Abstract
In this paper, preliminary results concerning the nature, subsurface structure and age of carbonate-cemented coquinite extending along a 1.5-km long and 40-m wide loose coquina beach on the Thracian (west Black Sea) coast of Turkey are presented. An Electrical Resistivity Tomography (ERT) survey showed that the coquinite has a maximum thickness of about 2m and comprises seaward dipping buried 20m-wide slabs under beach materials at the backshore. Cemented by low-magnesian calcite, the coquinite contains various bivalvia, benthic foraminifera, calcareous nannofossils or coccoliths and quartz sands. Diagenesis of the coquinite occurred as the result of sequential cementation, starting with the precipitation of micritic envelops typical of a marine phreatic zone. This early stage was followed by pore-lining cements and bladed rims composed of equal-sized subhedral and anhedral crystals of calcite, suggesting evidence of meteoric phreatic and meteoric vadose environments, respectively. Calibrated values from radiocarbon dating of four bulk samples of bivalvia revealed that the coquinite shells were deposited between 3730 and 2850years BP. During that period the sea-level was similar to the present at an early stage then dropped to −2m due to Phanagorian regression (between 3200 and 2200 BP), which is evidenced by consecutive cementation patterns of distinctive origin.
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