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-RECENT AND HOLOCENE BENTHIC OSTRACOD ASSEMBLAGES OF THE BAHIA BLANCA ESTUARY: (BUENOS AIRES, ARGENTINA): PALAEOENVIRONMENTAL INTERPRETATIONS. The study of ostracod fauna in sediment samples from present environments at the Bahía Blanca estuary led to the identification of different ostracod associations, through which it was possible to identify Holocene depositional environments. Based on the systematic analysis of the ostracods present in different core levels, a total of 11 genera represented by 13 species of benthic ostracods were identified, out of which Neocytherideis ruidis, Loxocythere variasculpta and Callistocythere litoralensis were dominant along the core. The quantitative and qualitative analysis of ostracods from the Holocene allowed us to determine the following palaeoenvironments: at the base of the core the sediments were deposited in an intertidal environment with developed mudflats; the middle sector evidenced an increase in environmental energy; and the upper portion of the core contained deposits of marshes environment with greater freshwater input. The detailed study of the benthic Ostracoda allowed to identify palaeoenvironments and to provide new evidence of negative fluctuations of the mean sea level for the Holocene.

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-INTERTIDAL OSTRACODE ASSEMBLAGES FROM THE ESTUARY OF BAHÍA BLANCA, ARGENTINA.The results of qualitative and quantitative analyses applied to the assemblages of ostracods recovered from bottom sediments are presented. The samples come from Puerto Rosales, Bahía Blanca estuary, Argentina. Seasonal sampling was performed along a transect perpendicular to the intertidal, from the lower to the upper intertidal. In the lower and upper intertidal the species Loxocythere variasculpta and Callistocythere nucleoperiscum are most abundant; the species Neocytherideis ruidis, Minicythere argentinensis, Cyprideis salebrosa hartmanni and Cyprideis multidentata are also present. In the upper intertidal was recovered only C. s. hartmanni. The qualitative and quantitative variations of the ostracod assemblages can be related to topography, sedimentology, vegetation and salinity variations. The results of this study are of importance in the interpretation of the environments recorded during the Quaternary, since these species are also registered as fossils.Key words: ostracods, estuary, Bahía Blanca, modern analogues, Argentina.RESUMO -Apresentam-se os resultados das análises qualitativa e quantitativa aplicada às faunas de ostracodes dos sedimentos atuais. As amostras foram extraídas de Puerto Rosales, estuário de Bahía Blanca, Argentina. A amostragem sazonal foi realizada ao longo de um transecto perpendicular ao intertidal, incluindo do intertidal inferior ao superior. No intertidal inferior e superior, as espécies Loxocythere variasculpta e Callistocythere nucleoperiscum são as mais abundantes; também estão presentes as espécies Neocytherideis ruidis, Minicythere argentinensis, Cyprideis salebrosa hartmanni e Cyprideis multidentata. Na região intertidal superior C. s. hartmanni é a única espécie presente. As variações qualitativas e quantitativas dos conjuntos de ostracodes podem estar relacionadas à topografia, sedimentologia, vegetação e variações de salinidade. Os resultados deste estudo são de importância na interpretação dos ambientes registrados durante o Quaternário, uma vez que estas espécies também ocorrem como fósseis.

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Depredation of Quaternary ostracods from southern Buenos Aires province, Argentina.The presence of fossil traces in ostracods valves from different quaternary palaeoenvironments in southern Buenos Aires province, Argentina, are studied in this paper. A number of 12500 specimens were analyzed and a total of 33 bored valves were separated. Two types of depredation fossil traces were determined: Oichnus simplex Bromley and Oichnus paraboloides Bromley, which comprised more than 60% of the total boreholes. The highest percentage of valves with evidence of predation (3.33%) was registered in sediments of a continental permanent lagoon with favourable trophic conditions and high density of ostracods. There was not relationship between the borehole diameter and the size of the predated valves. Evidences of depredation were registered in species with smooth valves as well as in species with adorned valves. Key words:Ostracods, fossil traces, depredation, Quaternary, Argentina.Resumen: En este trabajo se estudia la presencia de trazas fósiles en valvas de ostrácodos que provienen de distintos paleoambientes del Cuaternario de la provincia de Buenos Aires, Argentina. Se analizaron 12.504 especimenes y se separó un total de 33 valvas perforadas. Se determinaron dos tipos de trazas fósiles que representan estructuras de depredación: Oichnus simplex Bromley y Oichnus paraboloides Bromley, con más del 60% del total de las perforaciones. El mayor porcentaje de valvas con evidencias de depredación se registró en sedimentos de una laguna continental permanente con condiciones tróficas favorables y una alta densidad de ostrácodos. No existe una correlación entre el diámetro de las perforaciones y el tamaño de las valvas depredadas. Se registran evidencias de depredación tanto en especies con valvas lisas como ornamentadas.