Chronostratigraphy of the Barremian-Early Albian of the Maestrat Basin (E Iberian Peninsula): integrating strontium-isotope stratigraphy and ammonoid biostratigraphy

Abstract

A revised chronostratigraphy of the Barremian - Early Albian sedimentary record of the Maestrat Basin (E Iberian Peninsula) is provided based on a comprehensive synthesis of previous biostratigrahic data, a new ammonoid finding and numerical ages derived from 87Sr/86Sr values measured on shells of rudists, oysters and brachiopods. The succession, which comprises eight lithostratigraphic formations, is arranged into six major transgressive-regressive sequences and plotted against numerical ages, geomagnetic polarity chrons, ammonoid zones and the stratigraphic distribution of age-diagnostic ammonoids, orbitolinid fora- minifera and rudist bivalves. The oldest lithostratigraphic unit sampled, the marine Artoles Formation, is Early to Late Barremian. Above, the dinosaur-bearing deposits of the Morella Formation and its coastal to shallow-marine equivalent, the Cervera del Maestrat Formation, are of Late Barremian age and span at least part of the Imerites giraudi ammonoid zone. 87Sr/ 86Sr ratios from oyster shells in the upper part of the overlying marine Xert Formation are consistent with a latest Barremian-earliest Aptian age, while an ammonite belonging to the Late Barremian Martelites sarasini Zone was collected within the lowermost part of this lat- ter formation. The Barremian-Aptian boundary is tentatively placed close above the base of the succeeding transgressive marls of the Forcall Formation by analogy with nearby Tethyan basins, where major transgres- sive records contain latest Barremian ammonoids in their basal parts. The rest of the Forcall Formation and the platform carbonates of the Villarroya de los Pinares Formation are of Early Aptian age. The transition from the Barremian into the Aptian occurred in the course of a wide transgression, which was accompanied by the proliferation of Palorbitolina lenticularis. This transgressive event drowned Late Barremian carbonate platforms (Xert Formation) throughout the basin. Extensive carbonate platforms (Villarroya de los Pinares Formation) recovered coevally with a post-OAE 1a late Early Aptian major regression of relative sea level. The last lithostratigraphic unit analyzed, the marine Benassal Formation, spans the terminal Early Aptian- Late Aptian interval. Based on ammonite distributions, the lower part of the overlying coastal to continental coal-bearing Escucha Formation is Early Albian in age. This improved chronostratigraphic knowledge allows a more precise correlation of the sedimentary record studied with other coeval successions worldwide.