Charophyte record of the Early Cretaceous Cañadón Asfalto Basin (central Patagonia, Argentina): biostratigraphic and paleoenvironmental synthesis

This contribution presents an integrated synthesis of the freshwater calcareous microfossil record preserved in Lower Cretaceous continental successions of north-central Patagonia, focusing on two stratigraphically successive units of the Cañadón Asfalto Basin. Based on previously published data and the results synthesized herein, this review includes the taxonomic composition, biostratigraphic framework, paleoenvironmental evolution, and paleobiogeographic significance of the recorded assemblages. Charophytes from the lower unit (Los Adobes Formation) are characterized by distinctive Mesochara-dominated floras that developed in shallow freshwater settings within low-energy floodplains during the Barremian, the most probable age for the charophyte-bearing deposits studied herein. This vegetation inhabited temporary ponds and small lacustrine depressions that were subject to frequent water-level fluctuations and episodic sediment influx. The overlying unit (Cerro Barcino Formation) records species-rich assemblages, including both early characeans and clavatoraceans. These charophyte floras reflect Aptian–early Albian freshwater habitats established in volcaniclastic floodplains affected by recurrent volcanic disturbance and variable hydrological regimes. The higher diversity observed in this interval may partly reflect the occurrence of taxa with different ecological tolerances, some of which were able to persist under fluctuating hydrological and physicochemical conditions. Together, these records highlight the importance of the Cañadón Asfalto Basin for understanding the early diversification of Charoidae in southern Gondwana and provide new insights into the evolution of dynamic freshwater ecosystems in volcanically influenced continental settings during the Early Cretaceous.