INSTITUTO ARGENTINO DE NIVOLOGIA, GLACIOLOGIA Y CIENCIAS AMBIENTALES
Unidad Ejecutora - UE
congresos y reuniones científicas
A LACUSTRINE BIOTIC ASSEMBLAGE IN THE EARLY CRETACEOUS OF CENTRAL ARGENTINA: LA CANTERA FORMATION.
ARCUCCI, A.B , G. PUEBLA, , L. S CODORNIÚ , G. P. GIORDANO AND M. PRÁMPARO
Simposio; 10th MESOZOIC TERRESTRIAL ECOSYSTEMS SYMPOSIUM; 2009
The fossiliferous content from La Cantera Formation, San Luis Province in central western Argentina, is known from 20 years ago although was not systematically explored until the last five years. Its geographic position is strategic because it is the only lacustrine fossiliferous unit located outside Patagonia, in southern South America, recording the Aptian interval and including palynomorphs, macrofloristic remains, invertebrate and vertebrate material in relative abundance and good state of preservation. The La Cantera Formation provided one of the most ancient and completes association of pollen grains and plant remains of primitive angiosperms, which allowed considering the unit as Late Aptian in age. The palynoflora studied is constituted also by aquatic forms (chlorophycean algae), gymnosperms (mainly plicate and rimulate forms), briophytes and pteridophytes. The macrofloristic record of this unit includes small impressions /compressions of angiosperms leaves, fragments of sphenophytes (equisetales), briophytes, pteridophytes and diverse types of reproductive structures (seeds and flowers) . The morphotypes of angiosperms studies represent the earliest record of compound leaves in South America and the first definitive fossils with affinities to the eudicots. The invertebrate groups present are arthropods: ostracods, conchostraca and a wide variety of insects, both terrestrial and aquatic that are abundant in some levels. The aquatic insects are represented by adults and several different ontogenetic stages. The fishes from La Cantera Formation include two main groups: Chondrostei and Pholidophoridae. Specimens of both groups are small-sized and articulated although the state of preservation is delicate. Pholidophoridae are less abundant at the present state of the collection. These forms are recorded since the Middle Triassic to the Early Cretaceous generally from marine sediments in Europe, Asia, Africa and Australia. The freshwater pholidophorids from La Cantera are the only record of the group in the Cretaceous in America. The interest of the studies on these basal teleosts is related with its critical position in recent phylogenies proposed. Further collection and detailed studies about the paleoenvironmental aspects of this unit and the different biotic components of this assemblage are developing at present in order to complete the reconstruction of the original lacustrine system.