MAJOR PHASES OF HOLOCENE DUNE ACTIVITY ALONG THE COAST OF LITHUANIA: NEW OPTICAL DATES WITHIN A REGIONAL CONTEXT

The paraglacial coastline of the southern Baltic Sea is fronted by a series of long spits (30-100 km) covered by massive sand dunes, some exceeding 50 m in height. Most dunefields represent multiple phases of aeolian activity, with periods of stability alternating with dune reactivation. Paleosols have been used in many parts of Europe to determine the timing of dune stability. However additional methods are required to reconstruct the active phases, which are often represented by thick sand sequences with limited exposure. A combination of geophysical surveys, sediment cores, radiocarbon dates, and optically-stimulated luminescence (OSL) ages are used to reconstruct the chronology of dune evolution along the northern Curonian Spit, Lithuania. Ground-penetrating radar (GPR) profiles of relict Holocene dunes at the Nagliai Nature Reserve reveal buried slipfaces that extend 10-15 m below the deflation surface and dip landward at 31-34º. Based on partial exposures, the strongest reflections correspond to paleosols and laminae enriched in heavy minerals. Radiocarbon ages of four partially exposed paleosol horizons indicate dune stability during 5.69, 3.35, 1.25, and 0.70 ka BP (calibrated years before present). The youngest paleosol dated to AD 1780-1870 corresponds to some of the oldest surviving forests in this region. These ages correlate closely with paleosol chronologies in other parts of the spit and along the adjacent coast of Poland. A new set of OSL dates helps to constrain further the timing of dune activity, with ages ranging from 5.24±0.30 to 0.16±0.02 ka BP. The combined datasets suggest that prolonged (century-scale) periods of landscape stability alternated with at least four episodes of renewed aeolian activity, sand bypassing, and rapid dune migration. As discussed by several authors, the presence of charcoal in paleosols suggests that forest fires may have been responsible for remobilization of sand. During episodes of enhanced regional storminess, aeolian transport was facilitated by increased near-surface wind velocities, often manifested by mineral density lags within slipface strata. The last phase of massive dune migration was likely triggered by a combination of climatic deterioration during the Little Ice Age and extensive deforestation, causing the burial of forests and settlements.