MICROFOSSILS (FORAMINIFERA, OSTRACODA) AND THEIR RESPONSES TO THE PALEOENVIRONMENTAL CHANGES. AN EXAMPLE FROM THE ALLEN FORMATION (UPPER CRETACEOUS), NEUQUEN BASIN, ARGENTINA

MICROFOSSILS (FORAMINIFERA, OSTRACODA) AND THEIR RESPONSES TO THE PALEOENVIRONMENTAL CHANGES. AN EXAMPLE FROM THE ALLEN FORMATION (UPPER CRETACEOUS), NEUQUEN BASIN, ARGENTINA. 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 (69 degrees 00'W-37 degrees 30'S) constitute up to 74% of the total specimens. At the section close to Pellegrini lake (68 degrees 00'W-38 degrees 40'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.