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Abstract
A palynological investigation of 15 ditch cutting samples from Borehole 8, located off the Angolan coast, west-central Africa, revealed Late Oligocene (Chattian) to latest Middle to earliest Early Miocene (Serravallian/earliest Tortonian?) marine dinoflagellate cysts, freshwater colonial algae and terrestrial palynomorphs. Various early Miocene pollen characterising the Verrutricolporites rotundiporus Zone of Legoux (Citation1978) confirm the location of the Oligocene–Miocene boundary in relation to a new short-ranging early Miocene dinoflagellate cyst taxon Cristadinium headii sp. nov. The Oligocene to Miocene dinoflagellate cyst assemblages reflect three periods, A–C, with high palaeoproductivity, corresponding to periods in the latest Oligocene (late Chattian), Early Miocene (late Aquitanian–early Burdigalian?) and the base of the Middle Miocene (Langhian). Early to middle Miocene acme intervals of Cleistosphaeridium placacanthum and Cribroperidinium tenuitabulatum are considered to reflect two regional oceanographic events due to intense upwelling along the West African coast. A distinct Early Miocene episode of brackish-water outflow from the nearby Angolan mainland is also reflected by the palynological assemblages, perhaps linked to the global Mi-1 event. Changes in relative abundance of grass pollen indicate a gradual change towards a drier and perhaps also warmer Burdigalian–Langhian climate during which the Angolan savanna developed, followed by cooler and perhaps more humid conditions following the Miocene Climatic Optimum.
Acknowledgements
Dr. K. Dybkjaer (GEUS) and M. Jones (Palynological Laboratory Services Scotland) are thanked for their assistance in connection with the palynological processing. Prof. F. Oboh–Ikuenobe (Missouri University of Science and Technology) for constructive advice during the publishing process. The palynological data presented were collected as part of a postdoctoral project carried out at Oslo University, Department of Geology, during 2004 to 2007. The first author acknowledges Statoil ASA, for access to the Angolan cutting material and financial support in the form of a postdoctoral position at the University of Oslo. Dr. Iain Prince (then Statoil, now Shell) is thanked for his support and for initiating this research project. The two reviewers Dr. Dirk Munsterman and Dr. Martin J. Head are thanked for their constructive and careful reviews.
Additional information
Notes on contributors
Pi Suhr Willumsen
PI SUHR WILLUMSEN specialises in the global correlation of terrestrial and marine palynomorphs, palynofacies, integrated biostratigraphy, dinoflagellate cyst paleoecology and taxonomy. She gained her MSc in Geology in 1997 from Aarhus University, Denmark. Pi studied the palynology of the marine Eocene Mo-Clay Formation supervised by Kaj Raunsgaard-Pedersen. Her PhD was undertaken at the Victoria University of Wellington, New Zealand between 1998 and 2003. Pi researched the marine palynology and palynofacies across several Cretaceous-Paleogene boundary sections exposed in onshore New Zealand. After some consulting work from her home in Copenhagen, Denmark, she embarked on postdoctoral research at Oslo University, Norway (2004–2007), correlating terrestrial and marine palynomorphs from Oligocene to Miocene strata in eight offshore wells in the Angolan Basin in west-central Africa. This project was run by Barrie Dale and funded by Statoil ASA, Norway. From 2008 to 2012, Pi worked at Lund University, Sweden; since 2013 she has been an affiliated senior researcher at Aarhus University.
Gitte Vestergaard Laursen
GITTE VESTERGAARD LAURSEN has 20 years of experience as a Biostratigraphic Specialist in the Norwegian State oil company Statoil, in the Exploration Excellence division at the main office in Stavanger. She received her MSc (1990), and her PhD (1995) from the University of Aarhus, Denmark, on applied biostratigraphy of the North Sea Basin. She is the former chairman of the Regional Committee on Northern Neogene and Paleogene Stratigraphy and has been teaching applied biostratigraphy courses at the Universities of Bonn, Germany and Oslo, Norway. Her current research interest is the Oligo-Miocene of the Middle East, and the Jurassic of the North Sea.
