Abstract

BOUZA, Pablo José. Genesis of carbonate accumulations in North Patagonic aridisols: its paleopedological significance. Rev. Asoc. Geol. Argent. [online]. 2012, vol.69, n.2. ISSN 0004-4822.

The aim of this paper is to report on the origin of the carbonate accumulations in soils of the northeast of the Chubut province, through analysis of physical, chemical and mineralogical properties as well as to elucidate, in combination with these soil properties, if such accumulations can be used as paleopedological indicators by analyzing the isotopic compositions of d18O and d13C. The studied soils are associated with littoral terraces formed during the MIS 5e (Caleta Valdés Formation) and with glaciofuvial and pluviofuvial terraces of Plio-Pleistocene age (Rodados Patagónicos). The carbonate content increases with the age of the geomorphic surfaces (terraces), constituting a tool to correlate soils and paleosols (chronosequence). The accumulations of pedogenetic carbonates are revealed by the presence of typical morphological features (laminar structure, calcitic nodules, pendants, alpha-type fabric, pellets and ooids) and palygorskite and sepiolite formed during calcretización processes. The analysis of the isotopic compositions of d13C and d18O showed an acceptable positive correlation (r2 = 0.5, p <0.001) indicating a correspondence between assemblages of plants with higher proportion of C4, which are tolerant to water stress and high temperatures (values more positive of d13C and d18O respectively). The calcretes present in Caleta Valdés Formation were formed during the culmination of MIS 5 period (5a-c), while the carbonates present in the Rodados Patagónicos would have developed in a warmer and drier interglacial period, presumably during MIS 11.

Keywords : Calcretes; Palygorskite; Sepiolite; Stable isotopes; Chubut soils.

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