| Resumo: |
The aim of the present work is to determine the paleobiological and paleoenvironmental significance of fossil concentrations of Heleobia Stimpson, 1865 (Gastropoda) deposited during the last transgressiveregressive cycle along the Atlantic coast. The work was divided into two stages : 1) the analysis of living populations of H. australis (d'Orbigny), I-1. conexa (Gaillard) and H. parchappii (d'Orbigny) in two estuarine environments from the southeastern coast of the Buenos Aires Province (Mar Chiquita coastal lagoon and Quequen Grande estuary) in order to know the range of variation of the main biological and ecological factors and 2) the paleoecological analysis of three holocene sequences from the same region (mouth of the Quequen Grande River, Mouth of La Ballenera Creek and Punta Hermengo) to contrast the results obtained in modern environments . The comparisson of both methods allowed the recognition of spatial and temporal patterns of variation in the distributional ecology and morphology of species . All Heleobia species showed a high degree of ecological and phenotypic plasticity, allowing the recognition of distinct environmental conditions during the Holocene. H. australis has not significantly changed its ecological requirements during the Holocene, resulting a good bioindicator of environments close to the coast where exist a marked tidal influence . On the other hand, the distribution ofK parchappii has varied along the Holocene, being actually represented only in environments far away from the marine influence, whereas it was present in both coastal and freshwater environments during the maximum transgressive . H. conexa is not recorded in the southeastern Buenos Aires prior to 2,500 years BP.
Universidad Nacional de Mar del Plata, Facultad de Ciencias Exactas y Naturales (Argentina)
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