OSTRACODOS MARINOS DE LA FORMACION RIO NEGRO (PLIOCENO), PROVINCIA DE RIO NEGRO, ARGENTINA

Abstract

Samples from the marine facies Balneario La Lobería yielded few ostracodes. They are generally well preserved and belong to twenty six species and nineteen genera Nine species are proposed: Coquimba rionegrensis nov. sp., Cytherelloidea viedmaensis nov. sp., Hemicytherura playabonitaensis nov. sp., H. sanmatiasensis nov. sp., H. viedmaensis nov. sp.; Munseyella sanmatiasensis nov. sp. and Patagonacythere rionegrensisnov. sp. Five species previously described have been found: Callistocythere litoralensis Rossi de Garcia, 1966; Cushmanidea sp.; Cytheretta punctata Sanguinetti, 1979; Hemicytherura sp. and Soudanella? sp. 1. H enryhowella sp. aff. H. evax (Ulrich y Bassler, 1904) is the predominant species. Most taxa are ornamented, medium in size and moderately to strongly calcified. The six species of Hemicytherura are somewhat flattened ventrally. The species seem to be closely related with Argentinian microfaunas from lower Miocene age of Tierra del Fuego, upper Miocene age of Península de Valdés and Quaternary age of Buenos Aires and microfaunas from Pleistocene-lower Holocene age of Brazil. This could indicate the displacement of the species to the north because of the gradual deterioration of the climatic conditions. The ostracodes could belong to a shallow water environment with changes in its salinity and temperate to warm temperate paleotemperature.