Chronology of Late Pleistocene glacier advances in the Rı́o Mendoza Valley, Argentina

The Rı́o Mendoza valley at 33°S latitude has been repeatedly invaded by glaciers during the Late Pleistocene. Relative-age criteria, U-series ages, and thermoluminescense dating, permitted the glacial deposits to be separated into three mappable units, each less extensive than its predecessor, designed from oldest to youngest, Penitentes, Horcones and Almacenes drifts. Previous studies have shown that during the Penitentes advance the glacier system terminated at 2500 m, while during the subsequent Horcones advance, ice terminated at 2750 m and the Almacenes moraine reached 3250 m. A travertine layer overlying Penitentes till yielded 230Th/232Th ages of 38,300±5300, 24,200±2000 and 22,800±3100 yr B.P. This study focuses on dating interstadial sediments in the upper Rı́o Mendoza valley in order to constrain the ages of the drifts. A date was obtained from a composite stratigraphic profile based on exposures along the east side of the Rı́o de los Horcones Inferior valley, a tributary of the Rı́o de las Cuevas valley, which includes the Penitentes and Horcones tills separated by nonglacial sediments (silt, fine sand and clay), and are interpreted as representing the Penitentes–Horcones nonglacial interval. The fine quartz grains (4–11 μm) of these sediments were TL dated as 31,000±3100 yr. All these dates, which are minimum ages for the underlying Penitentes till, imply that the Penitentes ice advanced prior to the last glacial maximum and sometime before ca. 40,000 years ago. A minimum date for Horcones till comes from an exposure on the east side of the Rı́o de los Horcones Inferior valley where the Horcones and Almacenes tills are separated by sediments of nonglacial origin. The fine quartz grains (4–11 μm) of these sediments have been dated by TL as 15,000±2100 years ago. Almacenes till is inferred to represent a standstill or a readvance that occurred late during the Horcones glacier advance. These dates imply that the Penitentes advance may correlate with marine oxygen isotope stage 4. The Penitentes–Horcones nonglacial sediments may have been deposited during interglacial isotope stage 3. The Horcones advance and the nonglacial sediments deposited between Horcones and Almacens tills may likely equate with stage 2. The moraine sequence is compared with those studied by Espizua (1998) along the Rio Grande valley in the southwestern Mendoza Province.