CASADIO Silvio Alberto
ENCRUSTING AND BORING BARNACLES THROUGH THE CRETACEOUS/PALEOGENE BOUNDARY IN NORTHERN PATAGONIA (ARGENTINA)
BREZINA, S.S.; ROMERO, M. V.; CASADIO, SILVIO
ASOCIACION PALEONTOLOGICA ARGENTINA
Lugar: Buenos Aires; Año: 2016
Information about barnacles as fossil components of hard substrate communities from middle latitudes in the Southern Hemisphere is scarce. Changes in these barnacle communities during episodes of extinction such as occurred during the Cretaceous/Paleogene (K-Pg) boundary are almost unknown. We describe encrusting and boring barnacles associated with Maastrichtian and Danian oysters, evaluate taphonomic processes involved, and report changes in their frequencies over time. A total of 1,174 valves belonging to nine oyster species, collected from the Jagüel and Roca formations of the Neuquén Basin, were analyzed. Presence/absence of barnacles or their bioerosional traces were recorded, frequencies of host incrustation and bioerosion were calculated, and taphonomic and statistical analyses were performed. Encrusting barnacles identified on the oyster shells were assigned to Verruca rocana Steinmann and their traces assigned to the ichnospecies Centrichnus concentricus Bromley and Martinell. Boring barnacles are represented by traces assigned to the ichnogenus Rogerella De Saint-Seine. A preliminary taphonomic analysis indicated that late Maastrichtian and early Danian shells showed fair-poor condition by abrasion and fragmentation as taphonomic attributes, while late Danian shells exhibited mostly good-fair or mixed condition for both attributes. Verruca rocana shows no records during late Maastrichtian but high frequencies of encrusted valves after the K-Pg boundary. Boring barnacles represented by the trace Rogerella exhibited a decline in abundance during early Danian but an increase at late Danian. Both encrusting and boring barnacles associated with oysters presented an increase in theirfrequencies during late Danian.