Emiliana Bernasconi

Holocene benthic foraminifera from Bahía Blanca estuary: a review and update of systematic and palaeoenvironmental aspects

Assemblages of benthic foraminifera in a Holocene core from the outer area of Bahía Blanca estuary in Argentina were studied. The systematic of the group was updated, and provided 28 genera distributed among 59 species, six species with nomenclature aperta. The main species recorded were Buccella peruviana f. campsi (Boltovskoy), Ammonia beccarii (Linné), Elphidium gunteri Cole, Elphidium galvestonense Kornfeld, Elphidium articulatum d’Orbigny and Elphidium discoidale (d’Orbigny). These species allowed an estuarine environment to be determined. Qualitative and quantitative studies conducted on the faunistic content in the core allowed identification of three subenvironments closely linked to sea-level fluctuations during the mid Holocene: a lower zone (6350 yr BP) corresponding to a high intertidal environment, an intermediate zone (2460 yr BP) representing a low intertidal environment related to a system of channels and variations in environmental energy, and an upper zone characterized by the development of a high-energy littoral environment affected by the action of waves, tides and tidal currents, which underwent progressive change until it attained present-day conditions.

Study of the distribution of Elphidium aff. poeyanum (D’ORBIGNY) and Buccella peruviana (D’ORBIGNY) from the Colorado basin (South America): Holocene paleoenvironmental inferences

Benthic foraminiferal assemblages recovered from T1 core samples of the Colorado basin, in the continental margin of southeastern Argentina, were analyzed to understand their distribution patterns and ecological preferences. The foraminiferal assemblages showed two well-represented species: Elphidium aff. poeyanum (d’Orbigny) and Buccella peruviana (d’Orbigny), among others of very low proportion. Statistical analyses allowed identifying positive correlations between the abundance of E. aff. poeyanum and silt content and between B. peruviana and the sand content, reflecting better conditions for the development of both species. From a paleoenvironmental point of view, the assemblages recorded are characteristic of an inner shelf, showing a passage from typical shallow waters to normal marine conditions; such a passage represents a rise in the sea level during the post-last glacial maximum transgression. The results obtained contribute to the knowledge of South American foraminifers and paleoenvironments during the Holocene.