Charophyte palaeoecology in the Upper Eocene of the Eastern Ebro basin (Catalonia, Spain). Biostratigraphic implications

A micropalaeontological study of the non-marine Upper Eocene of the north eastern Ebro Basin (Catalonia, Spain) was carried out to clarify the palaeoecology of well-known charophyte species that are widely recognised as significant in charophyte biostratigraphy. Autochthonous specimens of the biozone index-species Harrisichara vasiformis-tuberculata were found in marlstones from the Sant Boi Formation (middle part of the Priabonian), which are associated with brackish water ponds laterally related to paralic marshes. In contrast, laterally equivalent assemblages found in white laminated marls from stable freshwater lakes were devoid of the index species and were dominated by Harrisichara lineata. Three more charophyte assemblages are reported from the continental Artés Formation (Stephanochara vectensis biozone, Upper Priabonian). Assemblages dominated by the species Nodosochara jorbae, reported only from Iberia at that age, occur in marlstones related to freshwater, temporary and turbid lakes within flood plains in medial fluvial fan environments. However, Lychnothamnus grambastii dominates locally in similar environments with higher organic matter content. Laterally equivalent assemblages from freshwater perennial lakes in distal alluvial fan facies were dominated by the biozone index-species Harrisichara tuberculata.These results provide evidence that important charophyte index species of the European charophyte biozonation were controlled by palaeoenvironmental factors such as water salinity, lake level changes or terrigenous input to the lakes. In consequence, these species should be used with caution in biostratigraphic studies, taking into account that their presence or absence may be palaeoecologically driven.

► Charophyte palaeoecology in the Priabonian of the Ebro Basin is characterised.
► Assemblages are defined from perennial lakes and temporary floodplain lakes.
► Significant species in biostratigraphy show restricted ecological distributions.
► Charophyte biostratigraphy depends on palaeoecological constraints.