Resumo

DIAZ, Silvana; DEL CARMEN BLANCO, María  e  AMIOTTI, Nilda Mabel. Rare Earth Elements (Ree) In The Solid Phase Of Calcic And Petrocalcic Horizons Of The Pampeana Austral Region. Cienc. suelo [online]. 2013, vol.31, n.2, pp.279-286. ISSN 1850-2067.

Soils of the Pampeana Austral region, formed in loessic parent materials, have calcic horizons (Ck) that evolved in the present pedogenetic cycle and/or were inherited (2Ck) and petrocalcic horizons (2Ckm) associated to paleoclimates that were more arid than the semiarid present climate. The geopedogenetic complexity affected by climate/paleoclimate and controlled by geomorphology determines variability in soil mineralogy having an impact in its elementary geochemistry. The Rare Earth Elements (REE) is a group of elements that provides information related to the sedimentary origin of soils and has been scarcely investigated. The objective of this study was to characterize the REE in the solid phase of Ck and Ckm horizons from soil profiles of the Arroyo El Divisorio. Four soil samples were collected: two from theupper and two from the lower basin. Quantitative analyses were performed by Neutron Activation Analysis (INAA-Code 1D-Enhanced; neutron flux: 7x10¹² n cm^-2 s^-1; Actlabs-Canada). The following REE were determined: La, Ce, Nd, Sm, Eu, Tb, Yb and Lu; other associated elements were also analyzed. Independently of soil position in the studied basin, the REE have a comparable distribution although with lower contents in the 2Ckm petrocalcic than in the Ck. On the other hand, in the Ck horizons, the highest content of REE was found in the stable interfluve plains of the lower basin (La 25.2 ppm, Ce: 41 ppm, Nd: 28 ppm, Sm: 4.1 ppm, Eu: 1,4 ppm, Tb: <0.5 ppm, Yb: 2.3 ppm y Lu: 0.44 ppm) while REE in aeolian dust presently deposited in the region are analogous to the Ck horizons of the studied basin. REE distribution was comparable although with lower contents in the petrocalcic 2Ckm compared to Ck of the valley slope. The similarity detected among the latter and the REE of present aeolian dust confirms their Patagonian procedence and the composition ofmixed parent materials with predominant loess sediments.

Palavras-chave : Geochemistry; Solid phase; Calcic and petrocalcic horizons; REE Elements.

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