Microendoliths in Lower Pliocene Oysters from the Alt Empordà Basin,NW Mediterranean: Paleoenvironmental Inferences

The study of traces made by microendoliths on Neopycnodonte cochlear shells from a coquina in the Vilacolum area (Alt Empordà basin) has permitted us to identify for the first time 18 ichnotaxa in the Lower Pliocene sediments of the NW Mediterranean. A shallow, euphotic environment with local shaded zones (corresponding to deep shallow conditions) is proposed for this shell bed, owing to the presence of abundant heterotroph microborings and rare cyanobacterial traces as well as to the high number of Rhopalia catenata and Ichnoreticulina elegans. This refines a former interpretation, mainly based on body fossils and macroborings, which suggested simply a shallow depositional environment. The ichnospecies Ichnoreticulina elegans, Rhopalia catenata, ?R. clavigera, Saccomorpha clava, S. terminalis, Polyactina araneola, Entobia mikra, Orthogonum lineare and Aurimorpha varia are identified for the first time in marine Pliocene materials, thus furnishing a more complete picture of the temporal span of some microborers.