Diatom-inferred Late Pleistocene and Holocene environmental and climatic changes in the southern Pampas, Argentina

ESPINOSA MARCELA A.; VELEZ AGUDELO CAMILO

Volume 0. Geology, Stratigraphy, Biostratigraphy, Palaeoenvironments and Climatology of the South American Pampas

Springer

Año: 2023;

Climatic and sea level changes have influenced the evolution of estuarine and coastal environments during the Late Pleistocene and Holocene. These sensitive systems rapidly respond to eustatic, climatic and anthropogenic forcing factors and their responses is stored in sediments, which can be analyzed through indirect indicators or proxies such as diatoms. This study focuses on characterizing the environmental and climatic changes of a temperate coast in the Southern Hemisphere that has not been significantly impacted by tectonic activity. The study also aims to reconstruct micro and mesotidal coastal systems in relation to sea level changes in the southern Pampas. To assess past environmental conditions, diatom assemblages were analyzed from outcropping profiles and cores in coastal plains and river basins of Buenos Aires province. The life form and salinity tolerance of diatoms were used to distinghish marine, brackish and freshwater sedimentary deposits from the late Pleistocene to Holocene. These sedimentary patterns were used to plot Holocene sea-level fluctuations along the Pampas coast. The studied sequences have chronological control, providing the necessary information to reconstruct environmental variability in the past. The sea-level curves proposed for the region indicate a late Pleistocene sea-level low and a mid-Holocene highstand. The identification of assemblages that characterize marine environments, tidal channels, coastal lagoons and marshes allowed for the adjustment of the diatom data to sea-level curves postulated for the region. The maximum sea level -between 6500 and 5500 years BP was recorded in sediments with diatoms typical of coastal marine environments. A diatom-based salinity transfer function was then quantitatively applied to twelve sedimentary sequences, enabling the inference of past salinity fluctuations along the Pampa coast during the Holocene.