The newly discovered section at Inchasi, located about 50 km southeast of Potosi, Bolivia, in the eastern Cordillera, consists of about 120 m of undeformed terrestrial sediments containing fossil mammals. Paleomagnetic analysis of 54 sites indicates a polarity pattern with an estimated duration of about 0.64 Ma. The rich Inchasi local fauna indicates a Montehermosan and/or Chapadmalalan land mammal age (Pliocene). Given these constraints, Inchasi correlates from the interval between the late Gilbert (within the Cochiti subchron) to the early Gauss (within the Mammoth subchron) chrons; that is, between about 4.0 and 3.3 Ma. The distinct lack of North American mammals in the Inchasi local fauna provides some of the first well-calibrated evidence that the Great American Interchange occurred after about 3.0 Ma, as has been previously stated based on other calibrations of the earliest immigrant (Uquian) faunas.
Nota bibliográficaFunding Information:
This research was supported by NSF grant EAR-8716207 to B.J. MacFadden. We thank COMSUR (Potosi office) for logistical support in the field, Michael J. Whitelaw for his excellent assistance in the paleomagnetic laboratory, and Carl C. Swisher for his analyses of the ash samples. This is University of Florida Contribution to Paleobiology 402.