engleski

MICROPALAEONTOLOGICAL AND GEOCHEMICAL CHARACTERIZATION OF HOLOCENE SEDIMENTS IN COASTAL KARST DOLINES UNDER THE MARINE INFLUENCE (ISLAND OF CRES, ADRIATIC SEA)

Numerous karst dolines have been formed along the coastline of Island of Cres, Croatia. Their genesis can be correlated with subaerial exposure of Cretaceous carbonates during the periods of sea- level lowstands (Surić, 2002). Holocene sea-level rise had significant impact on the dolines present in this area. Rise in the sea-level led to the rise in the ground water level that, together with precipitation, enabled water accumulation in inland dolines and marine inundation of nowadays submerged dolines. Three short sediment cores (up to 45 cm long) were extracted from inland dolines and two longer sediment cores (up to 370 cm long) were extracted from submerged dolines. Results indicate that interaction of sea-level rise, heat balance, tectonic activity, elevation and sediment accumulation had a fundamental impact on environmental development of investigated dolines located on the southwestern part of the Island of Cres near Town of Osor in Cretaceous limestones and dolomites. Marinska, Arcij and Podbrajde inland dolines differ in depth, size and distance from the sea. Furthermore, they can also be differentiated on the basis of the established environmental conditions, recognized foraminiferal assemblages in the sediment and sediment geochemistry. Marine influence with sea-water seepage through karstified underground is substantial. Dominant taxa in the brackish-water Marinska doline is typical for intertidal environments (Haplophragmoides canariensis and Trochammina inflata). Monospecific assemblage, comprising stress-tolerant species Ammonia tepida, has been identified in Arcij doline. Significant number of deformed specimens is present in this environment, indicating environmental stress. Established environmental conditions in doline Podbrajde did not allow diversification of foraminiferal fauna. Geochemically, these environments are characterized by high production rates (elevated N and P) and significant accumulation of algal organic matter. Sonte and Jaz submerged dolines with preserved thick sediment sequence have been studied in detail. The main aim was to recognize transitional terrestrial-marine intervals in sediment cores in order to compare Holocene environments with the present environments located along the Island of Cres. Special emphasis was on determination of the timing of marine inundation, that was based on micropalaeontological and geochemical data. Results revealed dynamic Holocene palaeoenvironmental development of submerged dolines. Environments similar to the present-day inland dolines have been recognized in the basal part of the cores. They are characterized by high abundance of organic matter and high Mo concentrations. Some differences in comparison to the present day inland dolines, that can probably be attributed to climate variations, have been recognized in geochemical data. Foraminiferal assemblages in these intervals contain low-diversity fauna predominantly composed of Ammonia tepida, Ammonia parkinsoniana and Haynesina depressula specimens.

Holocene, sediment cores, Island of Cres, karst dolines

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