SEA LEVEL FLUCTUATIONS IN THE WESTERN PART OF THE BLACK SEA DURING THE HOLOCENE

Although investigations have been going on for 20 years, the Holocene history of the Black Sea shelf is not yet fully understood. This is because much of the evidence has been removed by repeated displacement in the wave-breaking zone. The sediments are characterised by incomplete cross-sections and frequent lithological transitions, giving evidence for the heterogeneity and complexity of the conditions under which they were formed. Black Sea level changes during the Holocene are evidenced by biostratigraphical investigations based on spore-pollen, molluscan fauna and dinoflagellate cysts analyses, correlated with geomorphological, geological, archaeological and historical records. They have been delimited by analyzing the terrace complex along the seashore and locating marine phases which denote sea-lake oscillation. On the basis of the existing radiocarbon dates for the Bulgarian coastline a sea level change curve for the Holocene is suggested, the details of which can be filled out as new data become available. Sea level has exceeded the present level on a few occasions during the last 6000 years as evidenced by the sea terraces formed along the coast at an elevation of 2-6 m. The differences which have been observed while investigating the coastlines and their age is due to their heterogeneous structure, the neotectonic occurrences, and the lithological and physical - geographical characteristics of the individual areas along the coastline. The beginning and the end of the transgressions can be traced in the sediments of the flooded estuaries and the firths formed along the coast. At the present time a general transgression is observed due to the slow sea level rise from 2,5 to 3 mm/yr.