Fission-track dating of a tephra layer related to Poti-Malal and Seguro drifts in the Río Grande basin, Mendoza, Argentina

Two old drift units called Poti‐Malal and Seguro have been differentiated in the Río Grande basin based on relative‐age criteria, stratigraphical relationships, morphology and fission‐track dating. A tephra dated at 0.226 ± 0.025 Ma was deposited on the Poti‐Malal drift and underlies the Seguro outwash, which is inferred to equate with marine oxygen isotope stage 6. The stratigraphical position and age suggest that the tephra post‐dates the Poti‐Malal glaciation and that it is older than the Seguro drift. The Poti‐Malal glaciation must be at least as old as Early–Middle Pleistocene, and the Seguro glaciation is assigned to the penultimate glaciation. The tephra unit may have been deposited during marine oxygen isotope stage 7. Copyright © 2002 John Wiley & Sons, Ltd.