Upper Hauterivian nautiloids and related invertebrate assemblage from the Barranco de la Muela section (southeastern Spain): Systematic, biostratigraphical and palaeoenvironmental implications.

Abstract

The lower part of the Lower Cretaceous Bolos Sandstone Formation as exposed in the Barranco de la Muela section (Sierra de la Muela Range, southeastern Spain) yields two species of ornamented nautiloids, Cymatoceras neocomiense and Eucymatoceras plicatum. These have been collected togetherwith other cephalopods (ammonoids, belemnites) and different invertebrates (corals, brachiopods, bivalves, gastropods, echinoids). This fossil assemblage includes numerous large macroconchs of the ammonite Pseudothurmannia mortilleti, here considered as a senior synonym of P. catulloi, index species of the homonymous subzone of the upper Hauterivian ?Pseudothurmannia ohmi? Zone. On this basis, the here reported findings constitute the first biostratigraphically well-constrained records of C. neocomiense and E. plicatum, namely in the Pseudothurmannia catulloi Subzone. The presence of these two ornamented and relatively depressed nautiloids in finesandstone levels interbeddedwith sandymarlsof the Bolos Formation, togetherwith thepalaeoecological characteristics of the associated fauna suggest a nearshore to inner-middle shelf, shallowtomoderately deep palaeoenvironment with mixed siliciclastic-carbonate sedimentation, and high to moderate energy.