Stable Ca and Sr isotopes support volcanically triggered biocalcification crisis during Oceanic Anoxic Event 1a

Geology ◽  
2020 ◽  
Author(s):  
Jiuyuan Wang ◽  
Andrew D. Jacobson ◽  
Bradley B. Sageman ◽  
Matthew T. Hurtgen
Keyword(s):  
Isotope Fractionation ◽  
Variable Mass ◽  
Large Igneous Province ◽  
Emergent Properties ◽  
Ionization Mass ◽  
Sr Isotope ◽  
Ocean Drilling Program ◽  
Oceanic Anoxic Event ◽  
Anoxic Event ◽  
Mass Dependent Fractionation

Large igneous province (LIP) eruptions are hypothesized to trigger biocalcification crises. The Aptian nannoconid crisis, which correlates with emplacement of the Ontong Java Plateau and Oceanic Anoxic Event 1a (OAE 1a, ca. 120 Ma), represents one such example. The Ca isotope (δ44/40Ca) system offers potential to detect biocalcification fluctuations in the rock record because Ca isotope fractionation is sensitive to precipitation rate. However, other primary and secondary processes, such as input-output flux perturbations and early diagenesis, can produce similar signals. Here, we exploit emergent properties of the stable Sr isotope (δ88/86Sr) system to resolve the origin of δ44/40Ca variability during OAE 1a. This study reports high-precision thermal ionization mass spectrometry (TIMS) δ44/40Ca, δ88/86Sr, and 87Sr/86Sr records for Hole 866A of Ocean Drilling Program Leg 143 drilled in Resolution Guyot, mid-Pacific Ocean. The samples span ~27 m.y. from the Barremian (ca. 127 Ma) to the Albian (ca. 100 Ma). The δ44/40Ca and δ88/86Sr secular trends differ from the 87Sr/86Sr record but mimic each other. δ44/40Ca and [Sr], as well as δ44/40Ca and δ88/86Sr, strongly correlate and yield slopes predicted for kinetic control, which demonstrates that variable mass-dependent fractionation rather than end-member mixing dominated the isotopic relationship between carbonates and seawater. Positive δ44/40Ca and δ88/86Sr shifts that begin before OAE 1a and peak within the interval are consistent with reduced precipitation rates. All results combined point to a cascade of effects on rate-dependent Ca and Sr isotope fractionation, which derive from the dynamic interplay between LIP eruptions and biocalcification feedbacks.

scholarly journals 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

2018 ◽  
Vol 318 (8) ◽  
pp. 799-860 ◽  
Author(s):  
Lawrence M.E. Percival ◽  
Hugh C. Jenkyns ◽  
Tamsin A. Mather ◽  
Alexander J. Dickson ◽  
Sietske J. Batenburg ◽  
...  
Keyword(s):  
Large Igneous Province ◽  
Oceanic Anoxic Event ◽  
Igneous Province ◽  
Oceanic Anoxic Event 2 ◽  
Anoxic Event ◽  
Mercury Cycle

Major palaeoenvironmental upheavals in both marine and terrestrial realms during the Toarcian oceanic anoxic event: a multi-proxy approach

2020 ◽  
Author(s):  
Francesca Galasso ◽  
Susanne Feist­Burkhardt ◽  
Annette Schmid- Röhl ◽  
Stefano Benasconi ◽  
Elke Schneebeli-Hermann
Keyword(s):  
Carbon Isotope ◽  
Seawater Temperature ◽  
Black Shales ◽  
Land Plants ◽  
Open Pit ◽  
Large Igneous Province ◽  
Isotopic Study ◽  
Data Set ◽  
Oceanic Anoxic Event ◽  
Anoxic Event

<p>The Toarcian oceanic anoxic event (TOAE) ~183 Ma is not only associated with oceanic anoxia and rapid seawater temperature increase but also with a marine mass extinction event. These biotic and environmental upheavals are linked to the emplacement of the Karoo-Ferrar large igneous province. Negative carbon excursions and widespread deposition of black shales are typical for Toarcian sedimentary successions.</p><p>The occurrence and growth of dinoflagellates is influenced by environmental factors like oxygen content, salinity, temperature and nutrient availability. For land plants, changes in dominance structure of ecosystems reflected in spore pollen assemblages can be indicative of ecological disturbance. Thus species composition (and morphology) of dinoflagellates and land plants can be used to understand major environmental perturbations.</p><p>An extensively studied TOAE section is the former Rohrbach Zement quarry at Dotternhausen (today Larfarge-Holcim) with comprehensive data of carbon isotope analyses, total organic and inorganic carbon content and rock eval analysis.<br>The Dotternhausen quarry is not accessible anymore but a new open pit in Dormettingen ~2 km NW of Dotternhausen offers excellent outcrop conditions. Litho- and biostratigraphy of the new section is well documented and calibrated to the old Dotternhausen section on subzone levels. Comparison of the two sites showed that sedimentology, geochemistry and faunal data are laterally constant. <br>Palynological analysis of 59 outcrop samples from the Dormettingen section yielded an excellent quantitative data set of the Early Toarcian Posidonienschiefer sediments. Here we provide a high-resolution, multi-proxy study of this section including chemostratigraphy, particulate organic matter and palynology in order to understand the environmental conditions during the TOAE.</p><p>Carbon isotopic study reveals a negative excursion during the TOAE, varying between -33.49‰ and -26.5‰, with a negative shift in the Falciferum Zone (Elengatum, Exeratum and Elegans Subzone) concurrent with the dinoflagellate "blackout".  The vegetation shows significant changes from a mixed assemblage of pollen and spores in the lower part of the section, to exclusively spore-bearing during the negative carbon isotope excursion. The isotopic signal, the marine dinoflagellate “blackout” and the changes in terrestrial vegetation indicate/document major palaeoenvironmental upheavals in both the marine and terrestrial realms.</p>

Sills Sautéing Shales: Did Karoo Intrusions into the Ecca Formation cause the Toarcian Ocean Anoxic Event?

2020 ◽  
Author(s):  
Sean P. Gaynor ◽  
Urs Schaltegger ◽  
Henrik Svensen
Keyword(s):  
Climate Change ◽  
Global Change ◽  
Global Climate Change ◽  
Short Pulse ◽  
Global Climate ◽  
Large Igneous Province ◽  
Oceanic Anoxic Event ◽  
Karoo Basin ◽  
Anoxic Event ◽  
Intrusive Activity

<p>Eruptions of Large Igneous Provinces (LIP) are commonly correlated with global climate change, and environmental, as well as biological, crises. However, establishing a causative link via chemical and physical proxies for global change is more complicated and often ambiguous. As technical improvements have allowed for increasingly higher precision dates especially in U/Pb dating, it is possible to better assess hypotheses connecting LIP’s and environmental impact via their contemporaneity. Here, we focus on the early Jurassic period, which includes a period of global change known as the Toarcian oceanic anoxic event (TOAE), as well as emplacement of the Karoo Large Igneous Province (K-LIP). Previous work has tied these two events together due to overlapping chronology and observed metamorphism and degassing (e.g., Svensen et al., 2012; Sell et al., 2014), and excellent exposure allows for extensive sampling of both the intrusive and extrusive components of the K-LIP. Therefore it is possible to directly study the influence of intrusive LIP magmatism on potential climate forcing.</p><p>The K-LIP is comprised of a suite of basaltic lava flows, sills, dike swarms, centered in southern Africa. Approximately 340,000 km<sup>3</sup> of sills are interlaid within the Karoo Basin, and therefore served as significant heat source to the basin upon emplacement. While much of the sedimentary rocks of the basin are siliciclastic, the Ecca Group contains organic-rich facies and hosts 160,000 km<sup>3</sup> of basaltic sills (Svensen et al., 2012). This unit is therefore uniquely capable of generating large volumes of thermogenic gas through thermal metamorphism of the organic matter of the shale. Previous mass balance calculations indicate that between 7,000 and 27,000 Gt of CO<sub>2</sub> equivalents was released through metamorphic reactions in contact aureoles within the Ecca Group (Svensen et al. 2007). If intrusive magmatism was short lived within this formation, causing rapid volatilization and degassing from the shales, than this event could represent a mechanism to drive a short pulse of global climate change. Previous studies have shown that intrusions are coeval with the TOAE (Svensen et al., 2012; Corfu et al. 2016), however higher-precision geochronology data from the sills is necessary to determine if the flux and timing of thermogenic gases from the basin was sufficiently high to destabilize Earth’s climate. In order to test the hypothesis, we present single crystal U-Pb zircon dates from sills across the Ecca Group. These data will be used (i) to quantify the duration and flux rate of carbon gas during the intrusive event, and (ii) to better understand how and to what extent K-LIP intrusive activity and associated thermogenic gas release of Ecca wall rocks were able to drive global climate change.</p><p> </p><p>Corfu, F., et al., (2016) EPSL, 434, 349-352.</p><p>Sell, B., et al., (2014) EPSL, 408, 48-56.</p><p>Svensen, H., et al., (2007) EPSL, 3-4, 554-566.</p><p>Svensen, H., et al., (2012) EPSL, 325-326, 1–9.</p>

Record of the Toarcian oceanic anoxic event in the Grands Causses Basin (southern France) and its implications for vertebrate preservation

2021 ◽  
Author(s):  
Brahimsamba Bomou ◽  
Guillaume Suan ◽  
Jan Schlögl ◽  
Anne-Sabine Grosjean ◽  
Baptiste Suchéras-Marx ◽  
...  
Keyword(s):  
Soft Tissues ◽  
Clay Mineralogy ◽  
Lower Jurassic ◽  
Large Igneous Province ◽  
Volcanic Emissions ◽  
Oceanic Anoxic Event ◽  
Environmental Perturbations ◽  
Anoxic Event ◽  
Posidonia Shale ◽  
Rock Eval

<p>Paleontological excavations realized by our group in Toarcian shales (Lower Jurassic) of the Grands Causses Basin in Roqueredonde (Hérault, France), yielded several specimens of marine vertebrates. The newly discovered specimens are partly or entirely preserved in anatomical connection and include a partial ichthyosaur skeleton with soft tissues, and a 4 m-long thalattosuchian longirostrine marine crocodile. A multi-proxy approach has been developed (XRD-bulk and clay mineralogy, Rock-Eval pyrolysis, phosphorus and mercury contents) in order to replace these findings in a well-defined temporal and paleoenvironmental context, and hence constrain the factors that led to their remarkable preservation. The fossiliferous succession exposes a 3 m-thick upper Pliensbachian interval of marl and nodular carbonate beds, overlain by a 3 m-thick interval of lower Toarcian laminated shales and limestone beds. Our high-resolution ammonite biostratigraphy, combined with inorganic and organic carbon isotope chemostratigraphy, shows that the fossiliferous Toarcian strata were deposited at a time of global warming and major carbon cycle perturbation known as the Toarcian Oceanic Anoxic Event (T-OAE). The studied succession shows several similarities with the classical coeval fossiliferous levels of the Posidonia Shale in SW Germany, including high organic matter and hydrocarbon contents as well as extremely reduced sedimentation rates. These results indicate that the unusual richness in well-preserved vertebrates of the studied site can be explained by a combination of warming-induced, low salinity and stratified waters, prolonged seafloor anoxia and reduced dilution by low carbonate and terrigenous input due to rapid sea-level rise. Our results also reveal a significant peak in mercury at the base of the T-OAE interval, consistent with that recorded in several coeval sections (e.g. Portugal, Morocco, Argentina, Chile). This mercury anomaly, most likely resulting from intense volcanic activity Karoo-Ferrar large igneous province, suggests that widespread exceptional vertebrate preservation during the T-OAE was initiated by a suite of severe environmental perturbations ultimately triggered by intense volcanic emissions.</p>

scholarly journals Regional chronostratigraphic synthesis of the Cenomanian-Turonian Oceanic Anoxic Event 2 (OAE2) interval, Western Interior Basin (USA): New Re-Os chemostratigraphy and 40Ar/39Ar geochronology

2020 ◽  
Author(s):  
Matthew M. Jones ◽  
Bradley B. Sageman ◽  
David Selby ◽  
Brian R. Jicha ◽  
Brad S. Singer ◽  
...  
Keyword(s):  
Stable Carbon Isotope ◽  
Rapid Onset ◽  
Large Igneous Province ◽  
Oceanic Anoxic Event ◽  
The North ◽  
Marine Carbonate ◽  
Oceanic Anoxic Event 2 ◽  
Anoxic Event ◽  
Western Interior Basin ◽  
Astronomical Tuning

Fluctuations in depositional conditions during the onset of severe climate events in Earth history predispose stratigraphic archives to hiatuses, often hindering complete reconstructions of paleoclimate events and their triggers. Several studies have proposed that a hiatus of unknown duration exists at the base of Oceanic Anoxic Event 2 (OAE2) in the North American Western Interior Basin at the base Turonian global boundary stratotype section and point (GSSP) in Pueblo, Colorado, which potentially influences integrated radioisotopic, biostratigraphic, and astrochronologic age models of the Cenomanian-Turonian boundary interval. To quantify the duration of this hiatus, refine the chronology of OAE2, and assess marine geochemical perturbations associated with the onset of the event, we present new 40Ar/39Ar dates from regional bentonites along with a new proximal-distal chemostratigraphic transect of the epeiric Western Interior Basin (WIB), including initial osmium isotope (Osi) and stable carbon isotope (δ13C) data. The new 40Ar/39Ar age determinations confirm and further constrain previous estimates of Cenomanian-Turonian boundary timing. Further, the regional chemostratigraphic synthesis demonstrates the conformity of the OAE2 successions correlated to Pueblo, shows that the duration of the lag between the onset of the Osi and δ13C excursions is ∼60 k.y., and thus constrains the magnitude of the pre-OAE2 hiatus in Pueblo to less than this value. The new astronomically tuned, conformable Osi record across the onset of OAE2 captures a geologically rapid onset of large igneous province volcanism, consistent with other records, such that the addition of CO2 to the ocean-atmosphere system may have driven changes in marine carbonate chemistry. Additionally, the refined chronostratigraphy of OAE2 and the Cenomanian-Turonian boundary in the central WIB improves correlation with other records, such as those in the Eagle Ford Group, Texas. The correlations highlight that discrepancies among OAE2 age models from globally distributed sections commonly stem from differing definitions of the event and uncertainties associated with astronomical tuning, in addition to stratigraphic preservation.

scholarly journals Uranium isotope evidence for two episodes of deoxygenation during Oceanic Anoxic Event 2

2018 ◽  
Vol 115 (12) ◽  
pp. 2918-2923 ◽  
Author(s):  
Matthew O. Clarkson ◽  
Claudine H. Stirling ◽  
Hugh C. Jenkyns ◽  
Alexander J. Dickson ◽  
Don Porcelli ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Large Igneous Province ◽  
Global Ocean ◽  
Uranium Isotopes ◽  
Carbonate Sediments ◽  
Cold Event ◽  
Oceanic Anoxic Event ◽  
Oceanic Anoxic Event 2 ◽  
Anoxic Event ◽  
Isotope Evidence

Oceanic Anoxic Event 2 (OAE 2), occurring ∼94 million years ago, was one of the most extreme carbon cycle and climatic perturbations of the Phanerozoic Eon. It was typified by a rapid rise in atmospheric CO2, global warming, and marine anoxia, leading to the widespread devastation of marine ecosystems. However, the precise timing and extent to which oceanic anoxic conditions expanded during OAE 2 remains unresolved. We present a record of global ocean redox changes during OAE 2 using a combined geochemical and carbon cycle modeling approach. We utilize a continuous, high-resolution record of uranium isotopes in pelagic and platform carbonate sediments to quantify the global extent of seafloor anoxia during OAE 2. This dataset is then compared with a dynamic model of the coupled global carbon, phosphorus, and uranium cycles to test hypotheses for OAE 2 initiation. This unique approach highlights an intra-OAE complexity that has previously been underconstrained, characterized by two expansions of anoxia separated by an episode of globally significant reoxygenation coincident with the “Plenus Cold Event.” Each anoxic expansion event was likely driven by rapid atmospheric CO2injections from multiphase Large Igneous Province activity.

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