engleski

2 ka paleoenvironmental reconstruction of the Milna valley on the Vis Island (Central Adriatic)

The Island of Vis belongs to the Central Dalmatian Islands group. By its size (89.72 km2) it is the 9th island in the Adriatic Sea, located 45 km from the mainland. Today, it is dominated by Csa climate with a mean annual temperature of 17°C. The relief of the Island of Vis can be simply described through three main hilly ranges, between which dry valleys and poljes are situated. They are mainly of ENE-WSW orientation as defined by the spreading of main geological structures. The topographic ridges are formed in Cretaceous carbonates and separated by valleys filled with Quaternary deposits. This youngest sedimentary complex covers a great part of the island. It is developed in several continental facies: terra rossa, breccia, breccia-conglomerates and eolian sands. They are primarily remains from the past glacial periods – largely Pleistocene. Generally, the formation of dry valleys is a consequence of differential modelling during the colder and more humid phases of the Pleistocene. Whenever the rainfall is higher than potential evapotranspiration, surface drainage takes the main role in valley formation and permanent or temporary flows occur. One of such fluviokarstic form is the Milna valley. It is situated on the southern coast of the island and spread in the NE-SW direction following the Stupišće – Milna fault zone. Here we provide the 2 ka paleoenvironmental evolution of this small, today dry valley. Modal analysis of fine- grained sediment, their granulometric properties, and petrographic microscopy of pebbles were done as well as the determination of molluscs’ species. Charcoal and molluscs samples have been dated using 14C. This allows us to trace the evolution of the valley during the 2 ka. We evidenced the periods of rapid climate changes like the Dark Age Cold Period during which the closed forest habitat preferring and cold-resistant species has been found, such as Trichiahispida, Discus ruderatus shell, Macrogastraventricosa. This lead us to the conclusion that the area was covered by forest of Pinus sylvestris of which 2 species, probably Pinus cf. Sylvestris and Pinus cembra have been identified from the charcoal samples in the upper layer, Pinus cembra being again a cold climate indicator species. The fire, natural or anthropogenic, from which the charcoal derived, occurred during the 15th and 16th century that is during the period of the Little Ice Age. Consequently, the fire could be most probably of anthropogenic origin in order to obtain new areas for cultivation of crops. The destruction of vegetation caused by fire has further influence on the temporarily formation of the river bed. Indeed on the charcoal layer we found deposited pebbles and a deeply incised river bed in the middle of the valley. Obviously due to deforestation the temporal river has enough energy to incise the bed in soft sediments, supported additionally with favourable climate conditions which were relatively colder and particularly wetter than today. Wetter conditions during LIA have been already observed along the Croatian coast, manifested through the enhanced input of fresh water in the Mirna river valley in Istria. These periods of rapid climate changes have been also determined on the island of Vis by studying the relative sea level change and climate change during the last 2000 years. Afterwards the valley became dry again and has probably been continuously under anthropogenic impact, being also today a winegrowing area.

fluviokarst ; dry valley ; land cover changes ; Milna valley ; Island of Vis

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