ISLA Federico Ignacio
Diatom and sedimentary record during the Mid-Holocene evolution...
ESPINOSA, M; ISLA, F
ASOCIACION PALEONTOLOGICA ARGENTINA
Lugar: Buenos Aires; Año: 2011 vol. 48 p. 411 - 423
Diatom and sedimentological analyses of two cores from San Blas Bay and the analysis of historical charts provide information about the environmental evolution of this estuarine complex during the last 5000 yr BP. The Holocene sea-level regression is recorded in San Blas Bay by infilling of a tidal channel. Two sediment cores were drilled at Arroyo Jabalí (San Blas Bridge) and at the former inlet of Arroyo Walker and Arroyo Jabalí (Paso Seco). The diatom record of the San Blas Bridge sequence is dominated by marine and brackish/freshwater plankton and tychoplankton and composed by fine to very fine sand and mud characterizing the infilling of a tidal channel. The Paso Seco sequence is more abundant in sand. Textural and diatom facies are interpreted as the infilling of a tidal channel very similar to the one at San Blas Bridge, that evolved towards the top into a sandflat characterized by the dominance of marine and marine-brackish epipsammon accompanied by marine tychoplankton. Arroyo Walker and Arroyo Jabalí were flowing eastward across a tidal channel during the Holocene. Because of obstruction of the channel, the tidal channel assemblages were replaced by sandflat assemblages. According to historical charts, as late as 1833 a tidal inlet still existed in this sector, which was later obstructed completely according to Twentieth Century charts. At this timescale, eustasy is considered to be a minor environmental control on the dynamics of the system. Instead, control is forced by other fac-tors, such as inlet instability due to morphological changes of the sand barrier whether emergent or submerged.