(Table 1) Quantitative analysis of mollusk taxa from surface sediment samples in the Golfe d'Arguin

Ecological and taxonomic study of the mollusk-rich fauna of the Golfe d'Arguin, North Mauritania, investigates the various environmental influences affecting this tropical shelf. The upwelling of nutrient-rich waters leads to a highly productive environment under tropical conditions. The resulting mixed carbonate-siliciclastic sediment contains a large portion of calcareous components produced by heterotrophic organisms-e.g., mollusks, foraminifers, worms, barnacles-that are reworked on the open shelf. On the basis of mollusk assemblages, six taphocoenoses are defined, all being characterized by a mixed fauna of tropical (e.g., Tellina densestriata), subtropical (e.g., Macoma cumana) and temperate (e.g., Spisula subtruncata) species. Differences between the assemblages are related to the medium-grain size ranging from mud to gravel-that results from local hydrodynamic conditions and water depth. Among carbonate grains, Donax burnupi shells are very abundant in the swell-exposed, northern part of the Golfe d'Arguin and reflect the tropical to subtropical, high-energy, and high-nutrient waters. Mollusk assemblages are demonstrated to be a sensitive tool for deciphering complex environmental conditions in sedimentary archives.

Aptian to Cenomanian dinoflagellate cysts from the Mazagan Plateau

Eighty-eight samples of Aptian to lower Cenomanian sediments of Sites 545 and 547, DSDP Leg 79, from the Mazagan Plateau area (offshore Northwest Africa) were analyzed for palynomorphs. The very rich dinoflagellate cyst assemblages make it possible to narrow shipboard age determinations and to correlate Sites 545 and 547. The distribution of 174 dinoflagellate cyst taxa is tabulated in this study and the biostratigraphic value of selected dinoflagellate cysts is discussed. Additional taxonomic remarks are made about some species. The new dinoflagellate cyst species Aptea almohadensis, Occisucysta hinzü, O. mazaganensis, and the subspecies Maghrebinia perforata (Clarke and Verdier, 1967) Below, 1981 ssp. mirabilis are described.