La vida en un lago carbonático del Cretácico tardío

Abstract

Various authors have argued about the putative marine vs continental origin ofthe Yacoraite Formation (Salta Group) based mainly on its body fossil content and sedimentology. This work is focused on the ichnologic content of the Yacoraite Formation at the Tres Cruces sub-basin and reinforced by other paleontologic and sedimentologic evidences. The research reveals five ichnofabrics included in three ichnofacies models. The Lockeia ichnofabric record traces of epibentonic and infaunal subaqueous animals in shallow carbonatic environments, associated to domic microbialites, gastropods, ostracods, and scarce miliolid forams. The Treptichnus-SGP ichnofabric suggest an epibentonic and shallow endobentonic fauna developed in an oxygenated fresh water lake. lt is associated to smooth shelled heterodont bivalves and plant debris. Both ichnofabrics are included within the Mermia Ichnofacies. The Palaeophycus-Taenidium ichnofabric and the Scoyenia ichnofabric corresponds to the pre-desiccation and post-desiccation suits, respectively, ofthe Scoyenia Ichnofacies thus denoting the fluctuation (exposition vs. inundation) of the water in the shore margin. These ichnofabrics are associated to charophytes algae, ostracods, fragments of actinopterygian fishes, and dinosaur footprints. Finally, the Skolithos-Diplocraterion ichnofabric record semi-permanent structures of endobentonic animals which correspond to the continental Skolithos Ichnofacies in a underwater high energy setting, as a lake margin with strong wave influence. Accordingly, the present ichnological analysis of the Yacoraite succession, and in agreement with the paleontological and sedimentological information recovered, suggests deposition in a well oxygenated, relatively shallow carbonatic lake strongly influenced by climatic fluctuations which produced frequent contraction and expan - sion of the lake margin.