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PALEOCEANOGRAPHY, VOL. 19, PA1007, doi:10.1029/2003PA000933, 2004

Carbonate crash and biogenic bloom in the late Miocene: Evidence from ODP Sites 1085, 1086, and 1087 in the Cape Basin, southeast Atlantic Ocean

L. Diester-Haass

Zentrum für Umweltwissenschaften der Universität, Universität des Saarlandes, Saarbrücken, Germany


P. A. Meyers

Marine Geology and Geochemistry Program, Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan, USA


T. Bickert

Fachbereich Geowissenschaften, Universität Bremen, Bremen, Germany


Abstract

Middle/late Miocene to early Pliocene sedimentary sequences along the continental margin of southwest Africa have changes that correspond to the carbonate crash (12–9 Ma) and biogenic bloom events (∼7–4 Ma) described in the equatorial Pacific by Farrell et al. [1995] . To explore the origins of these changes, we analyzed the carbon and coarse fraction contents of sediments from ODP Sites 1085, 1086, and 1087 at a time resolution of 5 to 30 kyr. Several major drops in CaCO3 concentration between 12 and 9 Ma are caused by dilution from major increases in clastic input from the Oranje River during global sea level regressions. Abundant pyrite crystals and good preservation of fish debris reflect low oxygenation of bottom/pore waters. Regional productivity was enhanced during the time equivalent to the carbonate crash period. Higher benthic/planktic foraminiferal ratios indicate that CaCO3 dissolution at Site 1085 peaked between 9 to 7 Ma, which was after the global carbonate crash. This period of enhanced dissolution suggests that Site 1085 was located within a low-oxygen water mass that dissolved CaCO3 more easily than North Atlantic Deep Water, which began to bathe this site at 7 Ma. At 7 to 6 Ma, the onset of the biogenic bloom, increases and variations in total organic carbon and benthic foraminiferal accumulation rates show that paleoproductivity increased significantly above values observed during the carbonate crash period and fluctuated widely. We attribute the late Miocene paleoproductivity increase off southwest Africa to ocean-wide increases in nutrient supply and delivery 1 .

Received 26 May 2003; accepted 31 October 2003; published 4 February 2004.

Index Terms: 3022 Marine Geology and Geophysics: Marine sediments—processes and transport; 4267 Oceanography: General: Paleoceanography; 4279 Oceanography: General: Upwelling and convergences.

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Citation: Diester-Haass, L., P. A. Meyers, and T. Bickert (2004), Carbonate crash and biogenic bloom in the late Miocene: Evidence from ODP Sites 1085, 1086, and 1087 in the Cape Basin, southeast Atlantic Ocean, Paleoceanography, 19, PA1007, doi:10.1029/2003PA000933.