Nuevos hallazgos de palinomorfos en la Formación La Amarga, Miembro Bañados de Caichigüe, cuenca Neuquina sud oriental, Argentina

Abstract

The La Amarga Formation crops out near the southeastern border of the Neuquén Basin, immediately south of the Huincul arch. It is composed of continental sediments and its type locality is on the northern slope of Cerro China Muerta, near La Amarga creek. It is divided into three sub-units which are, from base to top: Puesto Antigua!, Bañados de Caichigüe and Piedra Parada Members. Based on stratigraphic relations and tectonosedimentary aspects, a Late Hauterivian to Barremian age is indicated. The two productive levels were obtained from the middle member of La Amarga Formation, 74 km south of Zapala, Neuquén province. The outcrop is characterized by green and grey pelites and marls, bearing a rich microflora, mainly composed of the freshwater algae Scenedesmus nooilunaris He et al. and Scenedesnius sp. cf. S. dimorphus (Turpin) Kützing. Tetraedron, Botryococcus and Leioephaeridia are less frequent. The abundance of colonial Chlorococcales at this eastern outcrop marks the environmental difference from the western Cerro China Muerta outcrops, formerly studied, where prasinophycean algae (Leiosphaeridio spp.) dominate the microflora. Thus, in the eastern area the abundant large coenobia (24 to 32 cells) indica te a lacustrine environment with a hígh nutrient content (eutrophic conditions), while in the western Cerro China Muerta area, the dominance of prasinophycean algae indica te s another time-slice of the lacustrine history. Conifer pollen grains are the most abundant within the terrestrial microflora. Spores of Bryophyta and Pteridophyta are poorly represented.