Residual dune ridges: Sedimentary architecture, genesis, and implications for palaeo‐climate reconstructions

Abstract

AbstractSedimentary architecture and genesis of residual dune ridges in a temperate climate are presented and implications for their use as archive of changes in long‐term precipitation and wind climate are discussed. Residual dunes are common features of wet aeolian systems, where they form sets of shallow ridges, oriented perpendicular to the prevailing wind direction. Residual dune ridges of the study area are vegetated and typically elevate 0.6 to 2.5 m above the surrounding interdune flats. They develop on the lower stoss side of active transgressive dunes, triggered by periods of elevated groundwater table and hence colonization of the foot of the dune by rapid growing pioneer vegetation. Stabilized by plants, the growing ridge detaches from the active transgressive dune and gets abandoned within years in the course of the downwind‐migration of the transgressive dune. Grain‐size data suggest a main sediment supply from the transgressive dune and only minor input from other sources. Ground‐penetrating radar reveals that the residual dune ridges are composed of windward‐dipping as well as leeward‐dipping sedimentary beds. Leeward‐dipping strata reflect sediment supply from the parental dune, whereas windward‐dipping beds are seen to result from sediment redistribution along the ridge and sediment supply from the adjacent swales during the ridge growth period. Multi‐annual to multi‐decadal variability in precipitation leads to the development of sequences composed of tens of ridges, spanning time periods of several centuries. Spacing of individual ridges in these sequences is controlled not by long‐term variability in precipitation alone, but probably also reflects variable wind intensity which affects the migration rate of the parental dune. The important role of vegetation in ridge construction makes these landforms a demonstrative example of landscape development by geo‐biosphere interacting processes.