Palynological data from the hauterivian Avilé Member, Pampa Tril section, Agrio Formation, Neuquén Basin, Argentina

Abstract

The present contribution provides data to the palynological characterization of the non-marine deposits of the Avilé Member, Agrio Formation (Pampa Tril and San Eduardo sections), Neuquén Basin, Argentina. The Avilé Member, which represent a low-order regressive event, is one of the most important hydrocarbon reservoirs in the subsurface of the eastern part of the basin. A continental palynological association mainly represented by gymnosperms with Classopollis as a dominant taxon was recorded. The findings of Shambeipollenites proxireticulatus in the unit, extend the biostratigraphical range of the species to the Hauterivian and suggest the Neuquén Basin as an important dispersal place for the species within Gondwana landmass during the Early Cretaceous. A conifer-dominated forest was indicated by the pollen assemblage. The high percentages of Classopollis, the presence of pollen with Gnetidae affinity (Weltwischia/Ephedra) added to the evidence of fluvial-aeolian interaction given by the lithology, may be indicative of a deposition in a dryland setting. The recovered palynoflora was compared to published palynological data from different units underlying and overlying the Avilé Member, in order to evaluate the response of the vegetation in the central part of the basin, during the onset of non-marine accumulation relative to a sea level fall and the subsequent flooding again of the basin. An important variation in abundance between two groups of conifers (Cheirolepidiaceae versus Araucariaceae) is observed throughout the Agrio Formation members. Going up in the stratigraphic column there is an evident increase in abundance of Araucariaceae and a decrease in Classopollis and ferns spores.