COMBINING GROUND PENETRATING RADAR (GPR) AND OPTICAL DATING TO DETERMINE DUNE MIGRATION IN NAMIBIA

Ground penetrating radar (GPR) profiles across the southern end of a large (5km long, 500m wide)complex linear dune at the northern edge of the Namib Sand Sea are used to image sets of cross-stratification and bounding surfaces within the dune. A combination of radar facies analysis and radar stratigraphy have been used to interpret the radar profiles and define a relative chronology. Dipping reflections are interpreted as sets of cross-stratification and bounding surfaces. There is a consistent dip towards the west showing that the dune has migrated from east to west. Thick sets of cross-stratification indicate when the dune was most active, while thin sets of cross-stratification are interpreted to indicate increased wind reversals and lower rates of dune migration with bounding surfaces formed during periods of stabilisation, non-deposition or erosion. A drilling and dating campaign was designed on the basis of the dune stratigraphy as defined by the GPR survey. Sampling is targeted at large sets of cross-stratification formed when the dunes were most active, and avoiding bounding surfaces formed when the dune was stable or even eroded. The results from optical dating give ages between 0.34 ± 0.02 ka and 1.57± 0.07 ka indicating a dune migration rate of around 0.12myr-1 over the past 1600 years. The westerly migration direction is probably driven by easterly berg winds which are dominant in the winter months and is consistent with local wind measurements at Gobabeb. The relatively young ages are attributed to Holocene reworking of the southern end of a large N-S oriented linear dune which may have formed under an earlier and different wind regime.