Case Studies from the Dinaric Karst of Slovenia

tion in the Divaški kras (Mihevc 1996; Mihevc& Zupan Hajna 1996). The thickness of rockoverburden removed above cavities was establishedto have been 50–100 m. The age ofcave fills was calculated from denudation ratesand the expected thickness of missing overburdento 0.7–5 Ma (Mihevc 1996, 2001). Thislarge time range resulted from the expectedminimum (20 m/Ma) and maximum denudationrates (50 m/Ma) calculated or measuredin the area (Gams 1962; Cucchi et al. 1994).Unroofed caves were also described by Šebela& Mihevc (1995), Šebela (1995, 1999), Mihevc,Slabe & Šebela (1998), Šušteršič (1998), Knez& Slabe (1999a, b).The study (Zupan Hajna et al. 2008a) ofcave deposits in unroofed caves of the Krasprovided entirely new insights into the age ofcave and karst sediments and introduced newideas concerning the development of karst.Geomorphic comparative method used fordating of processes and landforms showedthat many accessible caves in the Kras are ofPliocene age at least or even older (Mihevc1996, 2000, 2001).The shape of unroofed caves depends on(1) the morphology of the present surface; (2)size, type and original arrangement of caves,and (3) the cave fill. Unroofed caves are usuallyaltered by surface processes. They representan important element of the epikarst zone. Onthe surface, they are expressed as narrow andoften meandering shallow trenches, shallowoblong depressions, doline-like forms in rowsand collapsed dolines. Mihevc (1999a) offeredmodels of their origin and their relation to thepresently accessible caves.Lipove dolineUnroofed caves are an important part ofthe surface morphology of Divaški kras where2,900 m of the unroofed caves were mapped(Mihevc 2001). In such features, flowstone,allochtonous sediments and morphology aretestifying their cave origin. The proportion ofdenuded caves is small in area (only approximately0.16 % of the total area). The largestsuch denuded or unroofed cave of the Divaškikras is located on the surface northeast ofŠkocjanske jame, named after great number ofdolines Lipove doline. The mapping of the surfaceshowed a 1800-m long series of dolinesand elongated dolina-like depressions 450 mabove sea level and interconnected withouthigher thresholds. The bottoms of the dolinesare 5 m to 10 m below the level of the rest ofthe surface; the depressions are 20 m to 30 mwide. Chert pebbles, yellowish red sandy loamand massive flowstone were found at the bottomof the dolines. The denuded cave passageforks in a number of places. In the westernpart of this roofless cave, in one of the Lipovedolines, quartz sand was exploited, duringwhich a large amount of flowstone and a largestalagmite were exposed. The stalagmite andthe sediments were first described by Pleničar(1954), who interpreted the cave as small cavewith a collapsed roof located near the surface.The unroofed cave in Lipove doline is similarto Škocjanske jame in its dimensions, as thewidth of the tunnel was in some places likelyto be more than 20 m. Anticipation from themassive stalagmite, the ceiling of the cave wasat least 10 m thick and at least 500 m abovesea level during the time when flowstone wasdeposited.The unroofed cave Ulica and Ulica pečinacaveThe unroofed cave Ulica and Ulica pečinacave (Fig. 46) are situated in the southeastpart of the Matarsko podolje (SW Slovenia),near the Croatian border. They are presumablyremains of the same cave system as Račiškapečina (Mihevc 2004). The passages of Račiškapečina are in elevation between 598-589 m.The 1,200 m distant Ulica pečina cave has itsparagenetic ceiling in elevation 585-589 m,while sediments at the bottom of the passageare between 585-562 m. In similar height, 580-585 m, is also the floor of the unroofed caveUlica.64