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Sediment composition within relict and modern spits of the Late-Holocene Kiliya delta of the Danube

The authors aimed to perform granulometric analysis of coastal sediments in the area of scattering of long-shore drift in the Jebriani bay within the Danube delta on the basis of mass sampling on the ancient relict and modern accumulative forms. The present study used the standard lithodynamic research methods. The paper presents the study results of sand deposit samples on ancient relict and modern sandy spits (‘grindu’) in the northern part of the mouth of the Danube. Overall, 24 samples were analyzed: 12 samples were collected on the tops of the aeolian hills and the other 12 – between the hills and ridges. In addition to this at the middle part of the Jebriani spit a typical cross-section was made, where 24 samples were retrieved based on microrelief features. For the first time in coastal literature, comparisons of the granulometric composition of sediments which compose ancient and modern generations of wave shafts within the Kiliya part of the Danube Delta have been carried out. The obtained samples were processed in the laboratory using standard methods of water and sieve analysis. The results were presented in the form of histograms and other types of graphics which allowed to us to compare and analyze the ratio of the composition of the relic and recent grindu. The obtained results revealed that ancient generations of grindu were composed of sediments from the same sources and in accordance to the same laws as modern ones. They are both composed of the same minerals, among which the primary role is taken by quartz, calcite, feldspar, magnetite, with a corresponding density (2.6-2.7 g/cm3, increased in calcite). In recent decades, the so-called beaches and borders of the grindu have disappeared. “Carpathian gravels”, which are fragments of the Early-Holocene terrace of the ancient Dniester, are today located at the bottom of the Black Sea in offshore environment. The synthetic composition of modern grindu branches is characterized by a reduced content of fractions ≥ 0.5 mm and ≤ 0.1 mm. The primary fraction is 0.25-0.5 mm (56-61%), although in the ancient relict form it reaches 69-75%. The average concentration of the second fraction of 0.1-0.25 mm is surprisingly stable in the grindu of different ages, namely 20-22%, including on the beaches, on the tops of the shafts and in the inter-shaft lowlands. The shapes of particles are very similar on the forms of different ages, rounding points value 3-4 are of leading importance. The particle size distribution in the area of sediment flow scattering allows to determine the behaviour of rock particles in a moving marine environment, the structure of sediments and sedimentary rocks of coastal, marine and aeolian origin.