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Paleoenvironmental changes across the Mid Cenomanian Event in the tropical Atlantic Ocean (Demerara Rise, ODP Leg 207) inferred from benthic foraminiferal assemblages

Paleoenvironmental changes across the Mid Cenomanian Event in the tropical Atlantic Ocean (Demerara Rise, ODP Leg 207) inferred from benthic foraminiferal assemblages
Paleoenvironmental changes across the Mid Cenomanian Event in the tropical Atlantic Ocean (Demerara Rise, ODP Leg 207) inferred from benthic foraminiferal assemblages
This study is based on Cenomanian sediments of Ocean Drilling Program (ODP) Sites 1258 and 1260 from Demerara Rise (Leg 207, western tropical Atlantic, off Suriname, ~1000 and ~500 m paleo-water depth, respectively). Studied sediments consist of laminated black shales with TOC values between 3 and 18 % and include the Mid Cenomanian Event (MCE), a positive carbon isotope excursion predating the well-known Oceanic Anoxic Event 2 (OAE 2). Benthic foraminiferal assemblages of the continuously eutrophic environment at Demerara Rise are characterized by low diversities (? 9 species per sample) and large fluctuations in abundances, indicating oxygen depletion and varying organic matter fluxes. Dominant species at both sites are Bolivina anambra, Gabonita levis, Gavelinella dakotensis, Neobulimina albertensis, Praebulimina prolixa, and Tappanina cf. laciniosa. Benthic foraminiferal assemblages across the MCE show a threefold pattern: (1) stable ecological conditions below the MCE interval indicated by relatively high oxygenation and fluctuating organic matter flux, (2) decreasing oxygenation and/or higher organic matter flux during the MCE with decreasing benthic foraminiferal numbers and diversities (Site 1258) and a dominance of opportunistic species (Site 1260), and (3) anoxic to slightly dysoxic bottom-water conditions above the MCE as indicated by very low diversities and abundances or even the absence of benthic foraminifera. Slightly dysoxic conditions prevailed until OAE 2 at Demerara Rise. A comparison with other Atlantic Ocean and Tethyan sections indicates that the MCE reflects a paleoceanographic turning point towards lower bottom-water oxygenation, at least in the proto-North Atlantic Ocean and in the Tethyan and Boreal Realms. This general trend towards lower oxygenation of bottom waters across the MCE is accompanied by ongoing climate warming in combination with rising sea-level and the development of vast shallow epicontinental seas during the Middle and Late Cenomanian. These changes are proposed to have favoured the formation of warm and saline waters that may have contributed to intermediate- and deep-water masses at least in the restricted proto-North Atlantic and Tethyan Ocean basins, poor oxygenation of the Late Cenomanian sediments, and the changes in benthic foraminiferal assemblages across the MCE.
Benthic foraminifera, Mid Cenomanian Event, Cenomanian, Ocean Drilling Program, Cretaceous
0377-8398
28-40
Friedrich, Oliver
680f066c-a4b1-4647-beb3-281addc1ee17
Erbacher, Jochen
77fb7ba3-7411-4331-aa09-c467cd9c43ba
Wilson, Paul A.
f940a9f0-fa5a-4a64-9061-f0794bfbf7c6
Moriya, Kazuyoshi
d6b84bd5-a826-4cf9-8db3-5c65c4f1e93b
Mutterlose, Jörg
edc46210-d6c8-4709-9a8e-4f9d58092c45
Friedrich, Oliver
680f066c-a4b1-4647-beb3-281addc1ee17
Erbacher, Jochen
77fb7ba3-7411-4331-aa09-c467cd9c43ba
Wilson, Paul A.
f940a9f0-fa5a-4a64-9061-f0794bfbf7c6
Moriya, Kazuyoshi
d6b84bd5-a826-4cf9-8db3-5c65c4f1e93b
Mutterlose, Jörg
edc46210-d6c8-4709-9a8e-4f9d58092c45

Friedrich, Oliver, Erbacher, Jochen, Wilson, Paul A., Moriya, Kazuyoshi and Mutterlose, Jörg (2009) Paleoenvironmental changes across the Mid Cenomanian Event in the tropical Atlantic Ocean (Demerara Rise, ODP Leg 207) inferred from benthic foraminiferal assemblages. Marine Micropaleontology, 71 (1-2), 28-40. (doi:10.1016/j.marmicro.2009.01.002).

Record type: Article

Abstract

This study is based on Cenomanian sediments of Ocean Drilling Program (ODP) Sites 1258 and 1260 from Demerara Rise (Leg 207, western tropical Atlantic, off Suriname, ~1000 and ~500 m paleo-water depth, respectively). Studied sediments consist of laminated black shales with TOC values between 3 and 18 % and include the Mid Cenomanian Event (MCE), a positive carbon isotope excursion predating the well-known Oceanic Anoxic Event 2 (OAE 2). Benthic foraminiferal assemblages of the continuously eutrophic environment at Demerara Rise are characterized by low diversities (? 9 species per sample) and large fluctuations in abundances, indicating oxygen depletion and varying organic matter fluxes. Dominant species at both sites are Bolivina anambra, Gabonita levis, Gavelinella dakotensis, Neobulimina albertensis, Praebulimina prolixa, and Tappanina cf. laciniosa. Benthic foraminiferal assemblages across the MCE show a threefold pattern: (1) stable ecological conditions below the MCE interval indicated by relatively high oxygenation and fluctuating organic matter flux, (2) decreasing oxygenation and/or higher organic matter flux during the MCE with decreasing benthic foraminiferal numbers and diversities (Site 1258) and a dominance of opportunistic species (Site 1260), and (3) anoxic to slightly dysoxic bottom-water conditions above the MCE as indicated by very low diversities and abundances or even the absence of benthic foraminifera. Slightly dysoxic conditions prevailed until OAE 2 at Demerara Rise. A comparison with other Atlantic Ocean and Tethyan sections indicates that the MCE reflects a paleoceanographic turning point towards lower bottom-water oxygenation, at least in the proto-North Atlantic Ocean and in the Tethyan and Boreal Realms. This general trend towards lower oxygenation of bottom waters across the MCE is accompanied by ongoing climate warming in combination with rising sea-level and the development of vast shallow epicontinental seas during the Middle and Late Cenomanian. These changes are proposed to have favoured the formation of warm and saline waters that may have contributed to intermediate- and deep-water masses at least in the restricted proto-North Atlantic and Tethyan Ocean basins, poor oxygenation of the Late Cenomanian sediments, and the changes in benthic foraminiferal assemblages across the MCE.

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More information

Published date: April 2009
Keywords: Benthic foraminifera, Mid Cenomanian Event, Cenomanian, Ocean Drilling Program, Cretaceous

Identifiers

Local EPrints ID: 65029
URI: http://eprints.soton.ac.uk/id/eprint/65029
ISSN: 0377-8398
PURE UUID: 0d63c170-1ef8-4341-94a9-61049a46fe53
ORCID for Paul A. Wilson: ORCID iD orcid.org/0000-0001-6425-8906

Catalogue record

Date deposited: 27 Jan 2009
Last modified: 16 Mar 2024 03:13

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Contributors

Author: Oliver Friedrich
Author: Jochen Erbacher
Author: Paul A. Wilson ORCID iD
Author: Kazuyoshi Moriya
Author: Jörg Mutterlose

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