STRATIGRAPHY OF HOLOCENE SAND SHELL RIDGES IN THE BAHIA-BLANCA-ESTUARY, ARGENTINA

The Holocene marine transgression has left important testimonies to itself in the Bahia Blanca Estuary, with, mainly in the inner part of the estuary, set almost parallel to the isohypses between 8 and 10 m, sand-shell ridges being found. These structures are composed of a medium to fine sand with a high percentage of shells (47 species of mollusc). Radiocarbon dating of the shells in the oldest ridge gave a 14C age of 4615 ± 110 yrs B.P. The sand-shell ridges present a parallel bedding with slight inclination toward the sea. The two ridges studied stand discordantly on clay sandy silt containing laminated and flaser structures. These sediments change transitionally with depth to clay silt and silty sand. The marine sediments are distributed on a calcrete of late Pleistocene age. The types of sediments making up the ridges and their stratigraphical relationships are similar to those of cheniers. However, the term chenier is not used here because the sand-shell ridges and their associated deposits have been formed by transgressive-regressive sedimentary processes during the latest postglacial. © 1990.