Paleoenvironmental reconstruction of Holocene coastal deposits...

ESPINOSA, M; DE FRANCESCO, C; ISLA F

Journal of Paleolimnology

Kluwer Acad Publisher

Año: 2003 vol. 29 p. 49 - 60

0921-2728

An estuarine sequence outcropping at La Ballenera Creek (Buenos Aires Province), dated between 6,800 and 14 4,100 C years BP, was investigated for diatoms and molluscs. The sea level history along the Buenos Aires coastline has been reconstructed from discrete beach ridge sequences along low-lying plains. The La Ballenera profile is located on a cliff coast where a sequence recorded environmental changes. Fifty-eight diatom species were grouped based on their salinity and life form characteristics. Cluster analysis allowed the division of the sequence into three diatom zones. Mollusc tolerances were also used to discern the environmental changes induced by sea-level fluctuations. The base of the sequence recorded the initiation of the marine influence about 6,790?6,200 years ago. Diatom assemblages consist of brackish-freshwater tychoplankton accompanied by brackish benthic diatoms. Among the molluscs, the freshwater-brackish species Heleobia parchappii dominates. 14 Between 6,200 and ca. 4,800 C years BP, an estuarine lagoon environment is indicated by benthic and epiphytic 14 marine-brackish diatoms, as well as by the estuarine snail Heleobia australis. After 4,800 C years BP, the diatom assemblages and the relative abundance of freshwater molluscs indicate a marshy environment with lower salinity content. The La Ballenera records the salinity changes that affect an estuary that infilled during the 2,700 years after the maximum sea level reached in mid-latitudes of South America.