Bioerosion patterns in Cretaceous-Cenozoic benthic foraminiferal tests from Patagonia and Tierra del Fuego Island

MALUMIÁN, N., LÓPEZ C., M.I., NÁÑEZ, C. Y OLIVERO, E.B.

Trelew

Congreso; Ichnia 2004. First International Congress on Ichnology; 2004

Museo Paleontológico Egidio Feruglio

Cretaceous-Cenozoic benthic foraminiferal assemblages from Patagonia and Tierra del Fuego are mainly of shallow shelf settings of the temperate-cool Austral biogeoprovince, lacking larger foraminifera. A survey on more than 2000 samples, including occasional illustrations in systematic papers, shows that bioeroded tests are infrequent. However, a general pattern is indicated by (a) an apparent chronological distribution of boring abundance and (b) preference of predators upon most common species. (a) During the lower Cretaceous-Campanian, borings are very rare; in the Maastrichtian-Paleocene, rare. In the Mid-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 to main or supplementary apertures. A particular type (annular pits with central lowered shelf) was found on “Kolesnikovella”severini, a Patagonian endemic species. (b) The predators preference is mainly evident in genera either of Antarctic origin (e.g. Ammoelphidiella) or abundant in temperate-cool waters (e.g. Buccella), and in elongate thin-walled genera (e.g. Bulimina, Buliminella, Praebulimina). Scarcity or absence of bioerosion in the Lower 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 Mid Eocene, coincident with a temperature fall during the Cenozoic long cooling trend, affects genera that previously were recorded as intensely bored from the Antarctic Oligo-Miocene, giving a polar aspect to many Fuegian foraminiferal assemblages.