Genèse des laminites diatomitiques du Miocène supérieur de Sanlúcar de Barrameda (Cadiz, Espagne): données sur le nannoplancton siliceux et calcaire

The nannoplankton associations from upper Miocene (Tortonian) diatomitic laminites of Sanlucar de Barrameda (Betic System) have been studied and compared with those from Upper Miocene biogenic sediments of Beticas. This dominance is stronger in the laminated sediments where there is an increase of small forms of Distephanus speculum Ehrenberg, small Prinsiaceae and Coccolithus pelagicus (Wallich). These characteristics shown that the environment where nannoplankton associations from laminites developped were more productive than that in which biogenic sediments deposited. The lamination is preserved due to anoxic conditions established at the basin bottom