AEOLIAN-ACCUMULATIVE COMPLEX SARYKUM AS A UNIQUE GEOMORPHIC OBJECT OF RUSSIA: STRUCTURE, GENESIS AND SANDS SOURCES

Abstract

Aeolian-accumulative complex Sarykum is one of the highest isolated (i.e. formed away from the deserts) sandy landforms in Eurasia, located within the Terek-Sulak lowland plain at the north-eastern foothill of the Caucasus Mountains, 16–17 km towards WNW of the Makhachkala City port of Caspian Sea (Republic of Dagestan, Russia). On the basis of particle size distribution and mineralogical analysis of 59 sandy samples, the heterogeneous structure of the complex is defined. The coarsest sandy material (modal values are 352 micron and more) composes the central dune-ridge segment of Sarykum (of so-called Great (or West) Sarykum). The further from the dune constructions to the periphery, the thinner the average dimension of the sand particles and smaller the modal values (249 micron and less) of their granulometric spectra. This grain size distribution can be explained not only by windy sorting of the sands and further aeolian recast of dune-ridge segment, but also by spatial features of the facial changes during the period of initial sandy accumulation, and also by the differences in composition of rocks, which were the sources of denudation. In the vertical structure of Sarykum the heterogeneity is also expressed. It is associated with temporary changes of sandy sedimentation conditions in the region. So, the dune-ridge segment of Great Sarykum can be represented as a system of consistently accumulated sandy layers (lenses?) (which includes the gravelly sands), which differ in composition and age, having apparently the coarsest content in the middle part of its vertical geological cross-section. The material of overwhelming majority of the selected samples belongs to mineral group of quartz sands (quartz content is over 90%) and subgroup of quartz subarkose (quartz content is 80–90%). Moreover, the aeolian (defl ated) sands of the dune-ridge segment and its underlying cross-bedded sands of Great Sarykum entirely belong to the first group; the hilly and peripheral sands, which characterized by fine granulometry, refer to the second mineral subgroup. The Sarykum’s structure is due to the combination of gravelly sands, formed by the river Shura-Ozen’ deltaic accumulation in the Late Quaternary, and sandy (with gravels and pebbees) deposits proluvially and deluvially dislocated to the recent Sarykum massif territory from the slopes of the nearby Narat-Tube mountain range. The mixing of originally and compositionally different sediments that formed the Sarykum complex, likely have the complicated history, following by the staged changes of the periglacial landscape-climatic conditions in the Late Quaternary.