bracketing intervals of LIPs activity, because Hg is primarily introduced into the atmosphere, and from there into the sedimentary record, through volcanic inputs. 
The end-Triassic extinction (ETE), one of the big five mass extinction of the Phanerozoic, has been linked to the volcanic activity of the Central Atlantic Magmatic Province (CAMP). Correlation by radiochronologic dating of CAMP basalts has been further supported in recent years by detection of mercury anomalies in marine deposits of key sections recording the ETE, including the Kuhjoch GSSP in the Northern Calcareous Alps (Austria), St Audrie’s Bay (UK) and the New York Canyon (Nevada, USA). However, as the Hg proxy is investigated in more and more sections, a complicated pattern is emerging, which indicates that depositional and diagenetic processes can produce Hg anomalies unrelated to LIP magmatism. For this reason, it is important to test the proxy across a wide range of depositional environments. 
In this study, we present a high-resolution record of Hg concentration in an uppermost Triassic-Lower Jurassic carbonate platform section of the Pelagonian Domain (Greece). In this section the ETE is marked by the abrupt disappearance of megalodontid bivalves and involutinid benthic foraminifers. By integrating bio- and high-resolution carbon isotope stratigraphy, we correlate the studied section with reference sections for which a record of Hg concentration across the ETE has been published. Furthermore, we use facies analysis and geochemistry to unravel the role of local depositional and diagenetic processes in overprinting the global signal of volcanism on Hg concentration.

How to cite: Montanaro, A., Falzoni, F., Iannace, A., Adatte, T., and Parente, M.: Mercury anomaly as a proxy for volcanism in an isolated carbonate platform during the end-Triassic mass extinction, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4901, https://doi.org/10.5194/egusphere-egu22-4901, 2022.

Direct evidence of intense chemical weathering induced by volcanism is rare in sedimentary successions. Here, we undertake a multiproxy analysis (including organic carbon isotopes, mercury (Hg) concentrations and isotopes, chemical index of alteration (CIA), and clay minerals) of two well-dated Triassic–Jurassic (T–J) boundary sections representing high- and low/middle-paleolatitude sites. Both sections show increasing CIA in association with Hg peaks near the T–J boundary. We interpret these results as reflecting volcanism-induced intensification of continental chemical weathering, which is also supported by negative mass-independent fractionation (MIF) of odd Hg isotopes. The interval of enhanced chemical weathering persisted for ~2 million years, which is consistent with carbon-cycle model results of the time needed to drawdown excess atmospheric CO₂ following a carbon release event. Lastly, these data also demonstrate that high-latitude continental settings are more sensitive than low/middle-latitude sites to shifts in weathering intensity during climatic warming events. 

How to cite: shen, J.: Intensified continental chemical weathering and carbon-cycle perturbations linked to volcanism during the Triassic–Jurassic transition, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3179, https://doi.org/10.5194/egusphere-egu22-3179, 2022.

After 42 years, the debate over the end-Cretaceous mass extinction still rages with arguments made for Chicxulub impact and Deccan volcanism as the real cause of this catastrophe. We briefly review the evidence for the pre-KPB age of the Chicxulub impact based on the primary impact spherule layer, which we link to Deccan volcanism based on the global mercury (Hg) fallout from Deccan eruptions. Mercury from volcanic eruptions is distributed around the world during its atmospheric residence time of 6 months to one year, after which it rains out over land and oceans. Major pulsed volcanic eruptions yield high Hg concentrations during fallout, which we termed Extreme Events (EE). We identified 20 of these Hg extreme events during the last 550 ky of the late Maastrichtian in sequences from Tunisia, Israel, Egypt and Mexico. At Elles, Tunisia, we dated these events (EE1 to EE20) based on orbital cyclicity and biostratigraphy with precision of one cycle (20 ky) with an error margin of 10-20 ky (Keller et al., 2020). We linked these dates to U-Pb zircon ages of the Deccan Traps with similarly high precision (Schoene et al., 2019). The resulting mercury stratigraphy yielded excellent age control linking Deccan eruption pulses across the globe. Results from two localities in NE Mexico revealed the Chicxulub impact crashed into Yucatan above the base of the Plummerita hantkeninoides zone CF1 and EE6 at about 200 ky prior to the KPB mass extinction. This deposit is unlike any other of the over 100 reworked spherule layers mixed with abundant shallow water debris. This oldest and primary impact spherule layer consists of compressed pure melt rock glass and glass spherules that settled rapidly to the deep seafloor. The environmental effects of this large impact were short-lived and caused no species extinctions. The effects of this 10 km-sized bolide impact had been vastly overrated.

The KPB mass extinction was identified between the longest lava flows across India to the Krishna-Godavari Basin and into the Bay of Bengal. Based on peak Hg fallout, we identified these volcanic eruptions as the largest most rapid sequence of pulsed events in Tunisia, Israel, Egypt and Mexico, all coinciding with the rapid mass extinction observed in India. The mass extinction began with the onset and ramp-up of pulsed Deccan eruptions resulting in toxic and acidic waters that caused 50% species extinctions. Extremely rapid large pulsed eruptions followed and resulted in the longest lave flows and hyperthermal warming that caused the rapid demise of all but one species, the disaster opportunist Guembelitria cretacea. Deccan eruptions quickly diminished after the mass extinction and climate cooled rapidly giving rise to the first new species. Volcanic eruptions remained low and cool temperatures persisted through the early Paleocene interrupted by a smaller eruption phase about 100 ky after the mass extinction.  These data reveal that Deccan volcanism caused the KPB mass extinction without any extraterrestrial aid.

Keywords: Chicxulub, Deccan Volcanism, Mass Extinction, Mercury Stratigraphy, Age control

How to cite: Keller, G., Grasby, S., Khozyem, H., Punekar, J., Mateo, P., and Adatte, T.: Chicxulub Impact’s Real Age & Mass Extinction’s Real Cause, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11901, https://doi.org/10.5194/egusphere-egu22-11901, 2022.

Massive volcanic eruptions of the Deccan coincided with the end-Cretaceous mass extinction. Precisely dating when the most intense eruptions occurred is challenging because the resolution of geochronological techniques does not yet resolve events shorter than 20 kiloannum (ka). Volcanic eruptions outgas volatile metals, e.g., Cd, Te and Hg, along with SO₂ and other gases that may have contributed to high-stress environments for planktic foraminifera the 200 ka preceding the end-Cretaceous. Trace metals like Cd accumulate in sediments by deposition of aerosols, where the excess Cd reflects the intensity of volcanic emissions. Models show high frequency, low effusion rate eruptions result in low Cd enrichments, whereas low frequency, high effusion rate eruptions, the type likely to lead to deadly consequences, result in high enrichments of Cd within the sediments. The KPg section at Elles represents a middle neritic depositional environment with an average sedimentation rate of 4.7 cm/1,000 years for the late Maastrichtian. A series of sediment samples (marly limestone to shale) were taken from about 1 meter above the boundary to about 15 meters below the boundary. Elemental compositions of sediments (50 elements) were obtained by solution ICP-MS. Cadmium abundances ranged from values close to upper continental crust (UCC) to values approximately eight times higher. Such high enrichments were found in sediments from the 100 ka period preceding the boundary corresponding to the Poladpur phase of Deccan volcanism. A lack of correlation between Zn, P₂O₅, and Mo below the boundary suggest the Cd enrichments are not from an influx of biogenic detritus or TOC burial. Above the boundary, there is a 25 ka period of normal shale Cd values interpreted here to represent the period between the Ambenali and Poladpur phases. We have previously shown from the neighbouring El Kef section, representing ~ 10 ka, that Cd and Re are correlated in proportions similar to those from intraplate volcanoes. The Cd data for Elles complement Te and Hg data, all of which demonstrate the presence of volcanogenic trace metals over most of the period of the Poladpur phase of the Deccan eruption. Cadmium as a tracer enables better correlation between foram-based chronology and intense pulses of the Deccan eruption. The data obtained thus far confirm that the period prior to the extinction was dominated by intense volcanism followed by relative quiescence during the earliest Danian recovery with important implications for the cause of the extinction.

How to cite: Sillitoe-Kukas, S., Humayun, M., Adatte, T., and Keller, G.: Evidence of high effusion Deccan volcanism proceeding the KPg boundary at Elles, Tunisia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6736, https://doi.org/10.5194/egusphere-egu22-6736, 2022.

The Deccan flood basalt province in India was erupted within < 1 Myr and overlaps in age with the Cretaceous-Paleogene boundary (KPB) extinction event, and the Chicxulub impact in Mexico. Consequently, the role of Deccan volcanism in the KPB extinction is debated, and it has also been proposed that the Chicxulub impact triggered the largest Deccan lava formations (Poladpur, Ambenali and Mahabaleshwar (PAM)), which represent approximately 70% by volume of the total Deccan and may have been erupted within 500,000 years. Recent geochronological data studies debate whether the onset of the PAM eruptions began at the KPB as consequence of the Chicxulub impact, or whether the PAM lavas were erupted in several pulses, beginning several tens of thousands of years before the KPB (e.g., Sprain et al. 2019, Schoene et al., 2019).

The Rajahmundry Traps on the eastern side of India are believed to represent either the distal ends of voluminous Ambenali and Mahabaleshwar lava flows (e.g., Baksi et al. 1994), or lavas which were erupted locally through fault-controlled fissures unrelated to Deccan volcanism (Manikyamba et al. 2015). In contrast to lavas of the Main Deccan Province, the three separate lava flow units at Rajahmundry are interbedded with sediments, which constrain their age relative to the KPB (Keller et al. 2008; Fendley et al. 2020).

Here we present new major and trace element data for lavas from Rajahmundry and from the Main Deccan Province, and correlate the lavas from Rajahmundry with the younger formations of the Deccan Traps using machine learning algorithms. We find that flows of the Poladpur (lower flow), Ambenali (middle flow) and Mahabaleshwar (upper flow) formations are all present at Rajahmundry, confirming these as an eastward extension of the Deccan Traps. The geochemical classification is consistent with published paleomagnetic and geochronological data for these lavas. Our study shows that some Poladpur lava flows were of sufficient volume and were erupted rapidly enough to flow approximately 1000 km across the Indian subcontinent. The ages of sediments at Rajahmundry imply that eruption of the Poladpur Formation and thus the onset of voluminous PAM volcanic activity began close to the KPB (and Chicxulub impact), and at least the youngest Poladpur flows were emplaced in the Danian.

How to cite: Hoyer, P., Regelous, M., Adatte, T., and Haase, K.: Linking the Deccan lava stratigraphy with the end-Cretaceous extinction and impact – new insights from Rajahmundry, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7033, https://doi.org/10.5194/egusphere-egu22-7033, 2022.

Our systematic study of the spatial-temporal evolution of magmatism in the Deccan Traps   Large Igneous Province provides new data from the Malwa Plateau(MP) subprovince, which lies north of the comparatively well-studied Western Ghats. 40Ar/39Ar analysis was performed by incremental laser heating of multigrained plagioclase aliquots, in multiple (typically 4) experiments per sample.  Achievable precision is strongly anticorrelated with Ca/K of the plagioclase, reaching ~0.1% (pooled plateau ages, 1 s.d. intralaboratory precision) for some samples with Ca/K< 80. Results have been obtained from samples between ~100-800 m elevation, spanning virtually the entire exposed stratigraphy of the MP. Most of the MP overlaps in age with the older Kalsubai and Lonavala subgroups (~66.3 to 66.0 Ma) of the Western Ghats(WG), but MP basalts do not align with traditional WG chemical stratigraphy suggesting multiple contemporaneous eruptive centers and magma systems. The lowest (134 masl) lava dated is 66.8 ±0.07 Ma, significantly older than anything yet dated in the WG but identical to the result of Schöbel et al. (2014) for a stratigraphically low lava elsewhere in the MP. This is consistent with the consensus that the inception of volcanism progressed generally from North to South. Collectively, our data indicate a much slower mean lava accumulation rate for the basal MP, increasing sharply from 66.4 to 66.2 Ma and slowing by the Cretaceous-Paleogene boundary (KPB). MP lava accumulation rates decrease around the time of the KPB coincident with when eruption rates are inferred to increase in the WG. At similar elevations, our results overlap with the age model presented by Eddy et al. (2020) based on U/Pb dating of zircons from presumed silicic ashes preserved in red boles between lava flows, however our data span about twice their elevation range encompassing the lower portions of the section where we obtained the oldest ages. Our results indicate that the peak lava extrusion in the MP coincided closely with the Late Maastrichtian Warming Event (Barnet et al., 2017).

How to cite: Tholt, A., Renne, P., Vanderkluysen, L., Pande, K., Mohabey, D., and Dhobale, A.: 40Ar/39Ar dating of the Malwa Plateau subprovince, Deccan Traps, India, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11928, https://doi.org/10.5194/egusphere-egu22-11928, 2022.

The Late Maastrichtian Deccan volcanic pulses contributed to a cumulative biotic stress that set the stage for the Cretaceous-Palaeogene boundary (KPB) mass extinction. The high-flux emissions of volcanogenic CO₂ and SO₂ into the atmosphere likely led to ocean acidification. The resultant carbonate crisis has been hypothesized as a key stressor for marine calcifying biota such as planktic foraminifera. The final ~50 ky of the Cretaceous at Bidart (France) record a unique concurrence of anomalous bulk-rock low magnetic susceptibility, high Hg/TOC, and high planktic foraminifera fragmentation index. This study documents new evidence of a biological (calcification) crisis in the geochemical and taphonomic Deccan benchmark interval.

The onset of the hypothesized acidification interval (~0.5 m below KPB) coincides with abrupt changes in the relative abundances of the heavily calcified globotruncanid (~30 to ~17%) and larger biserial tests (~38 to ~55%). The absolute abundances of target groups/species however show a marked decline in both the biserials and globotruncanids. The counts per gram within the benchmark fluctuate considerably. At the KPB, the relative abundances of robust tests are high, partly due to taphonomic overestimation. However, absolute abundances unequivocally show a decline in all analyzed groups e.g., globotruncanids, biserials, racemiguembelinids and Planomalina brazoensis. The benchmark interval also records smaller-than-average test sizes of Globotruncana arca, Globotruncana mariei, Heterohelix globulosa, Pseudoguembelina hariaensis, Pseudotextularia elegans, Pseudoguembelina carsayae, Pseudoguembelina palpebra, Rugoglobigerina rugosa and P. brazoensis, indicating intraspecific dwarfing. This same interval also records a measurable decrease in the test-wall thickness amongst adult (>150 µm) specimens of H. globulosa, R. rugosa, P. elegans, P. brazoensis, further substantiating a carbonate crisis. The interpolation of geochemical, taphonomic and the new biological evidences strongly validate an ocean acidification event spanning ~50 ky preceding the KPB, a duration more consistent with Deccan volcanism as the cause.

How to cite: Punekar, J., Patra, S., and Keller, G.: On Planktic Foraminifera Calcification Crisis in the Deccan Benchmark Interval of Bidart, France, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10083, https://doi.org/10.5194/egusphere-egu22-10083, 2022.

Deep-water agglutinated foraminifera (DWAF) are investigated from the lower Paleocene of the Contessa Highway section in the Umbria-Marche Basin in Italy. In the lowermost meter of the Paleocene, corresponding the P0, Pa, and lowermost P1 planktonic foraminifera zones, a total of 46 species of DWAF are observed. A comparison with the uppermost Maastrichtian DWAF assemblages documented by Cetean (2009) yields a combined total of 94 DWAF species over the Cretaceous/Paleogene boundary interval at Contessa Highway. Of these, 49 species are listed as extinction taxa, nine are survivor taxa, 19 are Lazarus taxa, and 17 taxa display first occurrences in the Paleocene.

The record of DWAF in the Contessa Highway section displays a moderate decrease in diversity across the K/Pg boundary, followed by a gradual recovery in the first meter of the Paleocene. The lower Paleocene record is characterized by blooms of opportunistic species belonging to the genera Reophax, Subreophax, Repmanina, and Spiroplectinella. The K/Pg boundary interval records a major change in the proportions of DWAF morphogroups, from a suspension-feeding community in the Maastrichtian to one dominated by epifaunal detritivores in the lower Paleocene, reflecting a fundamental change in the nature of marine primary productivity following the bollide impact. 

How to cite: Kaminski, M., Hikmahtiar, S., and Cetean, C.: Deep-Water Agglutinated Foraminifera from the Contessa Highway Section, Umbria-Marche Basin, Italy: Assemblage turnover at the Cretaceous/Paleogene Boundary, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9536, https://doi.org/10.5194/egusphere-egu22-9536, 2022.

Large Igneous Provinces (LIPs) are commonly correlated with global climate change, and environmental, as well as biological, crises. These are short-lived igneous events, typically much less than 5 Ma, can erupt more than 1 Mkm³ of volcanic rocks, while potentially emplacing over 500,000 km³ of upper crustal intrusions. As a result, LIPs represent some of the most rapid periods of lithospheric growth, generating enormous volumes of mafic upper crust. Detailing the duration and pace of these high flux magmatic events has, however, is hampered by a lack of high-precision geochronology. We focus on the Karoo LIP in southern Africa as a natural laboratory for testing models on the formation of mafic upper crust through large-volume mafic LIP intrusions. The Karoo LIP is comprised of a suite of basaltic lava flows, sills, dike swarms, and was emplaced during the early Toarcian. Approximately 340,000 km³ of sills are interlaid within Karoo Basin sedimentary rocks. Differential uplift, erosion and availability of drill core material allows for sampling of the entire intrusive succession in the basin.

We report new high-precision U-Pb zircon and baddeleyite ages, Hf isotope compositions and apatite volatile compositions from sills emplaced from base to top of the Karoo Basin. Using these data, we are able to address several fundamental questions of LIP emplacement: (1) what is the total of intrusive LIP magmatism within the Karoo Basin; (2) is there variable magma flux during assembly of the intrusive complex; (3) is there is a relationship between age and structural position of sills within the basin; (4) is it justified to correlate the intrusion of the LIP with global climate change at this level of precision; (5) does the composition and extent of thermogenic degassing vary throughout the basin?

Our new data indicate that the 340,000 km³ of intrusive magmas were emplaced in approximately 500 kyr, solidifying new mafic upper crust through a downward stacking assembly, and that the entirety of intrusive magmas were emplaced within the uncertainty of the early Toarcian oceanic anoxic event. This pulsed assembly is in agreement with atmospheric models that require pulsed degassing of the basin to cause the observed early Toarcian isotope excursions. In addition, these data also indicate that dolerite sills throughout the basin assimilated sedimentary wall rock during crystallization, which helped facilitate zircon crystallization within pegmatitic pods interfingered within the sills. Finally, volatile compositions preserved in apatite indicate that thermogenic wallrock-sill interactions significantly affected the final volatile compositions of the sills, and trace the release of LIP-driven gases from the basin.

How to cite: Gaynor, S. P., Augland, L., Svensen, H. H., and Schaltegger, U.: Lithospheric and Atmospheric Changes Associated with Rapid, Pulsed Assembly of Mafic Upper Crust: Assembly of the Karoo LIP Intrusive Complex, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3162, https://doi.org/10.5194/egusphere-egu22-3162, 2022.

The Valanginian Weissert Event (~134 Ma) represented the first major carbon-cycle disturbance of the Cretaceous Period, characterized in the sedimentary record by a prolonged positive excursion in carbon-isotope ratios. The event has been widely linked with climate cooling, documented in several geographic regions; however, some areas show minimal evidence of temperature change at that time, or even warming and enhanced humidity around the onset of the event. Moreover, although the carbon-isotope excursion has generally been attributed to enhanced burial of organic matter, there is no evidence of widespread marine anoxia that would have promoted such deposition. Consequently, key questions remain regarding the causes of climate and environmental degradation during the early Valanginian. Understanding changes in volcanic activity and silicate weathering rates through late Berriasian to early Valanginian times is crucial for resolving this debate, as both processes influence atmospheric pCO₂ levels and global temperatures. In particular, volcanism associated with formation of the Paraná-Etendeka large igneous province (LIP) during the Valanginian has long been proposed as the ultimate trigger of the Weissert Event via carbon emissions and greenhouse warming,but weathering of juvenile LIP basalts could equally have caused climate cooling.

In this study, we investigated the osmium-isotope composition (¹⁸⁷Os/¹⁸⁸Os) of deep-marine organic-rich Berriasian–Valanginian sediments from two proto-Atlantic Ocean archives (DSDP sites 534 and 603). Given the palaeoenvironmental setting of the two sites, the recorded ¹⁸⁷Os/¹⁸⁸Os seawater compositions of the proto-Atlantic should be representative of the global ocean. We find that seawater ¹⁸⁷Os/¹⁸⁸Os shifted from ~0.6 to ~0.75 during the latest Berriasian, suggestive of an increased flux of radiogenic osmium to the ocean during that time, likely resulting from enhanced weathering of the continental crust. Interestingly, however, there is no evidence of global climate warming during the late Berriasian that would have caused this weathering. Following the late Berriasian radiogenic shift, seawater osmium gradually changed to a more unradiogenic isotopic composition (~0.45) during the early Valanginian; the lowest ¹⁸⁷Os/¹⁸⁸Os values correlating with both the peak in the Weissert Event carbon-isotope excursion and evidence for climate cooling. This unradiogenic shift could reflect a decline in weathering of radiogenic crustal material; however, it also stratigraphically correlates with geochronological and geochemical evidence for the time of maximum igneous activity on the western (Paraná) part of the Paraná-Etendeka LIP. Therefore, we conclude that the early Valanginian shift to unradiogenic ¹⁸⁷Os/¹⁸⁸Os seawater compositions resulted from erosion of juvenile primitive basalts, suggesting that combined weathering of the continental crust and the Paraná-Etendeka LIP played a key role in causing the global cooling associated with the Weissert Event.

How to cite: Percival, L., Selby, D., Robinson, S., Goderis, S., and Claeys, P.: Osmium-isotope records of volcanism and weathering before and during the Valanginian Weissert Event, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-779, https://doi.org/10.5194/egusphere-egu22-779, 2022.

The mid-Cretaceous (~120 Ma to ~90 Ma) is a well-known greenhouse period in the Earth’s history that was punctuated by multiple dramatic paleoceanographic changes known as oceanic anoxic events (OAEs). Among these OAEs, OAE2 occurred near the Cenomanian-Turonian boundary (CTB, ~93.9 Ma) and represents one of the most pronounced OAEs. OAE2 is widely believed to be triggered by submarine volcanism, primarily based on proxy records from the Northern Hemisphere in which a large osmium isotope excursion indicative of volcanism precedes the carbon isotope excursion (CIE) of OAE2. However, the timing and mechanism of the global initiation of OAE2 remain elusive in part due to the lack of detailed osmium-isotope proxy records across the OAE2 intervals in the Southern Hemisphere. Here we report a high-resolution initial osmium isotope (¹⁸⁷Os/¹⁸⁸Os_i, Os_i) and δ¹³C_org record from a highly expanded OAE2 interval in southern Tibet, China that was deposited in the northern margin of India Plate in eastern Tethys in the Southern Hemisphere. The Os_i record documents three distinct Os_i shifts toward unradiogenic compositions with increasing amplitudes at ~95.1 Ma, ~94.8 Ma, and ~94.5 Ma, respectively, indicating episodic, intensifying volcanism with the highest intensity episode at ∼94.5 Ma. In addition, the large Os_i excursion at ~94.5 Ma is followed by an ∼200 kyr Os_i minimum concomitant with a cooling interval as revealed by an overall broad minimum interval of the difference of the paired δ¹³C_carb and δ¹³C_org. This cooling interval is broadly synchronous with the Plenus Cold Event (PCE) recorded in the Northern Hemisphere. Furthermore, the large Os_i excursion paradoxically lags the onset of OAE2 by ∼50 kyr at the Tibetan section. Comparison with and re-examination of the expanded OAE2 record of the Yezo Group (Japan) and those from the western interior seaway (WIS) in North America reveal the regional difference in the phasing relationship between the large Os_i excursions and the CIEs of OAE2. Intriguingly, the large Os_i excursions occurred during a near synchronous global transgression at ~94.5 Ma that led to increased connectivity of global oceans. Taken together, these results suggest that enhanced ocean connectivity was essential in helping trigger the global onset of OAE2 at ~94.5 Ma.

How to cite: Li, Y.-X., Liu, X., Selby, D., Liu, Z., Montañez, I., and Li, X.: Deciphering the global onset of Oceanic Anoxic Event 2 (OAE2) in the mid-Cretaceous greenhouse world, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3366, https://doi.org/10.5194/egusphere-egu22-3366, 2022.

The emissions of volcanic gases over the Earth’s history have played a major role in changing the chemistry of the terrestrial atmosphere with implications for life development and sustainability (Kasting and Catling 2003). Sedimentary rocks record geological processes that occurred at the interface between water and/or surface and atmosphere such as volcanic eruptions and other (extra)terrestrial catastrophic events. In the last decade, anomalous concentrations of mercury (Hg) in the sedimentary record have been used as a global tracer of extensive volcanism, although other sources of Hg must be taken into account as massive wildfires and continental weathering (Grasby et al. 2019). In this ongoing study, we aim at establishing the relation between geochemistry and mineralogy to explain the occurrence of Hg anomalies in sedimentary rocks distributed at regional scale. We investigated the Bonarelli level, a 0.87-m thick layer made of organic-rich shales, that outcrops at Valle della Contessa section in Gubbio (Italy). This layer records the Oceanic Anoxic Event 2 (OAE2; Cenomanian-Turonian, ~93 Ma), an event likely triggered by submarine volcanic emission of High Arctic and Caribbean large igneous provinces (Turgeon and Creaser 2008).

We collected rock samples from ~1 m below up to ~1 m above the Bonarelli level every 5 to 10 cm including the confining limestones. Measurements of absolute Hg concentrations were performed using the Direct Mercury Analyzer (DMA-80 Tricell) and combined with the mineralogical abundance at each layer determined by X-ray diffraction (XRD). Additional measurements were carried out to determine the concentrations of trace elements using the inductively coupled plasma-mass spectrometry (ICP-MS). Analyses of δ¹³C and total organic carbon (TOC) were also performed on the collected samples.

Preliminary results show low Hg concentrations measured in the limestones less than 20 μg/kg, but anomalous high contents up to ~1600 μg/kg within the Bonarelli level. These high Hg concentrations correlate positively with chalcophile elements such as Cu, Ni and Fe. XRD semi-quantitative analysis show that oxidized (barite, jarosite) and reduced (pyrite) S-bearing minerals are among the minerals occurring in the Bonarelli level that, along with the organic matter, are good candidates to host the Hg released to the atmosphere by extensive volcanic eruptions.

Kasting, J. F., & Catling, D. 2003. Annual Review of Astronomy and Astrophysics, 41(1), 429-463.

Grasby, S. E et al. 2019. Earth-Science Reviews, 196, 102880.

Turgeon, S. C., & Creaser, R. A. 2008. Nature, 454(7202), 323-326.

How to cite: Marras, G., Brandano, M., Tomassetti, L., Morelli, G., Rimondi, V., Aldega, L., Barberio, M. D., Preto, N., and Stagno, V.: Geochemical and mineralogical investigations of the Bonarelli level (Gubbio, Italy): evidence of Hg anomalies, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-377, https://doi.org/10.5194/egusphere-egu22-377, 2022.