Changes in coastline positions during the Holocene in the shelf of the Northwestern Black Sea

摘要

The first evidence for the reconnection of the Black Sea with the Mediterranean Sea are euryhaline mollusc species that appear in the bottom sediments. Lacustrine conditions existed over the larger part of study area at the beginning of the Holocene. Early Holocene beds are characterized by a wide distribution of continental facies (e.g. lacustrine-marshy and alluvial). The lacustrine phase was followed by a marine phase and the transition occurred around ca. 8.9-8.5 ka BP. The Holocene was marked by a gradual increase of Mytilus sp. shells in sediments. Reconstructions of coastline positions during the Holocene in the Northwestern Black Sea shelf are presented. Extensive sampling of the study area during several decades allowed the acquisition of a comprehensive data base for paleogeographic reconstructions. Positions of ancient coastlines are discussed. Analysis of relief features, lithological composition and bottom sediments distribution and faunal complexes allowed identification of pale-ofacies in the northwestern part of the Black Sea. Facial and paloegeographic maps of the Holocene discrete time intervals such as the Bugazian (from ca. 10.5-10 to 8.9-8.5 ka BP), the Vityazevian (from ca. 8.9-8.5 to 7.1-6.2 ka BP), the Kalamitian (from ca. 7.1-6.2 to 4.1-4.0 ka BP), and the Dzhemetinian (from ca. 4.1 -4.0 to present) are presented. Dating of the sediments is based on uncalibrated radiocarbon determinations. Study of the granulometry of sediments provided evidence that supports the proposed ancient coastline positions. The samples from the cores recovered from different facial zones enabled the characterization of sedimentological environments for each time interval. The position of the early Holocene coastal sediments is marked out on the level of modern isobaths approximately from -25 to -35 m. In the range of time from ca. 8.9-8.5 to 7.1-6.2 ka BP, the coastline was located at depths from 20 to 25 m. The position of the coastline which existed from ca. 7.1-6.2 to 4.1-4 ka BP is allocated on the level of modern isobaths from -0 to -15 m. Comparison of the various positions of the coastline and their facies changes through time indicates that the Holocene transgression had a progressively and oscillatory course.