IMPACTS AS AN AGENT OF ENVIRONMNETAL UPHEAVAL IN THE ARGENTINE PAMPAS

During the last two decades, Schultz and coworkers (e.g., Geology, 1998; Science, 1998; EPSL, 2004; MAPS, 2006) have demonstrated the occurrence of at least seven separate asteroid or comet impact events in the Argentine Pampas. Each impact produced widely distributed melt ejecta that now mark distinct horizons in the Miocene to Recent stratigraphy. Schultz et al. (Science, 1998) proposed that one impact at approximately 3.27 Ma could have triggered a major turnover of fauna recorded in the mid-Pliocene sequences. Since that work was published, we have developed a more detailed understanding of the stratigraphy, petrology, potential source craters, and the asteroids associated with these ejecta. Each event created unique environmental and sedimentological circumstances that can be recognized in the local, regional, and even the global record. Locally, the reshaped landscape in and around each impact site changed drainage patterns and gradation rates. We review the latest findings of our investigations including the evidence for a major impact in the Bahía Blanca region at the Miocene-Pliocene boundary.