| Popis: |
The neotropical loess (primary and reworked) covers a large part of Argentina north of 30°S. It is different in some ways from the loess of the Pampa which is generally considered the typical Argentine loess. The mineralogical, chemical and physical composition of the neotropical loess has been analyzed and is here compared with both Pampean and northern hemisphere (European and North American) loess. The distribution of neotropical loess is established, following the former Teruggi scheme, and the bio-stratigraphical data indicating a Late Pleistocene age is described. The great climatic variability of this period is documented through description of a loess-paleosol sequence that mantles the pre-Andean valleys. The influence of loess influx upon the genesis of the paleosols, and the stadial-interstadial environmental changes are considered in relation to the generalized truncation of paleoedaphic sequences. The migration of the Polar Front and the weakness of the Pacific High pressure system are also analyzed in relation to South American environmental evolution during the Upper Quaternary. In that sense, the genesis of pre-Andean fluvial valleys and mega-fans (extending outward into the Andean piedmont plains) having sources on the eastern (dry) side of the Andes, would have been influenced by such a paleoclimatic situation. |
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