Formation conditions of coastal palaeolakes and associated abiotic aragonite deposition in the eastern Mediterranean during the upper Pleistocene

During the Last Glacial Period (LGP), when sea level was up to similar to 130 m lower than today, many of the currently semi-enclosed gulfs in the Eastern Mediterranean were isolated from the open sea, functioning as palaeolakes. This was the case for the western Saronikos Gulf in Greece, which was isolated from the Aegean Sea. The palaeogeographic evolution of this area was investigated by analyzing a 350 cm sediment core for grain size, inorganic geochemistry, mineralogy, and bulk delta C-13 and delta O-18 compositions. An age model was developed by combining radiocarbon (C-14) and uranium-thorium (U/Th) dating methods. Integrating all available data and accounting for eustatic sea-level fluctuations, the sedimentary units of core SARC-18 cover the last glacial-interglacial cycle, spanning from 44.5 kyr BP to the present. Two marine sedimentation intervals were identified, characterized by clay minerals, biogenic calcite, and light delta C-13 and delta O-18 isotopic signatures. These intervals are separated by a lacustrine sedimentation phase, marked by the exclusive deposition of authigenic aragonite and a significant enrichment in delta C-13 and delta O-18. The latter elevated delta C-13 and delta O-18 values suggest carbonate mineral formation in an evaporative and saline environment under low temperatures (5-10 degrees C). Sedimentation rates during the marine intervals range from 5.8 to 6.0 cm kyr(-)(1), and are more than double during the lacustrine interval (11.9-14.0 cm kyr(-)(1)) due to the extensive deposition of authigenic aragonite.