Late Jurassic – earliest Cretaceous prolonged shelf dysoxic–anoxic event and its possible causes

2020 ◽  
Vol 157 (10) ◽  
pp. 1622-1642
Author(s):  
MA Rogov ◽  
EV Shchepetova ◽  
VA Zakharov
Keyword(s):  
Organic Carbon ◽  
Black Shale ◽  
High Latitude ◽  
Late Jurassic ◽  
Black Shales ◽  
Time Interval ◽  
Oceanic Circulation ◽  
Anoxic Event ◽  
Anoxic Events

AbstractThe Late Jurassic – earliest Cretaceous time interval was characterized by a widespread distribution of dysoxiс–anoxiс environments in temperate- and high-latitude epicontinental seas, which could be defined as a shelf dysoxic–anoxic event (SDAE). In contrast to black shales related to oceanic anoxic events, deposits generated by the SDAE were especially common in shelf sites in the Northern Hemisphere. The onset and termination of the SDAE was strongly diachronous across different regions. The SDAE was not associated with significant disturbances of the carbon cycle. Deposition of organic-carbon-rich sediment and the existence of dysoxic–anoxic conditions during the SDAE lasted up to c. 20 Ma, but this event did not cause any remarkable biotic extinction. Temperate- and high-latitude black shale occurrences across the Jurassic–Cretaceous boundary have been reviewed. Two patterns of black shale deposition during the SDAE are recognized: (1) Subboreal type, with numerous thin black shale beds, bounded by sediments with very low total organic carbon (TOC) values; and (2) Boreal type, distinguished by predominantly thick black shale successions showing high TOC values and prolonged anoxic–dysoxic conditions. These types appear to be unrelated to differences in accommodation space, and can be clearly recognized irrespective of the thickness of shale-bearing units. Black shales in high-latitude areas in the Southern Hemisphere strongly resemble Boreal types of black shale by their mode of occurrence. The causes of this SDAE are linked to long-term warming and changes in oceanic circulation. Additionally, the long-term disturbance of planktonic communities may have triggered overall increased productivity in anoxia-prone environments.

scholarly journals "OAE 3" – regional Atlantic organic carbon burial during the Coniacian–Santonian

2012 ◽  
Vol 8 (5) ◽  
pp. 1447-1455 ◽  
Author(s):  
M. Wagreich
Keyword(s):  
Organic Carbon ◽  
Temporal Distribution ◽  
Black Shales ◽  
Time Interval ◽  
Temporal And Spatial Distribution ◽  
Oceanic Anoxic Event ◽  
The North ◽  
Carbon Burial ◽  
Organic Carbon Burial ◽  
Anoxic Event

Abstract. The Coniacian–Santonian time interval is the inferred time of oceanic anoxic event 3 (OAE 3), the last of the Cretaceous OAEs. A detailed look on the temporal and spatial distribution of organic-rich deposits attributed to OAE 3 suggests that black shale occurrences are restricted to the equatorial to mid-latitudinal Atlantic and adjacent basins, shelves and epicontinental seas like parts of the Caribbean, the Maracaibo Basin and the Western Interior Basin, and are largely absent in the Tethys, the North Atlantic, the southern South Atlantic, and the Pacific. Here, oxic bottom waters prevailed as indicated by the widespread occurrence of red deep-marine CORBs (Cretaceous Oceanic Red Beds). Widespread CORB sedimentation started during the Turonian after Oceanic Anoxic Event 2 (OAE 2) except in the Atlantic realm where organic-rich strata continue up to the Santonian. The temporal distribution of black shales attributed to OAE 3 indicates that organic-rich strata do not define a single and distinct short-time event, but are distributed over a longer time span and occur in different basins during different times. This suggests intermittent and regional anoxic conditions from the Coniacian to the Santonian. A comparison of time-correlated high-resolution δ13C curves for this interval indicates several minor positive excursions of up to 0.5‰, probably as a result of massive organic carbon burial cycles in the Atlantic. Regional wind-induced upwelling and restricted deep basins may have contributed to the development of anoxia during a time interval of widespread oxic conditions, thus highlighting the regional character of inferred OAE 3 as regional Atlantic event(s).

Modeling the impact of oceanic circulation and marine productivity on Cretaceous seafloor anoxia

2020 ◽  
Author(s):  
Yannick Donnadieu ◽  
Marie Laugie ◽  
Jean-Baptiste Ladant ◽  
François Raisson ◽  
Laurent Bopp
Keyword(s):  
Land Surface ◽  
Oceanic Circulation ◽  
Equatorial Pacific Ocean ◽  
Oxygen Minimum Zones ◽  
Tethys Sea ◽  
Marine Biogeochemistry ◽  
Anoxic Events ◽  
Marine Productivity ◽  
The Impact

<p>Oceanic anoxic events (OAEs) are abrupt events of widespread deposition of organic-rich sediments and extensive seafloor anoxia. Mechanisms usually invoked as drivers of oceanic anoxia are various and still debated today. They include a rise of the CO2 atmospheric level due to increased volcanic activity, a control by the paleogeography, changes in oceanic circulation or enhanced marine productivity. In order to assess the role of these mechanisms, we use an IPCC-class model, the IPSL-CM5A2 Earth System Model, which couples the atmosphere, land surface, and ocean components, this last one including sea ice, physical oceanography and marine biogeochemistry which allows to simulate oceanic oxygen.</p><p>We focus here on OAE2, which occurs during the Cretaceous at the Cenomanian-Turonian boundary (93.5 Ma), and is identified as a global event with evidence for seafloor anoxia in the Atlantic and Indian Oceans, the Southwest Tethys Sea and the Equatorial Pacific Ocean. Using a set of simulations from 115 to 70 Ma, we analyze the long-term paleogeographic control on oceanic circulation and consequences on oceanic oxygen concentration and anoxia spreading. Short-term controls such as an increase of pCO<sub>2</sub>, nutrients, or orbital configurations are also studied with a second set of simulations with a Cenomano-Turonian (90 Ma) paleogeographic configuration. The different simulated maps of oxygen are used to study the evolution of marine productivity and oxygen minimum zones as well as the spreading of seafloor anoxia, in order to unravel the interlocking of the different mechanisms and their specific impact on anoxia through space and time.</p>

scholarly journals Identification of early Llandovery (Silurian) anoxic palaeo-depressions at the western margin of the Murzuq Basin (southwest Libya), based on gamma-ray spectrometry in surface exposures

GeoArabia ◽  
2006 ◽  
Vol 11 (3) ◽  
pp. 101-118 ◽  
Author(s):  
Nuri Fello ◽  
Sebastian Lüning ◽  
Petr Štorch ◽  
Jonathan Redfern
Keyword(s):  
Black Shale ◽  
Gamma Ray ◽  
Regional Distribution ◽  
Uranium Content ◽  
Organic Content ◽  
Black Shales ◽  
Gamma Ray Spectrometry ◽  
Hydrocarbon Source Rock ◽  
Western Margin ◽  
Anoxic Event

ABSTRACT Following the melting of the Gondwanan icecap and the resulting postglacial sea-level rise, organic-rich shales were deposited in shelfal palaeo-depressions across North Africa and Arabia during the latest Ordovician to earliest Silurian. The unit is absent on palaeohighs that were flooded only later when the anoxic event had already ended. The regional distribution of the Silurian black shale is now well-known for the subsurface of the central parts of the Murzuq Basin, in Libya, where many exploration wells have been drilled and where the shale represents the main hydrocarbon source rock. On well logs, the Silurian black shale is easily recognisable due to increased uranium concentrations and, therefore, elevated gamma-ray values. The uranium in the shales “precipitated” under oxygen-reduced conditions and generally a linear relationship between uranium and organic content is developed. The distribution of the Silurian organic-rich shales in the outcrop belts surrounding the Murzuq Basin has been long unknown because Saharan surface weathering has commonly destroyed the organic matter and black colour of the shales, making it complicated to identify the previously organic-rich unit in the field. In an attempt to distinguish (previously) organic-rich from organically lean shales at outcrop, seven sections that straddle the Ordovician-Silurian boundary were measured by portable gamma-ray spectrometer along the outcrops of the western margin of the Murzuq Basin. It was found that the uranium content of the shales remained largely unaltered by the weathering processes and could therefore be used as a valid proxy parameter to distinguish between pre-weathering organically rich and lean shales. It is now possible to identify and map-out the thickness and approximate organic richness of the black shale using measurement of uranium radiation. Five of the newly measured sections are characterised by uranium-enriched intervals, representing areas of earliest Silurian palaeo-depressions. Major uranium peaks are absent in the spectral gamma-ray curves of two other sections, which are interpreted to mark earliest Silurian palaeo-highs. The new data on the distribution of Silurian black shales from the outcrop belt was integrated with subsurface data from the Murzuq Basin. The resulting map of the distribution of black shales may help with predictions of the occurrence of this unit in less well-explored areas of the basin. Graptolite biostratigraphic data suggests that the anoxic event centred on the middle Rhuddanian, with more oxygenated conditions and onset of deposition of organically leaner shales having commenced sometime during the late Rhuddanian. The presence of anoxic palaeo-depressions during the earliest Silurian within the Ghat outcrop belt indicates that the Tihemboka High at the western margin of the Murzuq Basin could not have been a positive structure during this time.

The Late Hauterivian Faraoni ‘Oceanic Anoxic Event’: an update

2014 ◽  
Vol 185 (6) ◽  
pp. 359-377 ◽  
Author(s):  
François Baudin ◽  
Laurent Riquier
Keyword(s):  
Middle Part ◽  
Time Interval ◽  
Oceanic Anoxic Event ◽  
Anoxic Event ◽  
Anoxic Events ◽  
The Mediterranean ◽  
Definition Of ◽  
Geochemical Studies ◽  
New Occurrences

AbstractMost oceanic anoxic events (OAEs) took place during the middle part of the Cretaceous and the Late Hauterivian probably recorded the first anoxic event within this peculiar time interval. The so-called Faraoni event (~131 Ma) was initially defined as a short-lived anoxic event restricted to the Mediterranean domain. Since its recognition, numerous geochemical studies were conducted on the Faraoni event and new occurrences of this event were suggested outside the Tethyan domain. This paper presents an update on the Late Hauterivian Faraoni event and examines if this event agrees with the definition of OAEs.

scholarly journals Black shale deposition during Toarcian super-greenhouse driven by sea level

2013 ◽  
Vol 9 (6) ◽  
pp. 2703-2712 ◽  
Author(s):  
M. Hermoso ◽  
F. Minoletti ◽  
P. Pellenard
Keyword(s):  
Organic Carbon ◽  
Water Column ◽  
Sea Level ◽  
Carbon Isotope ◽  
Carbon Isotopes ◽  
Black Shale ◽  
Black Shales ◽  
Positive Trend ◽  
Sea Level Changes ◽  
Organic Carbon Burial

Abstract. One of the most elusive aspects of the Toarcian oceanic anoxic event (T-OAE) is the paradox between carbon isotopes that indicate intense global primary productivity and organic carbon burial at a global scale, and the delayed expression of anoxia in Europe. During the earliest Toarcian, no black shales were deposited in the European epicontinental seaways, and most organic carbon enrichment of the sediments postdated the end of the overarching positive trend in the carbon isotopes that characterises the T-OAE. In the present study, we have attempted to establish a sequence stratigraphic framework for Early Toarcian deposits recovered from a core drilled in the Paris Basin using a combination of mineralogical (quartz and clay relative abundance) and geochemical (Si, Zr, Ti and Al) measurements. Combined with the evolution in redox sensitive elements (Fe, V and Mo), the data suggest that expression of anoxia was hampered in European epicontinental seas during most of the T-OAE (defined by the positive carbon isotope trend) due to insufficient water depth that prevented stratification of the water column. Only the first stratigraphic occurrence of black shales in Europe corresponds to the "global" event. This interval is characterised by >10% Total Organic Carbon (TOC) content that contains relatively low concentration of molybdenum compared to subsequent black shale horizons. Additionally, this first black shale occurrence is coeval with the record of the major negative Carbon Isotope Excursion (CIE), likely corresponding to a period of transient greenhouse intensification likely due to massive injection of carbon into the atmosphere–ocean system. As a response to enhanced weathering and riverine run-off, increased fresh water supply to the basin may have promoted the development of full anoxic conditions through haline stratification of the water column. In contrast, post T-OAE black shales during the serpentinum and bifrons Zones were restricted to epicontinental seas (higher Mo to TOC ratios) during a period of relative high sea level, and carbon isotopes returning to pre-T-OAE values. Comparing palaeoredox proxies with the inferred sequence stratigraphy for Sancerre suggests that episodes of short-term organic carbon enrichment were primarily driven by third-order sea level changes. These black shales exhibit remarkably well-expressed higher-frequency cyclicities in the oxygen availability in the water column whose nature has still to be determined through cyclostratigraphic analysis.

Bacterial weathering of fossil organic matter and organic carbon mobilization from subterrestrial Kupferschiefer black shale: long-term laboratory studies

2017 ◽  
Vol 9 (4) ◽  
pp. 459-466 ◽  
Author(s):  
Robert Stasiuk ◽  
Agnieszka Włodarczyk ◽  
Przemysław Karcz ◽  
Marcin Janas ◽  
Aleksandra Skłodowska ◽  
...  
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Black Shale ◽  
Laboratory Studies

scholarly journals First record of stable isotopes (δ13C, δ18O) and element ratios (Mg/Ca, Sr/Ca) of Middle to Late Jurassic belemnites from the Indian Himalayas and their potential for palaeoenvironmental reconstructions

2021 ◽  
Vol 10 (1) ◽  
Author(s):  
Matthias Alberti ◽  
Franz T. Fürsich ◽  
Dhirendra K. Pandey ◽  
Nils Andersen ◽  
Dieter Garbe-Schönberg ◽  
...  
Keyword(s):  
Late Jurassic ◽  
First Record ◽  
Time Interval ◽  
Temperature Decrease ◽  
Himalayan Orogeny ◽  
Palaeoenvironmental Reconstructions ◽  
Middle Callovian ◽  
Indian Himalayas ◽  
Iron And Manganese

AbstractMiddle to Late Jurassic belemnites from the Spiti and Zanskar valleys in the Indian Himalayas were used for stable isotope (δ13C, δ18O) and element (Mg/Ca, Sr/Ca) analyses. Although the Himalayan orogeny deformed and altered a large portion of the collected fossils, cathodoluminescence and scanning electron microscopy in combination with analyses of iron and manganese contents allowed the identification of belemnites believed to still retain their original chemical composition. Results indicate a long-term temperature decrease from the Middle Callovian–Oxfordian to the Tithonian, which is proposed to have been caused by a concomitant drift of eastern Gondwana into higher palaeolatitudes. Reconstructed absolute temperatures depend on the used equation and assumed δ18O value of seawater, but most likely varied between 17.6 °C to 27.6 °C in the Kimmeridgian and Tithonian with average values between 22 °C to 24 °C. This way, temperatures were similar to slightly warmer than today at comparable latitudes. The reconstruction of absolute temperatures for the Middle Callovian–Oxfordian was hindered by a larger number of poorly preserved belemnites representing this time interval.

scholarly journals Graphite from Palaeoproterozoic enhanced carbon burial, and its metallogenic legacy

2021 ◽  
pp. 1-8
Author(s):  
John Parnell ◽  
Connor Brolly ◽  
Adrian J. Boyce
Keyword(s):  
Organic Carbon ◽  
Black Shale ◽  
Carbon Deposition ◽  
Mafic Magma ◽  
Carbon Burial ◽  
Pge Mineralization ◽  
Ore Deposition

Abstract The episode of widespread organic carbon deposition marked by peak black shale sedimentation during the Palaeoproterozoic is also reflected in exceptionally abundant graphite deposits of this age. Worldwide anoxic/euxinic sediments were preserved as a deep crustal reservoir of both organic carbon, and sulphur in accompanying pyrite, both commonly >1 wt %. The carbon- and sulphur-rich Palaeoproterozoic crust interacted with mafic magma to cause Ni–Co–Cu–PGE mineralization over the next billion years, and much uranium currently produced is from Mesoproterozoic deposits nucleated upon older Palaeoproterozoic graphite. Palaeoproterozoic carbon deposition has thus left a unique legacy of both graphite deposits and long-term ore deposition.

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