Last interglacial sea level changes in Mallorca island (Western Mediterranean). High precision U-series data from phreatic overgrowths on speleothems

摘要

The karst of Mallorca Island (Balearic Archipelago, Western Mediterranean) is characterised by the occurrence of many coastal caves where phreatic speleothems accrete today, around conventional vadose-zone speleothems, in correspondence with the current sea level. Older deposits of this kind of carbonate precipitates have recorded ancient high and low sea stands by means of strictly horizontal alignments of the phreatic overgrowths on speleothems (POS) respectively located above and below present sea level. Mallorca has proved to be a good location for investigations on custatic sea level changes because it is located far from former margins of the major ice-sheets and was only affected by a minor tectonic tilt since the end of marine oxygen isotope stage (OIS) 5e. A number of POS now located above and below present sea level have been dated by the U-series method using MC-ICPMS and TIMS. The obtained high-precision ages fall within a time interval ranging from 144,000 to 78,000 yr ago and provide constraints on sea level changes curve during the last interglaciation in Mallorca. Three high stands have been recognised corresponding to OIS 5c (138,000-128,500 and 122,000-110,000 yr) and OIS 5a (84,000-82,000 yr) separated by very fast sea-level falls. The resulting eustatic curve emphasizes the occurrence of marine level fluctuations greater than IS in in amplitude within short time spans (< 5,000 yr).