Aeolian-accumulative complex Sarykum as a unique geomorphic object of Russia: research history and hypotheses of origin

Abstract

The aeolian-accumulative complex Sarykum is the biggest in Russia and one of the highest isolated sandy landforms in Eurasia with total area over 2500 ha. It is the whole system of sandy knolls and dunes, ridge sands located in the NE Caucasus foothill within the Terek-Sulak plain, 16-17 km towards NW of the Makhachkala City seaport (Republic of Daghestan, Russia). The origination and age of the sands, of which Sarykum massif has been formed, are still a big mystery. The existing hypotheses of the Sarykum sands genesis from those that considered the Sarykum as a relic phenomenon of the vast Central Asia deserts, widely stretched along the Caspian lowland, to aeolian versions explaining the origin by wind transportation from the Central Asia’s sandy deserts (namely the Karakums) across the Caspian Sea, or by weathering of indigenous sandstones composing the Foothill Daghestan and/or the loose pebble-clay-sandy deposits of high marine terraces of the Caspian Sea) are described and critically evaluated in the paper. Also the critical assessment to coastal-marine and relatively exotic volcanogenic versions is made. However, despite the different scientific validity of most of these hypotheses, none of them cannot convincingly answer the simple question: why did it happen here on the banks of the Shura-Ozen’ River, at the site of the river's exit from the Foothill Daghestan to the Caspian lowland? The author puts forward its own version of the sands genesis: originally, prior to their partial aeolian transformation, the Sarykum sands were the deltaic deposits of the Shura-Ozen’ River. The denudation area which supplied the sand material to the delta was the river basin upstream from the Kapchugay gorge of the Narat Tube ridge. According to one of the possible scenarios the sandy accumulation occurred in one of the stages of Late Pleistocene glaciation (presumably during the high Caspian transgression – the Early Khvalyn’ marine palaeo-basin, around 30-20 ka BP) under favorable conditions for intensive periglacial denudation of the sandstones of the ridge and deltaic sandy sedimentation. According to another version of the hypothesis the Sarykum sands are deltaic formation of the Late Khazar (Caspian) transgression epoch (around 120-75 ka BP).