First record of beachrock on Black Sea coast of Turkey: Implications for Late Holocene sea-level fluctuations

- The cementation and 14C age of beachrocks from Black Sea coast were first studied.
- Beachrock ages range between about 5.5 ka BP and 3.5 ka BP.
- Geophysical data showed vertical and lateral extension of beds under beach sands.
- The fabrics are typical of two-stage cementation, i.e., intertidal and supratidal.
- The etched early cements and pure low-Mg imply freshwater influx at lower sea-levels.

We present new data on the diagenetic characteristics, subsurface nature and radiocarbon ages of beachrock from the Thracian Black Sea coast of Turkey, indicative of sea-level changes and climatic conditions favoring lithification of beach sands between 5.4 ka and 3.5 ka cal BP. Micrite coatings and succeeding meniscus cements typify diagenetic history and suggest a two-stage cementation over this timeframe. The early cements are typical of upper intertidal zone when the sea-level was likely similar to that of today. The ensuing intergranular bridges refer to an approximate 2 m decline in sea-level, favoring downward percolation of meteoric waters related to subaerial exposure, marked by a reduction in Mg concentration and dissolution pits on early cement coatings. Formation of beachrock during this bimillennial period could be associated with relatively drier conditions promoting the precipitation of connective cements.