Análisis geomorfológico y primeras edades del campo de dunas Médanos Negros, provincia de La Rioja, Argentina

TRIPALDI, A.; FORMAN, S. L.; CICCIOLI, P. L

Córdoba

Congreso; III Congreso Argentino de Cuaternario y Geomorfología; 2006

Facultad de Ciencias Exactas,Fisicas y Naturales, Universidad Nacional de Córdoba

Médanos Negros (MN) dune field, partially covered by shrubs, is located in an aridintermontane valley (La Rioja province, NW Argentina). A complex dune-field patternformed by a relic landscape of transverse draas with superimposed transverse dunes appearsin central MN dune field. Transverse dunes extend beyond the draas to the west and south.The complex dune-field pattern is here interpreted as a result of different generations ofconstruction. Low longitudinal dunes, closely related to salt lake deposits, characterize thenorthern region while to the west eolian sand sheet deposits cover alluvial fans. Most dunesshow evidence of fluvial erosion and eolian reworking (blowout hollows and coppice dunes).OSL chronological studies of eolian deposits were carried out in two stratigraphic sections.Both sections are composed of well to very well sorted, fine-to-medium sand, with mm-scalelow angle and horizontal laminations or massive (disrupted by bioturbation). A section in alongitudinal dune yielded an age of 900 ± 70 yr at 2.60 m depth and 400 ± 60 yr. at 1 m depth,while eolian sand at 1.7 m in a complex dune section yielded the age of 2540 ± 240 yr.Therefore, MN dune field undergoes a Late Holocene episode of eolian sedimentation.However, considering the presence of a complex dune-field pattern and the shallow studiedsections, it is very likely that MN dune field must have been formed during a dry period of theLate Pleistocene. Then, younger ages point out at least two episode of eolian reworkingduring last millenium.