IDEAN   23403
INSTITUTO DE ESTUDIOS ANDINOS "DON PABLO GROEBER"
Unidad Ejecutora - UE
artículos
Título:
Weathering processes at the boundary between the Mercedes(Cretaceous) and Asencio Formations, Southwestern Uruguay
Autor/es:
MORRÁS, HÉCTOR; TOFALO, OFELIA RITA; SÁNCHEZ BETUCCI, LEDA
Revista:
recista de Geociencias de Río Claro
Editorial:
Universidad de Río Claro
Referencias:
Lugar: Sao Pablo; Año: 2010 vol. 4 p. 487 - 500
ISSN:
1980-900X
Resumen:
The boundary between the Mercedes (Late Cretaceous) and Asencio (Eocene) formations has been a subject of controversy
in the past. The morphological evidence about the contact between both formations obtained in this paper indicate that the geochemical
weathering processes that took place during the early Eocene forming the paleosols found in the Asencio Fm. would have penetrated
deeply in the light coloured sandstones of the top of the Mercedes Fm. This is shown by a transitional level composed of a marked
irregular boundary, where ferruginous materials co-exist with relicts of the greyish sandstone, as well as with pouches of ferrugination
within the body of the Mercedes Fm., several meters below that boundary. Likewise, the obtained evidence shows also that the nodular
strata present at the base of the Asencio Fm. are the result of the weathering of the greyish sandstones of the Mercedes Fm., due to their
fragmentation and ferrugination. As a consequence, it is herein proposed that the columnar structures of the so-called Gruta del Palacio
and other similar sites correspond to that transition level at the top of the Mercedes Fm.; the nuclei of the columns would be composed
of the ferruginous tongues whereas the hollows would be the result of the selective water erosion of the sandstone. On the base of the field
evidence, the stratigraphical nomenclature of the cited levels is discussed.