MACNBR   00242
MUSEO ARGENTINO DE CIENCIAS NATURALES "BERNARDINO RIVADAVIA"
Unidad Ejecutora - UE
capítulos de libros
Título:
Paleosols of the middle Cenozoic Sarmiento Formation, central Patagonia
Autor/es:
BELLOSI E. S. AND M. GONZÁLEZ
Libro:
The Paleontology of Gran Barranca: Evolution and Environmental Change through the Middle Cenozoic of Patagonia. Madden, R., A. Carlini & M.G. Vucetich (eds.)
Editorial:
Cambridge University Press
Referencias:
Lugar: Cambridge; Año: 2010; p. 289 - 301
Resumen:
In the loessic and fluvial pyroclastic deposits of the mammal-bearing Sarmiento Formation (middle Eocene –early Miocene) of the Gran Barranca (central Patagonia) several types of alkaline and oxidized paleosols are recognized. These are characterized by relative uniformparent material, diverse insect trace fossils (Coprinisphaera and Celliforma ichnofacies), and abundant opal phytoliths of grass and palms. The paleosol succession preserves changes in soil moisture, biogenic activity, chemical weathering, and sediment influx. Two maturationtrends of the paleosols are identified on the basis of field, micromorphologic, and geochemical analyses. Both trends alternated several times during Sarmiento time. Trend A developed exclusively from tephric loessites, and includes calcic Entisols, calcic Andisols, and Aridisols. It corresponds to periods of a semi-arid–arid climate represented in the Gran Barranca (middle Eocene), Vera (late Eocene – early Oligocene), and upper Colhue-Huapi(early Miocene) Members. Most paleosols are very weakly to weakly developed, indicating continuous or fast eolian sediment influx. They probably formed in grasslands, shrubby grasslands, and palm savannas. A moderately to strongly developed Aridisol, identified in theRosado Member (middle Eocene), represents the driest environmental conditions. Trend B is associated with fluvial facies (intraformational conglomerates and tufoarenites) and subordinately with loessic deposits, and includes non-calcic Andisols, Alfisols, and intermediate Alfisols–Ultisols. It records periods of seasonal, subhumid to humid climate, and woodland or wooded-grassland vegetation, corresponding to the Gran Barranca (partially), Lower Puesto Almendra (late Eocene), Upper Puesto Almendra (Oligocene), and lower Colhue-Huapi (lower Miocene) Members. The stronger development of these paleosols indicates more discontinuous or slower fluvial–eolian accumulation.