The palaeoenvironmental context of Toarcian vertebrate-yielding shales of southern France (Hérault)

AbstractThe Early Jurassic was marked by several episodes of rapid climate changes and environmental perturbation. These changes culminated during the Toarcian Oceanic Anoxic Event (T-OAE), an episode of global warming that led to the widespread deposition of organic-rich shales. The Toarcian shales of NW Europe have also yielded exceptionally preserved fossils of marine vertebrates and invertebrates, but the potential links between the occurrences of these exceptionally preserved fossils and the T-OAE remain poorly investigated. Palaeontological excavations realised in Toarcian strata near Lodève (Hérault, S France) have yielded several specimens of marine vertebrates and abundant invertebrate fauna. We have developed a multi-proxy approach (ammonite biostratigraphy, XRD-bulk mineralogy, Rock-Eval pyrolysis, stable isotopes, trace element, phosphorus and mercury contents) to place these findings in a well-defined temporal and palaeoenvironmental context, and hence constrain the factors that led to their remarkable preservation. The Jenkyns Event interval, unambiguously identified at the base of the Toarcian organic-rich shales by a 5 ‰ negative carbon isotope excursion (CIE), records higher mercury fluxes, which suggest a causal link with intense volcanic activity of the Karoo-Ferrar large igneous province. This interval is very condensed and unfossiliferous, and might have been deposited under abnormally low salinity conditions. Our data show that the deposition of the vertebrate-yielding horizons post-dated the T-OAE by several hundreds of kyr, and took place during a prolonged period of widespread oxygen-deficiency and elevated carbon burial. Our results indicate that the unusual richness in vertebrates of the studied site can be explained by a combination of regional factors such as warming-induced, prolonged seafloor anoxia, and more local factors, such as extreme condensation due to reduced dilution by carbonate and detrital input.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5509789

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Hardground, gap and thin black shale: spatial heterogeneity of arrested carbonate sedimentation during the Jenkyns Event (T-OAE) in a Tethyan pelagic basin (Gerecse Mts, Hungary)

Geological Society London Special Publications ◽

10.1144/sp514-2020-266 ◽

2021 ◽

pp. SP514-2020-266

Author(s):

Tamás Müller ◽

Gregory D. Price ◽

Emanuela Mattioli ◽

Máté Zs. Leskó ◽

Ferenc Kristály ◽

...

Keyword(s):

Carbon Isotope ◽

Black Shale ◽

Carbonate Production ◽

Content Type ◽

Oceanic Anoxic Event ◽

Carbonate Sedimentation ◽

Environmental Perturbations ◽

Carbon Isotope Excursion ◽

Supplementary Material ◽

Tethys Ocean

AbstractThe Jenkyns Event or Toarcian Oceanic Anoxic Event (T-OAE) was an episode of severe environmental perturbations reflected in carbon isotope and other geochemical anomalies. Although well studied in the epicontinental basins in NW Europe, its effects are less understood in open marine environments. Here we present new geochemical (carbon isotope, CaCO3, [Mn]) and nannofossil biostratigraphic data from the Tölgyhát and Kisgerecse sections in the Gerecse Hills (Hungary). These sections record pelagic carbonate sedimentation near the margin of the Tethys Ocean. A negative carbon isotope excursion of ∼6‰ is observed in the Tölgyhát section, in a condensed clay and black shale layer where the CaCO3 content drops in association with the Jenkyns Event. At Kisgerecse, bio- and chemostratigraphic data suggest a gap in the lower Toarcian. The presence of an uppermost Pliensbachian hardground, absence of the lowermost Toarcian Tenuicostatum ammonite zone, and the condensed record of the Jenkyns Event at Tölgyhát, together with a condensed Tenuicostatum Zone and the missing negative carbon isotope anomaly at Kisgerecse implies arrested carbonate sedimentation. A calcification crisis and sea-level rise together led to a decrease in carbonate production and terrigenous input, suggesting that volcanogenic CO2-driven global warming may have been their common cause.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5355342

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Biotic and stable-isotope characterization of the Toarcian Ocean Anoxic Event through a carbonate-clastic sequence from Somerset, UK

Geological Society London Special Publications ◽

10.1144/sp514-2020-263 ◽

2021 ◽

pp. SP514-2020-263

Author(s):

Ian Boomer ◽

Philip Copestake ◽

Kevin Page ◽

John Huxtable ◽

Tony Loy ◽

...

Keyword(s):

Stable Isotope ◽

Laminated Sediments ◽

Content Type ◽

Oceanic Anoxic Event ◽

The United Kingdom ◽

Clastic Sediments ◽

Carbon Isotope Excursion ◽

Anoxic Event ◽

Supplementary Material

AbstractThis study focuses on a condensed sequence of alternating carbonate-clastic sediments of the Barrington Member, Beacon Limestone Formation (latest Pliensbachian to early Toarcian) from Somerset (south west England). Abundant ammonites confirm (apart from the absence of the Clevelandicum and Tenuicostatum ammonite subchronozones) the presence of Hawskerense Subchronozone to Fallaciosum-Bingmanni subchronozones. Well-preserved, sometimes diverse assemblages of ostracods, foraminifera, nannofossils and low diversity dinoflagellate assemblages support the chronostratigraphic framework. Stable-isotope analyses demonstrate the presence of a carbon isotope excursion (CIE), relating to the Toarcian Oceanic Anoxic Event (T-OAE), within the early Toarcian. Faunal, geochemical and sedimentological evidence suggest that deposition largely took place in a relatively deep-water (sub-wave base), mid-outer shelf environment under a well-mixed water column. However, reduced benthic diversity, the presence of weakly-laminated sediments and changes in microplankton assemblage composition within the T-OAE indicates dysoxic, but probably never anoxic, bottom-water conditions during this event. The onset of the CIE coincides with extinction in the nannofossils and benthos, including the disappearance of the ostracod suborder Metacopina. Faunal evidence indicates connectivity with the Mediterranean region, not previously recorded for the United Kingdom during the early Toarcian.Supplementary material at https://doi.org/10.25500/edata.bham.00000574

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Molecular and petrographical evidence for lacustrine environmental and biotic change in the palaeo-Sichuan mega-lake (China) during the Toarcian Oceanic Anoxic Event

Geological Society London Special Publications ◽

10.1144/sp514-2021-2 ◽

2021 ◽

pp. SP514-2021-2

Author(s):

Weimu Xu ◽

Johan W. H. Weijers ◽

Micha Ruhl ◽

Erdem F. Idiz ◽

Hugh C. Jenkyns ◽

...

Keyword(s):

Organic Matter ◽

Sichuan Basin ◽

Large Scale ◽

Algal Growth ◽

Black Shales ◽

Content Type ◽

Oceanic Anoxic Event ◽

Anoxic Event ◽

Supplementary Material ◽

The Sichuan Basin

AbstractThe organic-rich upper Lower Jurassic Da'anzhai Member (Ziliujing Formation) of the Sichuan Basin, China is the first stratigraphically well-constrained lacustrine succession associated with the Toarcian Oceanic Anoxic Event (T-OAE; ∼183 Ma). The formation and/or expansion of the Sichuan mega-lake, likely one of the most extensive fresh-water systems to have existed on the planet, is marked by large-scale lacustrine organic productivity and carbon burial during the T-OAE, possibly due to intensified hydrological cycling and nutrient supply. New molecular biomarker and organic petrographical analyses, combined with bulk organic and inorganic geochemical and palynological data, are presented here, providing insight into aquatic productivity, land-plant biodiversity, and terrestrial ecosystem evolution in continental interiors during the T-OAE. We show that lacustrine algal growth during the T-OAE accounted for a significant organic-matter flux to the lakebed in the palaeo-Sichuan mega-lake. Lacustrine water-column stratification during the T-OAE facilitated the formation of dysoxic-anoxic conditions at the lake bottom, favouring organic-matter preservation and carbon sequestration into organic-rich black shales in the Sichuan Basin. We attribute the palaeo-Sichuan mega-lake expansion to enhanced hydrological cycling in a more vigorous monsoonal climate in the hinterland during the T-OAE greenhouse.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5433544

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The early Toarcian extinction event and associated Pliensbachian-Toarcian palaeoenvironmental perturbations in Bulgaria

10.7287/peerj.preprints.27948 ◽

2019 ◽

Author(s):

Autumn Pugh ◽

Crispin TS Little ◽

Ivan P Savov ◽

Lubomir Metodiev ◽

Paul B Wignall ◽

...

Keyword(s):

Carbon Isotope ◽

Oxygen Deficiency ◽

Lower Jurassic ◽

Significant Loss ◽

Large Igneous Province ◽

Driving Mechanism ◽

Oceanic Anoxic Event ◽

Biotic Crisis ◽

Marine Realm ◽

Balkan Mountains

The Early Toarcian was characterised by the eruption of the Karoo-Ferrar large igneous province (LIP), rapid global warming, significant perturbations in the global carbon cycle, the development of widespread anoxia known as the Early Toarcian Oceanic Anoxic Event (T-OAE) and a biotic crisis in the marine realm known as the Early Toarcian Mass Extinction (ETME). Despite the purported global nature of these environmental and biotic changes, the majority of records come from Western European sections, and remain particularly focused on settings in which the T-OAE was clearly expressed. Fewer studies focus on sections where the manifestation of ocean deoxygenation appears to have been considerably weaker, or even absent. We herein focus on Lower Jurassic successions of the Moesian Basin in the Balkan Mountains of the Balkan Mountains (Bulgaria) that were deposited on an open-ocean facing carbonate shelf. The Bulgarian δ13C and δ18O profiles show similar trends through the Lower Jurassic to coeval European sections, suggesting that seawater in the Moesian Basin was recording global palaeoclimatic and palaeoceanographic conditions during this time. Analysis of the carbon isotope record reveals a broad positive carbon isotope excursion (CIE) of 3‰ in δ13Cbel through the Early Toarcian, interrupted by a negative CIE of 3.5‰ recorded in organic carbon (Tenuicostatum–Falciferum zones). Progressive warming of seawater and increased influx of freshwater into the Moesian Basin through the Early Toarcian is recorded in δ18Obel isotopes. Such changes are attributed to the eruption of the Karoo-Ferrar LIP, reflected in the Moesian Basin by an enrichment in Mercury (Hg) recorded as a shift in sedimentary Hg/TOC values synchronous with the negative CIE. A biotic crisis is recorded amongst bivalves and considered to be part of the ETME, which is here recorded in Bulgaria for the first time. Although a significant loss amongst bivalves during the ETME often coincides with the spread of anoxia, this link is not clearly seen in Bulgaria as geochemical and sedimentological records do not support the prevalence of anoxic conditions. As such, oxygen deficiency cannot be considered a key driving mechanism for the ETME in this part of the ocean and other factors such as rapid warming may have been more important in this central Tethyan region.

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Primary versus carbonate production in the Toarcian, a case study from the Llanbedr borehole (Mochras Farm, Wales)

Geological Society London Special Publications ◽

10.1144/sp514-2021-19 ◽

2021 ◽

pp. SP514-2021-19

Author(s):

Alessandro Menini ◽

Emanuela Mattioli ◽

Stephen P. Hesselbo ◽

Micha Ruhl ◽

Guillaume Suan

Keyword(s):

Sea Water ◽

Initial Perturbation ◽

Carbonate Production ◽

Nutrient Delivery ◽

Content Type ◽

High Productivity ◽

Oceanic Anoxic Event ◽

The Core ◽

C Isotopes ◽

Supplementary Material

AbstractThe leading hypothesis for the Toarcian oceanic anoxic event (T-OAE; ∼183Ma) and the associated negative C-isotope excursion is the massive release of 12C favouring greenhouse and continental weathering. The nutrient delivery to shallow-basins supported productivity and, because of O2-consumption by organic-matter respiration, anoxia development. However, several works showed that calcareous nannoplankton experienced a decrease during the T-OAE. Nannofossil fluxes measured in the Llanbedr borehole (Mochras Farm; Wales, UK) were the highest prior to the negative C-isotope excursion, along with high amounts of taxa indicative of nutrient-rich environments (Biscutaceae). Such conditions attest to high productivity. Fluxes show the lowest values in the core of the event, along with a size decrease of Schizosphaerella and a peak in Calyculaceae. The recovery of nannofossil fluxes and Schizosphaerella size occurred concomitant with the return of C-isotopes to more positive values. Concomitantly, deep-dwellers (Crepidolithus crassus) dominated, indicating a recovery of the photic-zone productivity. These observations demonstrate that the cascade of environmental responses to the initial perturbation was more complex than previously considered. In spite of elevated nutrient delivery to epicontinental basins in the early Toarcian, carbonate and primary productions of nannoplankton were depressed in the core the T-OAE likely because of prolonged thermohaline sea-water stratification.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5541440

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Thallium isotopes reveal protracted anoxia during the Toarcian (Early Jurassic) associated with volcanism, carbon burial, and mass extinction

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1803478115 ◽

2018 ◽

Vol 115 (26) ◽

pp. 6596-6601 ◽

Cited By ~ 42

Author(s):

Theodore R. Them ◽

Benjamin C. Gill ◽

Andrew H. Caruthers ◽

Angela M. Gerhardt ◽

Darren R. Gröcke ◽

...

Keyword(s):

Mass Extinction ◽

Biological Evolution ◽

Oxygen Depletion ◽

Early Jurassic ◽

Large Igneous Province ◽

Mass Extinctions ◽

Oceanic Anoxic Event ◽

Carbon Burial ◽

Anoxic Basins ◽

Bottom Waters

For this study, we generated thallium (Tl) isotope records from two anoxic basins to track the earliest changes in global bottom water oxygen contents over the Toarcian Oceanic Anoxic Event (T-OAE; ∼183 Ma) of the Early Jurassic. The T-OAE, like other Mesozoic OAEs, has been interpreted as an expansion of marine oxygen depletion based on indirect methods such as organic-rich facies, carbon isotope excursions, and biological turnover. Our Tl isotope data, however, reveal explicit evidence for earlier global marine deoxygenation of ocean water, some 600 ka before the classically defined T-OAE. This antecedent deoxygenation occurs at the Pliensbachian/Toarcian boundary and is coeval with the onset of initial large igneous province (LIP) volcanism and the initiation of a marine mass extinction. Thallium isotopes are also perturbed during the T-OAE interval, as defined by carbon isotopes, reflecting a second deoxygenation event that coincides with the acme of elevated marine mass extinctions and the main phase of LIP volcanism. This suggests that the duration of widespread anoxic bottom waters was at least 1 million years in duration and spanned early to middle Toarcian time. Thus, the Tl data reveal a more nuanced record of marine oxygen depletion and its links to biological change during a period of climatic warming in Earth’s past and highlight the role of oxygen depletion on past biological evolution.

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Ocean acidification during the early Toarcian extinction event: Evidence from boron isotopes in brachiopods

Geology ◽

10.1130/g47781.1 ◽

2020 ◽

Vol 48 (12) ◽

pp. 1184-1188 ◽

Cited By ~ 4

Author(s):

Tamás Müller ◽

Hana Jurikova ◽

Marcus Gutjahr ◽

Adam Tomašových ◽

Jan Schlögl ◽

...

Keyword(s):

Ocean Acidification ◽

First Record ◽

Large Igneous Province ◽

Two Phase ◽

Carbonate Production ◽

Oceanic Anoxic Event ◽

Carbon Burial ◽

Seawater Ph ◽

Short Period ◽

Organic Carbon Burial

Abstract The loss of carbonate production during the Toarcian Oceanic Anoxic Event (T-OAE, ca. 183 Ma) is hypothesized to have been at least partly triggered by ocean acidification linked to magmatism from the Karoo-Ferrar large igneous province (southern Africa and Antarctica). However, the dynamics of acidification have never been directly quantified across the T-OAE. Here, we present the first record of temporal evolution of seawater pH spanning the late Pliensbachian and early Toarcian from the Lusitanian Basin (Portugal) reconstructed on the basis of boron isotopic composition (δ11B) of brachiopod shells. δ11B declines by ∼1‰ across the Pliensbachian-Toarcian boundary (Pl-To) and attains the lowest values (∼12.5‰) just prior to and within the T-OAE, followed by fluctuations and a moderately increasing trend afterwards. The decline in δ11B coincides with decreasing bulk CaCO3 content, in parallel with the two-phase decline in carbonate production observed at global scales and with changes in pCO2 derived from stomatal indices. Seawater pH had declined significantly already prior to the T-OAE, probably due to the repeated emissions of volcanogenic CO2. During the earliest phase of the T-OAE, pH increased for a short period, likely due to intensified continental weathering and organic carbon burial, resulting in atmospheric CO2 drawdown. Subsequently, pH dropped again, reaching the minimum in the middle of the T-OAE. The early Toarcian marine extinction and carbonate collapse were thus driven, in part, by ocean acidification, similar to other Phanerozoic events caused by major CO2 emissions and warming.

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The early Toarcian extinction event and associated Pliensbachian-Toarcian palaeoenvironmental perturbations in Bulgaria

10.7287/peerj.preprints.27948v1 ◽

2019 ◽

Author(s):

Autumn Pugh ◽

Crispin TS Little ◽

Ivan P Savov ◽

Lubomir Metodiev ◽

Paul B Wignall ◽

...

Keyword(s):

Carbon Isotope ◽

Oxygen Deficiency ◽

Lower Jurassic ◽

Significant Loss ◽

Large Igneous Province ◽

Driving Mechanism ◽

Oceanic Anoxic Event ◽

Biotic Crisis ◽

Marine Realm ◽

Balkan Mountains

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Low-Ti gabbroic pluton in Dali, SW China: new evidence for back-arc lithospheric melting inducing the early-stage magmatism of the Emeishan large igneous province

Journal of the Geological Society ◽

10.1144/jgs2020-224 ◽

2021 ◽

pp. jgs2020-224

Author(s):

Bei Zhu ◽

Zhaojie Guo ◽

Shaonan Zhang ◽

Ning Ye ◽

Ziye Lu ◽

...

Keyword(s):

Early Stage ◽

Large Igneous Province ◽

Spinel Peridotite ◽

Heavy Rare Earth Element ◽

Content Type ◽

Igneous Province ◽

Supplementary Material ◽

Back Arc ◽

Emeishan Lip ◽

Yangtze Plate

The latest studies proved contribution of the Emeishan mantle plume (the widely-regarded origin of the Emeishan LIP in the western Yangtze Plate. LIP: large igneous province) to the Palaeo-Tethys subduction. However, whether the Palaeo-Tethys subduction oppositely affected the formation of the Emeishan LIP remains poorly understood. Here, we report geochronological, petrological, geochemical and isotopic studies of a gabbroic intrusion in this LIP, located in Jiangwei, the Dali area. The gabbro has a weighted mean SHRIMP U-Pb age of ∼262 Ma. Key geochemical features include Nb, Ta and Ti depletion; Th, U and Sr enrichment, low light/heavy rare earth element ratios and ∼0.707 87Sr/86Sr(t) and ∼-0.21 εNd(t) values. We conducted pMELTS thermodynamic modeling and batch melting calculations to evaluate the origin and evolution of the gabbro, based on real components of low-Ti picrites and xenolith of the Yangtze lithosphere. The results support 3% melting of a hydrated spinel peridotite source from the Yangtze lithosphere can produce magma equivalent to the gabbro components. Integrating this conclusion with tectonic background of the western Yangtze Plate and volcano-stratigraphic record of the Emeishan LIP, we infer the early-stage magmatism of the Emeishan LIP was triggered by Paleo-Tethys back-arc extension with fluid modification from subductional slab.Supplementary material:https://doi.org/10.6084/m9.figshare.c.5433267

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Initial Cenozoic Magmatic Activity in East Africa: New Geochemical Constraints on Magma Distribution within the Eocene Continental Flood Basalt Province

Geological Society London Special Publications ◽

10.1144/sp518-2020-262 ◽

2021 ◽

pp. SP518-2020-262

Author(s):

R. Alex Steiner ◽

Tyrone O. Rooney ◽

Guillaume Girard ◽

Nick Rogers ◽

Cynthia Ebinger ◽

...

Keyword(s):

Shear Velocity ◽

Flood Basalt ◽

Main Phase ◽

Large Igneous Province ◽

Southern Ethiopia ◽

East African ◽

Continental Flood Basalt ◽

Content Type ◽

Supplementary Material ◽

African Rift

AbstractThe initial interaction between material rising from the African Large Low Shear Velocity Province and the African lithosphere manifests as the Eocene continental large igneous province (LIP), centered on southern Ethiopia and northern Kenya. Here we present a geographically well-distributed geochemical dataset comprising the flood basalt lavas of the Eocene continental LIP to refine the regional volcano-stratigraphy into three distinct magmatic units: (1) the highly-alkaline small-volume Akobo Basalts (49.4–46.6 Ma), representing the initial phase of flood basalt volcanism derived from the melting of lithospheric-mantle metasomes, (2) the primitive and spatially restricted Amaro Basalts (45.2–39.58 Ma) representing the early main phase of flood basalt volcanism derived from the melting of the upwelling thermochemical anomaly, and (3) the spatially extensive Gamo-Makonnen magmatic unit (38-28 Ma) representing the mature main phase of flood basalt volcanism that has undergone significant processing within the lithosphere resulting in relatively homogeneous compositions. The focused intrusion of these main phase magmas over 10 m.y. preconditioned the African lithosphere for the localization of strain during subsequent episodes of lithospheric stretching. The focusing of strain into the region occupied by this continental LIP may have contributed to the initial extension in SW Ethiopia associated with the East African Rift.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5557626

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