Pleistocene alluvial and aeolian deposits with tephra on the island of Lopud (eastern mid-Adriatic, Croatia): Provenance, wind regime, and climate controls

• Published in: Quaternary international 2018-11, Vol.494, p.92-104
• Main Authors: Kovačić, Marijan, Pavelić, Davor, Vlahović, Igor, Marković, Frane, Wacha, Lara, Kampić, Štefica, Rončević, Sanda, Drempetić, Dorotea
• Format: Article
• Language: English
• Subjects: Aeolian deposits; Alluvial deposits; Eastern mid-Adriatic; Pleistocene; Provenance; Tephra
• ISSN: 1040-6182; 1873-4553
• DOI: 10.1016/j.quaint.2017.11.054

Pleistocene alluvial and aeolian sediments occur as small patches in many places in the area of the eastern Adriatic coast and on the islands. On the southeasternmost mid-Adriatic island of Lopud they were studied along two lateral sections in Šunj Bay where a lense of reworked tephra is intercalated within the alluvial deposits. The interpretation of the depositional mechanism, the sand source, the wind regime and the volcanic activity, was based on facies analysis, sedimentological characteristics, and mineralogical and geochemical composition. Alluvial deposits represent recycled aeolian sand accumulated in a small-scale alluvial plain during a relatively long-lasting humid phase, while overlying aeolian sands were deposited under the influence of the sea-ward blowing NNW wind during more arid and windy periods. Sporadically occurring breccia lenses composed of limestone fragments from the Cretaceous basement strata are the result of occasional high sediment concentration flows, and deposition in shallow stream channels. Alluvial sand is composed of siliciclastic detritus derived from different metamorphic, magmatic and older sedimentary rocks of the Inner Dinarides, while the aeolian sand represents a mixture of siliciclastic detritus of the same provenance, and carbonate clastic detritus sourced from the Karst Dinarides. The lack of carbonate detritus in the alluvial deposits is probably a consequence of dissolution due to the humid climate. The tephra lense represents pyroclastic material that was reworked by water, and pedogenically altered. The tephra belongs to the high-K calc-alcaline and shoshonite series with a trachyte–trachydacite composition indicating an origin from the Campanian Province in Southern Italy as the most probable source area. The similar composition of clastic material on Lopud to the composition of aeolian and alluvial deposits on the neighbouring eastern mid-Adriatic localities (islands of Mljet, Korčula and Lastovo, and Pelješac Peninsula), suggests their common source, while the tephra lense documents Pleistocene volcanic activity and suggests the influence of a southern wind during the humid phase.