Antarcticella and Ammoelphidiella, typical austral Cenozoic extinct genera from southernmost South America

MALUMIÁN, N., NÁÑEZ, C. Y JANNOU, G.

Simposio; International Symposium on Foraminifera FORAMS 2014, Abstract Volume; 2014

The Patagonia was flooded by Atlantic transgressions in the Maastrichtian-Danian, late mid-Eocene, late Oligocene-early Miocene, and mid-Miocene; only in the Fuegian Andes the permanent marine conditions results in a rather complete Cenozoic sequence. Both areas provide an extended latitudinal and chronological study area, where most of the characteristic and abundant calcareous benthic foraminifera, endemic to southern high latitudes, have a partially or totally tuberculate test surface. They include the extinct genera Antarcticella, a small spherical form initially assigned to a planktonic habit, and Ammoelphidiella, a trochospiral Elphidiidae, both genera originally described from Antarctica; the origin of Antarcticella might be found in a Maastrichtian low spired and tuberculated new genus endemic to northern Patagonia. Antarcticella appears abruptly after the Cretaceous/Paleogene boundary, recorded by A. pauciloculata (Jenkins) from the Danian of New Zealand, Antarctica and Patagonia; A. cecionii (Cañón and Ernst), is constrained to the late early-early middle Eocene of the Fuegian Andes; A. antarctica (Leckie and Webb), originally described from the Antarctic latest Oligocene-early Miocene, ranges from the Fuegian late Eocene up to the mid-Miocene, reaching Peninsula de Valdes Basin (43°LS) in the early Miocene. Because micro and megalospheric tests are dissimilar and exhibit some differential paleogeographical distribution, the abundant microspheric tests are considered the typical form, and the megalospheric ones are informally named: A. pauciloculata forma primitiva, from the Danian of the Colorado and San Jorge basins; A. cecionii f. noguerense, from the Fuegian lower and lower middle Eocene; and A. antarctica f. incognita, from the Fuegian late mid-Eocene. The benthic habit previously assigned to Antarcticella is confirmed by: the accentuated dimorphism, unknown in planktonic foraminifera; the opportunistic behavior suggested by its distribution in different paleoenvironments, and by its abundance in organic-rich settings in correspondence with the preferences of similar modern spherical infaunal morphotypes. Ammoelphidiella, originally described from the Antarctic Pliocene, is recorded by a new species from the early Miocene of the Austral Basin up to the late early Miocene in the Colorado Basin. The geographic distribution of Antarcticella and Ammoelphidiella reveals the major penetration of Antarctic waters in the early Miocene on the Patagonian Platform. The tests of both genera share a preferential bioerosion among associated foraminifera and could be one of the causes that contributed to their disappearance in the late Pliocene.