Beachrocks and sea level changes since Mid-Holocene: comparison between the insular group of Mykonos-Delos-Rhenia (Cyclades, Greece) and the southern coast of Turkey.

International audienceThe small insular group of Mykonos–Delos–Rhenia in Cyclades, Greece, and the southern coast of Turkey from Andriake to Arsuz show three bands of beachrocks, emerged up to +0.35 m and submerged sometimes down to −4.3 m. Because beachrocks are formed within the intertidal zone by carbonate cementation of the beach deposits during stages of shoreline stabilisation (both eustatic and tectonic), they correspond todifferent generations indicating different sea level stands.11 sites on the southern coast of Turkey and 7 bays on the insular group of Mykonos–Delos–Rhenia were studied. 52 beachrock samples were analysed by polarizing microscope, cathodoluminescence and SEM. This study indicated that carbonate elements that constitute most of the samples were at least partly incorporated within the intertidal zone. The adequate method for radiocarbon dating (total sample or cement) was decided according to these observations. Because diagenetic cements seemed difficult to extract manually and the sources of carbonate pollution are limited in Mykonos–Delos–Rhenia, we performed 14C AMS dating on total samples. On the southern coast of Turkey, due to the abundance of micrite in between the limestone pebbles that often constitute the beachrocks, available cements had to be manually extracted for 14C AMS dating.The dates obtained from Mykonos–Delos–Rhenia beachrocks indicate 3 separate sea level stands: the first one at about −3.6 m (±0.5 m) around 2000 BC, the second one at about −2.5 m (±0.5 m) around 400 BC and finally the third sea level at about −1m(±0.5 m) around 1000 AD. On the southern coast of Turkey, several relative sea level positions in 4 areas (I to IV) are recognised. From Finike Bay to the west (area I), a post-Roman relative sea level rise is observed after a period of coastline stabilisation. The area from the east of Finike Peninsula to Çimtur (area II) witnessed relative sea level rise since mid-Holocene interrupted by 3 phases of stability corresponding to beachrock bands. Two levels have been dated. The first one is between 0 m and −0.8 m and dates from 5th to 7th century AD. The second one is between −1.5 m and −2.2 m and dates around 7th to 6th century BC. From Incekum to Karataş–Osmaniye Fault Zone to the south of Adana (area III), the shoreline was raised around +0.5mafter 19 BC–200 AD and later becomes stable at least since the 12th century AD as can be interpreted from archaeological remains. To the east, beachrocks in Gözcüler (area IV) indicate a relative sea level rise interrupted by a phase of coastline stabilisation between 0 m and −0.5 m from the 4th to the 7th century AD. Our southern Turkish coastline observations reveal a very dynamic tectonic regime – mainly subsidence to the west and uplift to the east – since at least mid-Holocene. The comparison of the results obtained from Greece and Turkey indicates a tectonic subsidence during the last 6000 years in the centre of Cyclades