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Carbon- and oxygen-isotope records of mid-Cretaceous Tethyan pelagic sequences from the Umbria – Marche and Belluno Basins (Italy)

Carbon- and oxygen-isotope records of mid-Cretaceous Tethyan pelagic sequences from the Umbria – Marche and Belluno Basins (Italy)
Carbon- and oxygen-isotope records of mid-Cretaceous Tethyan pelagic sequences from the Umbria – Marche and Belluno Basins (Italy)
The late Albian – early Turonian time interval was marked by major environmental changes at regional to global scales. Oceanic Anoxic Events (OAE) 1d and OAE 2 and the mid-Cenomanian Event (MCE I) are all associated with ?13C anomalies that indicate perturbations of the global carbon cycle. In this study, new carbon- and oxygen-isotope records are presented from four Italian Tethyan sections: Furlo, Le Brecce and Monte Petrano (Umbria – Marche Basin) and Cismon (Belluno Basin), deposited in pelagic settings characterized by the alternation of nannofossil-planktonic foraminiferal limestones, radiolarian-rich levels and shales. The ?13C records exhibit a ? 1 ‰ positive excursion in ?13Ccarb corresponding with OAE 1d and a much larger positive anomaly (? 3–4 ‰) in ?13Corg corresponding with OAE 2 (Bonarelli Level). Between the strata that record these two events a double-spiked minor (? 0.7 ‰) positive excursion in ?13Ccarb marks the MCE I. Locally, after deposition of the MCE I but before formation of the Bonarelli Level, sedimentation shifted to alternate dysoxic/anoxic and well-oxygenated conditions as represented by lithological rhythms of black shales/black chert bands and whitish limestones. ?18O data indicate a progressive decrease in values from the upper Albian up to the Bonarelli Level (uppermost Cenomanian), suggesting an overall warming trend. Carbon-isotope stratigraphy, calibrated against biostratigraphy, provides a robust framework for dating and correlation, and allows identification of hiatuses in the studied sections. In particular, the high-resolution ?13C profiles through the Bonarelli Level highlight the presence of hiatuses of variable extent that systematically affect the middle to upper part of the characteristic carbon-isotope excursion and part of the following interval in all of the studied sections. Locally, a hiatus may also be present at the base of the Bonarelli Level. Correlations with carbon-isotope reference curves from other localities allow the duration of the missing intervals to be estimated as between 160 and 510 kyr in the middle to latter part of OAE 2 and the succeeding interval, showing that the Bonarelli Level extends no higher than the uppermost Cenomanian, even though the isotopic definition of the oceanic anoxic event indicates continuation into the early Turonian. The origin of these stratigraphic gaps can be attributed to physical and/or chemical processes operating at the sea floor. Complete recovery from the peculiar physico-chemical conditions that characterized the deeper parts of the Tethys Ocean during OAE 2 took at least 1 million years.
carbon and oxygen isotopes, oae 1d, chemostratigraphy, cretaceous, mce I, oae 2
0078-0421
299-323
Gambacorta, G.
3c2dd6bb-9b61-4595-9864-147af8f4f6e1
Jenkyns, H.C.
0e652f8f-f9e1-48fe-b846-85811c73b0e7
Russo, F.
323c39e6-333c-47a0-8b90-af406132df62
Tsikos, H.
c93667dd-8b7b-41b8-8aa0-4fc5dbb5c336
Wilson, P.A.
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Faucher, G.
1f808779-9946-46c2-9cbc-cfdd1bb4f754
Erba, E.
0368967a-948f-450f-8f9d-188ef36e420d
Gambacorta, G.
3c2dd6bb-9b61-4595-9864-147af8f4f6e1
Jenkyns, H.C.
0e652f8f-f9e1-48fe-b846-85811c73b0e7
Russo, F.
323c39e6-333c-47a0-8b90-af406132df62
Tsikos, H.
c93667dd-8b7b-41b8-8aa0-4fc5dbb5c336
Wilson, P.A.
f940a9f0-fa5a-4a64-9061-f0794bfbf7c6
Faucher, G.
1f808779-9946-46c2-9cbc-cfdd1bb4f754
Erba, E.
0368967a-948f-450f-8f9d-188ef36e420d

Gambacorta, G., Jenkyns, H.C., Russo, F., Tsikos, H., Wilson, P.A., Faucher, G. and Erba, E. (2015) Carbon- and oxygen-isotope records of mid-Cretaceous Tethyan pelagic sequences from the Umbria – Marche and Belluno Basins (Italy). Newsletters on Stratigraphy, 48 (3), 299-323. (doi:10.1127/nos/2015/0066).

Record type: Article

Abstract

The late Albian – early Turonian time interval was marked by major environmental changes at regional to global scales. Oceanic Anoxic Events (OAE) 1d and OAE 2 and the mid-Cenomanian Event (MCE I) are all associated with ?13C anomalies that indicate perturbations of the global carbon cycle. In this study, new carbon- and oxygen-isotope records are presented from four Italian Tethyan sections: Furlo, Le Brecce and Monte Petrano (Umbria – Marche Basin) and Cismon (Belluno Basin), deposited in pelagic settings characterized by the alternation of nannofossil-planktonic foraminiferal limestones, radiolarian-rich levels and shales. The ?13C records exhibit a ? 1 ‰ positive excursion in ?13Ccarb corresponding with OAE 1d and a much larger positive anomaly (? 3–4 ‰) in ?13Corg corresponding with OAE 2 (Bonarelli Level). Between the strata that record these two events a double-spiked minor (? 0.7 ‰) positive excursion in ?13Ccarb marks the MCE I. Locally, after deposition of the MCE I but before formation of the Bonarelli Level, sedimentation shifted to alternate dysoxic/anoxic and well-oxygenated conditions as represented by lithological rhythms of black shales/black chert bands and whitish limestones. ?18O data indicate a progressive decrease in values from the upper Albian up to the Bonarelli Level (uppermost Cenomanian), suggesting an overall warming trend. Carbon-isotope stratigraphy, calibrated against biostratigraphy, provides a robust framework for dating and correlation, and allows identification of hiatuses in the studied sections. In particular, the high-resolution ?13C profiles through the Bonarelli Level highlight the presence of hiatuses of variable extent that systematically affect the middle to upper part of the characteristic carbon-isotope excursion and part of the following interval in all of the studied sections. Locally, a hiatus may also be present at the base of the Bonarelli Level. Correlations with carbon-isotope reference curves from other localities allow the duration of the missing intervals to be estimated as between 160 and 510 kyr in the middle to latter part of OAE 2 and the succeeding interval, showing that the Bonarelli Level extends no higher than the uppermost Cenomanian, even though the isotopic definition of the oceanic anoxic event indicates continuation into the early Turonian. The origin of these stratigraphic gaps can be attributed to physical and/or chemical processes operating at the sea floor. Complete recovery from the peculiar physico-chemical conditions that characterized the deeper parts of the Tethys Ocean during OAE 2 took at least 1 million years.

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More information

Published date: 1 August 2015
Keywords: carbon and oxygen isotopes, oae 1d, chemostratigraphy, cretaceous, mce I, oae 2
Organisations: Paleooceanography & Palaeoclimate

Identifiers

Local EPrints ID: 382589
URI: http://eprints.soton.ac.uk/id/eprint/382589
ISSN: 0078-0421
PURE UUID: 3918a151-86e7-49b4-a71e-c7c684204fae
ORCID for P.A. Wilson: ORCID iD orcid.org/0000-0001-6425-8906

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Date deposited: 07 Oct 2015 09:58
Last modified: 15 Mar 2024 03:05

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Contributors

Author: G. Gambacorta
Author: H.C. Jenkyns
Author: F. Russo
Author: H. Tsikos
Author: P.A. Wilson ORCID iD
Author: G. Faucher
Author: E. Erba

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