Surface and subsurface stratigraphic record of aeolian mobility on the southernmost coast of Brazil

Abstract

Many drivers are responsible for dunefield morphology and changes from mobile to stable states, with surface and subsurface records potentially registering past drivers acting on dunes. Phases of aeolian transgressive sand sheets (TSS) are recorded in an extensive stretch of the Holocene barrier of the southernmost coast of Brazil from the millennial to modern ages. Ancient phases of TSS are evident in the modern transgressive dunefield (TDf) of the Concheiros Barrier, marked by vegetated, crenulate low precipitation ridges. In this work, we examined surface and subsurface records of aeolian deposits, exploring possible past climate conditions that led to the formation of these features. A 1000 m-long Ground Penetrating Radar (GPR) cross-section was conducted to determine whether these aeolian morphologies are observed in the stratigraphic subsurface record. Optical Stimulated Luminescence (OSL) dates were taken from vegetated relict TSS phases on the coastal barrier. The GPR section identified a single radarfacies, interpreted as a TSS. A few TSS units could be individually recognized, indicating overlapping low precipitation ridges/TSS margins. OSL dating indicated aeolian activity at 30 ± 3 years (P01), 1244 ± 123 years (P02), and 1464 years ± 130 years (P03). The youngest age is correlated with sand mobilization from AD 1996–2000, as described by previous studies. This phase was induced by climate conditions and it was caused by decreased vegetation cover, lower rainfall and water tables, and increased wind velocity and aeolian drift potential. The episodes of TSS mobilization at 1244 (±123) and 1464 (±130) years ago may have been caused by either drier conditions or intensified wind regimes, as noticed in different parts of southern Brazil by other studies. These drivers likely have been shaping the Holocene barrier geomorphology at the Concheiros Barrier for over 1400 years, considering the ancient phases of TSS formation in the subsurface stratigraphic record.