engleski

Perspectives on magnetic research of sediments of Northern Velebit deep caves, Dinaric karst, Croatia

Caves formed in karst terrains are often trapping big amounts of different kinds of sediments. Cave sediments can be very useful for the determination of conditions and processes that were present at the time of their deposition. They are usually well preserved so they can give us a lot of i nformation about changing of the conditions over a long period (sometimes even over a few million years). One of the key methods that can provide us with a deeper insight into the complex karst systems is magnetic susceptibility, which shows the magnetism of measured material. Magnetic susceptibility measuring allows recognition of iron-rich minerals (together with their concentration and volume), classification of different types of materials and a better understanding of tectonic events. This is also particularly important in the context of exploration of karst waters that are important from the aspect of vulnerable karst ecosystems and strategic reserves of drinking water. In this research, two caves were chosen for sediment analysis. Both caves are located in the northern part of Velebit mountain, named Nedam and Ledena jama. Nedam is Croatia's fourth deepest pit with a depth of 1021 m. Ledena jama, is 536 m deep pit that is significant by the perennial ice between depths of 50 and 160 m, and is located in a paleoglacier valley. Nedam is located on steeper and more inaccessible karst terrain. The entrances are at different altitudes – at 1420 m for Nedam, and at 1235 m for Ledena jama. That altitude difference and different terrain morphology (paleoglacier valley vs. steep karst), suggest that interesting differences in the sediments studied may be present. Sediment samples were taken at 50 m depth in Ledena jama, and at 100 m depth in Nedam. Preliminary magnetic measurements were performed using the SM30 instrument (ZH instruments). The additional analyzes made on the sediment samples were the determination of mineralogical composition – identification of clay minerals by X-ray diffraction analysis, separation of light and heavy mineral fraction, and observing under the microscope. Magnetic research provides complementary data to these methods. From this analyzes, we can deduce the province of the sediments, and some conditions that were present during their deposition and terrain formation. The mineral composition of the samples from both pits was compared. This work was done in collaboration with Northern Velebit National Park, Krasno (project Exploration of the deep pits of the Northern Velebit National Park), Department of Geology, Faculty of Science, University of Zagreb and Speleological Society Velebit, Zagreb.

magnetic research ; Dinaric karst ; deep caves ; Croatia

nije evidentirano