The emplacement of Large Igneous Provinces (LIPs) has been interpreted as the cause of many environmental and biotic crises during Earth's history, largely due to their potential for introducing massive volumes of volcanogenic and thermogenic gases into the atmosphere. To assess this potential link, it is crucial to evaluate the potential coincidence of environmental perturbation, fluctuations in biodiversity, and extinction periods with LIP emplacement, requiring high-precision geochronology of LIP rocks. Volumetrically, most magmas and lavas associated LIPs are mafic, which presents as a significant challenge for high-precision geochronology, as mafic magmas rarely saturate U-bearing minerals, such as zircon or baddeleyite. In such a case, ⁴⁰Ar/³⁹Ar dating of plagioclase from these rocks is carried out, which has geological and analytical complications that may lead to inaccurate ages, and subsequently to flawed geologic models (Antoine et al., 2022).

Recent work has shown that high-silica melt pockets in LIP intrusions, contaminated by wall rock at the emplacement level, can crystallize mineral phases useful for high-precision U-Pb dating. The process of sedimentary wall rock contamination directly affects the composition of these minerals, as anatexis of this material significantly shifts the Hf isotope composition of zircon (and baddeleyite) away from mantle composition. These interactions between LIP intrusions and their wall rock can cause significant complications within the age spectra of these mineral phases.

Baddeleyite, the first U-rich phase to saturate during LIP magma crystallization, commonly yields anomalously young and scattering dates from partial loss of radiogenic Pb. Zircon is a rare mineral in these rocks. Its scatter in U-Pb dates is a combination of residual Pb loss after chemical abrasion and traces of xenocrystic components in the zircon grain, derived from inherited zircon during the contamination process. Zircon U-Pb ages are particularly significant, as zircon crystallization not only records igneous solidification, but also wall rock interaction and thermogenic gas generation, allowing for high-precision geochronology of potential climate altering events.

We will present new data sets of high-precision zircon and baddeleyite U-Pb and Hf isotope data, from sills of the Karoo and the Siberian Trap LIPs and highlight the potential implications for thorough understanding of the intrusive emplacement mechanisms. The Hf isotope compositions from both LIPs indicate localized contamination of the magma, indicating entrainment, anatexis and assimilation of wall rock during emplacement and sill inflation. Interpreted U-Pb ages of samples throughout the intrusive structure of the Siberian Trap LIP and the Karoo LIP indicate that not only was magma emplacement protracted over a few 100 ky within their subvolcanic domains, but that there was a similar temporal-structural progression of downward migrating emplacement through intrusive assembly. Finally, intrusive emplacement and associated wall rock thermogenic reactions for both LIPs are coeval with well documented periods of global climate change and carbon cycle perturbation in the lower Toarcian and lower Triassic, respectively.

Cited reference: Antoine et al. (2022) Chem. Geol. 610, 121086

How to cite: Schaltegger, U., Gaynor, S. P., Paul, A., Davies, J. H. F. L., Svensen, H., and Ramezani, J.: Challenges and insights from zircon and baddeleyite U-Pb ages and Hf isotope analyses of Karoo and Siberian LIP intrusive rocks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16856, https://doi.org/10.5194/egusphere-egu24-16856, 2024.

The total Hg (Hg_T) concentration data for geological samples, of interest as it may link to enhanced volcanic activity or other environmental changes, is a complex amalgamation of numerous surface and sediment processes. Drawdown by organic matter (OM) and sulfides (often approximated by total sediment sulfur concentrations, TS) have long been recognized as key drivers of variability in sedimentary Hg_T data. Most studies, therefore, employ a degree of normalization to a Hg “host” (Hg_T/TOC, Hg_T/TS) to extract anomalous Hg cycle behavior. The dominant host is often determined solely based on the strongest observed (linear) correlation but this widely applied method has been shown to suffer from various non-linearities in environmental processes and conditions that underlie the host-Hg relations and, crucially, does not allow succession-level, let alone sample-level, Hg speciation changes to be taken into account.

We here explore the use of thermal desorption characteristics for geological sediment (rock) samples. Thermal desorption profiles (TDPs) for many Hg species are well-established and have been used to, for example, distinguish between OM-bound Hg and different Hg sulfides, as well as Hg-oxides in (sub-)recent sediments. The typical method of analysis for TDPs is to use long (>15 minutes) multi-step temperature ramps. We adapt this technique to use only the rapid (< 3 minute) desorption that is obtained as standard for each sample analyzed in continuous-flow direct Hg analyzers. Using the rapid TDPs, we can clearly distinguish at least two Hg release phases, and find that (almost) all of the analyzed sedimentary silt and mud rock samples of Tithonian age (ca. 146 – 145 Ma) contain multiple Hg release phases. Analysis of each TDP allows quantification of the abundance of each phase, which can then be compared to potential hosts (TOC, TS) and other geochemical data on a sample and succession level.

Initial analyses of the TDP-informed Hg release for our samples indicate TOC concentration may determine 60 – 70% of the variability in the first (lower temperature) Hg release phase in our succession. This is a stark difference with the total Hg released from the same samples, for which only 20% of variation can be explained by TOC variability. The difference results from the variable presence of a later-stage (higher temperature) Hg phase that is anti-correlated with TOC.

The TDPs provide insight into sample-level Hg speciation and clearly demonstrate that the common assumption that Hg is exclusively associated with a single phase in sedimentary rocks throughout a succession is a large oversimplification. Further, we show that differences in Hg speciation can be detected and quantified in individual samples with minor adaptations of existing techniques. The TDPs offer a novel perspective on Hg analyses in geological samples and have the potential to test, validate, and supplement existing statistical models to detect anomalous Hg cycle behavior.

How to cite: Frieling, J., Fendley, I. M., Nawaz, M. A., and Mather, T. A.: Assessment of Hg speciation changes from thermal desorption characteristics in sedimentary rocks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10827, https://doi.org/10.5194/egusphere-egu24-10827, 2024.

In recent decades, enrichment of mercury (Hg) in sedimentary deposits has been widely used as a proxy for volcanism from Large Igneous Provinces (LIPs). Mercury is naturally released into the atmosphere through volcanic exhalations and other processes, then dispersed and sequestered in sediments. Recent studies have delved into the impact of extremely high-temperature exposure on Hg in sediments, such as intrusion and contact metamorphism. However, the behaviour of sedimentary Hg exposed to more moderate warming, such as associated with thermal maturation and hydrocarbon formation in a sedimentary basin is still underexplored.

We conducted a series of artificial maturation experiments on immature organic-rich marine mudrocks, specifically the Posidonienschiefer or Posidonia Shale (Lower Jurassic) in the Lower Saxony Basin, Germany. These pyrolysis experiments enabled us to investigate the changes in Hg concentration within rock residues and evolved organic fluids across varying maturation stages.

Our findings reveal a progressive decline in Hg concentrations in sediments with increasing thermal maturity throughout the experiments (24 hours to 5 weeks at 325 ºC). Notably, the most significant Hg concentration loss occurs between the time-steps 5 days and 15 days. However, the substantial Hg loss from the pyrolysis experiments strongly differs from observations from naturally matured Posidonia Shale. In contrast to the slight decrease observed in the pyrolysis experiments, we recorded a trend of increasing Hg concentrations associated with higher maturity on three Posidonia Shale cores., We explore the mechanisms for these striking differences between the experimental and natural maturation and how these effects may have controlled Hg mobility during hydrocarbon formation and impacted the use of sedimentary Hg as a proxy for LIP-related volcanism.

How to cite: Indraswari, A. O., Frieling, J., Mather, T. A., Dickson, A. J., Idiz, E., Jenkyns, H. C., and Robinson, S.: Investigating the influence of natural and artificial thermal maturation on sedimentary mercury (Hg), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4010, https://doi.org/10.5194/egusphere-egu24-4010, 2024.

The End Permian Mass Extinction (EPME) occurred at 251.9 Ma and is the largest extinction event in the Phanerozoic. More than 80% of marine species and ~75% of terrestrial species were wiped out in <100 kyr. The event is marked by a negative carbon isotope excursion (CIE) that has a rapid onset and sustained duration, indicating the release of huge volumes of isotopically light carbon to the ocean-atmosphere system. The scientific consensus is that the carbon cycle disturbances were caused by the emplacement of the Siberian Traps large igneous province (LIP), likely from a combination of magmatic degassing and contact metamorphism in the organic carbon- and evaporite-rich Tunguska Basin. However, the timing and tempo of the Siberian Traps emplacement relative to the environmental disturbances can be better constrained. We investigated four shallow localities from Svalbard and the Barents Sea, which during the Permian-Triassic interval were part of a semi-enclosed epicontinental sea on the northern margin of Pangaea. We use osmium isotopes (¹⁸⁸Os/¹⁸⁷Os) and mercury (Hg) enrichments to identify when the Siberian Traps were most active with respect to carbon cycle disturbances (δ¹³C_org) through these four shallow marine archives. Our results indicate a strong volcanic signature coincident with the main negative CIE, with fluctuating signals through the body of the CIE itself that are indicative of pulsed Siberian Traps activity. Osmium isotopes show considerable variations through the Permian-Triassic boundary, suggesting that the enclosed nature of the seaway preserved rapid seawater chemistry changes in response to changing climatic and volcanic conditions. These far-field results can be directly tied to biomarker and radiometric age estimates of the EPME to improve the relative and absolute chronologies of the extinction event and the elevated magmatic activity.

How to cite: Jones, M., Rooney, A., Zuchuat, V., Turner, H., Frieling, J., Mather, T., Augland, L., Sleveland, A., Senger, K., Betlem, P., Sartell, A., Hammer, Ø., Faleide, J. I., and Planke, S.: Volcanic proxies from the northern Pangean margin across the Permian-Triassic boundary: Evidence of intermittent Siberian Traps activity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12292, https://doi.org/10.5194/egusphere-egu24-12292, 2024.

The study of mass extinctions is invaluable for understanding the effects of extreme environmental change on the different components of the Earth system and their responses and implications. Growing interest in extinctions, combined with new field evidence and analytical breakthroughs over recent years, has enabled us to zoom into individual events, construct their high-resolution chronologies and proxy records and start untangling their cause mechanisms from consequences. This is fundamental to progressing our knowledge, however, how far can we zoom in without overlooking the wider context? To what extent does the prior background climate state influence the outcome and magnitude of an extinction? For example, how would our understanding of the Permian-Triassic mass extinction change if we were to find the late Permian had low or high background CO₂? And what was CO₂’s fate in its aftermath? We present a new multi-million-year boron isotope-derived record of ocean pH and atmospheric CO₂ spanning the Permian-Triassic, which allows us to establish the climate conditions before and after the mass extinction, as well as during the eruption of the Siberian Traps Large Igneous Province (LIPs) considered the ultimate cause (i.e. the trigger) of the extinction. We discuss the implications of our new CO₂ record, and more broadly reflect on the role of background climate as a generalizable component of extinctions.

How to cite: Jurikova, H., Whiteford, R., Garbelli, C., Wang, W., Shi, G. R., Shen, S., Angiolini, L., and Rae, J.: Permian-Triassic CO2 before, during and after the mass extinction, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10625, https://doi.org/10.5194/egusphere-egu24-10625, 2024.

How to cite: Grasby, S., Ardakani, O., Liu, X., Bond, D., Wignall, P., and Strachan, L.: Marine snowstorm during the Permian−Triassic mass extinction  , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20588, https://doi.org/10.5194/egusphere-egu24-20588, 2024.

The end-Triassic mass extinction (ETE), one of the “Big Five” in Earth history, was triggered by Central Atlantic Magmatic Province (CAMP) volcanism, releasing voluminous CO₂, SO₂ and halocarbons, which affected global marine and terrestrial ecosystems through atmospheric circulations. The terrestrial ecosystem collapse is commonly attributed to CO₂-drivengreenhouse effects changing climates that consequently impacted flora and fauna, but this fails to explain why atmospheric CO₂ with long retention timejust dominates a range of short-lived crises. Here, we investigate two terrestrial Triassic-Jurassic sections in each high- and low/middle- paleolatitude, finding anomalies of sulfur-associated molecular fossils, biomarker proxies of “high-temperature wildfires” and higher plants burial. These coincide with relatively short CAMP climax (lasting ~ 60,000 years). We propose a novel hypothesis that the high-intensity pulses of acid rains originated from CAMP climax dominated catastrophic defoliation, which oversupply dead moisture-free biomass as fuels in unusual rates, leaving coeval widespread abnormally high-temperature wildfires and spikes of sulfur compound-specific molecules in terrestrial sediments as fingerprints of acid rain deposition.

How to cite: Fang, L., Li, H., Zhang, X., Wang, G., Lu, Y., Deng, S., Li, M., Wignall, P., and Newton, R.: Anomalies of sulfur compound-specific molecular fossils link terrestrial ecosystem collapse to the end-Triassic crisis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22352, https://doi.org/10.5194/egusphere-egu24-22352, 2024.

The Carnian is marked by major environmental changes, including multiple carbon-cycle perturbations, global warming and enhanced hydrological cycling that have been linked to the effects of the emplacement of Wrangellia large igneous province. The environmental perturbations occurred in an interval of about 1–2 Myr between the Julian 2 and the base of the Tuvalian 2. This interval is named Carnian Pluvial Episode (CPE). The widespread and pronounced sedimentological changes observed in marine sedimentary records, which abruptly shift towards mainly siliciclastic deposition, point to general higher continental runoff during the CPE. However, quantification of actual changes in sediment flux to marine basins is still lacking. We calculated changes in linear and relative sedimentation rates in Carnian well age-constrained marine successions. During the Julian 2, the lithological changes are coupled to increases of up to ca. 3000% in relative sedimentation rates in the marine sequences of Western Tethys and Panthalassa, and to slight decreases (< -100%) in sedimentation rates in successions of Eastern Tethys. Sedimentation rates then decrease in the Tuvalian 1 in all the successions. The higher siliciclastic delivery to the basins is likely the result of the interplay of higher precipitation and continental runoff under conditions of higher atmospheric pCO₂, eustatic sea-level changes and local depositional contraints, which could all be relatable to the effects of volcanic gases emissions from Wrangellia large igneous province.

How to cite: Dal Corso, J., Sun, Y., and Kemp, D. B.: Massive changes in marine sedimentation rates during the Carnian Pluvial Episode (Late Triassic), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6915, https://doi.org/10.5194/egusphere-egu24-6915, 2024.

The Triassic–Jurassic transition (~201.5 Ma) is marked by abrupt positive and negative Carbon-isotope excursions in marine and terrestrial sedimentary records. These excursions reflect global carbon cycle perturbations occurring in response to the massive volume of carbon released from the Central Atlantic Magmatic Province (CAMP). The subsequent doubling to tripling in atmospheric pCO₂ led to ocean acidification and the development of marine anoxia, thought to have caused the end-Triassic mass extinction, one of the biggest mass extinctions of the Phanerozoic. Organic-rich sediments can record the evolution of the seawater osmium (Os) isotopic composition, which is controlled by the balance between weathering inputs from continental crustal rocks (¹⁸⁷Os/¹⁸⁸Os ~ 1.4) and from mafic and ultramafic basalts (¹⁸⁷Os/¹⁸⁸Os ~ 0.13). Here, we present the first ¹⁸⁷Os/¹⁸⁸Os isotope data across the Triassic–Jurassic transition from the Prees core (Cheshire Basin, UK), drilled for the International Continental Scientific Drilling Program (ICDP) Early Jurassic Earth System and Time-scale (JET) project. Our new Os-isotope data show two major excursions towards mantle ¹⁸⁷Os/¹⁸⁸Os signature across the Triassic–Jurassic transition which we interpret to be the result of the emplacement of CAMP and the fast weathering of juvenile basalts.

How to cite: Ballabio, G., Xu, W., Hnatyshin, D., Ruhl, M., van Acken, D., Dickson, A. J., and Hesselbo, S. P.: Enhanced global weathering in response to Central Atlantic Magmatic Province volcanism across the Triassic–Jurassic transition: an osmium isotope record from the Prees borehole (UK), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9491, https://doi.org/10.5194/egusphere-egu24-9491, 2024.

The Toarcian Oceanic Anoxic Event (T-OAE, ~183 Ma) was one of the most significant hyperthermal events in the Phanerozoic, characterized by a series of climatic and environmental perturbations on land and in the oceans. The climate warming was accompanied by an abrupt negative carbon-isotope excursion (N-CIE) in the biospheric carbon reservoir, suggesting the driver of this event was the massive release of ¹²C-enriched carbon. However, the source, rate, and cumulative mass of carbon emitted during the T-OAE are poorly constrained, leaving the specific mechanisms of climate change uncertain. Here, we simultaneously assimilate atmospheric pCO₂ reconstructions and carbon-isotope data from 24 well-constrained T-OAE profiles in an Earth system model to quantify carbon emission masses, rates, and sources. Our simulations suggest the emission of 10,900 Pg C across the event at rates of up to 0.8 Pg C yr^-1. A clear pulse of extremely ¹²C-enriched carbon release occurred at the onset of the T-OAE, likely indicative of a biogenic (e.g., methane hydrate) source. This was followed by the release of carbon consistent with a magmatic source, with two transient pulses potentially indicative of thermogenic carbon emission superimposed on a protracted input of volcanic carbon. The complex pattern of carbon release revealed by our modeling emphasizes the interplay of both deep and surficial Earth processes in driving the T-OAE event. Negative carbon fluxes characterize the N-CIE recovery phase, underlining the crucial roles of enhanced continental weathering and massive burial of organic carbon in facilitating Earth system recovery from massive warming.

How to cite: Chen, W., Kemp, D., Cui, Y., and Li, C.: Large-scale carbon release from multiple sources caused an Early Jurassic hyperthermal event, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2596, https://doi.org/10.5194/egusphere-egu24-2596, 2024.

The Jenkyns Event (i.e. the early Toarcian Oceanic Anoxic event, ca. 183 Ma) represents a notable short-term environmental and climatic perturbations. It is hypothesized to have originated from a substantial release of ¹³C-depleted carbon into the global ocean-atmosphere system, culminating in a globally synchronized negative carbon isotope excursion (N-CIEs). While this event has been extensively studied within the Tethyan Ocean, it remains inadequately characterized in continental domains beyond Europe. Here, lower Toarcian lacustrine successions from the QZ-16 well in the Qiangtang Basin, situated along the northern passive continental margin of the Meso-Tethys Ocean, is studied based on a multi-proxy approach of  organic and inorganic and isotope geochemistry, mineralogy, sedimentology, and palynology.

Chronostratigraphic calibration of the successions within the Quemo Co Formation is achieved through carbon isotope (δ¹³C_org and δ¹³C_carb) records and palynostratigraphy. Notably, a long-term positive δ¹³C trend is identified, which is interrupted by pronounced 4–5‰ N-CIEs in δ¹³C_org and δ¹³C_carb during the early Toarcian. This perturbation is interpreted as the terrestrial counterpart of the marine Jenkyns Event within the Qiangtang Basin, reinforcing a synchronicity to marine records. The Toarcian interval of the Qiangtang Basin is characterized by fully oxidizing conditions intermittent with minor phases of dysoxic settings, especially during the Jenkyns Event, resulting in a low organic carbon burial within the Quemo Co Formation.

Sedimentological analyses within the Jenkyns Event interval indicate the presence of storm deposits, as evidenced by siltstones, graded siltstones, small-scale hummocky cross-stratification, and sharp erosive bases. These features suggest a strong correlation between warming events and increased tropical storm activity during this period, leading to intensified hydrological cycles. Furthermore, elevated ratios of fluvial detrital proxies, such as Si/Al and Ti/Al, along with the deposition of silty mudstone facies at the onset of the Jenkyns Event point to enhanced terrigenous input. This can be attributed to accelerated continental weathering, coinciding with the climatic changes at this time.

Palynological analyses reveal a progressive shift from arid to humid climate conditions, consistent with the carbon-isotope perturbation, supporting the accelerated hydrological cycling during the Toarcian. However, the enhanced freshwater input, associated with the enhanced hydrological cycling, was counterbalanced by a decline in lake levels. These records were completely documented in lacustrine deposits within the Qiangtang Basin dating from the isotope perturbation, which is consistent with the early Toarcian global regression. Lacustrine deposits with marine influences suggest sporadic connectivity between the Qiangtang Basin and the Tethys Ocean during the Toarcian, underscoring a strong link between regional shoreline progradation and evolution of global climate and sea-level.

How to cite: Zhang, H. and Wang, J.: Terrestrial responses to the Jenkyns Event within a lacustrine system of the Qiangtang Basin (Tibet, China): Insights from sedimentology, palynology, and carbon-isotope geochemistry, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5117, https://doi.org/10.5194/egusphere-egu24-5117, 2024.

Oceanic Anoxic Event 1a (OAE 1a, ~120Ma) during the early Aptian represents a dramatic perturbation of the global carbon cycle and is associated to widely deposition of black shale [1]. The emplacement of the Ontong Java Plateau is considered to be the trigger of OAE 1a, which led to a series of environmental perturbations including marine anoxia [2]. However, whether Ontong Java Plateau volcanism is the direct driving factor of oceanic deoxygenation is still under debate. Most research suggested that the eruption of Ontong Java Plateau injected enormous CO₂ into the atmosphere-ocean system and accelerated continental weathering, which eventually resulted in ocean anoxic/euxinic conditions [1]. Few argued that oceanic deoxygenation was an immediate response to the Ontong Java Plateau volcanism [3].

Here, we select DSDP Site 463 and ODP Site 866A in the Pacific Ocean near Ontong Java Plateau as study sections. We present high-resolution δ⁹⁸Mo records to reflect changes in ocean redox conditions and use Mn and Fe abundances and Eu/Eu^* ratios to resolve volcanic phases. Combined with other redox, biological productivity, and weathering proxies, we reconstruct the history of Ontong Java Plateau eruption and ocean redox environment across OAE 1a. Our data reveal that oceanic deoxygenation started before OAE 1a and was driven by Ontong Java Plateau volcanism instead of continental weathering. Volcanically sourced nutrients fluxed into the ocean and stimulated local organic productivity, resulting in ocean deoxygenation. During OAE 1a, ocean maintained anoxic/euxinic conditions. The coeval global seawater δ⁹⁸Mo was probably around or greater than 2.1‰.

[1] Jenkyns, 2010, Geochemistry Geophysics Geosystems 11.

[2] Percival et al., 2021, Global and Planetary Change 200.

[3] Bauer et al., 2021, Geology 49, 1452-1456.

How to cite: Wu, S., Li, C., Huang, J., and Sun, W.: The influence of Ontong Java Plateau volcanism on oceanic deoxygenation during Oceanic Anoxic Event 1a: evidence from Mo isotope, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7064, https://doi.org/10.5194/egusphere-egu24-7064, 2024.

The Phanerozoic Aeon was marked by several variations in global oxygenation levels, occuring both gradually over multi-million year timescales and also more abruptly as transient perturbations lasting typically a million years or less. Following an overall trend of rising atmospheric oxygen levels in the mid–late Palaeozoic, marine redox conditions are thought to have been close to modern by the time of the Cretaceous Period (145–66 Ma). However, the Cretaceous Period also featured multiple episodes of geologically abrupt depletions in seawater oxygen levels, known as Oceanic Anoxic Events (OAEs), one of the most severe of which occurred during the Early Aptian (OAE 1a, ~120 Ma). This environmental crisis is thought to have been triggered by major carbon emissions related to the volcanic formation of the Greater Ontong-Java Plateau. Several OAE 1a sites are marked by the preservation of organic-rich laminated shales, indicative of oxygen-depleted conditions in the water column and at the sediment-water interface. However, the relative paucity of Early Aptian open-ocean sedimentary records means that the degree to which anoxic conditions spread throughout the global marine realm during OAE 1a remains poorly constrained.

Here, we aim to verify the nature of seawater oxygen levels prior to, during, and after OAE 1a, using uranium-isotope (δ²³⁸U) records of that event. Under iron-reducing conditions, soluble U⁶⁺ transforms to insoluble U⁴⁺, which is associated with a pronounced isotopic fractionation in favour of ²³⁸U in U⁴⁺ ions. Thus, the subsequent sequestration of U⁴⁺ in organic-rich sediments causes depletion of ²³⁸U in the water column and a shift to an isotopically lighter δ²³⁸U composition of seawater. This change in marine δ²³⁸U is recorded by carbonates precipitated in seawater. Thus, δ²³⁸U trends across various records of OAE 1a enable the hypothesis that background Cretaceous ocean redox conditions were comparable to today to be tested, and the change in geographic extent of anoxic water masses during the environmental change quantified. By further comparing the δ²³⁸U data with other geochemical proxies (e.g., carbon-isotope evidence of organic-matter burial; osmium-isotope evidence of volcanism), we further explore the causes and environmental consequences of transient ocean redox fluctuations in the Early Cretaceous oceans.

How to cite: Percival, L., Dickson, A., Basu, A., Castro, J., Ruiz-Ortiz, P., Bottini, C., Erba, E., Mutterlose, J., Goderis, S., and Claeys, P.: Uranium-isotope records of global ocean deoxygenation during the Early Aptian Oceanic Anoxic Event (OAE 1a), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11863, https://doi.org/10.5194/egusphere-egu24-11863, 2024.

Global and local paleo-environmental changes across Earth’s history can be tracked by investigating the sedimentary record. Large Igneous Provinces (LIPs), whose activity spans from 250 to 50 Ma, are known to be coeval to the Phanerozoic largest mass extinctions and the Oceanic Anoxic Events (OAEs), the latter identified in the marine sedimentary rocks through key geochemical proxies such as high organic matter content (up to 30%) and positive excursions in the δ¹³C values. The Bonarelli level, a ~0.9-m thick layer made up of organic-rich shales, cropping out at Valle della Contessa section in Gubbio (Italy) within the pelagic limestones of the Scaglia Bianca Formation, is the stratigraphic marker of OAE2 (Cenomanian-Turonian, ~93 Ma). This event was likely triggered by submarine volcanism of the High Arctic and Caribbean LIPs, although clear evidence is missing at present, that might be given by the study of geochemical markers like mercury (Hg) claimed as a signature within sedimentary layers for large volcanic eruptions.
We present the results of X-ray diffraction, petrographic and geochemical (Total Organic Carbon, Hg concentration, trace elements, Hg, S and Sr isotopes) analyses on eleven rock samples collected from the Bonarelli level along with eleven rocks samples from the Scaglia Bianca Formation, to establish a potential link between OAEs and LIP volcanism.
LIP-related basalts are known to have 1 to 4 µg/kg of Hg (Yin et al. 2022). Interestingly, our results show a sharp Hg anomaly up to ~1600 µg/kg measured in the black shales, pointing out episodes of large Hg emissions accompanied by volatile degassing. Such anomaly correlates positively with the concentration of chalcophile elements such as Cu, Ni and Fe and with the amount of sulfate (barite and jarosite) + sulfide (pyrite), likely the main Hg-bearing minerals. A major effect of organic matter accumulation on the Hg contents was excluded because of the high Hg/TOC ratios. Hg isotopic data suggest a (deep) mantle-derived magmatic contribution that is not accompanied by a similar mantle signature of Sr and S isotopes. In contrast, we observed a continental input for Sr and S signature controlled by diagenetic processes in marine environment (e.g., pyrite deposition in anoxic seawater), atmospheric oxidation and seawater mixing. We interpret these findings as evidence of large-scale magmatism, which triggered greenhouse state increasing continental weathering. 

Yin, R., et al. (2022). Mantle Hg isotopic heterogeneity and evidence of oceanic Hg recycling into the mantle. Nature communications, 13(1), 948.

How to cite: Marras, G., Stagno, V., Aldega, L., Barberio, M. D., Benedetti, F., Cornacchia, I., Labidi, J., Morelli, G., Preto, N., Rimondi, V., and Brandano, M.: The Bonarelli level (Gubbio, Italy) reveals a potential correlation between the occurrence of oceanic anoxic events and large-scale magmatic activity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18517, https://doi.org/10.5194/egusphere-egu24-18517, 2024.

The Cenomanian–Turonian Oceanic Anoxic Event (OAE2; ~94.5 million years ago) represents an episode of global-scale marine anoxia and biotic turnover, which corresponds to one of the warmest time intervals in the Phanerozoic. Despite its global significance, information on the dynamics of continental ecosystems during this greenhouse episode is scarce. Here we present a terrestrial palynological record combined with chemostratigraphic data from an expanded marine OAE2 section from the Iberian Basin, Central Spain. Carbon isotope records of carbonate and organic carbon from two nearby sections show the characteristic positive CIE (carbon isotope excursion) associated with OAE2 and, together with ammonite finds, facilitate the construction of a stratigraphically well-constrained composite record. The spore-pollen assemblage is dominated by non-saccate gymnosperm (Classopollis, Araucariacites, Inaperturopollenites) and angiosperm pollen (mainly representatives of the Normapolles group incl. Atlantopollis and Complexiopollis), with pteridophyte spores being quantitatively less abundant. With stratigraphic height, the spore-pollen assemblage shows distinct changes in frequency distribution including a distinct rise in the angiosperm pollen Atlantopollis within an interval assigned to the Plenus Cold Event. In contrast, a pronounced increase in Classopollis reaching >50% of the total palynoflora parallels the 2^nd peak of the CIE and is followed by an abrupt decline. These palynofloral changes indicate changing proportions of arborescent conifer forests and more open, non-arborescent, angiosperm-rich vegetation. Despite the exceptional warmth associated with OAE2, the continental hinterland bordering the Iberian seaway did support a diverse vegetation, adapted to persist under elevated temperatures. Fluctuations in spore-pollen frequency distribution are considered to reflect significant climatic changes over the course of OAE2 controlled ultimately by the interplay of large-scale magmatic activity and enhanced organic carbon burial.

How to cite: Heimhofer, U., Barroso-Barcenilla, F., Berrocal-Casero, M., Li, S., Müller, K., and Wheeler, A.: Palynofloral change across Oceanic Anoxic Event 2 in the Iberian Basin, Spain, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5694, https://doi.org/10.5194/egusphere-egu24-5694, 2024.

The Chicxulub impact in Mexico and Deccan volcanism in India are both linked to the end-Cretaceous mass extinction but the relative timing of the impact, volcanic eruptions, and environmental changes remain controversial, precluding a full assessment of their respective roles. The bulk (80%) of Deccan Trap eruptions occurred over a relatively short time interval in magnetic polarity C29r. U-Pb zircon geochronology reveals the onset of this main eruption phase 350 ky before the Cretaceous-Tertiary (KT) mass extinction.

U-Pb zircon geochronology from Malwa Plateau basalts on the northern margin of the Deccan LIP are temporally correlative with the first pulse of Deccan volcanism, which is coeval with a ∼200 kyr Late Maastrichtian warming event preserved globally in contemporaneous stratigraphic sections. This 2.5–8°C warming has been inferred by several studies on the basis of δ¹⁸O in benthic foraminifera, pedogenic carbonate and bivalve shells, as well as changes in leaf morphology. The onset of this excursion is temporally correlative to the initial decline in oceanic ¹⁸⁷Os/¹⁸⁸Os toward more radiogenic values and increasing Hg contents.

This first pulse of Deccan magmatism erupted through organic-rich sedimentary Permian rocks of the Narmada-Tapi rift basin. Direct CO₂ emissions from basalt are unlikely to cause this magnitude of warming, except at extreme eruption rates, which is difficult to reconcile with the likely longer duration and lower eruption rates inferred from this first eruptive pulse. Thermal contact metamorphism of these sediments could have been a source of sufficient CO₂ to drive the Late Maastrichtian warming event. The aim of this study is to understand the fate of C, Hg and S during the contact metamorphism associated with the first Deccan pulse and to evaluate the importance of this process in the global C, Hg and S cycles.

Our data are based on measurements of contact aureoles around several dikes and sills intruding in Permian organic-rich coal located in the Narmada-Tapi rift basin. We focused on TOC, Hg and S contents. While the sediments further away from the intrusions show high levels of TOC (>20%) and significant contents in Hg and S, the samples located in the aureoles (around 5 m thick) show a nearly total loss of the same elements. Our initial results demonstrate that the global C, S and Hg cycles can be substantially perturbed after LIP-scale sill and dyke emplacement in organic-rich sedimentary rocks. Deccan volcanism likely contributed to climate instability in the late Cretaceous and may have exacerbated the environmental effects of the Chicxulub impact.

How to cite: McKeegan, R., Adatte, T., Schoene, B., Eddy, M. P., Galvez, M., Khadri, S. F., and Omodeo Sale, S.: Earliest eruption of the Deccan Large Igneous Province: a potential trigger of the Late Maastrichtian abrupt warming event , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22199, https://doi.org/10.5194/egusphere-egu24-22199, 2024.

Formation of the ± 200 km in size Chicxulub crater is widely regarded as the leading cause of the Cretaceous-Paleogene (K-Pg) boundary mass extinction, 66 million years ago. Nevertheless, the precise climatic outcome of the various debris ejected into the atmosphere following the crater excavation, thus the killing mechanisms remain not definitely understood. Present paleoclimate scenarios confer a substantial role in sulfur components released by the vaporization of evaporite layers present in the upper part of the target rock. Sedimentological constraints acquired from an expanded terrestrial K-Pg boundary deposit in North Dakota and measured volumetric size distribution of silicate dust indicate the release into the atmosphere of fine silicate dust (~0.8-8 μm). The new general circulation model simulations of the injection of such a plume of micrometer-sized silicate dust (2x10¹⁸g) suggest a long atmospheric residence time (±15 years) with a global-average surface temperature falling by as much as 15ºC. Simulated effects on the post-impact active solar radiation support a dust-induced photosynthetic shut-down for approximately 2 years. Contrary to previous work, these new paleoclimate simulations, relying on robust sedimentological field data at the K-Pg boundary revealed that the impact-generated silicate dust plume plays a pivotal role in driving the K-Pg climate and biotic crisis. The new scenarios showcase that the global darkness and prolonged loss in the planet's photosynthetic activity happen solely in the silicate dust scenario, up to nearly 1.7 years after impact; a sufficiently long timescale to pose severe challenges for terrestrial and marine habitats. Biotic groups not adapted to survive the dark, cold, and food-deprived conditions for almost two years, experienced massive extinctions. In addition, this emission scenario shows that the photosynthetic recovery to the pre-impact levels first occurred in the austral summer season, ~1.7 years after impact. This would imply a potential earlier recovery of primary productivity in the Southern Hemisphere. These new findings highlight that the photosynthetic shut-down induced by the large volume of silicate dust, together with additional effects of sulfur and soot likely led to the collapse of primary productivity in land and ocean realms, steering the global mass extinction at the K-Pg boundary.

How to cite: Claeys, P., Senel, C. B., Kaskes, P., Temel, O., Vellekoop, J., Goderis, S., Prins, M. A., and Karatekin, O.: Fine silicate dust from Chicxulub crater excavation shuts down photosynthesis for up to 2 years after the K-Pg impact. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6595, https://doi.org/10.5194/egusphere-egu24-6595, 2024.

The final 0.5 m of the Cretaceous-Paleogene (K/Pg) boundary at Bidart (France) is characterized by geochemical, taphonomic, and biotic vestiges of an ocean acidification event linked with Deccan volcanism. The larger (>150 μm) planktic foraminifera morphogroups show varying populations (absolute abundance), with lowered abundances within the Deccan benchmark (final 0.5 m) and a demographic collapse at the K/Pg boundary. Additionally, the Deccan benchmark exhibits diminished test size (p: <0.00001), wall thickness (p: 0.0005), and mixed-layer diversity (p: 0.000967), suggesting the presence of calcification stress. Nevertheless, the benthic environment presents contrasting results, with rare occurrences of size and wall thickness reduction or significant census disturbances in the benchmark, suggesting a lower degree of environmental stress. Notably, a significant increase in the relative proportion of Cibicidoides spp. (~48%; p: <0.00001), Steinsioenia spp. (~11%; p: <0.00001) and Coryphostoma spp. (~9%; p: 0.000033) is recorded at the K/Pg. Near the boundary, there is a significant decrease in the relative abundance (p: 0.001097) and diversity of infaunal benthic foraminifera (p: 0.000035). This decline signifies a collapse in productivity, aligning with a negative excursion in the carbon isotope signature at the K/Pg boundary. These results suggest that the acidification was restricted to the surface ocean and had a limited effect on benthic environment. This is consistent with the lack of extinction within the benthic community at K/Pg. A Graphic correlation of zone CF1 at Bidart with the auxiliary GSSP at Elles (Tunisia) through Hg peaks constrain the Deccan benchmark interval to the final ~58 ky of the late Maastrichtian, culminating in the K/Pg mass extinction.

How to cite: Patra, S., Kesen, K., Keller, G., Font, E., Adatte, T., and Punekar, J.: The age and extent of the late Maastrichtian calcification stress at Bidart, France, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14532, https://doi.org/10.5194/egusphere-egu24-14532, 2024.

Morphogroup analysis of benthic foraminifera is a useful tool that reflects the nature of the trophic continuum, and in particular the flux of organic matter to the sea floor and its source. In broad terms, agglutinated benthic foraminifera can be placed in four morphotypes based on their test morphology and feeding preference. Morphotype M1 constitutes tubular suspension feeders that trap food particles carried in suspension. Morphotypes M2 and M3 are the coiled multichambered forms, which are epifaunal detritivores, and M4 is the group of elongated and rectilinear infaunal deposit feeders. Their relative proportions tell us something about flux of particulate organic carbon (POM) to the sea floor and its mode of delivery, which is ultimately a function of water depth, currents, and the amount of surface-water phytoplankton production.

To assess the trophic structure of the benthic foraminiferal community across the Cretaceous/Paleogene boundary in the western Tethys, we examined >70 samples from the Scaglia Rossa Formation in Gubbio, Italy. Samples were mostly collected at 10 cm spacing. We also recalibrated the age model for the Scaglia Rossa Formation in Gubbio using the 2020 geologic time scale. In the top two meters of the Maastrichtian, a gradual increase in the proportion of M4 is observed (to ca. 20%) leading up to the K/Pg boundary. These values fall abruptly to 7% in the beds immediately above the boundary clay, with more variable values in the lower Paleocene. This pattern can be interpreted as reflecting a modest but short-lived reduction in the total sea-floor organic flux following the boundary event (but not a “Strangelove Ocean”). Morphotype M1 shows a major reduction above the boundary, and there is a concurrent increase in the M2 morphotype. This implies a reduction in the amount of POM arriving at the sea floor from suspension. The increase in M2 suggests that there was greater influence of organic matter from bacterial sources in the early Paleocene.

The recovery of the deep-marine ecosystem was prolonged, with M1 returning to Maastrichtian values approximately 3.4 m above the K/Pg boundary clay. Using our new age model, this is equivalent to 1.8 m.y. after the event. Our findings of a prolonged recovery are in line with the conclusions of nannofossil workers, who estimated that it took approximately 2 m.y. for the marine food web to fully reestablish itself after the K/Pg boundary event.

How to cite: Kaminski, M., Hikmahtiar, S., and Cetean, C.: Benthic foraminiferal morphogroups track the recovery of the deep-marine ecosystem after the K/Pg boundary, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3736, https://doi.org/10.5194/egusphere-egu24-3736, 2024.