The response of marine phytoplankton and sedimentary organic matter to the early Toarcian (Lower Jurassic) oceanic anoxic event in northern England

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.

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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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Onset of Oceanic Anoxic Event 2 in the Lower Saxony Basin – Insights fromhigh-resolution stable isotope stratigraphy and geochemical modelling

10.5194/egusphere-egu21-8748 ◽

2021 ◽

Author(s):

Pia Müller ◽

Ulrich Heimhofer ◽

Christian Ostertag-Henning

Keyword(s):

Organic Matter ◽

High Resolution ◽

Stable Isotope ◽

Carbon Cycle ◽

Geochemical Modelling ◽

Positive Anomaly ◽

Lower Saxony ◽

Data Set ◽

Oceanic Anoxic Event ◽

Anoxic Event

The Oceanic Anoxic Event (OAE) 2 spanning the Cenomanian-Turonian boundary (93.5 Ma) represents a major perturbation of the global carbon cycle and is marked by organic-rich sediments deposited under oxygen-depleted conditions. In many studies the eruption of the Caribbean LIP is considered to be the cause for rapidly increasing CO2 concentrations and resulting global warming accompanied by widespread oceanic anoxia. In the Lower Saxony Basin of northern Germany, the deposits of the OAE 2 are exposed in several industry drill cores. In this study, the lower part of the OAE 2 has been studied in the HOLCIM 2011-3 drill core. Sedimentary rocks are composed of limestones, marly limestones, marls and black shales and have been analysed with a high-resolution stable isotope approach (approximately one sample every 2 cm) combined with geochemical modelling. Using stable carbon isotopes, bulk rock parameters and petrographic analysis, the onset of OAE 2 has been investigated in detail. The high-resolution &#948;13C curve exhibits overall stable values around 3 &#8240; before the onset of the Plenus event. This background level is interrupted by three short-lived and small but significant negative carbon isotope excursions (CIEs) down to &#948;13C values of 2.5 &#8240;, 2.7 &#8240; and 1.9 &#8240;. Immediately before the main rise in the Plenus bed, a longer-lasting negative CIE down to 2.8 &#8240; is observed, preceding the large positive CIE of the OAE 2 to values of 5.2 &#8240; over 33 ka. Thereafter, the &#948;13C values decrease to 3.5 &#8240; over a period of approximately 130 ka. The results can be correlated with the lower-resolution data set of Voigt et al. (2008) but enable a more accurate characterization of the subtle features of the CIE and hence events before and during this time interval. Carbon cycle modelling with the modelling software SIMILE using a model based on Kump & Arthur (1999) reveals that the negative excursion before the Plenus bed can be explained by a massive volcanic pulse releasing of 0.95*1018 mol CO2 within 14 ka. This amount corresponds to only 81 % of the calculated volume of CO2 release during emplacement of the Caribbean LIP by Joo et al. (2020). In the model the volcanic exhalation increases atmospheric CO2 concentrations. This will increase global temperatures, intensify the hydrological cycle and thus increase nutrient input into the ocean, resulting in an expansion of the oxygen minimum zone, the development of anoxic conditions and an increase in the preservation potential for organic material. In the model enhanced primary productivity and organic matter preservation can be controlled by the implemented riverine phosphate input and the preservation factor for organic matter. For the positive anomaly, the riverine phosphate input must be nearly doubled (from 0.01 &#956;mol/kg PO4 to 0.019 &#956;mol/kg) for the period of the increasing &#948;13C values (app. 33 ka), with a concomitant rise of the preservation factor from 1 % to 2 %. This model scenario accurately reproduces the major features of the new high-resolution &#948;13C record over the onset of the OAE 2 CIE.

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Compositional and isotopic characteristics of organic matter for the early Aptian Oceanic Anoxic Event at Shatsky Rise, ODP Leg 198

Palaeogeography Palaeoclimatology Palaeoecology ◽

10.1016/j.palaeo.2005.09.028 ◽

2006 ◽

Vol 235 (1-3) ◽

pp. 168-191 ◽

Cited By ~ 59

Author(s):

Mirela Dumitrescu ◽

Simon C. Brassell

Keyword(s):

Organic Matter ◽

Shatsky Rise ◽

Oceanic Anoxic Event ◽

Anoxic Event

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Benthic microbial mats: a possible major component of organic matter accumulation in the Lower Aptian oceanic anoxic event

Terra Nova ◽

10.1111/j.1365-3121.2008.00848.x ◽

2009 ◽

Vol 21 (1) ◽

pp. 21-27 ◽

Cited By ~ 10

Author(s):

Georges Gorin ◽

Nicolas Fiet ◽

Muriel Pacton

Keyword(s):

Organic Matter ◽

Microbial Mats ◽

Oceanic Anoxic Event ◽

Organic Matter Accumulation ◽

Lower Aptian ◽

Anoxic Event

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The Oceanic Anoxic Event 2 organic record in the South Iberian Paleomargin.

10.5194/egusphere-egu21-11868 ◽

2021 ◽

Author(s):

Carolina Fonseca ◽

João Graciano Mendonça Filho ◽

Matías Reolid ◽

Luís Vítor Duarte ◽

Carine Lézin

Keyword(s):

Sea Level ◽

Source Area ◽

First Record ◽

Marine Phytoplankton ◽

The South ◽

Oceanic Anoxic Event ◽

Organic Facies ◽

Oceanic Anoxic Event 2 ◽

Anoxic Event ◽

Marine System

The Cenomanian&#8212;Turonian boundary is marked by one of the warmest periods of the Mesozoic, associated with high pCO2 levels and global sea-level highstands. Coupled to these extreme conditions is a massive magmatic episode, the establishment of worldwide marine anoxia, the deposition of organic-rich facies, and perturbations of the global carbon cycle, the so-called Oceanic Anoxic Event 2 (OAE2). In order to define the organic facies variability, this stratigraphic interval was analysed in the Ba&#241;os de la Hedionda, a reference section positioned in the W part of the Internal Subbetic, representing the sedimentary record of a pelagic plateau located in the most distal part of the South Iberian Paleomargin. Regarding this goal, a high resolution study was developed on the Capas Blancas Formation (Capas Blancas, Black radiolaritic shales, and Boquer&#243;n members &#8211; Mb.), using organic petrographic and geochemical techniques. Carbon isotopic profile, for the isolated kerogen (&#948;13Ckerogen), displays a positive excursion of ~2.5&#8240; observed in the Black radiolaritic shales Mb., which is in accordance with the worldwide recognized trend for the OAE2 isotopic record.The pre-OAE2 is represented by the Capas Blancas Mb., with the majority of the samples of this unit showing no organic matter (OM) recovery (0.01&#8212;0.57 wt.% total organic carbon; TOC). Palynofacies analysis displayed an association co-dominated by the Amorphous and Palynomorph groups. The Amorphous Group is characterized mostly by marine phytoplankton-derived amorphous OM (AOM), while the Palynomorph Group is co-dominated by freshwater microplankton (Zygnemataceae and&#160;Closterium) and choanoflagellates, with some specimens of marine microplankton, sporomorphs, and zoomorphs being also identified. The mixture of freshwater and marine components suggest deposition in a platform environment with shallow depths and oscillating oxygen regimen (oxic to dysoxic conditions). The freshwater components are most likely transported into the marine system due to the lower amorphization state, with the source area being in high proximity.The OAE2, represented by the Black radiolaritic shales Mb., is characterized by a dominance of: (i) marine phytoplankton-derived AOM; (ii) plate-like bacterial AOM; and, (iii) sheet-like bacterial AOM with a cratered aspect (0.36&#8212;31.48 wt.% TOC). Choanoflagelates (with high degree of amorphization) at the base of the unit, zooclasts, sporomorphs, and solid bitumen are also present. The change in the organic facies suggests the occurrence of a transgressive phase. This organic facies is indicative of a relative sea level rise, with O2 conditions deteriorating with the emplacement of reducing conditions, possibly related to an increase in primary productivity.The post-OAE2, recognized in the Boquer&#243;n Mb., is characterized by a co-dominance of marine phytoplankton-derived AOM and palynomorphs, namely zoomorphs, and high percentages of opaque phytoclasts (below 0.25 wt.% TOC). Nevertheless, kerogen displays a reworked character and, therefore, data should be used with caution.Furthermore, this study constitutes the first record of Closterium in sediments from the Cretaceous, and the first identification of choanoflagellates, the closest living relatives of Metazoa, in the fossil record.

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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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Boosted microbial productivity during the Toarcian Oceanic Anoxic Event in the Paris Basin, France: new evidence from organic geochemistry and petrographic analysis

Geological Society London Special Publications ◽

10.1144/sp514-2020-167 ◽

2021 ◽

pp. SP514-2020-167

Author(s):

Carolina Fonseca ◽

João Graciano Mendonça Filho ◽

Carine Lézin ◽

François Baudin ◽

António Donizeti de Oliveira ◽

...

Keyword(s):

Marine Environment ◽

Organic Geochemistry ◽

Bacterial Biomass ◽

Integrated Approach ◽

Organic Content ◽

Marine Phytoplankton ◽

Petrographic Analysis ◽

Paris Basin ◽

Oceanic Anoxic Event ◽

Anoxic Event

AbstractThe Toarcian Oceanic Anoxic Event (T-OAE) is marked by major paleoenvironmental and paleoceanographical changes at a global scale, associated to a severe disturbance of the global carbon cycle, and organic-rich facies deposition. Here, a multi-proxy approach (petrographic and geochemical techniques) was applied to the study of the organic content of the T-OAE of the Paris Basin, whose phytoplanktonic origin has been previously inferred by its geochemical signature.The top of tenuicostatum Zone is characterized by palynomorphs and marine phytoplankton-derived amorphous organic matter (AOM), representing a proximal marine environment with emplacement of euxinic conditions to the top (total organic carbon/sulfur content and increase in AOM). At the base of the serpentinum Zone the proliferation of bacterial biomass begins, with phytoplankton playing a secondary role. This indicates the development of stagnant and restrictive conditions in a proximal environment, with water column stratification (neohop-13(18)-ene). The majority of the serpentinum Zone is dominated by bacterial biomass, suggesting a marine environment with bottom waters stagnation, possibly related to basin paleogeomorphology and circulation patterns, with episodic euxinia.This therefore suggests that the T-OAE organic fraction is dominated by bacterial biomass, not phytoplankton, showing the importance of an integrated approach to the determination of the organic facies.

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