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

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

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2016 vol. 70 p. 198 - 210

0895-9811

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 obtainedfrom intercalated tuffs from four inland sections of the SCF: 17.36 ± 0.63 Mafor the westernmost Río Bote locality, and 17.04 ± 0.55 Mae16.32 ± 0.62 Ma forcentral Río Santa Cruz localities. All ages agree with the bounding age ofunderlying marine units and with equivalent strata in coastal exposures. Newages and available sedimentation rates imply time spans for each section of~18.2 to 17.36 Ma for Río Bote and 17.45e15.63 Ma for central Río Santa Cruz(Burdigalian). These estimates support the view that deposition of the SCFbegan at western localities ~1 Ma earlier than at eastern localities, and thatthe central Río Santa Cruz localities expose the youngest SCF in southern SantaCruz Province. Associated vertebrate faunas are consistent with ourgeochronologic synthesis, showing older (Notohippidian) taxa in westernlocalities and younger (Santacrucian) taxa in central localities. TheNotohippidian fauna (19.0e18.0 Ma) of the western localities is synchronouswith Pinturan faunas (19.0e18.0 Ma), but older than Santacrucian faunas of theRío Santa Cruz (17.2e15.6 Ma) and coastal localities (18.0e16.2 Ma). TheSantacrucian faunas of the central Río Santa Cruz localities temporally overlapColloncuran (15.7 Ma), Friasian (16.5 Ma), and eastern Santacrucian faunas