Sedimentology and sedimentary paleoenvironments of Río Colorado Subgroup (Upper Cretaceous), Neuquén Group, in Neuquén city and surrounding areas

Abstract

Upper Cretaceous deposits included in Río Colorado Subgroup crop out in Neuquén city and surrounding areas. This work shows the results of the sedimentogical and paleoenvironmental analysis of Bajo de la Carpa (Santonian) and Anacleto (Lower Campanian) Formations. The studies allowed defining four conglomeratic lithofacies, nine sandy and two pelitics, which were grouped into nine lithofacies associations, being two of them eolian and the other fluvial. Bajo de la Carpa Formation is represented by an ephemeral fluvial system at its base, and fluvio-eolian interactions deposits on the top. Fluvial deposits belong to channalized flows during maximum discharge events. Then a transverse dune field affected by ephemeral currents that invaded interdune areas, and parabolic dunes, were the result of the remobilization of the underlying system, with periodic flood events by sheet ephemeral flows were also identified. The extension and geometry of the dune fields responded to short term climatic variability, fluvial system interference, water table fluctuations, low supply and/or availability of sediments and tectonic factors. Stabilization surfaces, suggested by truncated paleosoils, and a super bounding surface, have been recognized and both responded to climatic and tectonic factors. At its base, Anacleto Formation is bounded by a flood surface and is made of fluvial deposits of low sinuosity, high energy and quickly aggradation systems, controlled by low accommodation space and strong seasonal climatic conditions. Towards the top an anastomosed fluvial system were identified and reflects climatic variations and an increasing subsidence rate accompanied by a slow rise base level related to Maastrichtian atlantic ingression.