Pleistocene Pisolites as Archives of Hydrological Variability in Mediterranean Coastal Environments: Evidence from Eivissa (Balearic Islands, Spain)

Pisolites are carbonate-coated grains whose nucleus–cortex architecture may provide insights into carbonate formation and modification in terrestrial coastal settings. This study examines pisolite-bearing horizons within the Pleistocene coastal successions of Eivissa (Balearic Islands, western Mediterranean) using field sedimentology, quantitative morphometry, petrography, and X-ray diffraction (XRD). These successions record alternating aeolian and alluvial–colluvial deposition, palaeosol development, and carbonate cementation, locally including documented interdune settings. Quantitative analyses focus on two samples from pisolite-bearing intervals within unit U9 at the nearby outcrops of Cala Bassa (CC1) and Cala Compte (CC2), situated between carbonate crusts. Matrix-associated and manually isolated fractions differ significantly in maximum grain and nucleus diameters in both samples, whereas calculated cortical thickness differs significantly in only one. These preparation-defined comparisons may be affected by recovery bias and do not establish distinct genetic populations. Petrography reveals successive cortical layers with variable thickness, continuity, and symmetry, consistent with repeated accretion and modification. XRD identifies calcite as the dominant mineral in both pisolites and host matrices, accompanied by subordinate brushite and quartz. The combined observations are compatible with local to near-local development, although short-distance reworking cannot be excluded. A working model links carbonate dissolution, redistribution, and cortical reprecipitation to changing sediment moisture within an evolving coastal depositional and pedogenic system. The timing of carbonate-crust development relative to pisolite growth remains unresolved, as do the relative contributions of infiltration, runoff, temporary ponding, and shallow groundwater.