Sands and clay mineralogy in soils, fluvial and eolian Present sediments in the southern sector of the Chacoparanense basin: Different regions and source areas.

Abstract

Mineralogical analysis based on fine sand and coarse silt fraction from soils and fluvial and aeolian recent sediments of the Pampa Húmeda (Wet Pampas) and the northen region of Santa Fe province and part of the Mesopotamia (Entre Ríos and Corrientes provinces) allowed to define two zones characterized by two genetically different mineralogical associations. Minerals of volcanic - pyroclastic origin (heavy: green, basaltic and brown hornblende, hypersthene, enstatite, augite, magnetite, hematite, ilmenite, leucoxene, epidote, zoicite, and light: plagioclase, volcanic fragments, pumice and glass shards, quartz, orthoclase) are observed over a broad area including whole Buenos Aires and Cordoba provinces, northwestern regions of La Pampa, central and southern Santa Fe and southern Entre Ríos. The provenence of these minerals included the pampean and post-pampean sediments and scarce contribution from volcanic Mesozoic rocks of north Patagonia, Sierras Pampeanas and also Quaternary pyroclastic eruptions. Conversely, a heavy suite of metamorphic provenence (staurolite, kyanite, sillimanite, andalusite, hornblende, epidote, opaques) and a light association composed of igneous and metamorphic clast (monocrystalline and polycrystalline quartz, orthoclase,microcline, schists) and others of sedimentary origin (quartz arenites) is recorded in Corrientes and northern Santa Fe and Entre Ríos provinces. These minerals are coming from older basement rocks outcropping in Brazil and Uruguay and the younger overlain sedimentary succession. The peculiar material distribution is related to the drainage systems and wind pattern. Quartz 30% frecuency isoplet points out the limit between both mineralogical associations.