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ITCZ controls on Late Cretaceous black shale sedimentation in the tropical Atlantic Ocean

Lookup NU author(s): Professor Thomas Wagner


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This study presents high resolution organic and inorganic proxy records for Coniacian to Santonian black shale on the Demerara Rise (ODP Site 1261) in the western tropical Atlantic off South America. We integrate these records with approximately time equivalent geochemical data from the eastern tropical Atlantic off tropical Africa (ODP Site 959) to extract the underlying relationships of Intertropical Convergence Zone (ITCZ) dynamics and black shale formation in the tropical Cretaceous Atlantic at orbital time scales. The geochemical records from the Demerara Rise show repetitive fluctuations in productivity, ocean redox conditions, and clastic sediment supply consistent with a dynamic paleo-upwelling regime off tropical South America. Upwelling intensity most likely was driven by shifts of the mean annual position of the ITCZ, which connects the large-scale precipitation and wind field patterns of the Hadley cells. Upwelling was strongest off South America and burial of oil-prone organic matter most pronounced when the ITCZ was in its southernmost position, which maximized the impact of NE trade winds on the inner, tropical part of the northern Hadley cell. Geochemical records from the Deep Ivorian Basin (equatorial Atlantic) suggest that source rock formation occurred in phase with regions north of the equator. Off tropical Africa, however, black shale formation was primarily driven by regional rainfall and nutrient export. The results of this study provide a conceptual framework that explains the formation, distribution and quality of petroleum source rocks below the tropical component of the Hadley cells on orbital time scales.

Publication metadata

Author(s): Hofmann P, Wagner T

Publication type: Article

Publication status: Published

Journal: Paleoceanography

Year: 2011

Volume: 26

Issue: 4

Pages: PA4223

Print publication date: 23/12/2011

ISSN (print): 0883-8305

ISSN (electronic): 1944-9186

Publisher: American Geophysical Union


DOI: 10.1029/2011PA002154


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Funder referenceFunder name
Royal Society
HO 2188/4German Science Foundation
WA 1036/11German Science Foundation