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>

scholarly journals An open marine record of the Toarcian oceanic anoxic event

2011 ◽  
Vol 3 (1) ◽  
pp. 385-410 ◽  
Author(s):  
D. R. Gröcke ◽  
R. S. Hori ◽  
J. Trabucho-Alexandre ◽  
D. B. Kemp ◽  
L. Schwark
Keyword(s):  
Organic Matter ◽  
Carbon Cycle ◽  
Carbon Isotope ◽  
Isotope Composition ◽  
Global Carbon Cycle ◽  
Open Ocean ◽  
Black Shales ◽  
Oceanic Anoxic Event ◽  
Anoxic Event ◽  
Global Carbon

Abstract. Oceanic anoxic events were time intervals in the Mesozoic characterized by widespread distribution of marine organic-rich sediments (black shales) and significant perturbations in the global carbon cycle. The expression of these perturbations is globally recorded in sediments as excursions in the carbon isotope record irrespective of lithology or depositional environment. During the Early Toarcian, black shales were deposited on the epi- and peri-continental shelves of Pangaea and these sedimentary rocks are associated with a pronounced (ca. 7‰) negative (organic) carbon isotope excursion (CIE) which is thought to be the result of a major perturbation in the global carbon cycle. For this reason, the Early Toarcian is thought to represent an oceanic anoxic event (the T-OAE). Associated with this event, there were pronounced perturbations in global weathering rates and seawater temperatures. Although it is commonly asserted that the T-OAE is a global event and that the distribution of black shales is likewise global, an isotopic and/or organic-rich expression of this event has as yet only been recognized on epi- and peri-continental Pangaean localities. To address this issue, the carbon isotope composition of organic matter (δ13Corg) of Early Toarcian cherts from Japan that were deposited in the open Panthalassa Ocean was analysed. The results show the presence of a major (>6‰) negative excursion in δ13Corg that, based on radiolarian biostratigraphy, is a correlative of the Early Toarcian negative CIE known from European epicontinental strata. Furthermore, a secondary ca. −2‰ excursion in δ13Corg is also recognized lower in the studied succession that, within the current biostratigraphical resolution, is likely to represent the excursion that occurs close to the Pliensbachian/Toarcian boundary and which is also recorded in European epicontinental successions. These results from the open ocean realm suggest that, in conjunction with other previously published datasets, these major Early Jurassic carbon cycle perturbations affected all active global reservoirs of the exchangeable carbon cycle (deep marine, shallow marine, atmospheric). An extremely negative δ13Corg value (−57‰) during the peak of the T-OAE is also reported, which suggests that the inferred open ocean mid-water oxygen minimum layer within which these sediments are thought to have been deposited was highly enriched in methanotrophic bacteria, since these organisms are the only plausible producers of such 12C-enriched organic matter.

Astronomical pacing of relative sea level during Oceanic Anoxic Event 2: Preliminary studies of the expanded SH#1 Core, Utah, USA

2019 ◽  
Vol 131 (9-10) ◽  
pp. 1702-1722 ◽  
Author(s):  
Matthew M. Jones ◽  
Bradley B. Sageman ◽  
Rosie L. Oakes ◽  
Amanda L. Parker ◽  
R. Mark Leckie ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Sea Level ◽  
Carbon Isotope ◽  
Geochemical Data ◽  
Relative Sea Level ◽  
Data Set ◽  
Sequence Stratigraphic ◽  
Oceanic Anoxic Event ◽  
Oceanic Anoxic Event 2 ◽  
Anoxic Event

AbstractProximal marine strata of the North American Western Interior Basin (WIB) preserve a rich record of biotic turnover during Oceanic Anoxic Event 2 (OAE2; ca. 94 Ma), a pronounced Late Cretaceous carbon cycle perturbation interpreted to reflect global warming, widespread hypoxia, and possible ocean acidification. To develop a more robust synthesis of paleobiologic and geochemical data sets spanning this Earth-life transition, we drilled the 131 m Smoky Hollow #1 Core (SH#1), on the Kaiparowits Plateau of southern Utah, USA, recovering the Cenomanian–Turonian Boundary (CTB) interval in the Tropic Shale Formation. A 17.5 m positive excursion in high-resolution bulk carbon isotope chemostratigraphy (δ13Corg) of SH#1 characterizes the most expanded OAE2 record recovered from the mid-latitudes of the WIB.Depleted values in a paired carbonate carbon isotope (δ13Ccarb) chemostratigraphy cyclically punctuate the OAE2 excursion. These depletions correspond to intervals in the core with a higher degree of carbonate diagenesis and correlate well to an existing sequence stratigraphic framework of flooding surfaces in the shoreface facies of the Markagunt Plateau (∼100 km west). We detect statistically significant evidence for astronomical cycles in the δ13Ccarb data set, imparted by diagenesis at flooding surfaces, and develop a floating astronomical time scale (ATS) for the study interval. Stable eccentricity cycles (405 k.y.) align with stratigraphic sequences and associated trends in sedimentation rate, and short eccentricity cycles (∼100 k.y.) pace nested parasequences. These results confirm an astronomical signal and, therefore, climatic forcing of relative sea level during OAE2 in the WIB. Furthermore, cross-basin correlation of the ATS and expanded δ13C chemostratigraphy of SH#1 suggests that these transgressive-regressive parasequences modulated siliciclastic sediment delivery in the seaway and contributed to deposition of prominent rhythmically bedded CTB units across the WIB, including the Bridge Creek Limestone. The presented approach to analysis of these proximal offshore siliciclastic facies links early diagenetic influences on chemostratigraphy to astronomically modulated sequence stratigraphic horizons, and helps to resolve rates of paleobiologic and paleoenvironmental change during a significant Mesozoic carbon cycle perturbation.

scholarly journals An open ocean record of the Toarcian oceanic anoxic event

Solid Earth ◽  
2011 ◽  
Vol 2 (2) ◽  
pp. 245-257 ◽  
Author(s):  
D. R. Gröcke ◽  
R. S. Hori ◽  
J. Trabucho-Alexandre ◽  
D. B. Kemp ◽  
L. Schwark
Keyword(s):  
Organic Matter ◽  
Carbon Cycle ◽  
Carbon Isotope ◽  
Isotope Composition ◽  
Global Carbon Cycle ◽  
Open Ocean ◽  
Black Shales ◽  
Oceanic Anoxic Event ◽  
Anoxic Event ◽  
Global Carbon

Abstract. Oceanic anoxic events were time intervals in the Mesozoic characterized by widespread distribution of marine organic matter-rich sediments (black shales) and significant perturbations in the global carbon cycle. These perturbations are globally recorded in sediments as carbon isotope excursions irrespective of lithology and depositional environment. During the early Toarcian, black shales were deposited on the epi- and pericontinental shelves of Pangaea, and these sedimentary rocks are associated with a pronounced (ca. 7 ‰) negative (organic) carbon isotope excursion (CIE) which is thought to be the result of a major perturbation in the global carbon cycle. For this reason, the lower Toarcian is thought to represent an oceanic anoxic event (the T-OAE). If the T-OAE was indeed a global event, an isotopic expression of this event should be found beyond the epi- and pericontinental Pangaean localities. To address this issue, the carbon isotope composition of organic matter (δ13Corg of lower Toarcian organic matter-rich cherts from Japan, deposited in the open Panthalassa Ocean, was analysed. The results show the presence of a major (>6 ‰) negative excursion in δ13Corg that, based on radiolarian biostratigraphy, is a correlative of the lower Toarcian negative CIE known from Pangaean epi- and pericontinental strata. A smaller negative excursion in δ13Corg (ca. 2 ‰) is recognized lower in the studied succession. This excursion may, within the current biostratigraphic resolution, represent the excursion recorded in European epicontinental successions close to the Pliensbachian/Toarcian boundary. These results from the open ocean realm suggest, in conjunction with other previously published datasets, that these Early Jurassic carbon cycle perturbations affected the active global reservoirs of the exchangeable carbon cycle (deep marine, shallow marine, atmospheric).

Carbon-isotope and microfaunal stratigraphy bounding the Lower Aptian Oceanic Anoxic Event 1a in northeastern Tunisia

2013 ◽  
Vol 39 ◽  
pp. 133-148 ◽  
Author(s):  
Abdallah Elkhazri ◽  
Hassen Abdallah ◽  
Saloua Razgallah ◽  
Michel Moullade ◽  
Wolfgang Kuhnt
Keyword(s):  
Carbon Isotope ◽  
Oceanic Anoxic Event ◽  
Lower Aptian ◽  
Anoxic Event ◽  
Northeastern Tunisia

The chemostratigraphy and environmental significance of the Marlstone and Junction Bed (Beacon Limestone, Toarcian, Lower Jurassic, Dorset, UK)

2021 ◽  
pp. 1-15
Author(s):  
Hugh C. Jenkyns ◽  
Sophie Macfarlane
Keyword(s):  
Carbon Isotope ◽  
Oxygen Isotopes ◽  
Lower Jurassic ◽  
Carbon And Oxygen Isotopes ◽  
Oceanic Anoxic Event ◽  
Nodular Limestone ◽  
Anoxic Event ◽  
Reference Curves ◽  
High Degree ◽  
Organic Rich Sediment

Abstract Two fallen blocks of the Marlstone and stratigraphically overlying Junction Bed sampled on the beach below Doghouse Cliff in Dorset, UK (Wessex Basin) have been examined for carbon and oxygen isotopes of bulk carbonate as well as for strontium, carbon and oxygen isotopes and Mg:Ca ratios in the contained belemnites. The sequence, which contains most of the Toarcian zones and subzones within a metre or less of grey to yellow to pink, red and brown fossil-rich nodular limestone, is extremely condensed and lithologically similar to pelagic red limestones of the Tethyan Jurassic that are locally mineralized with Fe-Mn oxyhydroxides (e.g., Rosso Ammonitico). Strontium-isotope ratios of the contained belemnites are compatible with existing reference curves and both blocks show a rise to more radiogenic values post-dating the Pliensbachian–Toarcian boundary. The high degree of correlation between the relatively negative carbon and oxygen isotopes of the bulk carbonate is compatible with significant diagenetic overprint, and contrasts with higher carbon-isotope values in coeval condensed coccolith-rich limestones elsewhere. Evidence for the characteristic signature of the Toarcian Oceanic Anoxic Event, as represented by organic-rich sediment, is absent, possibly owing to a stratigraphic gap. Both blocks exhibit abrupt carbon-isotope shifts to lower values, one of which could represent the limbs of an incompletely recorded negative excursion associated with the Toarcian Oceanic Anoxic Event. That the Toarcian Oceanic Anoxic Event was also a significant hyperthermal is illustrated in both blocks by a drop in oxygen-isotope values and rise in Mg:Ca ratios of belemnites close to the base of the Junction Bed in the lowest part of the serpentinum zone.

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

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

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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