Late Neogene foraminifera from the northern Namibian continental shelf and the transition to the Benguela Upwelling System. (May 2018)

• Record Type: Journal Article
• Authors: Bergh, Eugene W.; Compton, John S.; Frenzel, Peter
• Is Part Of: Journal of African earth sciences. Volume 141(2018)
• Page Start: 33
• Page End: 48
• Publication Date: 2018-05
• Subjects: Foraminifera -- Continental shelf -- Palaeoenvironment -- Miocene -- Mid-Miocene Climatic Optimum -- Pleistocene -- Southeast Atlantic -- Benguela Upwelling System -- Namibia -- Oligotrophic; Earth sciences -- Africa -- Periodicals; Earth sciences -- Middle East -- Periodicals; Geology -- Africa -- Periodicals; Geology -- Middle East -- Periodicals; Sciences de la terre -- Afrique -- Périodiques; Sciences de la terre -- Moyen-Orient -- Périodiques; Géologie -- Afrique -- Périodiques; Géologie -- Moyen-Orient -- Périodiques; Earth sciences; Geology; Africa; Middle East; Periodicals; Electronic journals; 556.05
• DOI: 10.1016/j.jafrearsci.2018.01.018
• Languages: English
• ISSNs: 1464-343X

Abstract

Abstract: Middle Miocene to Plio-Pleistocene foraminifera provide insights into the palaeoenvironment on the northern Namibian continental shelf located at the far northern end of the present-day Benguela Upwelling System (BUS). Biostratigraphy and Strontium Isotope Stratigraphy (SIS) of the recovered basal olive-green mud unit indicate an age of 16 to 14 Ma. A sharp, erosional contact separates the basal mud from the overlying Plio-Pleistocene gravelly pelletal phosphorite sands. Grain size data, P/B ratios and benthic diversity indices indicate a change between the middle Miocene and overlying Plio-Pleistocene palaeoenvironments linked to the timing and conditions associated with the initiation of the BUS. The different lithological units and microfossil assemblages in the olive-green mud unit and the overlying pelletal phosphorite units support the late Miocene initiation of the BUS and the northwards migration of the Angola-Benguela Front. Planktic foraminifera indicate a shift from warmer surface water conditions to cooler conditions during the initiation of the BUS. Benthic palaeobathymetric ranges and P/B ratios are consistent with outer shelf water depths suggesting a deeper palaeoenvironment during the Mid-Miocene Climatic Optimum (MMCO) than today. Benthic foraminifera in the middle Miocene are dominated by large (>1 mm) taxa and adapted to oligotrophic environments before the initiation of the BUS. The benthic assemblage composition indicates that bottom water conditions changed to eutrophic conditions during the Plio-Pleistocene under intensified upwelling conditions. Highlights: Biostratigraphy and Strontium Isotope Stratigraphy indicate middle Miocene age for basal mud unit. Warm subtropical sea surface conditions during middle Miocene. Deep water benthic foraminifera indicate higher sea levels during the middle Miocene. Deep, warm water conditions transition to shallow, cooler water conditions. Bottom water conditions changed from oligotrophic to eutrophic after middle Miocene.