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 rhythmic expression of mid-Cretaceous Oceanic Anoxic Event 2 at IODP Sites U1513 and U1516 (southwest of Australia)

10.5194/egusphere-egu21-11977 ◽

2021 ◽

Author(s):

Sietske Batenburg ◽

Kara Bogus ◽

Matthew Jones ◽

Kenneth Macleod ◽

Mathieu Martinez ◽

...

Keyword(s):

Organic Matter ◽

Indian Ocean ◽

Water Column ◽

North Atlantic ◽

Black Shales ◽

Carbonate Content ◽

Intergovernmental Panel ◽

Oceanic Anoxic Event ◽

Oceanic Anoxic Event 2 ◽

Anoxic Event

The widespread deposition of organic-rich black shales during the mid-Cretaceous hothouse at ~94 Ma marked a climatic extreme that is particularly well studied in the Northern Hemisphere. The expression of Oceanic Anoxic Event 2 (OAE 2) in the NH was characterised by low oceanic oxygen concentrations, likely caused by the input of nutrients through volcanism and/or weathering in combination with a peculiar geography in which the proto-North Atlantic was semi-restricted (Jenkyns, 2010; Trabucho Alexandre et al., 2010). The extent of water column anoxia outside the North Atlantic and Tethyan domains remains poorly resolved, as few Southern Hemisphere records have been recovered that span OAE 2, and only a portion of those Indian and Pacific Ocean localities experienced anoxia and organic matter deposition (Dickson et al., 2017; Hasegawa et al., 2013).&#160;Here we present new results from IODP Expedition 369 offshore southwestern Australia. Sedimentary records across the Cenomanian-Turonian transition from Sites U1513 and U1516 in the Mentelle Basin (Indian Ocean) display rhythmic lithologic banding patterns. The OAE 2 interval is marked by a dramatic drop in carbonate content and the occurrence of several thin organic-rich black bands. The spacing of dark bands within a rhythmic sequence suggests a potential orbital control on organic matter deposition at our study sites. Time series analyses of high-resolution (cm-scale) elemental data from XRF-core scanning reveal the imprint of periodicities that can be confidently linked to Earth&#8217;s orbital parameters. The new OAE 2 records from Sites U1516 and U1513 allow us to i) evaluate existing time scales over the Cenomanian-Turonian transition, and ii) investigate the mechanisms leading to a recurrent lack of oxygen in the Indian Ocean.&#160;Climatic mechanisms translating changes in insolation to variations in organic matter deposition may have included variations in nutrient input from nearby continents and shifts in water column structure affecting local to regional stratification versus deep water formation and advection. Investigating ventilation of the deep sea during the OAE2 interval is of heightened relevance as current global warming is leading to a worldwide expansion of oxygen minimum zones&#160;(P&#246;rtner et al., 2019).&#160;References:Dickson, A.J., et al., 2017. Sedimentology 64, 186&#8211;203.Hasegawa, et al., 2013. Cretaceous Research 40, 61&#8211;80.Jenkyns, H.C., 2010. Geochemistry, Geophysics, Geosystems 11, Q03004.P&#246;rtner, H.O., et al., 2019. IPCC Intergovernmental Panel on Climate Change: Geneva, Switzerland.Trabucho Alexandre, J., et al., 2010. Paleoceanography 25, PA

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Stenopterygiids from the lower Toarcian of Beaujolais and a chemostratigraphic context for ichthyosaur preservation during the Toarcian Oceanic Anoxic Event

Geological Society London Special Publications ◽

10.1144/sp514-2020-232 ◽

2021 ◽

pp. SP514-2020-232

Author(s):

Jeremy E. Martin ◽

Guillaume Suan ◽

Baptiste Suchéras-Marx ◽

Louis Rulleau ◽

Jan Schlögl ◽

...

Keyword(s):

Content Type ◽

Oceanic Anoxic Event ◽

Sulfate Reducing ◽

Exceptional Preservation ◽

Environmental Perturbations ◽

Anoxic Event ◽

European Distribution ◽

Supplementary Material ◽

Carbonate Concretion ◽

Early Carbonate

AbstractWe report new ichthyosaur material excavated in lower Toarcian levels of the LafargeHolcim Val d'Azergues quarry in Beaujolais, SE France. A partially articulated skull and a smaller, unprepared but likely subcomplete skeleton preserved in a carbonate concretion are identified as stenopterygiids, a family of wide European distribution during the Early Jurassic. These specimens are among the finest preserved Toarcian exemplars known from Europe and in one of them, soft tissue preservation is suspected. Their state of preservation is attributed to the combination of prolonged anoxic conditions near the water-sediment interface and early carbonate cementation resulting from the activity of sulfate-reducing bacteria. We also present carbon and strontium isotope values obtained from the study site that allow detailed temporal comparisons with other Toarcian vertebrate-yielding sites and environmental perturbations associated with the Toarcian Oceanic Anoxic Event (T-OAE). These comparisons suggest that the relatively high abundance and good preservation state of Toarcian vertebrates was favoured by a prolonged period of low bottom water oxygenation and accumulation rates. The environmental conditions that prevailed during the T-OAE were probably responsible for the extensive nature of Lagerstätte-type deposits with exceptional preservation of marine organisms. Whether the T-OAE had a biological impact on marine vertebrates requires a precise chemostratigraphic context of the fossil record spanning the Pliensbachian-Toarcian interval.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5315223

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An open marine record of the Toarcian oceanic anoxic event

Solid Earth Discussions ◽

10.5194/sed-3-385-2011 ◽

2011 ◽

Vol 3 (1) ◽

pp. 385-410 ◽

Cited By ~ 17

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.

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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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An open ocean record of the Toarcian oceanic anoxic event

Solid Earth ◽

10.5194/se-2-245-2011 ◽

2011 ◽

Vol 2 (2) ◽

pp. 245-257 ◽

Cited By ~ 63

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).

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