Asociaciones De Foraminíferos Bentónicos En Secciones Holocenas Del Estuario De Bahía Blanca (Buenos Aires, Argentina): Caracterización Paleoambiental

Abstract

ASSEMBLAGES OF BENTHIC FORAMINIFERA FROM HOLOCENE SECTIONS IN THE BAHÍA BLANCA ESTUARY (BUENOS AIRES, ARGENTINA). Benthic foraminifera associations are described from two Holocene sections, Canal Tres Brazas (38°54′S–62°14′W) and Canal del Medio (38°49′S–62°17′W), in the Bahía Blanca estuary, Buenos Aires Province. Micropaleontological analysis shows that both sections represent low intertidal to subtidal estuarine environments, affected by sea-level variations during the late Holocene. Among hyaline foraminifera, Buccella frigida (Cushman, 1922) dominates in both sections, mainly associated to Elphidium gunteri Cole (1931) and other species of Elphidium Montfort, 1808. Also present, but in low proportions are Ammonia tepida (Cushman, 1926) and Ammonia parkinsoniana (d'Orbigny, 1839) with bolivinids such as Bolivina striatula Cushman (1922) and Bolivina pseudoplicata Heron-Allen and Earland (1930). Among the most conspicuous miliolids are Miliolinella subrotunda (Montagu, 1803) and Quinqueloculina seminulum (Linné, 1767). The Canal del Medio section, dated at about cal. 3700 years BP represents a low intertidal to shallow subtidal estuarine environment, revealing energy oscillations in the depositional environment attributed to the cyclical action of tides. Features of these deposits indicate that the mean sea level at 3831–3610 years BP was located in a similar position to that of the present one. The Canal Tres Brazas section, the base of which was dated in cal. 1589–1371 years BP, shows a typical shallow intertidal fauna that gradually gives way to environments with greater continental influence, and without microfosiliferous content.