Understanding Polydirectional Aeolian Cross-Strata Architecture In A Coastal Unidirectional Wind Regime

Crescentic dune fields along the NE coast of Brazil were analyzed to justify processes associated with the wide range of cross-strata dip directions in aeolian deposits found in a unidirectional wind regime. Multiple spatial and temporal field-based methodologies were employed, including trenching, ground penetrating radar (GPR), and photogrammetry. Wind dynamics, coastline morphology, bounding surface developing processes, and dune migration patterns were also considered. Analysis revealed a relationship between small- and large-scale morphologies of the crescentic dune field. The interactions of crescentic dune crests, in association with the superposition of multiple superposed dunes, explain the majority of cross strata and dip directions found in dune trenches and GPR sections. This study provides convincing evidence that microscale structures observed within trenches and GPR sections are compatible with the macroscale slipface position observed within the dune field. Small-scale changes in wind direction, caused by the dune crest morphologies themselves, explain much of the supposedly unexpected strata dip directions that arc through from 90 degrees to 180 degrees. The presence of near-surface water tables supports the formation and preservation of aeolian cross-strata sequences.