Resumen

CARIGNANO, Ana Paula  y  BALLENT, Sara. Microfossils (Foraminifera, Ostracoda) and their responses to the paleoenvironmental changes: An example from the Allen Formation (Upper Cretaceous), Neuquén Basin, Argentina. Ameghiniana [online]. 2009, vol.46, n.2, pp.307-320. ISSN 1851-8044.

Morphological abnormalities in benthic foraminifer tests and ostracods shells and carapaces from the Allen Formation (late Campanian-early Maastrichtian) in northern Patagonia, Argentina are analized. Abnormal tests of Protelphidium sp. from the Auca Mahuevo section (69º00´W-37º30´S) constitute up to 74% of the total specimens. At the section close to Pellegrini lake (68º00´W-38º40´S), Cophinia alleniensis Ballent with phenotypic hollow nodes reach near 30% of the total specimens. The sedimentology of the sections and the character of the accompanying microfauna indicate that the morphological deformities in both taxa were probably caused by hypersalinity and/or fluctuations in salinity, and also by eutrophication during deposition of Auca Mahuevo section. Descriptions and systematic updating of both taxa are included.

Palabras clave : Microfossils; Systematics; Morphological deformities; Upper Cretaceous; Argentina.