An Isotopic Mixing Model To Explain Dust Sources For Pampean Loess.

DIEGO M. GAIERO

Córdoba, Argentina

Congreso; Iii Congreso Argentino De Cuaternario Y Geomorfologia; 2006

Escuela de Geologia, FCEFyN, UNC

The Andean volcanic rocks (20°S-55°S) have differing isotopic compositions in a clear north-south gradient, which in turn are inherited by eolian sediments exported from the sources. This geochemical “fingerprint” seems to be reflected in the Argentinean loess deposits showing different Nd isotopic composition in a similar north-south path (31°S-38°S)(Smith et al., 2003). This evidence suggests two main questions about the Pampean loess provenance: i) are these isotopic signatures provided by a direct west-east dust transport? or ii) could they indicate a mixed contribution from different dust source areas? The first transport mechanism was explored by Smith et al. (2003) but some arguments contradict their hypothesis. The second possibility is investigated in this contribution using an isotopic mixing model. The two end-members of this model are represented by the isotopic composition of dust exported from two potential dust source areas containing the most contrasting isotopic composition of the Andean volcanic rocks: i.e., Patagonia and Puna-Altiplano Plateau. This mixing model reproduces very well the Pampean loess (from 26°S to 38°S) and the isotopic composition of marine sediments deposited during the LGM. Moreover, after correcting the Sr isotope composition (sorting effect), the model also reproduce satisfactorily the isotopic composition of Antarctic dust deposited during cold periods.