Palinología del Miembro Gran Bajo de la Formación San Julián (Oligoceno Tardío) en su Localidad Tipo, Santa Cruz, Argentina: Consideraciones Paleoambientales

Abstract

PALYNOLOGY OF THE GRAN BAJO MEMBER, SAN JULIÁN FORMATION (LATE OLIGOCENE) IN ITS TYPE LOCALITY, SANTA CRUZ, ARGENTINA: PALEOENVIRONMENTAL CONSIDERATIONS. The aim of this paper is to present the palynological results from the Gran Bajo Member of the San Julián Formation in its type area (Gran Bajo de San Julián). The studied section crops out in the eastern Santa Cruz Province and has been assigned to the late Oligocène based on 87Sr/86Sr data. The sedimentological analysis suggests a shallow marine environment close to the coast barely influenced by ocean waters at the lower part of the section, which evolved toward a foreshore-shoreface environment at the middle part of the section and to a shoreface-offshore towards the upper part of the section. The palynological assemblages from Gran Bajo section are primarily conformed by terrestrial elements with high preservation stage. A detailed palynological study allowed reconstructing the structure and composition of the forest in relation to depositional environments. Changes in the depositional environments correlate with the pollen zones determined by cluster analysis. Among the arboreal elements, the Podocarpaceae dominated the middle part of the section and Nothofagaceae (mainly Nothofagidites brassii type) dominates in the upper part, associated with Araucariaceae and Proteaceae in lower proportions. Myrtaceae, Arecaceae, Sapindaceae and Anacardiaceae were scarcely represented. The understory was composed by different species of monilophytes, mainly Cyatheaceae and Dicksoniaceae that decrease towards the top of the analyzed interval.