Holocene Sea-Level Changes in Southern Brazil Based on High-Resolution Radar Stratigraphy

Eduardo Guimarães Barboza,Rodolfo José Angulo,Sergio Rebello Dillenburg,Maria Luiza Correaa Da Camara Rosa,Anderson Biancini Da Silva,Felipe Caron,Matias Do Nascimento Ritter,Maria Cristina De Souza

doi:10.3390/geosciences11080326

Eduardo Guimarães Barboza, Rodolfo José Angulo + Show 6 more

Open Access

https://doi.org/10.3390/geosciences11080326

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Abstract

This paper focuses on high-resolution coastal stratigraphy data, which were revealed by the Ground Penetrating Radar (GPR) system. Surveys performed with GPR on the surface of prograded barriers reveal patterns of reflections that allow the interpretation of the geometry and stratigraphy of coastal deposits in a continuous mode. At the Curumim prograded barrier in southern Brazil (29°30′ S–49°53′ W), a two-dimensional transverse GPR survey revealed, with high precision, a serial of contacts between aeolian deposits of relict foredunes and relict beach deposits that have a strong correlation with sea level. In a 4 km GPR profile, a total of 24 of these contacts were identified. The high accurate spatial positioning of the contacts combined with Optical Stimulated Luminescence dating resulted in the first confident sea-level curve that tells the history of sea-level changes during the last 7 ka on the southernmost sector of the Brazilian coast. The curve shows that sea-level was still rising before 6 ka BP, with a maximum level of 1.9 m reached close to 5 ka BP; after that, sea-level started to falling slowly until around 4 ka BP when fall accelerated.

Highlights

The pursuit of a confident sea-level curve representing oscillations of the sea level during the middle and late Holocene has been a constant goal in the last decades
Ground Penetrating Radar (GPR) record obtained alongwave a 4.3energy km long tidal range), it is possible to access past sea-level positions by subtracting the vertical made possible the identification of different patterns of reflectors, which were separated as distance from the heights of the contact of relict foredune and backshore deposits distinct radarfacies (Rdf) (Figure 3)
The two-dimensional GPR profile performed on the prograded barrier of Curumim revealed a detailed stratigraphy, showing patterns of reflectors that allowed the identification of the geometries of foredunes and beach deposits

Summary

Introduction

The pursuit of a confident sea-level curve representing oscillations of the sea level during the middle and late Holocene has been a constant goal in the last decades. In Brazil, since 1979, when the first most detailed curve was proposed [1], and later contested [2], two groups have debated the existence of high-frequency oscillations (2–3 m), operating in the scale of centuries (500–600 years), that could have occurred during the overall sea-level fall established after a maximum level of few meters was reached between 6–5 ka BP [3,4]. In South Brazil, to the south of the Santa Marta Cape (28◦ 350 S-48◦ 490 W–Figure 1), a formal and confident curve was never proposed due to the lack of confident indicators of paleo sea level along with this almost entirely sandy coast. Vermetid incrustations occur fixed on coastal rocks, which do not occur to the south of the Santa

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