Early and Middle Miocene calcareous nannofossil distribution in the North Atlantic Ocean

Deep Sea Drilling Project Site 563, located on the west flank of the northern Mid-Atlantic Ridge, recovered a long Miocene section from which magnetostratigraphic and isotopic stratigraphy are available. Quantitative analyses of calcareous nannofossil assemblages have been performed in the Lower and Middle Miocene sediments from Site 563. The abundance patterns of the identified species allow us to determine several bioevents for this time interval. The recognized biohorizons, related to the available magnetostratigraphy, provide new data on the biostratigraphic value of many species and on the synchroneity of the events over a wide geographic area. Relations with the oxygen isotope stratigraphy are also reported. Sphenolith distribution is examined in particular detail due to their biostratigraphic importance in the Early Miocene. In particular the recently described species Sphenolithus procerus, Sphenolithus tintinnabulum and Sphenolithus multispinatus can be useful to subdivide the Lower Miocene zones NN2 and NN3. A large variety of Reticulofenestra pseudoumbilicus has been identified within zones NN6 and NN7.

Compound specific stable isotopes, BIT, pollen and spores of Miocene to Pliocene sediments of ODP Hole 175-1085A

Pollen and stable carbon (d13C) and hydrogen (dD) isotope ratios of terrestrial plant wax from the South Atlantic sediment core, ODP Site 1085, is used to reconstruct Miocene to Pliocene changes of vegetation and rainfall regime of western southern Africa. Our results reveal changes in the relative amount of precipitation and indicate a shift of the main moisture source from the Atlantic to the Indian Ocean during the onset of a major aridification 8 Ma ago. We emphasise the importance of declining precipitation during the expansion of C4 and CAM (mainly succulent) vegetation in South Africa. We suggest that the C4 plant expansion resulted from an increased equator-pole temperature gradient caused by the initiation of strong Atlantic Meridional Overturning Circulation following the shoaling of the Central American Seaway during the Late Miocene.