A U-PB DATED GLACIAL ISOSTASY CORRECTED PLIOCENE SEA-LEVEL RECORD IN MALLORCA (WESTERN MEDITERRANEAN) BASED ON PHREATIC OVERGROWTHS ON SPELEOTHEMS

Since the Early Pliocene the caves along the coast of Mallorca Island in the western Mediterranean were repeatedly flooded by hydro- and glacio-eustatic sea-level oscillations. The seawater level of each flooding event formed distinct encrustations of calcium carbonate over preexisting vadose speleothems and along cave walls. These encrustations are referred in the literature as phreatic overgrowths on speleothems (POS). Because the littoral caves are within 300 m from the coast, the brackish water table in them is, and was in the past, coincident with sea-level. The precipitation mechanism of POS arguably provides the most precise indicator of the timing and the absolute elevation of the sea-level in this part of the Mediterranean basin. The timing of POS deposition is accurately provided by dating them with U-Th and U-Pb methods.

Here we present six clear POS levels (ranging from 22.5 to 32 m above present sea level; mapsl) from Coves d’Artà, which returned U-Pb ages between 4.39 ± 0.39 and 3.27 ± 0.12 Myr. These results represent directly dated sea-level elevations during the Early to Middle Pliocene. Of a significant importance is the youngest sample, which documents the sea elevation at 23.5 mapsl during the Mid-Pliocene Warm Period (MPWP), an interval that is most often invoked as the best analogue for climate change in the near future. Nevertheless, our results indicate higher sea-levels during the Early Pliocene, compared to the MPWP, time period which is notably less studied.

In order to translate site-specific data into eustatic sea-level, we corrected the post-depositional displacement caused by glacial isostatic adjustment (GIA) and dynamic topography (DT). A downward correction of a few meters is indicated by GIA simulations when using the local elevation to infer eustatic sea level, while DT simulations are significantly less constrained. We provide a robust dataset of sea-level elevations during Early-Middle Pliocene, corrected for GIA, that can put unique constraints on models of dynamic topography and the evolution of global mean sea level during the Pliocene.