INGEIS   05370
INSTITUTO DE GEOCRONOLOGIA Y GEOLOGIA ISOTOPICA
Unidad Ejecutora - UE
artículos
Título:
Palynology and paleoenvironment of the Jurassic lacustrine Cañadón Asfalto Formation at Cañadón Lahuincó locality, Chubut province, central Patagonia, Argentina
Autor/es:
VOLKHEIMER, WOLFGANG; QUATROCCIO, MIRTA; CABALERI, NORA G.; GARCÍA, VIVIAN
Revista:
REVISTA ESPANOLA DE MICROPALEONTOLOGIA
Editorial:
Instituto Geológico y Minero de España
Referencias:
Lugar: La Rioja , España; Año: 2007
ISSN:
0556-655X
Resumen:
In the context of Jurassic extension of southwestern Gondwana, the Cañadón Asfalto Formation was filling hemigrabens located in the central area of Chubut province, with its principal outcrops in the middle Chubut river valley, where volcanites, biochemical, pyroclastic and epiclastic deposits are alternating. The objectives are the palynologic and palynofacial study of dark grey pelites of the Cañadón Asfalto Formation at Cañadón Lahuincó locality, Cerro Cóndor Depocenter, for obtaining a fuller paleoenvironmental, paleoclimatic and biostratigraphic characterization of this central part of the Basin. The methods comprise geologic fieldwork, palynologic sampling, physical/chemical extraction of palynomorphs in the paleopalynologic laboratory, taxonomic study of the palynomorphs, using interference contrast microscopy and SEM, study of the organic matter and palynofacies, statistic counts for environmental interpretation and biostratigraphic evaluation. Results: The abundance of amorphous organic matter (80-90%) in all palynologic samples studied is characteristic for stagnant bottom conditions. The material corresponds mostly to destroyed palynomorphs, including Botryococcus.  The scarce opaque phytoclasts consist of black, equidimensional, structureless material. The presence of Botryococcus indicates falling lake levels and probably more saline conditions. Diagenetic processes such as degradation, corrosion and the absence of pyrite in all the samples indicate that bottom conditions were aerobic, alternated with dysaerobic conditions. The Cheirolepidiaceae dominated the spectrum (up to 80% of Classopollis spp.), associated with Araucariaceae (up to 20%). Warm and relatively humid climatic conditions are indicated by high percentages of the thermophilic Cheirolepidiaceae, associated with Araucariaceae, which need relatively humid conditions. The presence of Bryophyta (Nevesisporites cf. radiatus) and pteridosperms (Alisporites similis) are suggesting probable loc