Ichnology of the shallow marine Paraná Formation (Middle to Upper? Miocene), Entre Rios Province, Argentina

MARIANO VERDE; MIGUEL GRIFFIN; CARLOS A. CONSOLE GONELLA; FLORENCIO G. ACEÑOLAZA

Nueva Delhi

Congreso; 36 International Geological Congress; 2020

Organizing committee 36 International Geological Congress

We present the ichnological and sedimentary characterization of the Paraná Formation, a key unit to understand the marine ingressions of the Middle Miocene in southern South America. Exposures f this lithostratigraphic unit are widespread along the Mesopotamia region in Argentina; with a counterpart in Uruguay, the Camacho Formation. We analyzed two main sections of the Entre Ríos Province. At the Cantera Cristamine locality (Diamante department) there is a section of 8 m section in which the ichnogenera Thalassinoides, Ophiomorpha and Maiakarichnus were recorded in facies of siltstones and less commonly in cross-bedded carbonatic sandstones. At Molino Doll (Victoria department) the analyzed section is about of 4 m thick. The documented ichnoassociations are two, from bottom to top: I- a firmground suite composed of Gastrochaenolites ornatus; Gastrochaenolites isp. and Trypanites isp. emplaced in limestones, and II- a softground suite composed of Ophiomorpha isp.-Skolithos isp. found in fine massive to cross-stratified carbonatic sandstones. The associations of Cantera Cristamine are assigned to the Skolithos ? Cruziana Ichnofacies transition. Regardingf the Molino Doll ichnoassociations, the suite I was assigned to the Glossifungites Ichnofacies which usually represents an omission surface, where the low or absent sediment influx allowed the sessile boring fauna to colonize the firm-hardground. This situation changes at the top with the suite II, which can be related with to Skolithos Ichnofacies, suggesting an abrupt increase in sedimentation rate probably due to the cyclicity of the depositional system.