El registre sedimentari eòlic del Plistocè Litoral d'Eivissa

Resumo

-Introduction Past Aeolian sediments are abundant in the Balearic Islands. The most common registers are bioclastic carbonate sandstones locally known in the islands as “mares”, which has been traditionally used as a basic building material. Along the island of Eivissa, this type of sedimentary deposits has received very little scientific attention, resulting in a very few mentions in the scientific literature. Aeolian sedimentary deposits from the Pliocene to the Holocene, show a very important development in the Pleistocene, associated with coastal systems. Along the coast of the islands, we find a continuous register of littoral marine deposits associated with beaches, aeolian sand dunes deposits and colluvial or alluvial deposits. The sedimentary deposits of aeolianites, colluvials and palaeosols are an exceptional palaeoenvironmental register of the different climate episodes of the Quaternary. Aeolianites are the most characteristic quaternary deposits of the island of Eivissa. These deposits are mainly formed by marine sediments transported by the wind. This process was favoured by drops in the sea level that exposed great extensions of marine sand deposits -Research content We have characterised Pleistocene aeolian coastal outcrops of the island of Eivissa, by stratigraphic analysis, sedimentology and chronology by means of optically stimulated luminescence (OSL). We have developed the first regional synthesis of the aeolian deposits of Eivissa and their genetic and paleoclimatic significance. Nineteen different sedimentary facies have been identified and eight of them belong to aeolian sand deposits. Also we have identified red palaeosol (terra rossa), aeolian silt deposits (loess) and marine beach deposits. Aeolian deposits are abundant and the tridimensional morphology of the different units has been easily studied in sandstone quarries, along coastal cliffs and in small coves. We have identified five different types of dunes: parabolic dunes, climbing dunes, sand ramps, descending dunes and cliff-dunes. In the stratigraphic sequences of Eivissa twelve phases of aeolian accumulation have been identified. Dating by optically stimulated luminescence (OSL) has revealed the chronology of these phases with the isotopic stadiums: MIS 18, MIS 16, MIS 12, MIS 10, MIS 8, MIS 7, MIS 6, MIS 5c i MIS 4/3. The OSL dates reveal that the aeolian deposits of Eivissa where formed in cold and arid conditions, related with low sea level conditions. -Conclusion The OSL dating of the sediments has provided a chronology from the Middle Pleistocene to the Upper Pleistocene, and is one of the most complete Pleistocene sedimentary registers of the Balearic Islands and the Western Mediterranean.