Pleistocene carbonates from Dobrogea (E Romania) and their relationship with Black Sea level fluctuations

The eastern part of Romania, bordering on the Black Sea, is generally poor in speleothems and only Piatra Cave has important speleothem occurrences. This cave is positioned close to the present-day shoreline, forcing the local aquifer to completely flood it when it rose synchronously with sea level. The flooding of the cave prevented speleothem formation. Conversely, sub-aerial carbonate deposition took place when the sea level was lower than today and the cave was dry. The study of speleothems from Piatra Cave could bring more insight on past Black Sea level fluctuations, as well as on the isotopic composition of percolating water.

Some 50 km to the south of Piatra Cave, around the town of Mangalia, botryoidal calcite has been deposited inside small voids formed between Sarmatian limestone beds. Such calcite formations are considered to form close to the water table, at the contact with the underground atmosphere. If so, they could be used to track the position of past water tables, as well as the isotopic composition of those waters. Moreover, as these samples are found only close to the present-day shoreline, they might have been deposited from underground water whose level was directly controlled by the sea.

Here we present the results of δ¹⁸O and δ¹³C measurements on 75 samples and sub-samples of botryoidal calcite. We explore the implications of their isotopic variability, by comparison with speleothems from Piatra Cave as well as to other speleothems from Romania. Moreover, we explore their isotopic variability across the sampling area, in order to better assess their possible use as sea level markers.