AN EARLY PERMIAN LYCOPOD FOREST FROM PATAGONIA, ARGENTINA, AND ITS PALEOCLIMATIC IMPLICATIONS

Lycopods were uncommon plants at the beginning of the Permian in Gondwana. Reasons for that were mostly of climatic origin linked with the glaciation event that occupied extended regions of the southern land-masses. Western Gondwana, Patagonia in particular, seems to have been exceptionally different in that regard, with inferred macroclimatic conditions that allowed the growth of diverse and dense lycopod communities. The case of the Rio Genoa Formation is perhaps one of the most iconic examples on this respect, as one of the few in situ lycopod forest was formerly described from this unit. We provide new information regarding the possible structure of this plant community by means of recent calculations of density, height, biomass, etc. As a result, the lycopod forest of the Rio Genoa Formation occurs as a relatively dense monotypic community (260 to 520 ind.ha^-1), with individual trees reaching diameters up to 60 cm and calculated heights from 20 to 30 m. Lycopod plant communities in the Early Permian Río Genoa Formation grew along upper delta plain deposits, and two subtypes can be identified, i.e. those associated with swampy environments, and those growing on wet areas with no stagnant waters. The association of this type of plants with other climatic sensitive groups including tree-ferns, sphenophytes, etc., is highly contrasting with coeval Gondwana counterparts, and suggests atypical climatic conditions in Western Gondwana by the beginning of the Permian, when glacial conditions were still prevailing in most parts of the supercontinent.