GLAUCONITE-COATED SAND IN CURONIAN DUNES, LITHUANIA: TRANSPORT MECHANISMS AND PALEOENVIRONMENTAL IMPLICATIONS

Along parts of the Curonian Spit, Lithuania, layers of “green sand” have been sourced to Cretaceous to Oligocene glauconite-bearing formations of the Baltic Sea basin. They serve as lithological markers in Holocene sequences, however questions remain about their transfer from nearshore transgressive-phase to aeolian depocenters in parts of the Great Dune Ridge. Previous workers refer to horizons of >90% “glauconite sand”, but our analyses show that they consist of well-sorted, medium-fine (0.255 mm) quartz-rich sand covered with glauconitic clay (coating contribution: 6% weight; +0.3% mean grain size). Iron content of this glauconite-coated sand (GCS) causes high bulk magnetic susceptibility (~160 μSI), more than double that of background dune sediment and quartz sand fraction separated by sonication. Thick GCS units have been recovered by drilling behind the foredune ridge and are currently sheltered from wave and wind entrainment. Exposures of lightly cemented GCS pedestals in 300-year-old slipfaces occur downwind of historically deforested spit sections, which facilitated transport by westerly winds. Selective transport of GCS culminated with density separation into 2-30-cm-thick “green” layers interbedded with quartzose horizons. Stoss sides of relict (>5,000 yBP) dunes likely acted as regions of sediment bypassing, with deflation of paleo-slipfaces during dune migration. Along younger segments of the Great Dune Ridge, no GCS have been reported from rapidly migrating dunes (>100 m/century). Due to limitations of discrete marine-to-aeolian transport mechanisms of diagenetic glauconite mud fraction over large distances across the spit (>1,000 m), we propose a model of GCS delivery to the dunes: 1) erosion and transport of ancient glauconite mud and coated sand from coastal and seafloor exposures; 2) influx to the beach by storm surges, with percolation and adhesion of remaining mud fraction to quartz grains; 3) aeolian entrainment and selective landward movement, especially through non-vegetated areas (transport corridors), and 4) final density segregation on active dune surfaces. As suggested by previous workers, GCS and other lithological anomalies within dunes provide important insights into phases of increased storminess combined with persistent aeolian activity.