Palynofacies analysis and sedimentary environment of Early Jurassic coastal sediments at the southern border of the Neuquén Basin, Argentina

A.M. ZAVATTIERI, U. ROSENFELD & W. VOLKHEIMER

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

Elsevier Science

Lugar: Oxford; Año: 2006

0895-9811

Objectives of this study were the understanding of paleoenvironmental dynamics through sedimentologic and palynofacies analysis, showing how a pronounced geodiversity is conditioning a high biodiversity within a near-coast ecotonal system. The Nestares Formation outcrops at its type locality Alicurá Dam, northern Patagonia. Through sedimentologic and palynofacies analysis a coastal environment of the Formation could be recognized. Lithology and sedimentary structures indicate fluvial conditions in the lower part of the outcropping Nestares Formation with a high input of terrestrial derived organic material as shown by palynofacies. The middle and upper part represent a relatively quiet environment of an interdistributary paralic bay with tidal influence (flaser-bedding), between deltaic channels, probably surrounded by marshes. Alternating palynofacies dominated by amorphous organic matter of algal origin suggest episodes of restricted conditions of deposition in which energy levels changed frequently. A marine Late Toarcian palynologic assemblage means that the Nestares sequence constitutes the basal stratigraphic unit of the Cuyano Group and that the marine transgression of the Neuquén Basin arrived, at this southernmost part of the basin, as late as during the Late Toarcian. Together with the incoming of Callialasporites, the presence of the Parvocysta suite, with Phallocysta, Nannoceratopsis, and Suessiaceae support a Late Toarcian age.