Sea-level fluctuations and coastline migration in the northwestern Black Sea area over the last 18 ky based on high-resolution lithological-genetic analysis of sediment architecture

Abstract

This paper reconstructs sea-level fluctuations and coastline migration in the northwestern part of the Black Sea for the last 18 ky using high-resolution lithological-genetic analysis of shelf sediments. The analysis includes study of geomechanical and geochemical properties (textures, grain size, Corg, CaCO3, pore water salinity and chemical composition, density, bulk density, water content, liquid limit, void ratio, and shear strength). The author's tech- nique allows the rhythmic variations of geomechanical and geochemical properties to be used as a basis for reconstructing oscillating sea-level changes and coastline migration, which is demonstrated in three exemplary cores recovered in Karkinitsky Bay and th e Dnieper Paleovalley, both on the Black Sea's northwestern shelf. Sedimentary episodes attributable to Shnitnikov's climatic (humidity) cycles have been revealed during the intervals between calendar years 1415, 551, 336, 286, 214, 169, and 136. Based on the length of these cycles, the mean sedimentation rate in Karkinitsky Bay is estimated as 0.34-0.51 mm/y, and in the Dniepe r Paleovalley, 0.29-0.36 mm/y. The coastline migrated from ~ -90 m (ca. 18 ky BP) to ~ -30 m (ca. 12 ky BP), and then to ~ -20 m (9.5-9.2 ky BP), when the first penetration of Mediter- ranean water and its biota occurred. The Holocene transgression occurred in an oscillating manner with 'centennial' regression-transgression cycles, each lasting 1600-2000 years. The suggested technique of lithological-genetic analysis and the model of sedimentogenesis provide a basis for forecasting future sea-level changes, coastline migration, and sedimentogenesis on the northwestern shelf.