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

Abstract

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.

Keywords:

• Microbioerosion
• Marine paleonvironments
• Pliocene
• NW Mediterranean

ACKNOWLEDGMENTS

The authors express their gratitude to Dr. M. Wisshak (Senckenberg am Meer, Germany) for introducing one of the authors (ARM) to the field of microbioerosion, and for his useful guidance. The authors also thank Dr. G. Radtke (Hessisches Landesamt für Umwelt und Geologie, Germany) and Dr. M. Carreiro da Silva (Universidade de Açores, Portugal) for help with identification and discussion. We are especially indebted to two reviewers, Dr. S. Golubic and Dr. R. Mikulás, for their invaluable assistance that has helped us to improve the original manuscript greatly. We also thank A. Gallardo and the staff of the Scientific and Technical Services of the Barcelona University (CCiTUB) for their crucial assistance in the preparation and SEM observation of samples.

Funding

This research was conducted within the framework of the Research Group Paleobiologia del Neogen Marí at the Universitat de Barcelona, and is a contribution to the project CGL2010-15047 funded by the Spanish Ministerio de Economía y Competitividad (MINECO).