Late Pleistocene paleoclimates and sea-level change in the Mediterranean as inferred from stable isotope and U-series studies of overgrowths on speleothems, Mallorca, Spain

Phreatic overgrowths on speleothems form at the surface of brackish pools w hich are present in many coastal caves of Mallorca (Spain). Unlike common v adose speleothems formed in subaerial environments, their occurrence direct ly identifies the height of the sea level at the time of the carbonate depo sition, because such pools are physically connected with the sea. These dep osits from the Late Pleistocene have recorded the same global variations in oxygen isotopes as planktonic and benthonic foraminifera, corals and cave deposits. A number of phreatic overgrowths on speleothems have been dated u sing the Th/U method in order to determine the position of the sea level du ring Late Quaternary. The same samples, as well as some subaerial speleothe ms, have been analysed for O-18/O-16 and C-13/C-12 ratios. The former sampl es allow the analysis of variations in sea water component in the brackish pools associated with glacio-eustatic Mediterranean fluctuations, and the l atter permit inferences concerning past continental climate changes. Some h igh sea-stands have been recognized in correspondence with Oxygen Isotope S tages (OIS): 9 or older, 7, 5e, 5c and 5a. Phreatic overgrowths on speleoth ems have also been formed during a colder phase (OIS 4), demonstrating that also in that period there were environmental conditions favourable for thi s kind of carbonate precipitation. Vadose crystallizations have recorded a cold period at 36 ka, corresponding with the end of OIS 3. (C) 2000 Elsevie r Science Ltd. All rights reserved.