An integrated analysis of palynofacies and diatoms in the Jucuruçu River valley, northeastern Brazil: Holocene paleoenvironmental changes

This study demonstrates the usefulness of palynofacies as a tool for characterizing the origin, transport, and settling of particulate organic matter preserved in fluvial plain sediments and its integration with diatoms for inferring past depositional environments. Palynofacies, diatoms, and organic geochemistry (S, C/S) data from a sediment core (PR07) collected from the Jucuruçu River valley in coastal southern Bahia, northeastern Brazil were used to better understand ecosystem changes that occurred in the region during the last ~7.5k years. Elemental values (S: 0.15–5.9%; C/S: 0.12–41.5) suggest marine and fluvial influences in the valley during the Holocene, and organic matter was derived from freshwater and marine phytoplankton. The presence of heterolithic deposits, brackish/marine diatoms, predominance of amorphous group, non-opaque phytoclasts, pyrite crystals, and marine microfossils suggests that a tidal flat formed during a mid-Holocene sea-level highstand. A fluvial plain developed in the last 5k years, due to marine regression and an increase in fluvial sediment supply to the region. •Palynofacies, diatoms and organic geochemistry were used in river valley sediments in northeastern Brazil.•Holocene sea-level changes influenced the particulate organic matter deposition in the Jucuruçu River valley.•Marine and brackish diatoms characterized a mid-Holocene highstand.•Higher fluvial sediment supply occurred in the last 5k years.