Early-mid XX century aeolian reactivation in the western Pampas

TRIPALDI, A.; ZÁRATE, M.A.; FORMAN, S.L.; DOYLE, M.

Ciudad de Mendoza, Argentina

Congreso; 18th International Sedimentological Congress; 2010

International Asociation of Sedimentologist

<!-- /* Font Definitions */ @font-face {font-family:Calibri; mso-font-alt:"Century Gothic"; mso-font-charset:0; mso-generic-font-family:swiss; mso-font-pitch:variable; mso-font-signature:-1610611985 1073750139 0 0 159 0;} /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin-top:0cm; margin-right:0cm; margin-bottom:10.0pt; margin-left:0cm; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:Calibri; mso-fareast-font-family:Calibri; mso-bidi-font-family:"Times New Roman"; mso-ansi-language:ES-AR; mso-fareast-language:EN-US;} p.MsoTitle, li.MsoTitle, div.MsoTitle {mso-style-link:" Char Char"; margin:0cm; margin-bottom:.0001pt; text-align:center; mso-pagination:widow-orphan; font-size:12.0pt; mso-bidi-font-size:10.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman"; mso-ansi-language:ES-MX; font-weight:bold; mso-bidi-font-weight:normal; text-decoration:underline; text-underline:single;} span.CharChar {mso-style-name:" Char Char"; mso-style-locked:yes; mso-style-link:Title; mso-ansi-font-size:12.0pt; mso-ansi-language:ES-MX; mso-fareast-language:ES; mso-bidi-language:AR-SA; font-weight:bold; mso-bidi-font-weight:normal; text-decoration:underline; text-underline:single;} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> The western Pampean plain of La Pampa and San Luis provinces (western Pampa) is covered by a mantle of late Quaternary aeolian sandy deposits, including dune fields and sand mantles. The present climate is characterized by arid-semiarid conditions with mean annual rainfalls ranging from 750 to 250 mm. This precipitation occurs mostly during spring and summer months associated with an intensified South Atlantic Convergence Zone (SACZ; Doyle & Barros 2002). The low level meridional jet transports warm and moist air, derived from tropical forests and humid lowlands of Bolivia and Brazil, southward along the eastern margin of the Andes (Wang & Paegle, 1996). The aeolian sandy deposits are the dominant parent material of the surface soils, consisting of A,C horizons developed under a psammophityc and xerophytic woodland vegetation cover, which is deeply modified by agriculture. Recently obtained OSL dates indicate that major eolian activity occurred during the LGM whereas several episodes of aeolian reactivation took place during the Holocene. The most recent episodes, yielding ages from ca. 95 to 65 yr AP (Tripaldi & Forman, 2007), dates back from the early-mid XX century. It involved renewed deflation of blowouts and parabolic dunes. High angle cross-stratified beds are frequently observed in several localities suggesting dune migration due to high sediment availability under a sparse vegetation cover. At some places, present soils are buried by these aeolian deposits (Szelagowsky et al., 2004). The most sensitive areas for aeolian activity were those anthropogenically modified either by tillage, grazing, quarrying and housing. Historical lower precipitation values along with increasing aridity index have been reported from central-western Argentina (Scian & Donnari, 1997; Compagnucci et al., 2002). This variability is possibly linked to the two dominant midsummer low-level circulation patterns of negative (positive) precipitation anomalies during weak (intense) SACZ and warmest (coldest) SST in the subtropical western South Atlantic Ocean (Barros et al., 2002). South American early-mid XX century dry periods and the associated aeolian reactivation is synchronous with drought events of North American (Cook et al., 2007) adding new information to the proposition of a likely interhemispheric linkage (Herweijer & Seager 2008).