INVESTIGADORES
CABALERI nora Graciela
artículos
Título:
Facies lacustres de la Formación Cañadón Asfalto (Caloviano-Oxfordiano) en la quebrada Las Chacritas, Cerro Cóndor, provincia del Chubut
Autor/es:
CABALERI, NORA G.; ARMELLA, CLAUDIA
Revista:
Revista de la Asociación Geológica Argentina
Editorial:
Asociación Geológica Argentina
Referencias:
Lugar: Buenos Aires; Año: 1999 vol. 54 p. 377 - 388
ISSN:
0004-4822
Resumen:
The lower section of Cañadón Asfalto Formation (Callovian-Oxfordian) is studied in the Las Chacritas, Cerro Cóndor area, located at the central Chubut province. The sedimentary sequence represented by lacustrine carbonate facies interbedded with volcanic episodes developed in the rift system of Somuncurá-Cañadón Asfalto Basin. Eight microfacies (MF), define the lake paleoenvironments and three biohermal facies (MFB) that correspond to an extensive microbialitic belt laying on eulittoral sediments have been recognized: The microfacies are the following, MF1: Mudstone with microbial lamination, related to supralittoral shallow ponds; MF2: Biohermal intraclastic floastone related with storm episodes; this microfacies culminates with evaporitic levels; MF3: Mudstone with drying evidences formed during stagnant waters; MF4: Microbial-peloidal mudstone/wackestone affected by sporadic wave currents, in eulittoral environment; MF5: Intraclastic grainstone/rudstone with pedogenic alterations and affected by waves, in eulittoral area; MF6: Oncoidal floastone interpreted as an hiperconcentrated flow; MF7: Bio-intra-siliciclastic packstone/wackestone accumulated in infralittoral conditions, and MF8: Silicified bulbous stromatolites related to the outlet of fluvial channels. The biohermal facies are: MFB9: Mudstone with stromatolites and wackestone levels; MFB10: Planar stromatolites and MFB11: Hemispherical stromatolites with chalk crust. Behind the biohermal belt, palustrine limestones locally show layers with episodic storm floods. The microfacial and facial distribution represent expansion and contraction cycles of a closed lake, controlled mainly by the precipitations.