Holocene glacier chronology of Valenzuela Valley, Mendoza Andes, Argentina

Abstract

Glacial geologic evidence and radiocarbon-dated glacial deposits provide evidence of glacier fluctuations during the last 5 ka years in the Andes. Radiocarbon-dated moraines, morphological and stratigraphical studies permit the reconstruction of glacier fluctuations during the Holocene in the Valenzuela area of the Mendoza Andes valley located at 35S, in the upper Rio Grande basin. The Holocene record in this part of the Andes is mostly unknown, so this research is relevant for palaeoclimatic reconstructions in South America. In the Rio Valenzuela, glacier variations were dated in the El Azufre and El Pefión valleys. The first Neoglacial advance occurred at c. 5700 yr BP and a very close re-advance of similar magnitude occurred at 4700-4300 yr BP which formed well-preserved lateral-terminal moraines. The first Neoglacial advance occurred in the El Pefión valley at c. 4400 yr BP and a well-preserved terminal moraine is observed. A second Neoglacial advance reached its maxima at c. 2500-2200 yr BP in the El Azufre and El Pefión glaciers. A third, corresponding to the ‘Little Ice Age’, culminated at c. 400 yr BP (C. AD 1451-1641 cal. yr) and 350 +60 yr BP (c. AD 1460-1644 cal. yr) in the El Azufre valley. The third Neoglacial advance is distinguished in the El Pefión valley based on morphological characteristics, colour, freshness of the glacial deposits and the proximity to the active glacier. It is indicated by the Amarilla I, II, III lateral moraines. An estimation of the magnitude of snowline depression is obtained comparing the altitude of the present snowline with that of the reconstructed snow line for the first Neoglacial and ‘Little Ice Age’ advances.

Climate in the Monte Desert: Past trends, present conditions, and future projections

“…Based on historical records, three (1627, 1649 and 1651) of the four coldest years during the XVII century in Mendoza were recorded during the same interval (Prieto, 1983). Glacier advances from the second half of the XV to the middle XVII century have also been reported at 34-35 S in the Central Andes (Espizua, 2005).…”

Late Pleistocene and Holocene environmental and climatic conditions in the eastern Andean piedmont of Mendoza (33°–34°S, Argentina)

“…This coincides with a period of active aeolian sedimentation across central Argentina during the Last Glacial Maximum and the Late Glacial documented by loess accumulation in the eastern and central Pampas of Buenos Aires and Córdoba provinces (Kemp et al, , 2006Frechen et al, 2009) and sand dune formation in the western Pampas of San Luis province (Tripaldi and Forman, 2007). Synchronously, mountain glaciation was active in the high upper basins of the main Andean fluvial systems, where maximum extension of the last glaciation occurred close to 21 ka (Espizua, 2005). Terraces formation has been reported at other Andean fluvial systems during the late Pleistocene (Table 3).…”

“…In central Chile, this pattern is illustrated by the records of Laguna Aculeo (33 50 0 S) and Laguna Las Ranas (39 11 0 S and 72 05 0 W) suggesting that arid conditions dominated during the early Holocene until ca. 5700 cal yr BP, and 5 ka respectively, when more humid conditions began to prevail (Jenny et al, 2002;Abarzúa et al, 2010) Accordingly, mid-late Holocene glacier advances are recorded at the upper basin of the Grande River (35 S) in the eastern Andean piedmont (Espizua, 2005). Instead, the mid-late Holocene of central Argentina is marked by increasing aeolian activity (Muhs and Zárate, 2001;Zárate, 2007) resulting in dune reactivation in several localities of central-western Argentina (Tripaldi and Forman, 2007;Kemp et al, 2004;Frechen et al, 2009).…”

“…Therefore, it is hypothesized that the climatic fluctuation occurring prior to at least 5, 7 ka cal BP may have triggered the first episode of degradation recorded in the analyzed piedmont fluvial systems. Assuming more humid conditions in the high Andes, due to a northern shift of the westerlies (Piovano et al, 2009;Labraga and Villalba, 2009), winter snowfalls increased resulting in glacial advances (Espizua, 2005) and greater fluvial dischargesgroundwater flows; this, coupled with much drier conditions across the eastern piedmont may have triggered fluvial incision.…”

“…The area is located within the domain of the South American Arid Diagonal (Bruniard, 1982) and the source area of the late PleistoceneeHolocene aeolian deposits of central Argentina (Iriondo, 1997;Zárate, 2007). In this region several papers have been published on the Quaternary glacial dynamic of the upper mountain valleys of the Atuel River (Gosse, 1994) and the Grande River (Espizua, 2004(Espizua, , 2005. Recently some other contributions focused on the geomorphology and geochronology of Quaternary fluvial landforms at the upper Atuel River (Messager, 2010), the Diamante River (Baker et al, 2009) and the mountain and proximal piedmont reach of Las Tunas River (Pepin, 2010) have been published.…”