Influence of early/mid-Holocene climate change and sea level rise on a coast with barrier islands, Rio de Janeiro State, SE Brazil

Abstract

This work aims to identify the influence of climate change on sedimentary processes associated with the usual regression process during the rise of sea level in the early/middle Holocene in southeastern Brazil. The studied area is on the eastern side of Marambaia Barrier Island, which borders the eastern side of Sepetiba Bay (Rio de Janeiro State, SE Brazil). Nowadays, the Marambaia Barrier Island, a ≈ 40 km long and ≈ 5 km wide sandy ridge, shields Sepetiba Bay from the direct influence of the Atlantic Ocean. To achieve this goal, grain size, geochemical data (including elemental and stable isotopes), and radiocarbon dating data from sediment core SP10 (spanning depths from 8.2 to 45.5 m), collected in the eastern sector of the Marambaia Barrier Island were analyzed. Core SP10 predominantly consists of sandy sediments with some textural variations. However, Sr/Ba ratios suggest that brackish waters primarily influenced the depositional environment, which was also subject to cyclical marine incursions. The essentially felsic sediments of the interval between 45 and 41 m (≈ 10.0–8.5 ka BP) were probably deposited in a protected tidal plain estuary with mangroves. They were possibly mainly sourced from the nearby Pedra Branca Complex. Subsequently, between ≈ 41 and 11 m, the marine influence and hydrodynamics increased, and the sediments exhibited a more mafic mineralogical composition resulting probably from the erosion of the Rio Negro Complex, which is mainly found in the northern region of Sepetiba Bay. The mafic component likely reached the study area through coastal drift connected with Sepetiba Bay. During the drought period, recorded between ~ 7.5 and 7.0 ka cal BP (section 25–21 m), the contribution of the mafic component from the Rio Negro Complex decreased and less weathered sediments were accumulated. On the other hand, marine incursions into the study area became more prominent. During the drier climate phase recorded in the interval ≈ 11–9 m (after ≈ 4.0 ka BP), the La/Sc values indicate that the sediment included a higher proportion of felsic particles, probably due to more significant restrictions on the connection of the study area with Sepetiba Bay due to the development of the Marambaia Barrier Island. These findings are significant as they demonstrate the influence of geomorphology, climate change, sea level, and the development of Holocene barrier islands on the sedimentation in coastal regions.