engleski

Foraminifera-bearing aeolianites of SE Adriatic islands, Croatia

Late Pleistocene sands of SE Adriatic islands (Vis, Hvar, Lastovo, Korčula, Mljet) are generally thought to be aeolian in origin and to have been deposited at the time when present-day islands were parts of the mainland. It has been suggested that the sands derived from the Dinaric mountains and/or from land areas (now submerged) situated between the present-day islands and the mainland which included alluvial deposits. New data confirm the aeolian origin of most of these sands and suggest that they predominantly derived from marine sands exposed during sea-level lowstands. SE Adriatic islands mainly consist of carbonates originated on Mesozoic carbonate platforms of the Adria, and to lesser extent within a Palaeogene shallow sea. Only Vis Island includes a small area of Permian and Triassic rocks. Quaternary sediments occur in smaller patches. Tertiary deformation resulted in folds and SW-verging thrust faults. The work in progress includes field observations of sedimentary features and facies within the Pleistocene sands, as well as related studies of particle composition, heavy mineral associations and in particular, biogene constituents. Foraminiferal assemblages have been studied qualitatively (genera and species) and quantitatively. The studied Pleistocene deposits consist of aeolian sands, as well as of fluvial deposits derived from neighbouring highs. Aeolian sands are represented by cross-stratified units formed by the migration of dunes, and low-angle sand sheets. Dominant winds were from NE, E and SE. Main particles in the aeolian sands are quartz and limestone clasts which are followed by quartzite and chert. Clasts of ultramafic and mafic rocks may be common, while metamorphic clasts, as well as feldspars and shales, are rare. Heavy mineral associations are dominated by clinopyroxenes, orthopyroxenes and amphiboles. This compositional data, if taken alone, would indicate source areas located in the Dinaric orogen to the NE. However, the sands also contain marine fossils such as foraminifera, echinoid spines, mollusc and bryozoan debris and corallinaceans. Foraminiferal assemblages mainly include smaller benthic foraminifera, and in some cases, they are accompanied by globigerinids. Some samples contained as much as 84 specimens belonging to 20 taxa in 100g of sand. It is suggested that a major part the aeolian sands (if not all) of the SE Adriatic islands derived from exposed marine sands during glacial lowstands. The sands were initially supplied by rivers from the Dinaric mainland to ancient coasts, have subsequently experienced a reworking by marine processes, and were finally brought to present-day islands by aeolian processes. By this way marine biogene constituents were incorporated in the sands. Hence, the search for smaller marine fossils, e.g. foraminifera and echinoid spines, which represent a minor component of the Pleistocene sands, may help in a better understanding of the relevant geological situation, and in deciphering the provenance of aeolian sands. This work is part of the projects "Evolutionary changes of the Dinarides from subduction to modern Adriatic beaches", “Recent sediments and fossil environments of Adriatic coastal zone” and "Quaternary sediments of the Adriatic area", all of them supported by the Ministry of Science, Education, and Sport of the Republic of Croatia.

Late Pleistocene; Aeolianites; Foraminifera; Adriatic Sea

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