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Book Chapter

No extinctions during Oceanic Anoxic Event 1b: the Aptian–Albian benthic foraminiferal record of ODP Leg 171

By
Ann Holbourn
Ann Holbourn
Institut für Geowissenschaften, Christian Albrechts Universität, Olshausenstr. 40, 24118 Kiel, Germanyah@gpi.uni-kiel.de
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Wolfgang Kuhnt
Wolfgang Kuhnt
Institut für Geowissenschaften, Christian Albrechts Universität, Olshausenstr. 40, 24118 Kiel, Germanyah@gpi.uni-kiel.de
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Published:
January 01, 2001

Abstract

Outstandingly well-preserved benthic foraminiferal successions from upper Aptian-lower Albian sediments at Site 1049 (Leg 171, Blake Nose escarpment, western North Atlantic) provide a detailed record of the faunal turnover across Oceanic Anoxic Event lb (OAE lb). Changes in abundance, diversity and species composition reflect strong fluctuations in carbon flux and bottom-water oxygenation. Before the onset of black shale sedimentation, the originally diverse assemblages are replaced by low-diversity associations, dominated by species inferred to be opportunistic phytodetritus feeders and thriving on an enhanced carbon flux to the sea floor. The 46 cm thick laminated black shale horizon corresponding to OAE lb is virtually devoid of benthic foraminifers or contains highly impoverished assemblages, suggesting that intense eutrophication and/or strong stratification triggered near anoxia at the sea floor during black shale deposition. Above the black shale, reoccurrence of the pre-black shale fauna points to relatively rapid bottom-water reoxygenation. The benthic foraminiferal record of Leg 171 provides clear evidence that no major extinctions occurred across OAE lb, as most of the species occurring below the black shale reappear above it. In contrast to other Cretaceous anoxic events, OAE lb may have been more limited in duration or in geographical and water-depth extent, allowing recolonization from adjacent, more hospitable areas, once local conditions improved at the sea floor. Prolific radiation within the suborder Rotaliina and diversification of Textulariina with calcareous cement appear to have started in the Aptian time before OAE lb, and continued into early AIbian time to give rise to many of the modern lineages.

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Contents

Geological Society, London, Special Publications

Western North Atlantic Palaeogene and Cretaceous Palaeoceanography

Dick Kroon
Dick Kroon
University of Edinburgh, UK
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R. D. Norris
R. D. Norris
Woods Hole OI, USA
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A. Klaus
A. Klaus
Ocean Drilling Program, USA
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Geological Society of London
Volume
183
ISBN electronic:
9781862394315
Publication date:
January 01, 2001

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