engleski

Paleolake In Bribir-Ostrovica Karst Polje in Dalmatia

The Bribir-Ostrovica karst polje is one of a series of karst poljes in Ravni Kotari region in Dalmatia filled with lake sediments. They are surrounded with Cretaceous and Paleogene carbonate rocks and Eocene flysch. The central parts of the poljes are filled with Quaternary lake sediments, while the edges are covered with colluvial and alluvial sediments (sands and pebbles). The distribution of lake sediments in the Bribir-Ostrovica polje was analyzed based of geomorphological characteristic of the polje and the analysis of the undisturbed lake sediment sequences at three sites. Lake sediments contain a record of past environmental changes. Lake sedimentation depends on the surface water inflow and terrigenous material input from the surrounding basin, and climatic conditions. Lake sediments are used in archaeological studies for the reconstruction of a paleoenvironment of the area and in recent times are used in geoacrheology. The lake sediments indirectly point to the environmental changes that took place near archeological sites that could have had an impact on the movement of people in the past. Paleolimological study involve a multi- proxy approach through sedimentological, mineralogical, geochemical and micropaleontological analysis of lake sediment core. The OSP-3 sediment core contains lake sediments in a total length of 472 cm, spanning to 13200 years BC. During this period, in the Bribir-Ostrovica polje the lake-wetland environment was developed and thus during the Neolithic period (6000-4000 years BC). The Neolithic settlement in Krivače archaeological site existed near the lake environment. Changes in sedimentation of lake carbonates and siliciclastic material point to a dynamic environment and changes in climatic conditions. Lake carbonate sedimentation is characterized by the deposition of endogenic calcite from the water column due to favorable biochemical conditions of lake water. It is indicative for a warm climatic conditions and a deeper lake environment, recorded in the period from 10000 to 8000 BC. The Ostracod assemblage points to a dynamic, shallow environment under the influence of erosional processes and cold climatic conditions in older lakes sediments. It gradually decreases and converts into assemblage typical for shallow lakes and wetlands in younger lake sediments. Based on the geomorphologic characteristic of the polje and the analysis of lake sediment core, the paleolake in the Bribir-Ostrovica polje could not be deeper than 6 m. The thickest lake sediments are assumed in the geomorphologically lowest part of the terrain, west of Mount Školj, in the area that floods in wet periods at present times. Proximal parts of the polje, as well as the area within the archaeological site of Krivače, contain alluvial and colluvial sediments, deposited by streams that created a system of pools within the tufa barriers. Lake as a permanent water body could not be developed in the polje south of the Brbišnica River, west of Brbirske Mostine, due to higher elevation and slope relief. More likely, a cascade of smaller periodical lakes/ponds were formed separated by tufa barriers and flowing water. Paleolimnological study of lake sediments in the Bribir-Ostrovica polje can indirectly point to the paleoenvironment that prevailed in the period when Neolithic site in Krivače was inhabited.

paleolimnology, Dinaric karst, lake sediments, paleoenvironment, geomorphology

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