Reactivation of Coastal Dunes Documented by Subsurface Imaging of the Great Dune Ridge, Lithuania

BUYNEVICH, I., BITINAS, A. and PUPIENIS, D., 2007. Reactivation of coastal dunes documented by subsurface imaging of the Great Dune Ridge, Lithuania. Journal of Coastal Research, SI 50 (Proceedings of the 9th International Coastal Symposium), 226 – 230. Gold Coast, Australia, ISSN 0749.0208 Large coastal and inland dunefields often consist of multiple generations defined by periods of stability and reactivation. Where earlier phases of aeolian activity are masked by subsequent deposition, continuous highresolution geophysical images help to reconstruct the history of landscape change. Ground-penetrating radar (GPR) profiles from relict Holocene dunes on the northern Curonian Spit, Lithuania reveal distinct contacts between older deposits (barrier-spit facies, older aeolian strata, paleosols) and overlying dune sands. Early stages of dune migration began prior to 6,000 years B.P. followed by several periods of stabilisation and subsequent reactivation. Parabolic and transverse dunes, some attaining heights of 40-60 m, have migrated to the east in response to westerly winds from the Baltic Sea. In several places, similar to a number of sites in Northern Europe, the upper sections of large dunes have been deflated leaving near-horizontal exposures where subsurface imaging extends the continuity of key stratigraphic horizons. Within dune sequences, oblique lateral accretion surfaces indicate the direction of earlier migration phases and exhibit distinct meso-scale geometries. In GPR images and shallow trenches, buried slipfaces have dip angles varying from 10-15o to 31-34o, the latter being similar to the angle of repose maintained by modern unvegetated dunes. A series of cores taken through sequences of stacked buried slipfaces show little visible variation in sediment properties with depth, suggesting that minor changes in texture, mineralogy and grain packing may be responsible for individual reflections in geophysical records. Occasionally, laterally extensive horizons enriched in heavy minerals produce prominent subsurface reflections and are indicative of periods of increased wind activity.