Trace fossil assemblages on Miocene rocky shores of southern Iberia
The use of rocky palaeoshore bioerosion analysis in the study of palaeontological and geological questions is beginning to bear fruit. Five southern Iberian Neogene rocky shores have been analysed and their bioerosion structures have been identified. The
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act. The use of rocky palaeoshore bioerosion analysis in the study of palaeontological and geological questions is beginning to bear fruit. Five southern Iberian Neogene rocky shores have been analysed and their bioerosion structures have been identified. The observed ichnodiversity is rather low; eleven ichnospecies were identified. These include bioerosion structures produced by polychaete annelids (Caulostrepsis, Maeandropolydora), clionaid sponges (Entobia), echinoids (Circolites), and endolithic bivalves (Gastrochaenolites). The different ichnoassemblages present in Miocene rocky shores in both Portuguese and Spanish sectors correspond to the Entobia ichnofacies. Comparison with the northeastern counterparts of these shores has also been carried out. The study of southern Iberian Miocene rocky shores made it possible to correlate them with the regional tectonic evolution and the main Neogene transgressive events affecting the region. Keywords. Bioerosion, endolithic communities, rocky shores, transgression, Neogene, Iberian Peninsula
Introduction As recently as two decades ago, ancient rocky shores were still considered geological rarities (Boucot 1981). Since then, growing scientific interest in these palaeoenvironments has generated a wealth of publications (e.g., Palmer 1982; Brett and Brookfield 1983; Wilson 1985, 1987; Johnson 1988a, b, 1992; Pirazzoli et al. 1994; Brett 1998; Bertling 1999; Johnson and Baarli 1999; Ekdale and Bromley 2001; Benner et al. 2004; Johnson 2006; Plag 2006). This proliferation clearly demonstrates that fossil rocky shores are more common than previously believed. Because of their particular location, bordering marine and coastal environments, rocky shores react to any modification of physical or chemical parameters. So, they may be successfully used to estimate ancient sedimentation and erosion rates, M. Wisshak, L. Tapanila (eds.), Current Developments in Bioerosion. Erlangen Earth Conference Series, doi: 10.1007/978-3-540-77598-0_22, © Springer-Verlag Berlin Heidelberg 2008
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Santos, Mayoral, da Silva, Cachão, Domènech, Martinell
oceanic geochemistry, and eustatic fluctuations in sea level. Moreover, rocky coasts are special environments, with exceptional conditions for colonisation by boring and encrusting organisms due to their reduced or null sedimentation rates. The study of bioerosion structures produced in palaeoshores is invaluable for the identification and quantification of the relative oscillations of the sea level, past shoreline positions, the erosion / sedimentation rates associated with them, movements and reliefs of tectonic origin, depositional and / or stratigraphic hiatuses and the intensity of the physical disturbance of coastal environments. In addition, from a strictly palaeontological point of view, the analysis of rocky palaeoshore biota makes it possible to investigate ecological parameters such as spatial distribution, competitive overgrowth interactions and community succession (Brett 1988). Lastly, it is paramount for the study of the evolution
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