MARINE BLACK SHALE AT DEMERARA RISE, EQUATORIAL ATLANTIC OCEAN, AT THE INCEPTION OF CRETACEOUS OCEANIC ANOXIC EVENT 2: A RECORD OF DISTURBANCE IN TERRESTRIAL SEDIMENT INFLUX, MARINE PRODUCTIVITY, NUTRIENT CYCLING, OCEANIC ANOXIA AND CIRCULATION

Abstract. In Livello Bonarelli black shale deposited during Cretaceous Oceanic Anoxic Event 2 (OAE-2, ca. 94 Ma), nitrogen isotopic compositions of bulk sediments are mostly in a narrow range from –2.7 to –0.7‰. We also determined molecular distribution and nitrogen isotopic compositions of geoporphyrins extracted from the black shale. The nitrogen isotopic compositions of C32 Ni deoxophylloerythroetioporphyrin (DPEP) and total Ni porphyrins are –3.5 and –3.3‰, respectively, leading us to the estimation that the mean nitrogen isotopic composition of photoautotrophic cells were around +1‰ during the formation of Bonarelli black shale. This value is suggestive of N2-fixation, a dominant process for these photoautotrophs when assimilating nitrogen. Furthermore, Ni-chelated C32 DPEP, derived mainly from chlorophyll a had the highest concentration. Based on this evidence, we conclude that diazotrophic cyanobacteria were major primary producers during that time. Cyanobacteria may be key photoautotrophs during the formation of black shale type sediments intermittently observed throughout the later half of the Earth's history, and hence may have played a crucial role in the evolution of geochemical cycles even in the later half of the Earth's history.

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The Plenus Cold Event Record in the Abyssal DSDP Site 367 (Cape Verde, Central Atlantic): Environmental Perturbations and Impacts on the Nitrogen Cycle

Frontiers in Earth Science ◽

10.3389/feart.2021.703282 ◽

2021 ◽

Vol 9 ◽

Author(s):

Laurent Riquier ◽

Pierre Cadeau ◽

Julien Danzelle ◽

François Baudin ◽

Emmanuelle Pucéat ◽

...

Keyword(s):

Atlantic Ocean ◽

Water Column ◽

Nitrogen Cycle ◽

Cape Verde ◽

Cold Event ◽

Oceanic Anoxic Event ◽

Carbon And Nitrogen ◽

Oceanic Anoxic Event 2 ◽

Anoxic Event ◽

Central Atlantic

The Oceanic Anoxic Event 2, at the Cenomanian-Turonian boundary (∼93.9 Ma), was an episode of widespread burial of organic matter in marine sediments, underlined by a positive carbon-isotope (δ13C) excursion observed worldwide. Within this episode of O2-depleted conditions, a short interval of cooling, termed as the Plenus Cold Event, has been recorded in many sites and sections in the northern hemisphere (Tethyan domain, Western Interior Seaway, proto-North Atlantic Ocean). But, its record and its impact on the biogeochemical cycles of carbon and nitrogen in the southern part of Central Atlantic Ocean has not been explored yet. Here, we present a detailed geochemical study of the Deep Sea Drilling Project site 367 (Cape Verde) based on a compilation of previous and new data of carbon and nitrogen isotope signals as well as trace element concentrations. The aim of this study is to better constrain the evolution of oxygenation in the water column and the associated changes in nitrogen cycle before and during the Oceanic Anoxic Event 2 in order to understand the paleoceanographic and environmental consequences of the Plenus Cold Event at one of the deepest site of the Central Atlantic Ocean. Our new dataset improves the resolution of the δ13C curve for this site, and we propose a new chemo-stratigraphic frame of the carbon excursion allowing for a better identification of the short-term negative carbon isotope excursion associated to the Plenus Cold Event. The detailed evolution of redox-sensitive proxies (Mo, U, V, Fe, Cu, Ni enrichments and Corg/Ptotal) and isotopic signals (δ13Corg and δ15Ntotal) evidence that this deep site was impacted by this cooling event. While anoxic conditions prevailed in bottom waters before and during the onset of the Oceanic Anoxic Event 2 characterized by euxinic NH4+-rich water column, this cooling event was accompanied by reoxygenation of the water column, which had affected the behavior of the redox-sensitive elements and caused changes in nitrogen biogeochemical cycling.

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A continental-weathering control on orbitally driven redox-nutrient cycling during Cretaceous Oceanic Anoxic Event 2

Geology ◽

10.1130/g36837.1 ◽

2015 ◽

Vol 43 (11) ◽

pp. 963-966 ◽

Cited By ~ 48

Author(s):

Simon W. Poulton ◽

Susann Henkel ◽

Christian März ◽

Hannah Urquhart ◽

Sascha Flögel ◽

...

Keyword(s):

Nutrient Cycling ◽

Oceanic Anoxic Event ◽

Oceanic Anoxic Event 2 ◽

Anoxic Event ◽

Continental Weathering

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Calcareous nannofossil assemblages of Oceanic Anoxic Event 2 in the equatorial Atlantic: Evidence of an eutrophication event

Marine Micropaleontology ◽

10.1016/j.marmicro.2007.07.007 ◽

2007 ◽

Vol 66 (1) ◽

pp. 52-69 ◽

Cited By ~ 47

Author(s):

P. Hardas ◽

J. Mutterlose

Keyword(s):

Calcareous Nannofossil ◽

Equatorial Atlantic ◽

Oceanic Anoxic Event ◽

Oceanic Anoxic Event 2 ◽

Anoxic Event

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The Cenomanian–Turonian Oceanic Anoxic Event 2 and the Late Turonian-Coniacian Event in the Mexican Interior Basin

10.5194/egusphere-egu21-13968 ◽

2021 ◽

Author(s):

Fernando Nunez ◽

Azucena Colin-Rodríguez ◽

Thierry Adatte ◽

Lourdes Omaña-Pulido ◽

Pura Alfonso ◽

...

Keyword(s):

Cold Climate ◽

Geochemical Data ◽

Equatorial Atlantic ◽

Cold Event ◽

Climate Conditions ◽

Oceanic Anoxic Event ◽

Initial Stage ◽

Igneous Provinces ◽

Oceanic Anoxic Event 2 ◽

Anoxic Event

In the modern ocean, deoxygenation is a major consequence of climate change induced by eutrophication and expansion of oxygen minimum zones.&#160; To better understand the exact mechanisms that promote the development of anoxia requires observations not available at human time scale, and therefore demand the study of intervals of rapid warming in the geologic past. During the Cretaceous Period, massive submarine volcanism during the construction of Large Igneous Provinces gave rise to the development of several episodes of widespread oxygen-depleted waters and enhance organic carbon deposition, including the &#160;Cenomanian-Turonian Oceanic Anoxic Event 2 (OAE 2) and the &#160;Late Turonian&#8211;Coniacian Event (LTCE). In this study, we reconstruct climate and oceanographic conditions in the Mexican Interior Basin during these events, a key area that connected the Western Interior Seaway to the equatorial Atlantic Tethyan water mass. To accomplish this, we applied an integrated multi-proxy approach that includes sedimentological, microfacies, mineralogical and geochemical data from a upper Cenomanian&#8211;lower Coniacian section.Organic-rich sediments were accumulated during the initial stage of OAE 2 and the middle stage of LTCE (Hitchwood Event), under increasingly warm and humid conditions, as evidenced by high chemical index of alteration (CIA) values. High detrital index (DI) values coupled with high phosphorus mass-accumulation rates suggest that this scenario increased detrital and nutrients fluxes. Eutrophic-anoxic/dysoxic marine conditions are corroborated by the highest TOC values coinciding with significant enrichments in redox- and productivity-sensitive trace elements. Moreover, they are supported by the abundant presence of radiolarians and filaments in the OAE 2 interval, and the occurrence of opportunistic foraminifera in the LTCE interval. Oxygen-depleted bottom waters are also indicated by Mo&#8211;U systematics and a small-sized population of pyrite. The onset of the Mexican Orogen tectonic uplift together with upwelling intensified the transference of nutrients and enhanced organic matter burial during the initial stage of OAE 2. In the mid-OAE 2 &#948;13C trough&#160;interval equivalent to the Plenus Cold Event, bioturbated sediments with low TOC values accumulated during a short episode of cold climate conditions reflecting the southward flow&#160;of&#160;boreal&#160;water throughout the Mexican Interior Basin. The minimum &#948;34Spy value occurring within the OAE 2 interval in the Mexican Interior Basin is lower than elsewhere due to a local increase in sulfate concentrations.

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An importance of diazotrophic cyanobacteria as a primary producer during Cretaceous Oceanic Anoxic Event 2

Biogeosciences Discussions ◽

10.5194/bgd-3-575-2006 ◽

2006 ◽

Vol 3 (3) ◽

pp. 575-605 ◽

Cited By ~ 8

Author(s):

N. Ohkouchi ◽

Y. Kashiyama ◽

J. Kuroda ◽

N. O. Ogawa ◽

H. Kitazato

Keyword(s):

Black Shale ◽

Oceanic Anoxic Event ◽

Isotopic Compositions ◽

Oceanic Anoxic Event 2 ◽

Nitrogen Isotopic Composition ◽

Anoxic Event ◽

Primary Producer ◽

Dominant Process ◽

Diazotrophic Cyanobacteria ◽

The Mean

Abstract. In Livello Bonarelli black shale deposited during Cretaceous Oceanic Anoxic Event 2 (OAE-2, ca. 94 Ma), nitrogen isotopic compositions of bulk sediments are in a narrow range from −2.7 to −0.7. We also determined molecular distribution and nitrogen isotopic compositions of geoporphyrins extracted from the black shale. The nitrogen isotopic compositions of C32 Ni deoxophylloerythroetioporphyrin (DPEP) and total Ni porphyrins are −3.5 and −3.3, respectively, leading us to the estimation that the mean nitrogen isotopic composition of photoautotrophic cell was around +1 during the formation of Bonarelli black shale. This value is suggestive of N2-fixation a dominant process for these photoautotrophs when assimilating nitrogen. Furthermore, Ni-chelated C32 DPEP, derived mainly from chlorophyll a was the highest concentration. Based on these evidence, we conclude that diazotrophic cyanobacteria were major primary producers during that time. The cyanobacteria may be key photoautotrophs during the formation of black shale type sediments intermittently observed throughout the later half of the Earth's history, and hence may have played a crucial role in the evolution of geochemical cycles.

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