EFFECT OF ANDEAN VOLCANISM ON NEOGENE MARINE INVERTEBRATES ON PENINSULA VALDÉS, ARGENTINA

Five localities within the Puerto Madryn Formation on Peninsula Valdés, Chubut Province, Argentina were investigated in order to assess the effects of volcanic ash on shallow marine communities during the late-middle Miocene (Tortonian). All five localities expose shallow marine deposits, and contain invertebrate fossils including abundant decapod crustaceans. Sediments and fossils were analyzed using multiple geochemical and visual methods including scanning electron microscopy (SEM), electron dispersive spectroscopy (EDS), X-ray diffraction spectroscopy (XRD), petrographic microscopy, and reflected light microscopy. The sediments uniformly contain a high percentage of very fine volcanic ash. Three previously unstudied localities including two paleosurfaces and a stratigraphic section which record a single mass mortality event were documented. Two paleosurfaces described by Casadío et al., 2005, were revisited in order to assess the cause of death of the fossil assemblages at those sites. The crustaceans are interpreted to have been the victims of acute respiratory failure due to the introduction of volcanic ash to the branchial chamber. Research supported by the Amoco Foundation, a grant from the Graduate Student Council and Sigma Gamma Epsilon at Kent State University, and Consejo Nacional de Investigaciones Cientificas y Técnicas (CONICET), Argentina.