Hallazgo de depósitos cretácicos en la Precordillera de La Rioja (Formación Ciénaga del Río Huaco).

CICCIOLI, P.L.; BALLENT, S.; TEDESCO, A.M.; BARREDA, V.; LIMARINO, C.O.

Revista de la Asociación Geológica Argentina

Asociación Geológica Argentina

Año: 2005 vol. 60 p. 385 - 394

0004-4822

ABSTRACT. Cretaceous deposits in the Precordillera of La Rioja (Ciénaga del Río Huaco Formation). This paper deals with the finding of Maastrichtian rocks in the north of the Precordillera (La Rioja province). The Cretaceous succesion (122 m thick) is a classical red bed sequence composed of sandstones, mudstones, marls and thin levels of evaporites. According to lithological features 6 facies associations have been recognized that mainly characterize a lacustrine system developed under arid to semiarid conditions. Probably, as a result of an increase in aridity eolian sediments were deposited at the top of the Cretaceous unit. At least two transgressive-regressive events have been recognized in the lacustrine sequence. The better developed is the first event formed by fossiliferous black shales corresponding to the maximum flooding stage. These rocks have yield remains of calcareous microfossils, palynomorphs and gasteropods. The former comprises charophytes and ostracods. Among algae have been identified Platychara compressa and Tectochara sp. A. while ostracods correspond to Ilyocypris wichmanni punctata, Eucandona? sp., Cypridopsis sp. and Ovocytheridea? rionegrensis. Palinomorphs form a monospecific assemblage of algae colonies corresponding to Pediastrum. The lithological features, stratigraphic location and fossiliferous remains clearly suggest a regional correlation with the Ciénaga del Río Huaco Formation. This correlation considerably enlarge the regional distribution of the Cretaceous sediments which were previously limited to the Precordillera of San Juan province.