ASGP (2014), vol. 84: 185-212

UNCONFORMITY SURFACES IN PELAGIC CARBONATE ENVIRONMENTS: A CASE FROM THE MIDDLE BATHONIAN OF THE BETIC CORDILLERA, SE SPAIN

Luis M. Nieto (1), Francisco J. Rodríguez-Tovar (2), José M. Molina (1), Matías Reolid (1) & Pedro A. Ruiz-Ortiz (1)

1) Departamento de Geología and CEACTierra, Universidad de Jaén, 23071 Jaén, Spain; e-mails: lmnieto at ujaen.es, jmmolina at ujaen.es, mreolid at ujaen.es, paruiz at ujaen.es
2) Departamento de Estratigrafía y Paleontología, Universidad de Granada, 18002 Granada, Spain; e-mail: fjrtovar at ugr.es

Nieto, L.M., Rodríguez-Tovar, F.J., Molina, J.M., Reolid, M. & Ruiz-Ortiz, P.A., 2014. Unconformity surfaces in pelagic carbonate environments: A case from the Middle Bathonian of the Betic Cordillera, SE Spain. Annales Societatis Geologorum Poloniae, 84: 281–295.

Abstract: Integrative studies of sedimentary and palaeontological topics for unconformity surfaces are useful in basin analysis. A middle Bathonian unconformity surface in the Ammonitico Rosso facies cropping out in the La Mola Unit (Subbetic Domain, Betic External Zone) was studied by integrating ichnological, palaeotectonic, and sedimentological analyses to decipher sea-level, tectonic, and palaeogeographic conditions during its development. The trace-fossil assemblage mainly consists of the Glossifungites (Thalassinoides, Arenicolites, and Gastrochaenolites) and Trypanites ichnofacies elements. Probable Ophiomorpha represents previous softground stages, Thalassinoides and Arenicolites were formed in firmground, Gastrochaenolites reflects an evolved firmground or early hardground, and Trypanites can be attributed to an incipient hardground. The degree of firmness, relative sea-level position, and continuity of deposition were related. The softground stage corresponds to a fall in relative sea level and continued deposition. The firmground (semi-consolidated substrate) probably reflects an extremely low sea level characterized by non-deposition, whereas the incipient hardground stage indicates an initial phase of relative sea-level rise, with an increase in marine current energy. The presence of two neptunian dyke systems reflects significant tectonic activity related to the transtensional deformation that affected the South Iberian Palaeomargin. Lateral variations in sedimentological and ichnological features recorded at similar discontinuity surfaces in nearby areas were considered and related to differences in bottom topography, with associated changes in sedimentation, and to the variable duration of the hiatus.

Manuscript received 4 July 2014, accepted 5 November 2014