Fosildiagénesis del anélido Rotularia spirulaea (Lamarck, 1818) (Polychaeta, Serpulidae) en el Eoceno del dominio pirenaico occidental

Abstract

The presence of the fossil polychaete Rotularia spirulaea (Lamarck, 1818) in Eocene deposits (middle Lutecian – upper Bartonian and (?) Priabonian) belonging to the western Pyrenean Domain is verified. In this paper, a fossildiagenetic study has been carried out. Fossils from three areas, corresponding to diff erent depositional settings, have been analysed. In area 1, sediments of the Ardanatz Sandstone and Ilundain Marls formations [Pamplona Basin and adjoining areas (Navarre)], were sampled. Here, the specimens of R. spirulaea  were not substantially affected by taphonomic reworking and the original microstructure of the carbonate tube is preserved. The test consists of a thick external shell layer, composed of three zones in succession, and another extremely thin inner shell layer. The lumen of the tube is filled in by fine-grained sediment and/or calcitic cement. In area 2 , which includes the town of Anderatz and several outcrops of the Urbasa mountain range (Navarre), Urbasa-Andia Formation and overlying deposits, as well as in area 3 , located on the upper part of the calciclastic fl ysch of Punta Galea (Biscay), fossils are included in sediments deposited in high-energy environments. In this case, the microstructure of R. spirulaea  tube is not completely recognized due to intense, early diagenetic silicifi cation aff ecting the tests. The lumen is filled in with fragments of foraminifera and calcareous algae, quartz-feldespathic sediment and cemented by calcite. Therefore, in zones 2 and 3 the fossildiagenetic processes are substantially different from those recognized in zone 1.