IADO   05364
INSTITUTO ARGENTINO DE OCEANOGRAFIA
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Paleoenvironmental implications of resting, locomotion and equilibrium/escape structures of freshwater bivalves, Río Negro Formation (late Miocene-early Pliocene).
Autor/es:
CARMONA, NOELIA B.; PONCE, JUAN J.; WETZEL, ANDREAS; BOURNOD, CONSTANZA N.; CUADRADO, DIANA G.
Lugar:
Santa Rosa, La Pampa
Reunión:
Simposio; II Simposio Latinoamericano de Icnología (SLIC 2013); 2013
Institución organizadora:
Universidad Nacional de La Pampa
Resumen:
Unionid are freshwater bivalves that live buried in muddy or sandy sediments in fluvial and marginal-lacustrine environments. These bivalves are suspension-filter feeders that form dense communities. Trace fossils produced by unionid bivalves are extremely common in wet-interdune deposits of the continental members of the Río Negro Formation (Late Miocene-Early Pliocene), forming almost monospecific assemblages. Based on ichnologic and sedimentologic analyses of these deposits, the paleoenvironmental evolution of these wet-interdune settings can be inferred. When the water level was high and relatively stable, bivalves colonized the muddy bottom, producing a great abundance of resting structures (cubichnia), most of which were oriented to the dominant currents. Some of these specimens are connected to lateral chevronate structures (repichnia), which are interpreted as short displacements of the bivalves during changes in current direction. In some of the wet-interdunes, water level dropped to the point of desiccation. In those cases, the resting and locomotion structures are found in association to desiccation cracks and they were covered subsequently by the migration of adjacent dunes. A different scenario is found if the dune migration occurred while the wet-interdunes were active. In these cases, the bivalves produced equilibrium or escape structures depending on the thickness of eolian sand deposited to keep pace with the continuous input of sand. At the end of some of these structures, the producer?s body fossils are preserved. These examples show that the information obtained from the ichnologic data has important implications for the understanding of the paleoenvironmental evolution of these Neogene eolian systems.