U-PB GEOCHRONOLOGY OF THE SANTA CRUZ FORMATION (EARLY MIOCENE) AT THE RÍO BOTE AND RÍO SANTA CRUZ (SOUTHERNMOST PATAGONIA, ARGENTINA): IMPLICATIONS FOR THE CORRELATION OF FOSSIL VERTEBRATE LOCALITIES

FERNICOLA, J. C.; CUITIÑO, J. I.; KOHN, M. J.; TRAYLER, R.; NAIPAUER, M.; BARGO, M. S.; KAY, R. F.; VIZCAÍNO, S. F.

Mar del Plata

Jornada; Reunión de la Asociación Paleontológica Argentina; 2015

Asociación Paleontológica Argentina

The early Miocene Santa Cruz Formation (SCF) in southern Patagonia hoststhe Santacrucian South American Land Mammal Age (SALMA), whose age is knownmainly from exposures along the Atlantic coast. Zircon U-Pb ages were obtained fromintercalated tuffs from four inland sections of the SCF: 17.36±0.63 Ma for thewesternmost Río Bote locality, and 17.04±0.55 Ma to 16.32±0.62 Ma for centralRío Santa Cruz localities. All ages agree with the bounding age of underlyingmarine units and with equivalent strata in coastal exposures. New ages andavailable sedimentation rates imply time spans for each section of ~18.20 to17.36 Ma for Río Bote and 17.45 to 15.63 Ma for central Río Santa Cruz. Theseestimates support the view that the SCF began depositing at western localities~1 Ma earlier than at eastern localities, and that the central Río Santa Cruzlocalities expose the youngest SCF in southern Santa Cruz Province. Associatedvertebrate faunas are consistent with our geochronologic synthesis, showingolder (Notohippidian) taxa at western localities and younger (Santacrucian)taxa at central localities. The Notohippidian fauna (19.0 to 18.0 Ma) of thewestern localities is synchronous with Pinturan faunas (19.0 to 18.0 Ma), butolder than Santacrucian faunas of the Rio Santa Cruz (17.2 to 15.6 Ma) andcoastal localities (18.0 to 16.2 Ma). The Santacrucian faunas of the centralRío Santa Cruz localities temporally overlap Colloncuran (15.7 Ma), Friasian(16.5 Ma), and eastern Santacrucian faunas.