Evolution of the Toarcian (Early Jurassic) carbon-cycle and global climatic controls on local sedimentary processes (Cardigan Bay Basin, UK)

The late Early Jurassic Toarcian Stage represents the warmest interval of the Jurassic Period, with an abrupt rise in global temperatures of up to ∼7 °C in mid-latitudes at the onset of the early Toarcian Oceanic Anoxic Event (T-OAE; ∼183 Ma). The T-OAE, which has been extensively studied in marine and continental successions from both hemispheres, was marked by the widespread expansion of anoxic and euxinic waters, geographically extensive deposition of organic-rich black shales, and climatic and environmental perturbations. Climatic and environmental processes following the T-OAE are, however, poorly known, largely due to a lack of study of stratigraphically well-constrained and complete sedimentary archives. Here, we present integrated geochemical and physical proxy data (high-resolution carbon-isotope data (δ13C), bulk and molecular organic geochemistry, inorganic petrology, mineral characterisation, and major- and trace-element concentrations) from the biostratigraphically complete and expanded entire Toarcian succession in the Llanbedr (Mochras Farm) Borehole, Cardigan Bay Basin, Wales, UK. With these data, we (1) construct the first high-resolution biostratigraphically calibrated chemostratigraphic reference record for nearly the complete Toarcian Stage, (2) establish palaeoceanographic and depositional conditions in the Cardigan Bay Basin, (3) show that the T-OAE in the hemipelagic Cardigan Bay Basin was marked by the occurrence of gravity-flow deposits that were likely linked to globally enhanced sediment fluxes to continental margins and deeper marine (shelf) basins, and (4) explore how early Toarcian (tenuicostatum and serpentinum zones) siderite formation in the Cardigan Bay Basin may have been linked to low global oceanic sulphate concentrations and elevated supply of iron (Fe) from the hinterland, in response to climatically induced changes in hydrological cycling, global weathering rates and large-scale sulphide and evaporite deposition

Pre-Cenozoic cyclostratigraphy and palaeoclimate responses to astronomical forcing

Astronomical insolation forcing is well established as the underlying metronome of Quaternary ice ages and Cenozoic climate changes. Yet its effects on earlier eras (Mesozoic, Palaeozoic and pre-Cambrian) are less understood. In this Review, we explore how cyclostratigraphy can help to distinguish climate modes over the pre-Cenozoic era and aid our understanding of climate responses to astronomical forcing over geological time. The growing uncertainties with geologic age mean that pre-Cenozoic astronomical solutions cannot be used as tuning targets. However, they can be used as metronomes to identify the pacing of distinct climate states. Throughout the pre-Cenozoic, global average temperature differences between climate states were even more extreme (5–32 °C) than in the Cenozoic (14–27 °C), and these, combined with an evolving biosphere and changing plate tectonics, led to distinct Earth-system responses to astronomical forcing. The late Palaeozoic icehouse, for example, is characterized by a pronounced response to eccentricity, caused by nonlinear cryosphere and carbon-cycle behaviour. By contrast, the Devonian warmhouse and the Late Cretaceous hothouse featured recurrent episodes of marine anoxia that may have been paced by astronomical forcing. Formally defining 405,000-year eccentricity cycles as chronostratigraphic units (astrochronozones) throughout the Phanerozoic eon will enable a more comprehensive understanding of how astronomical forcing has shaped Earth’s climate over geologic time.</p

Links between temperature changes and oceanic-plateau emplacement during the Cenomanian–Turonian Oceanic Anoxic Event (OAE 2)

The Cenomanian–Turonian boundary interval (~94 Ma) was marked by a period of climatic turbulence, and featured the widespread expansion of strongly oxygen-depleted conditions across a large part of the global ocean; collectively these environmental degradations are referred to as an oceanic anoxic event or OAE (specifically OAE 2 for this time interval). Extremely high sea-surface temperatures are documented for several regions during OAE 2, likely beginning at the onset of the event, but a shift towards colder conditions during the early stages of the OAE (the Plenus Cold Event or PCE) is also recorded in several locales, before a return to a very warm climate during the latter part of the crisis. The overarching high temperatures are thought to have resulted from major volcanic activity during the emplacement of one or more oceanic plateaus, as evidenced by a globally documented shift in osmium-isotope ratios to very unradiogenic values just below the base of OAE strata that indicates a very large flux of mantle-like osmium to the open ocean at that time. Intriguingly, the PCE cooling has been shown as likely non-synchronous globally, suggesting a local control in addition to/instead of global forcing; whilst the high temperatures associated with OAE 2 appear to have continued long after the OAE itself ceased. This study presents new osmium-isotope data from the New Jersey shelf of the proto-North Atlantic (ODP Leg 174AX: Bass River), correlating the results with a previously generated sea-surface temperature dataset from the same site. These results are then compared with other temperature archives and osmium records of oceanic-plateau activity for OAE 2. The new data indicate intense oceanic-plateau activity prior to and in the earliest stages of the OAE, with a decline in mantle-osmium output before the end of the event, consistent with previous findings. However, when the osmium data are directly correlated with temperature records, both at Bass River and other sites, they clearly show that not only were high sea-surface temperatures maintained after the OAE, but also after oceanic-plateau activity (and presumably associated volcanism and CO2 emissions) fell. Thus, a reduction in mantle carbon output did not manifestly result in an immediate reduction of atmospheric CO2. Moreover, the beginning of the osmium recovery broadly correlates with the end of the PCE cooling at all locations where both osmium and temperature trends have been studied. Consequently, although the PCE cooling was not globally synchronous and its precise timing at individual locations was likely controlled by local processes, some feature of the oceanic-plateau development allowed the cooling spells to occur when plateau activity was most intense, before a reduction in that intensity stymied the spread of cold conditions and resulted in the restoration of high temperatures in the latter stages of the OAE and beyond. These data highlight the need for further work to understand the complexity of and nuances in the relationships between large-scale volcanism and major climate/environment perturbations, both for OAE 2 and for other events

Links between temperature changes and oceanic-plateau emplacement during the Cenomanian–Turonian Oceanic Anoxic Event (OAE 2)

The Cenomanian–Turonian boundary interval (~94 Ma) was marked by a period of climatic turbulence, and featured the widespread expansion of strongly oxygen-depleted conditions across a large part of the global ocean; collectively these environmental degradations are referred to as an oceanic anoxic event or OAE (specifically OAE 2 for this time interval). Extremely high sea-surface temperatures are documented for several regions during OAE 2, likely beginning at the onset of the event, but a shift towards colder conditions during the early stages of the OAE (the Plenus Cold Event or PCE) is also recorded in several locales, before a return to a very warm climate during the latter part of the crisis. The overarching high temperatures are thought to have resulted from major volcanic activity during the emplacement of one or more oceanic plateaus, as evidenced by a globally documented shift in osmium-isotope ratios to very unradiogenic values just below the base of OAE strata that indicates a very large flux of mantle-like osmium to the open ocean at that time. Intriguingly, the PCE cooling has been shown as likely non-synchronous globally, suggesting a local control in addition to/instead of global forcing; whilst the high temperatures associated with OAE 2 appear to have continued long after the OAE itself ceased. This study presents new osmium-isotope data from the New Jersey shelf of the proto-North Atlantic (ODP Leg 174AX: Bass River), correlating the results with a previously generated sea-surface temperature dataset from the same site. These results are then compared with other temperature archives and osmium records of oceanic-plateau activity for OAE 2. The new data indicate intense oceanic-plateau activity prior to and in the earliest stages of the OAE, with a decline in mantle-osmium output before the end of the event, consistent with previous findings. However, when the osmium data are directly correlated with temperature records, both at Bass River and other sites, they clearly show that not only were high sea-surface temperatures maintained after the OAE, but also after oceanic-plateau activity (and presumably associated volcanism and CO2 emissions) fell. Thus, a reduction in mantle carbon output did not manifestly result in an immediate reduction of atmospheric CO2. Moreover, the beginning of the osmium recovery broadly correlates with the end of the PCE cooling at all locations where both osmium and temperature trends have been studied. Consequently, although the PCE cooling was not globally synchronous and its precise timing at individual locations was likely controlled by local processes, some feature of the oceanic-plateau development allowed the cooling spells to occur when plateau activity was most intense, before a reduction in that intensity stymied the spread of cold conditions and resulted in the restoration of high temperatures in the latter stages of the OAE and beyond. These data highlight the need for further work to understand the complexity of and nuances in the relationships between large-scale volcanism and major climate/environment perturbations, both for OAE 2 and for other events

Upper Devonian mercury record from North America and its implications for the Frasnian–Famennian mass extinction

The Frasnian–Famennian biotic crisis (~372 Ma) was one of the “big five” mass extinction events in the Phanerozoic. This event was associated with dramatic climatic and oceanographic perturbations, including oceanic anoxia, global cooling, sea-level fluctuations. Large-scale volcanic activity is one of several possible triggers that have been suggested as the ultimate cause of this crisis, based on Hg enrichment data from widespread sections. However, there are also sections that do not show a Hg enrichment across the Frasnian–Famennian boundary. To further investigate the hypothesis of a volcanic trigger for the Frasnian–Famennian mass extinction event, mercury (Hg) analyses were performed on six North American records (five from the Appalachian Basin and one in the Illinois Basin) that include the Frasnian–Famennian boundary. There is no uniformly observed Hg enrichment at or below the Frasnian–Famennian boundary across the six sites. A potentially volcanically driven Hg anomaly is found in the Illinois Basin; however, the Hg enrichment occurs stratigraphically above the Frasnian–Famennian boundary. Mercury records from the studied sites question the timing of the volcanism that may be responsible for the mass extinction event. Further studies are needed to fully understand the geographic distribution and eruption history of the large igneous provinces, as well as the link between Hg and volcanism during the Frasnian–Famennian interval

Assessing the Contributions of Comet Impact and Volcanism Toward the Climate Perturbations of the Paleocene‐Eocene Thermal Maximum

The Paleocene‐Eocene Thermal Maximum is marked by a prominent negative carbon‐isotope excursion, reflecting the injection of thousands of gigatons of isotopically light carbon into the atmosphere. The sources of the isotopically light carbon remain poorly constrained. Utilizing a multiproxy geochemical analysis (osmium isotopes, mercury, sulfur, and platinum group elements) of two Paleocene‐Eocene boundary records, we present evidence that a comet impact and major volcanic activity likely contributed to the environmental perturbations during the Paleocene‐Eocene interval. Additionally, Earth system model simulations indicate that stratospheric sulfate aerosols, commensurate with the impact magnitude, were likely to have caused transient cooling and reduced precipitation. Plain Language Summary The Paleocene‐Eocene Thermal Maximum (~55.9 Ma) records a period of climate warming associated with the injection of thousands of gigatons of carbon into the atmosphere. However, the sources of the carbon are still unclear. Our study uses geochemical data (osmium isotopes, mercury, sulfur, and platinum group elements) of two North Atlantic Ocean drill cores across the Paleocene‐Eocene interval to suggest that both a comet impact and large‐scale volcanism occurred at that time. The comet is estimated to be small (~3.3 km diameter) with ~0.4 Gt carbon and thus cannot be responsible for the Paleocene‐Eocene Thermal Maximum. However, climate modeling suggests that the comet impact might have caused transient cooling and reduced precipitation

Does Large Igneous Province Volcanism Always Perturb the Mercury Cycle? Comparing the Records of Oceanic Anoxic Event 2 and the End-cretaceous to Other Mesozoic Events

Mercury (Hg) is increasingly being used as a sedimentary tracer of Large Igneous Province (LIP) volcanism, and supports hypotheses of a coincidence between the formation of several LIPs and episodes of mass extinction and major environmental perturbation. However, numerous important questions remain to be answered before Hg can be claimed as an unequivocal fingerprint of LIP volcanism, as well as an understanding of why some sedimentary records document clear Hg enrichment signals whilst others do not. Of particular importance is evaluating the impact of different volcanic styles on the global mercury cycle, as well as the role played by depositional processes in recording global Hg-cycle perturbations. Here, new mercury records of Cretaceous Oceanic Anoxic Event 2 (OAE 2: ?94 Ma) and the latest Cretaceous (?67?66.0 Ma) are presented. OAE 2 is associated with the emplacement of multiple, predominantly submarine, LIPs; the latest Cretaceous with subaerial volcanism of the Deccan Traps. Both of these connections are strongly supported by previously published trends towards unradiogenic osmium- (Os) isotope values in globally distributed sedimentary records. Hg data from both events show considerable variation between different locations, attributed to the effectiveness of different sediment types in registering the Hg signal, with lithologically homogeneous records documenting more clear Hg enrichments than sections with major changes in lithology such as limestones to claystones or organic-rich shales. Crucially, there is no geographically consistent signal of sedimentary Hg enrichment in stratigraphic records of either OAE 2 or the latest Cretaceous that matches Os-isotope evidence for LIP emplacement, indicating that volcanism did not cause a global Hg perturbation throughout the entire eruptive history of the LIPs formed at those times. It is suggested that the discrepancy between Os-isotope and Hg trends in records of OAE 2 is caused by the limited dispersal range of Hg emitted from submarine volcanoes compared to the global-scale distribution of Os. A similar lack of correlation between these two proxies in uppermost Cretaceous strata indicates that, although subaerial volcanism can perturb the global Hg cycle, not all subaerial eruptions will do so. These results highlight the variable impact of different volcanogenic processes on the efficiency of Hg dispersal across the globe. Factors that could influence the impact of LIP eruptions on the global mercury cycle include submarine versus subaerial volcanism, volcanic intensity or explosivity, and the potential contribution of thermogenic mercury from reactions between ascending magma and surrounding organic-rich sediments

Geochemical records of the end-Triassic Crisis preserved in a deep marine section of the Budva Basin, Dinarides, Montenegro.

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Volcanism and carbon cycle perturbations in the High Arctic during the Late Jurassic – Early Cretaceous

Dataset for Vickers, M.L., Jelby, M.E., Śliwińska, K.K., Percival, L.M., Wang, F., Sanei, H., Price, G.D., Ullmann, C.V., Grasby, S.E., Reinhardt, L. and Mather, T.A., 2023. Volcanism and carbon cycle perturbations in the High Arctic during the Late Jurassic–Early Cretaceous. Palaeogeography, Palaeoclimatology, Palaeoecology, 613, p.111412