Stratigraphy, palynology, and conchostracans of a Lower Cretaceous sequence at the Cañadón Calcáreo locality, Extra-Andean central Patagonia: age and palaeoenvironmental significance

VOLKHEIMER, W.; GALLEGO, O.F; CABALERI, N.; ARMELLA, C.; NARVÁEZ, P.L.; SILVA NIETO, D.; PÁEZ, M.

CRETACEOUS RESEARCH (PRINT)

Elsevier

Lugar: London; Año: 2009 vol. 30 p. 270 - 282

0195-6671

The objective of this contribution is to characterize the palynobiota of the Cañadón Calcáreo Formation at its type locality and to study the biostratigraphic and paleoecologic significance of the palynoflora and the fauna of conchostracans. The sedimentary environments are studied in the context of a model of the tectogenetic development of the Cañadón Calcáreo Depocenter, which is an integrating part of the Cañadón Asfalto Basin. The methods include detailed measuring of stratigraphic  / sedimentologic sections with sampling for palynomorphs and conchostracans and for sedimentary facies / microfacies studies. In the laboratories the physical y chemical extraction of palynomorphs and the preparing of slides for microscopic studies were performed, as well as taxonomic studies of palynomorphs and conchostracans under light microscopy and SEM. The assemblages of microfossils are compared, for stratigraphic correlation, with those resulting from previous studies in other areas. Results and conclusions: From palynostratigraphic studies results a Valanginian age, for the middle part of the Cañadón Calcáreo Formation. The palynoflora is characterized by the dominance of the genera Classopollis and Callialasporites, with an incipient presence of the genus Cyclusphaera. The fauna of conchostracans identified is composed by species of the genera Nemestheria (Zhestheria), Pseudestherites and Euestheria? The age resulting from the palynoflora is compatible with the data from the fauna of conchostracans. The sedimentary environment of the Cañadón Calcáreo Formation, at the type locality, is in the lower part lacustrine / palustrine, grading to fluvial. The middle and upper section of the unit is fluvial, with prevailing levels of sandstones and tuffs. Paleoclimate: The prevailing of the thermophilous genus Classopollis indicates warm climatic conditions and the high frequency and diversity of trilete spores, corresponding to a hygrophile vegetation of ferns and bryophytes, indicates locally humid conditions.