Preservation potential of foredunes in the stratigraphic record

Foredunes occur worldwide on shorelines, especially those which are wave-dominated and with moderate to high sediment supply. Pelotas Basin, located in southern Brazil, has a significant record of foredunes which are present on modern beaches as well as in the geological record. Many locations along the Holocene coastal plain of Pelotas Basin were investigated with a Ground Penetrating Radar (GPR). Foredunes are present in almost all the investigated areas. However some peculiarities were found along these areas. At some places it is still possible to see foredune morphology in the field. At these places GPR profiles show a convex ridge morphology preserved and its separation by concave, sometimes filled swales. At other sites foredunes are covered by transgressive dunes, the morphology is not preserved and erosive surfaces are found on the top of the unit. Along the progradational sectors, dip profiles show that even where foredunes have their morphology preserved, some erosive scarps are found at the seaward face. These patterns indicate that high frequency events lead to the erosion of foredunes. The combination of sedimentary budget with climatic events sets foredune preservation and its pattern. Where sedimentary budget is high, progradation occurs faster and foredunes are preserved. However, where the sedimentary budget is not very expressive, the progradation is slower and part of the foredune is destroyed forming transgressive dunes or sand sheets.