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

Abstract

The analysis of diatoms from three sedimentary sequences in the Queque´n 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 14 C 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 14 C years BP), brackish lagoons evolved into estuarine settings in the lower valley, but shallow freshwater ponds with salinities 54% persisted at 32 km from the mouth.