Bioerosion Patterns in Cretaceous-Cenozoic Benthic Foraminiferal Tests from Patagonia and Tierra Del Fuego Island, Argentina

Cretaceous-Cenozoic benthic foraminiferal assemblages from Patagonia and Tierra del Fuego are characteristic mainly of shallow settings of the cool-temperate Austral geobioprovince, lacking larger foraminifera. A survey of more than 2000 samples, including illustrations in systematic papers, shows that bioeroded tests are uncommon. However, a general pattern is indicated by (a) an apparent chronological distribution of boring abundance and diversity: during the early Cretaceous-Campanian, borings are very rare, and in the Maastrichtian-Paleocene, rare. In the Middle Eocene an increased abundance of borings and boring types is apparent, including: circular, subcircular, roughly or neatly beveled; multiple, concentrated in juvenile chambers or one per chamber; and associated with main or supplementary apertures. (b) Taxa selectivity: predator preferences are evident mainly among the most common species, in genera either of Antarctic origin (e.g., Ammoelphidiella) or abundant in cool-temperate waters (e.g., Buccella), and in elongate thin-walled genera (e.g., Bulimina, Buliminella, Praebulimina). (c) Site selectivity: this is evident in a non-random distribution of borings observed in several cases. Scarcity or absence of bioerosion in the Early Cretaceous may be related to widespread dysaerobic-anaerobic conditions, that could diminish predation pressure and/or the dominance of finely perforate thick-walled Nodosariacea. Increased bioerosion in the Middle Eocene, coincident with a temperature fall during the Cenozoic long cooling trend, affects genera that previously were recorded as intensely bored from the Antarctic Pliocene, giving a polar aspect to many Fuegian foraminiferal assemblages.