Cesta – a historical road on Velebit Mt . with a special review of Jurassic carbonate rocks

important value in Croatia as well as worldwide. The road transversely crosses almost a completely Jurassic sequence (201.3-148 Ma). It offers an exceptional view into the geological history of the Karst Dinarides, particularly the fossiliferous Jurassic rocks, comprising index fossils for a complete stratigraphic span, including contact with Triassic as well as Cretaceous and Palaeogene rocks. The Velebit Mt. Jurassic rocks were deposited on the Adriatic Carbonate Platform (AdCP; ), which existed during the Mesozoic Era over the area of the present-day Karst Dinarides. It comprises carbonate sequences of total thickness between 6 and 12 km. The size and age of the AdCP


Introduction
Majstorska Cesta on Velebit Mt., connects Sv. Rok and Obrovac. It is protected as a natural monument, according to Croatian legislature. The road has been built over Upper Carboniferous, Middle and Upper Permian, Triassic, Jurassic, Cretaceous, Palaeogene and Quaternary rocks. The outcrops of Jurassic carbonates between Mali Alan Saddle and Tulove Grede Ridge are especially important value in Croatia as well as worldwide.
The road transversely crosses almost a completely Jurassic sequence . It offers an exceptional view into the geological history of the Karst Dinarides, particularly the fossiliferous Jurassic rocks, comprising index fossils for a complete stratigraphic span, including contact with Triassic as well as Cretaceous and Palaeogene rocks. The Velebit Mt. Jurassic rocks were deposited on the Adriatic Carbonate Platform (AdCP; ), which existed during the Meso-zoic Era over the area of the present-day Karst Dinarides. It comprises carbonate sequences of total thickness between 6 and 12 km. The size and age of the AdCP Therefore, it is very important to preserve such localities and outcrops, keeping the evidence of the AdCP evolution intact. With respect to the fact that Majstorska Cesta is already protected as tangible cultural heritage (under the category of protected cultural property), the exposed geological heritage can represent additional value for visitors. Such heritage must be described, explained and presented to the public in handbooks, informative pamphlets and signs.
The announcement of the renewal of this locality impelled us to prepare this review. This paper recommends that the representative and exceptional geological outcrops, from the Upper Palaeozoic to Mesozoic and Cainozoic, should be evaluated and considered as a part of national geological heritage. In that case, they would be preserved during the road reconstruction and presented to visitors on informative signs along the road. In this way, visitors could also use this road as an educational trail. Visitors of the Nature Park would be able to appreciate interesting and informative descriptions of the particular sites and sections, beautiful viewpoints and geological history of Velebit Mt. and the Croatian karst.

History
Majstorska Cesta had been planned with the purpose to shorten the voyage from Vienna, as a capital and land-locked part of the Austro-Hungary monarchy, to Dalmatia and its administrative centre Zadar. The construction of that trans-Velebit road started in 1825, from Obrovac to Tulove Grede, crossing the Alan Depression, Mali works.
The road is 41 km long. It was completed in 1832 and named Majstorska Cesta (= Craftsman Road). The name steep Velebit Mt. slopes, with numerous serpentines, among canyons and gulches, which represented great progress in road construction for that time. The maximal road dip was up to 5.5%, corresponding to current rules for road building ( ). That new Velebit transversal had been used for trade and until the early 60's of the 20 th century, i.e. until the opening of the Jadran Highway (Jadranska magistrala), and ska Cesta passes near the geomorphologically famous feature Tulove Grede Ridge, which is composed of vertical carbonate plates, beams and pillars as well as the attractive Alan Depression.
Majstorska cesta is a historical Velebit pathway (see ) and that is the reason it was included on the list of cultural heritage of the Republic of Croatia in 2007. Its main value is the fact that the road has been preserved since 1832 with its original route from the Paljenik locality (see ) on the NW point of Sveti Rok to Obrovac (see ). Its cuttings and outcrops comprise the rocks of very wide stratigraphic range, from Upper Palaeozoic to Lower Cainozoic (i.e. Upper Carboniferous to Upper Palaeogene; 315 to 25 Ma, 290 Ma in total). Thus, the deposits along the road ) and their explanatory books ( , ). Since that time, until the research for the Basic Geological Map of SFRY 1:100000, been recorded.
published the biostratigraphical data from Velebit Mt. and described the lithostratigraphy of the Lower Jurassic deposits exposed along the road. During the explorations for the Basic Geological Map, the sheets Udbina ( ) and Obrovac ( ), as well as their explanatory books ( for Udbina; for Obrovac) were published.
Some valuable data was published in the guidebook of the 9 th International symposium on fossil algae ( ) on Majstorska Cesta, where in the introduction described geological characteristics of Velebit Mt.
presented Permian Mizzia Dolomites (Micijski dolomiti) in Sv. Rok, Ladinian Diplopora Limestones, Lower Jurassic with algae Palaeodsycladus, Lower Jurassic Orbitopsella Limestones, Lithiotis Lime-  represent a natural geological museum of carbonates of the Dinaric Karst. The road was built from Obrovac to Sveti Rok, but the geological review in this paper runs in the opposite direction, thus respecting the rule that the and present the parts of the Basic Geological Maps of SFRY (1:100000), Obrovac ( ) and Udbina ( ) sheets, with selected parts of the geological maps of Lika and Velebit where the road was constructed.
stones and Spotted Limestones, Upper Jurassic Limestones, and Oligocene -Miocene Jelar Breccia (i.e. Velebit Breccia). One of the more recent papers ( ) presents a short description of Velebit Mt. geology. This paper describes the entire road section, with an emphasis on geological showpieces.

Results
Majstorska Cesta is described from the older toward the younger stratigraphic units, starting with the Sv. Rok locality, across Velebit Mt., towards Obrovac. At the start, from Paljenik to the centre of Sv. Rok, the road was radically on the Carboniferous shales and sandstones and on the Lower Triassic micaceous sandstones.
In the majority of Sv. Rok, the road was built over the Middle Triassic Diplopora Limestones, and, near ). Further, up until Egeljac, it is positioned on the alluvial deposits between the Diplopora Limestones and the Mizzia Dolomites.    roundabout, the road leaves the breccia and runs through the Lower Cretaceous limestones. The roundabout gives the best view of Tulove Grede and the S slope of Velebit Mt. where the road passes. At the very end, the road reaches the former alumina factory, where it passes over the Vrakon dolomites and dolomitic breccia and the Upper Cretaceous rudist limestones. The road ends at the bridge over Zrmanja River in Obrovac, in Promina conglomerates and sandstones (see ) with intercalations of marlstones.

Conclusion
The rocks along the road were presented on many geodomestic and international geological meetings; pers, reports, projects, graduate, master and doctoral thesis; detailed geoscientists' research along the road made the construction of the Sv. Rok Tunnel possible, on the A1 Highway (with a margin error of strata positions of less than 1 m). the road was, and always will be an attractive locawell as for guided sightseeing tours.
fessor (University of Zagreb-Faculty of Mining, Geology and Petroleum Engineering support: "Mathematical Research in Geology IV."), for professional support. Our thanks goes to anonymous reviewers as well, for their suggestions in both versions of the manuscript. They inspired us to present the obtained data in a more appropriate form and greatly improved the manuscript. Mizzia-ternational Symposium on Fossil Algae, Croatia 2007, Field Trip Guidebook and Abstracts, Hrv. geol. institut (Croatian Geological Survey), Zagreb, 7-11. th International sysmposium on fossil algae, Croatia 2007., Field trip and abstracts. Hrvatski geološki institut -Croatian geological survey, I-V+1-261, Zagreb.