Nd isotopic excursion across Cretaceous ocean anoxic event 2 (Cenomanian-Turonian) in the tropical North Atlantic

MacLeod, Kenneth G.; Martin, E. E.; Blair, Susanna W

doi:10.1130/g24999a.1

Cited by 106 publications

(119 citation statements)

References 31 publications

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“…Meter composite depth (mcd) below seafloor for holes 1258B and 1258C for the new data presented here were adjusted based on correlation with the carbon isotope stratigraphy of hole 1258A. This approach was adopted by Erbacher et al (2005) and subsequently used in additional publications (Hetzel et al, 2009;MacLeod et al, 2008;Owens et al, 2012). This composite section is characterized by a nearly continuous record of finely laminated, organic-rich sedimentary deposition preceding, during and subsequent to the OAE-a unique feature among sites that record OAE2.…”

Section: Samplesmentioning

confidence: 99%

Empirical links between trace metal cycling and marine microbial ecology during a large perturbation to Earth's carbon cycle

Owens

Reinhard

Rohrssen

et al. 2016

Earth and Planetary Science Letters

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Available online xxxx Editor: D. Vance Keywords: oceanic anoxic event (OAE2) trace metal drawdown geochemistry anoxia euxinia biomarkersUnderstanding the global redox state of the oceans and its cause-and-effect relationship with periods of widespread organic-carbon deposition is vital to interpretations of Earth's climatic and biotic feedbacks during periods of expanded oceanic oxygen deficiency. Here, we present a compilation of new and published data from an organic-rich locality within the proto-North Atlantic Ocean during the Cenomanian-Turonian boundary event that shows a dramatic drawdown of redox-sensitive trace elements. Iron geochemistry independently suggests euxinic deposition (i.e., anoxic and sulfidic bottom waters) for the entire section, thus confirming its potential as an archive of global marine metal inventories. In particular, depleted molybdenum (Mo) and vanadium (V) concentrations effectively record the global expansion of euxinic and oxygen-deficient but non-sulfidic waters, respectively. The V drawdown precedes the OAE, fingerprinting an expansion of oxygen deficiency prior to an expansion of euxinia. Molybdenum drawdown, in contrast, is delayed with respect to V and coincides with the onset of OAE2. Parallel lipid biomarker analyses provide evidence for significant and progressive reorganization of marine microbial ecology during the OAE in this region of the proto-North Atlantic, with the smallest relative eukaryotic contributions to total primary production occurring during metal-depleted intervals. This relationship may be related to decreasing supplies of enzymatically important trace elements. Similarly, box modeling suggests that oceanic drawdown of Mo may have approached levels capable of affecting marine nitrogen fixation. Predictions of possible nitrogen stress on eukaryotic production, locally and globally, are consistent with the low observed levels of Mo and a rise in 2-methylhopane index values during the peak of the OAE. At the same time, the environmental challenge presented by low dissolved oxygen and euxinia coincides with increased turnover rates of radiolarian clades, calcareous nanofossils, and foraminifera, suggesting that the temporal patterns of anoxia/euxinia and associated nutrient limitation may have contributed to the fabric of OAE2-related turnover.

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Section: Samplesmentioning

confidence: 99%

Empirical links between trace metal cycling and marine microbial ecology during a large perturbation to Earth's carbon cycle

Owens

Reinhard

Rohrssen

et al. 2016

Earth and Planetary Science Letters

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“…The hydrothermal model for supplying Fe is challenged by the assumption of widespread euxinia in the water column and the insolubility of iron under those conditions; not surprisingly, the record of hydrothermal Fe signal does not correlate in a straightforward manner with the distribution of organic-rich facies throughout the entire North Atlantic (20,27). However, neodymium isotope ratios in fish teeth from the western equatorial Atlantic (Demerara Rise) and the north European Chalk Sea may reflect hydrothermal input from the Caribbean and/or Arctic Large Igneous provinces (23,28). Alternatively, geochemical box modeling suggests that enhanced P from continental weathering was important for the initiation of OAE 2, followed, as a positive feedback, by its sustained availability due to the widespread reduction of P-bearing iron oxides (29) and more generally enhanced P recycling under anoxic conditions (26).…”

Section: Significancementioning

confidence: 99%

“…to the ocean. Identification of the mechanisms behind such increased nutrient delivery has been a major topic of investigation (21), and three main mechanisms have been proposed: (i) hydrothermal activity (22,23,24), (ii) enhanced continental weathering (18,19), and (iii)…”

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confidence: 99%

Sulfur isotopes track the global extent and dynamics of euxinia during Cretaceous Oceanic Anoxic Event 2

Owens

Gill

Jenkyns

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

144

136

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The Mesozoic Era is characterized by numerous oceanic anoxic events (OAEs) that are diagnostically expressed by widespread marine organic-carbon burial and coeval carbon-isotope excursions. Here we present coupled high-resolution carbon-and sulfurisotope data from four European OAE 2 sections spanning the Cenomanian-Turonian boundary that show roughly parallel positive excursions. Significantly, however, the interval of peak magnitude for carbon isotopes precedes that of sulfur isotopes with an estimated offset of a few hundred thousand years. Based on geochemical box modeling of organic-carbon and pyrite burial, the sulfur-isotope excursion can be generated by transiently increasing the marine burial rate of pyrite precipitated under euxinic (i.e., anoxic and sulfidic) water-column conditions. To replicate the observed isotopic offset, the model requires that enhanced levels of organic-carbon and pyrite burial continued a few hundred thousand years after peak organic-carbon burial, but that their isotope records responded differently due to dramatically different residence times for dissolved inorganic carbon and sulfate in seawater. The significant inference is that euxinia persisted post-OAE, but with its global extent dwindling over this time period. The model further suggests that only ∼5% of the global seafloor area was overlain by euxinic bottom waters during OAE 2. Although this figure is ∼30× greater than the small euxinic fraction present today (∼0.15%), the result challenges previous suggestions that one of the best-documented OAEs was defined by globally pervasive euxinic deep waters. Our results place important controls instead on local conditions and point to the difficulty in sustaining wholeocean euxinia.carbonate-associated sulfur | geochemical modeling

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“…Since the discovery of OAEs, a number of isotopic/elemental proxies that are sensitive to the chemical perturbations (e.g. Sr, Os, Ca, Nd, P, Pb, Li, U, S; Arthur et al, 1987;McArthur et al, 2004;Forster et al, 2007;MacLeod et al, 2008;Turgeon and Creaser, 2008;Voigt et al, 2008;Montoya-Pino et al, 2010;Blättler et al, 2011;Kuroda et al, 2011;Mort et al, 2011;Pogge von Strandmann et al, 2013;Owens et al, 2013;Du Vivier et al, 2014 have aided the understanding of the driving mechanisms of oceanic anoxia, and deciphering responses of seawater chemistry in multiple basin environments.…”

Section: Introductionmentioning

confidence: 99%

Pacific 187 Os/ 188 Os isotope chemistry and U–Pb geochronology: Synchroneity of global Os isotope change across OAE 2

Vivier

Selby

Condon

et al. 2015

Earth and Planetary Science Letters

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Studies of OAE 2 sections beyond the Atlantic Ocean, Western Interior Seaway (WIS) and European pelagic shelf are limited. Here, we present initial osmium isotope stratigraphy ( 187 Os/ 188 Os-Os i ) from two proto-Pacific sites that span the Cenomanian-Turonian boundary interval (CTBI): the Yezo Group (YG) section, Hokkaido, Japan, and the Great Valley Sequence (GVS), California, USA; to evaluate the 187 Os/ 188 Os seawater chemistry of the proto-Pacific. Additionally we combine new 206 Pb/ 238 U zircon CA-ID-TIMS geochronology from five volcanic tuff horizons of the Yezo Group section to test and facilitate inter-basinal integration with the WIS using radio-isotopically constrained age-depth models for both sections, and quantitatively constrain the absolute timing and duration of events across the CTBI. The YG shows an almost identical Os i profile to that of the WIS, and very similar to that of other sites of the proto-Atlantic and European pelagic oceans (Turgeon and Creaser, 2008;Du Vivier et al., 2014). The characteristics of the Os i profile are radiogenic and heterogeneous (∼0.55-0.85) prior to the OAE 2, and synchronous with the inferred OAE 2 onset the Os i abruptly become unradiogenic and remain relatively homogeneous (∼0.20-0.30) before showing a gradual return to more radiogenic Os i (∼ 0.70) throughout the middle to late OAE 2. A 206 Pb/ 238 U zircon age of an interbedded tuff (HK017) in the adjacent horizon to the first unradiogenic Os i value constrains the age of the Os i inflection at 94.44 ± 0.14 Ma. This age, including uncertainty, agrees with the interpolated age of the same point in the Os i profile (94.28 ± 0.25 Ma) in the only other dated OAE 2 section, the WIS; indicating a coeval shift in seawater chemistry associated with volcanism at the OAE 2 onset at the levels of temporal resolution (ca. 0.1 Myr). Further, prior to the onset of OAE 2 an enhanced radiogenic inflection in the Os i profile of the YG is correlative, within uncertainty, with a similar trend in the WIS based on the U-Pb agedepth model. The interpolated ages, 94.78 ± 0.12 Ma and 94.66 ± 0.25 Ma for this Os i inflection in the YG and WIS, respectively, indicate that palaeocirculation was sufficient to simultaneously influence transbasinal seawater chemistry. In contrast, the pre-OAE 2 Os i profile for the GVS is disparate to that of the YG and those of the proto-Atlantic and European pelagic shelf locations. We interpret the pre OAE 2 heterogeneous Os i values (0.30-0.95) to record a palaeobasin that was regionally influenced interchangeably by both unradiogenic (hydrothermal flux) and radiogenic (continental flux) Os. We conclude that the Os i profiles from the proto-Pacific sections record both trends that are consistent globally (OAE 2 onset, syn and post OAE 2), but also show regional differences (pre OAE 2) between OAE 2 sections worldwide. As such the Os i profiles coupled with U-Pb geochronology facilitate the correlation of OAE 2 stratigraphy, and demonstrate both regional and global ocean dynamics.

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Nd isotopic excursion across Cretaceous ocean anoxic event 2 (Cenomanian-Turonian) in the tropical North Atlantic

Cited by 106 publications

References 31 publications

Empirical links between trace metal cycling and marine microbial ecology during a large perturbation to Earth's carbon cycle

Empirical links between trace metal cycling and marine microbial ecology during a large perturbation to Earth's carbon cycle

Sulfur isotopes track the global extent and dynamics of euxinia during Cretaceous Oceanic Anoxic Event 2

Pacific 187 Os/ 188 Os isotope chemistry and U–Pb geochronology: Synchroneity of global Os isotope change across OAE 2

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