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

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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Sedimentology, Petrology, and Volcanology of the Lower Aptian Oceanic Anoxic Event (OAE1a), Shatsky Rise, North-Central Pacific Ocean

10.2973/odp.proc.sr.198.109.2005 ◽

2005 ◽

Author(s):

K.M. Marsaglia

Keyword(s):

Pacific Ocean ◽

Central Pacific ◽

Shatsky Rise ◽

North Central ◽

Oceanic Anoxic Event ◽

Central Pacific Ocean ◽

Lower Aptian ◽

Anoxic Event

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Central Tethyan platform-top hypoxia during Oceanic Anoxic Event 1a

Climate of the Past ◽

10.5194/cp-15-1327-2019 ◽

2019 ◽

Vol 15 (4) ◽

pp. 1327-1344 ◽

Cited By ~ 5

Author(s):

Alexander Hueter ◽

Stefan Huck ◽

Stéphane Bodin ◽

Ulrich Heimhofer ◽

Stefan Weyer ◽

...

Keyword(s):

Trace Elements ◽

Shallow Water ◽

Oxygen Depletion ◽

Water Masses ◽

Time Resolved ◽

Oceanic Anoxic Event ◽

Driving Mechanisms ◽

Lower Aptian ◽

Anoxic Event ◽

Coral Communities

Abstract. Short-term hypoxia in epeiric water masses is a common phenomenon of modern marine environments and causes mass mortality in coastal marine ecosystems. Here, we test the hypothesis that during the early Aptian, platform-top hypoxia temporarily established in some of the vast epeiric seas of the central Tethys and caused, combined with other stressors, significant changes in reefal ecosystems. Potentially interesting target examples include time intervals characterized by the demise of lower Aptian rudist–coral communities and the establishment of microencruster facies, as previously described from the central and southern Tethys and from the proto-North Atlantic domain. These considerations are relevant as previous work has predominantly focused on early Aptian basinal anoxia in the context of Oceanic Anoxic Event (OAE) 1a, whereas the potential expansion of the oxygen minimum zone (OMZ) in coeval shallow-water environments is underexplored. Well-known patterns in the δ13C record during OAE 1a allow for a sufficiently time-resolved correlation with previously studied locations and assignment to chemostratigraphic segments. This paper presents and critically discusses the outcome of a multi-proxy study (e.g., rare earth elements (REEs), U isotopes, and redox-sensitive trace elements) applied to lower Aptian shallow-water carbonates today exposed in the Kanfanar quarry in Istria, Croatia. These rocks were deposited on an extensive, isolated high in the central Tethys surrounded by hemipelagic basins. Remarkably, during chemostratigraphic segment C2, the depletion of redox-sensitive trace elements As, V, Mo, and U in platform carbonates, deposited in normal marine oxic waters, record the first occurrence of basinal, organic-rich sediment deposition in which these elements are enriched. During the C3 segment, seawater oxygen depletion established on the platform top as indicated by the patterns in Ce/Ce* and U isotopes. Shifts in redox-sensitive proxies coincide with the expansion of microencruster facies. Segment C4 witnesses the return to normal marine reefal faunas on the platform top and is characterized by patterns in redox-sensitive proxies typical of normal marine dissolved oxygen levels. It remains unclear, however, if platform-top hypoxia resulted from the expansion and upwelling of basinal, oxygen-depleted water masses or if spatially isolated, shallow hypoxic water bodies formed on the platform. Data shown here are relevant as they shed light on the driving mechanisms that control poorly understood faunal patterns during OAE 1a in the neritic realm and provide evidence on the intricate relation between basinal and platform-top water masses.

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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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Lower Aptian Comparative Stratigraphy of the Basco-Cantabrian Region (Spain) and Eastern Cordillera (Colombia): implications for local factors in the depositional record of Oceanic Anoxic Event 1a (OAE-1a)

10.25148/etd.fi13080717 ◽

2013 ◽

Author(s):

Tatiana Gaona Narvaez

Keyword(s):

Oceanic Anoxic Event ◽

Local Factors ◽

Eastern Cordillera ◽

Lower Aptian ◽

Cantabrian Region ◽

Anoxic Event

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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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