Bioerosion patterns in benthic foraminiferal tests through the Cretaceous and Cenozoic of Patagonia and Tierra del Fuego, Argentina

MALUMIÁN, N.; LÓPEZ C. M.I.; NAÑEZ, C.; OLIVERO, E.B.

Bromley, R.G., Buatois, L.A., Mángano, M.G., Genise, J.F. & Melchor, R.N. (Eds.). Sediment - Organism interactions: A multifaceted ichnology. . SEPM Special Publication 88, p. 299–306. SEPM (Society for Sedimentary Geology), ISBN 978-1-56576-129-2

Año: 2007; p. 301 - 310

ABSTRACT: 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 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 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.,BSTRACT: 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 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 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.,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 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 Pliocene, giving a polar aspect to many Fuegian foraminiferal assemblages., 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 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 Pliocene, giving a polar aspect to many Fuegian foraminiferal assemblages.