Morphological abnormalities in Late Cretaceous and early Paleocene foraminifer tests (northern Patagonia, Argentina)

Morphological abnormalities are common in Late Cretaceous and early Paleocene foraminifer tests at two localities in northern Patagonia, Argentina. Protelphidium sp. in the Auca Mahuevo section (late Campanian–early Maastrichtian) exhibit abnormal size or shape of the later chambers, with the last chamber commonly larger than normal or inflated and variably extending onto one of the lateral sides of the test; modification of the coiling plane; protuberances near the proloculus or on one or more chambers; a double last chamber, and complex forms. Protelphidium hofkeri Haynes in the Cerro Azul section (Danian) exhibit abnormal size or shape of one or more chambers, producing peripheral irregularities. In addition, there are rare multiple tests in planktic species from the Cerro Azul section, probably teratological specimens. The sedimentology of the sections and the character of the accompanying faunas indicate that the abnormalities in the two benthic foraminiferal taxa were most probably caused by hypersalinity and/or fluctuations in salinity. The fossil occurrence of assemblages with abundant deformed specimens suggests that investigators should carefully look at many aspects of the environment before concluding that anthropogenic pollution is the only cause of deformations of living benthic foraminifera.