PALEOECOLOGY OF FORAMINIFERA FROM A HOLOCENE CORE RECOVERED IN THE COASTAL PLAIN OF MAR CHIQUITA LAGOON, BUENOS AIRES, ARGENTINA. Foraminifera associations from a 182 cm long sediment core drilled east of Mar Chiquita Lagoon were studied in order to provide evidence of Holocene paleoenvironmental evolution and its probable relationship with the last transgressive-regressive cycle. A total of 91 taxa were recorded. The most frequent and abundant species were Buccella peruviana (d'Orbigny) f. campsi (Boltovskoy) and Elphidium discoidale (Boltovskoy) followed by Ammonia beccarii s.l. (Linné) and Elphidium gunteri Cole. Qualitative and quantitative analyses allowed the recognition of four sections and three main stages in the paleoenvironmental evolution of the studied sequence. In the first stage (Section A) previous to 8500 years BP, estuarine and low salinity conditions would have prevailed; it should be associated to a low sea-level position before sea advance over the continent. In a second stage (Sections B-C) deposited between ca. 8000 and 5000 years BP, marine influence increased probably representing the transgressive event; the early stages of a gradual decrease of marine influence is noted towards the top of Section C. Finally, the third stage (Section D) —after 5000 years BP— reveals a progressive evolution towards brackish, low energy and more restricted environments. This last phase may be explained by the onset of the sand-dune barrier during the regressive phase of the Holocene transgression as proposed by other authors.