The Chubut Group at the San Bernardo fold belt, Golfo San Jorge basin, Argentina: A review of fossil plant localities and its sedimentological setting

The Chubut Group (Cretaceous) consists of continental volcaniclastic deposits widely distributed in the Golfo San Jorge and Canadon Asfalto basins of Central Patagonia. In the San Bernardo Fold Belt, numerous outcrops with fossil plants have been historically mentioned. In this contribution, a precise geographical and stratigraphic position of localities with megafloral records was carried out, identifying six plant localities. These fossil assemblages belong to the Matasiete, Castillo and Bajo Barreal formations (Chubut Group) covering a time span ranging from the Aptian-earliest Turonian. The fossiliferous content of each flora is briefly characterized, and the sedimentological context is detailed. Most of these floras have been preserved in proximal floodplain facies, but also occurred as part of debris-flow deposits associated with fluvial channels with high discharge variability. The fossil assemblages are characterized by relatively low species richness. Angiosperms leaves are the main component and their physiognomic traits are homogeneous among floras prevailing microphyll, elongate, untoothed morphotypes. Few gymnosperms and ferns are also present. This study provides a general framework that will support future and more detailed paleobotanical studies, already underway, of each of these floras.