Quaternary Glaciations in the Río Mendoza Valley, Argentine Andes

Abstract

In the Río Mendoza valley, five Pleistocene drifts and one Holocene drift are distinguished by multiple relative-age criteria, including surface-rock weathering, development of rock varnish, moraine morphology, soil-profile development, and stratigraphic relationships. Several absolute ages suggest a preliminary chronology. During the oldest (Uspallata) glaciation, a system of valley glaciers flowed 110 km from the Andean drainage divide and 80 km from Cerro Aconcagua to terminate at 1850 m. Drift of this ice advance is older than a widespread tephra dated by fission-track at 360,000 ± 36,000 yr. During the Punta de Vacas advance, ice terminated at 2350 m, while during the subsequent Penitentes advance, the glacier system ended at 2500 m. A travertine layer overlying Penitentes Drift has U-series age of 24,200 ± 2000 yr B.P. The distribution of Horcones Drift, which is inferred to represent the last glacial maximum, delimits an independent ice stream that flowed 22 km down Horcones valley to 2750 m. A later readvance (Almacenes) reached 3250 m. Confluencia Drift is considered to be Neoglacial in age and extends downvalley to 3300 m. The moraine sequence is compared with those studied by Caviedes (1972) along Río Aconcagua on the Chilean flank of the Andes.

36 Cl terrestrial cosmogenic nuclide dating suggests Late Pleistocene to Early Holocene mass movements on the south face of Aconcagua mountain and in the Las Cuevas–Horcones valleys, Central Andes, Argentina

“…3). Espizua (1993) and Fauqué et al (2009) agree upon the glacial origin of the deposit and Espizua (1999) maps this deposit as the Almacenes lateral moraine. She assigns a maximum age of 15 000 + 2100 years of underlying fluvial sediments to this unit that is in agreement with a single 36 Cl age obtained from a boulder, (which suggests that this moraine is 13 900 + 2200 years old; see Fauqué et al (2009)).…”

“…4) is identical with the lateral moraine deposit. The deposit is interpreted by Espizua (1993) and Fauqué et al (2009) as basal moraine. However, Espizua (1999) dates the deposit by thermoluminescence (TL) of quartz grains extracted from overlying fluvial deposits, up to 30 cm thick (photo in Fig.…”

“…All large landslide deposits have been sampled for age determination. Our earlier detailed mapping and dating (Fauqué et al 2009) have shown that various deposits that had previously been interpreted as being of glacial origin based on relatively scarce chronological data with huge uncertainties (Espizua 1993), are instead deposits of large mass movements while others indeed have a typical glacial morphology and are therefore of glacial age. This is suggested at least at two localities where lateral moraines were dated with single samples (Fauqué et al 2009).…”

“…Calcite and muscovite are nearly absent from the deposit. Espizua (1993Espizua ( , 1999 maps this deposit as the Almacenes moraine, and describes it as indistinguishable from the lateral moraine in Confluencia. We took three samples for TCN dating of the deposit using 36 Cl (samples H 13, H 21, DT 02 in Table 1).…”

“…With an altitude of 6959 m Aconcagua is the highest mountain in the Andes; due to their relatively easy access, the glacial deposits in Horcones, Las Cuevas and Mendoza valleys ( Fig. 1) have been well studied (Espizua 1993;Espizua & Bigazzi 1998;Espizua 1999). However, the origin of the supposed glacial deposits has been under dispute for a long time (Pereyra & González Díaz 1993).…”