Diatom-inferred salinity changes in relation to Holocene sea-level fluctuations in estuarine environments of Argentina

The analysis of diatoms from three sedimentary sequences in the Quequen Grande River basin (Buenos Aires province, Argentina) has allowed the reconstruction of local and regional palaeosalinity changes in relation to Holocene sea level fluctuations. An established diatom-based salinity transfer function is used in combination with autecological methods to reveal a maximum sea level between ca 7000 and 6000 C-14 years BP. This marine influence was recorded in deposits exposed 2 km and 12 km upstream, but not 32 km from the mouth. The fossil diatom assemblages are characteristic of an estuarine lagoon with maximum inferred salinities of 15%. When the Holocene transgression began to flood the former valley (ca 7000 C-14 years BP), brackish lagoons evolved into estuarine settings in the lower valley, but shallow freshwater ponds with salinities <4% persisted at 32 km from the mouth.