MARINE PALYNOLOGY OF THE ODP SITE-658 (N-W AFRICA) AND ITS CONTRIBUTION TO THE STRATIGRAPHY OF LATE PLIOCENE

A relatively high resolution pollen analysis (a sample each ca 5 ka) h as been made on ODP site 658, off Cap Blanc, N-W Africa. In the same c ores detailed palaeomagnetism, biostratigraphy, sedimentology and stab le isotopes provided a chronology based on the cyclic forcing by the a stronomical parameters. The period previous to 3.5 Ma corresponds to a warmer and wetter climate from northwestern Europe as far south as eq uatorial West Africa. Long term variation shows a first step towards a drier climate between 3.5 and 3.2 Ma. At 3.2 Ma, the pollen record es tablishes the aridification of northwestern Africa probably in connect ion with enhanced Trade winds. This phase may correspond to a prelimin ary stage of the Northern Hemisphere glaciation. Spectral analyses sho w a positive correlation between low deep sea temperatures in the Atla ntic Ocean and aridity in northwestern Africa. After a period of reest ablished humidity, a second and stronger step to aridification started at ca. 2.6 Ma. Before that date, there is a northern emplacement of s avannah and tropical forest that probably shifted southwards afterward s. Already from 2.8 Ma, a reduction of savannah vegetation took place, probably as a result of the development of a desert in West Africa. H owever, mean percentages of steppe elements of North Africa are five t imes lower during the Pliocene than during the Late Pleistocene indica ting that arid periods were still less prolonged and/or less severe du ring the Late Pliocene. Spectral analyses suggest that forcing of the climate by obliquity started after or ca. 2.6 Ma.