Palynostratigraphy and paleoenvironmental shifts in upper Oligocene to Miocene strata off Angola, west-central Africa

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 characterizing the <i>Verrutricolporites rotundiporus</i> Zone of Legoux (1978) confirm the location of the Oligocene-Miocene boundary in relation to a new short ranging early Miocene dinoflagellate cyst taxon <i>Cristadinium headii</i> sp. nov.The Oligocene to Miocene dinoflagellate cysts assemblages reflect three periods, A-C, with high paleo-productivity, 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 <i>Cleistosphaeridium placacanthum</i> and <i>Cribroperidinium tenuitabulatum</i> 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.