Substrate-related changes in pectinid fossil assemblages

Quantitative analysis of pectinid (Bivalvia) assemblages in the Lower Pliocene deposits of the Almeria-Nijar and Poniente basins in southeastern Spain reveals changes in the taphonomical attributes, taxonomical composition, and shell morphology of these assemblages in relation to the sediments in which they occur. The lower Pliocene deposits in both basins consist of outer-platform clays, silts, and fine sands, which laterally and vertically pass into innerplatform and deltaic sands and conglomerates. Proximal and distal tempestite beds are intercalated in the sands and silts. Calcirudites accumulated in shallow water settings with no influx of terrigenous sediments. The variations of pectinid assemblages according to the embedding sediments represent changes in the assemblages in proximal—distal depth gradients. Pecten and Chlamys species predominate in shallow water conglomerates and calcirudites. Chlamys seniensis (Lamarck) and Flabellipecten bosniasckii (Stefani and Pantanelli) are the most abundant pectinids in coarseto-medium sands and in intercalated proximal tempestites from the inner platform and delta front. Amusium cristatum (Bronn) is the most common component in the assemblages from outer-platform fine sands, silts, clays, and distal tempestites. Assemblages from shallow-water, coarse-grained deposits comprise strongly-ribbed, inflated shells, while those from deep-water, fine-grained lithofacies are mainly composed of smooth, flat-shelled species.