Holocene marginal marine ostracod successions from the Kızılırmak River delta; Implications for depositional environments and sea-level changes at the Southern Black Sea coast

Holocene delta formations are unique records of regional sea-climate interactions. The Kızılırmak Delta is the biggest and richest wetland ecosystem in the Black Sea region of Turkey. The Black Sea was uniquely affected by rising sea levels due to its disconnection from the world oceans during the last glacial period. To understand the palaeoenvironmental impact on the delta plain we analysed a 14.5-m-long sediment core using palaeoecological ostracod analyses accompanied by a palaeo-salinity reconstruction based on sieve pore analysis on the ostracod Cyprideis torosa. This study depicts the interplay of terrestrial and marine settings forming mesohaline, shallow lagoons and deltaic lakes since ca. 7.9 ka cal BP. Lagoons with α-mesohaline to polyhaline salinities and β-mesohaline to oligohaline lake environments were identified. Reconstructed palaeo-sea level estimations depict a remarkable environmental variability. The lagoon habitats at 7.9 to 7.0 and 5.3 to 4 ka cal BP were dominated by Cyprideis torosa. Marine influence led to ostracod associations with Loxoconcha spp. and Tyrrhenocythere amnicola especially between 7.9 and 7.0 ka cal BP. Riverine influence in the same period, but especially at about 7.7 ka cal BP, caused dominating Amnicythere spp. Cyprideis torosa and Candona neglecta that characterise short phases of a mesohaline deltaic lake environment at about 7.7 and 7.0 ka cal BP as well as after 4 ka cal BP. With a subsequent salinity decrease, C. neglecta and (later on) Pseudocandona marchica became dominant with an interruption by another short-term lagoonal phase that might be associated with a ‘megadrought’ between 3.7 and 3.0 ka cal BP.