The Middle-Upper Jurassic oolitic ironstone level in the Iberian range (Spain). Eustatic implications.

Abstract

The oolitic ironstone level occurring at the Callovian-Oxfordian boundary across wide areas in the central Iberian Range (Eastern Spain) is interpreted here as formed on an extended, very shallow to temporarily emerged, uniform carbonate platform. Main evidence to support this interpretation comes from both sedimentological analysis of facies and taphonomic analysis of the ammonites. The sedimentological analysis gives support to the idea of iron oolites being formed on, or in the surroundings of, emerged areas. On the other hand, the taphonomic analysis shows that some inner moulds of ammonites from this level display evidence of taphonomic reworking, such as the presence of ellipsoidal abrasion facets on the final part of the last preserved whorl, or annular abrasion furrows carved on the external region. These features would have developed by the action of directional currents under extremely shallow conditions. Bathymetric implications are relevant for the interpretation of the sea level fluctuations at this stratigraphic interval: A relative lowstand of sea level is proposed for the Upper Callovian-Lower Oxfordian interval in the studied area.