Devonian conodonts from the Fo~a–Pra~a Paleozoic complex (Durmitor Nappe, southeastern Bosnia and Herzegovina)

Conodont study of the Crna Rijeka borehole CR-17, positioned in the frontal part of the Durmitor Nappe (Fo~a – Pra~a Paleozoic complex, SE Bosnia and Herzegovina) is presented. The obtained fauna indicates an Early-Middle Devonian age and due to poor preservation an identification at a generic level is possible only. The recovered conodont elements have a high Color Alteration Index (CAI = 6,5–7) indicating a degree of metamorphism correspon ding to a temperature interval from 440 °C to 720 °C.


Introduction
The goal of the CR-17 borehole ( Fig. 1) was to acquire knowledge about the thickness of Devonian carbonate in the Crna Rijeka area of Bosnia and to recognize the geological characteristics of the area to support the project of the »Crna Rijeka Dam«, near Sarajevo (Ba{aGi} & skoPljak, 2007).
In this short report a documentation is presented of a conodont study carried out in Paleozoic strata of the Crna Rijeka CR-17 borehole, interval from 12 to 203 meters. The obtained conodont fauna indicates an Early-Middle Devonian age of the investigated samples present in some of the oldest strata in Bosnia and Herzegovina.

Geological setting
Geographically, the Crna Rijeka is located southeast of Sarajevo (Fig. 1). The area of Crna Rijeka is included in the Fo~a-Pra~a Paleozoic complex of southeastern Bosnia and Herzegovina and is positioned in the frontal part of the Durmitor Nappe, which tectonically overlies the Bosnia Flysch Nappe (Fig. 2).
Southeastern Bosnia and Herzegovina comprises the areas of Fo~a, Goražde and Pra~a. In the between the Fo~a and Goražde areas the oldest Paleozoic formations crop out in which Variscian age structures are preserved. Thick-bedded limestone occurs at Ustikolina with Late Silurian conodonts Ozarkodina and Panderodus present (Buzaljko, 1971;ra Mov{, 1989).
In the area of Klek on the easternmost slopes of Mt. Jahorina, "Orthoceras limestone" with Early and Late Silurian conodonts and tentaculides are present in the Pra~a thrust below Triassic formations (kosti}-PoDGorska, 1958 Lower and Middle Devonian limestone (kosti}-PoDGorska, 1958;živanovi}, 1963;Panti}, 1963). Some Paleozoic formations of the Fo~a area are of a presumed Devonian age. The thickness of the Paleozoic formations attains up to 800 m in the area (Buzaljko, 1971).

Conodont study
The present study is based on collections from the borehole CR 17 of Crna Rijeka and made in 2006 (kolar-jurkov{ek & jurkov{ek, 2006). Ten carbonate samples were collected, averaging approximately 2 kg each. They were processed for conodont analyses. All of them are composite samples, covering over one meter of the most perspective divisions, i. e. in the less recrystallized and less tectonized parts of the drill hole. Three samples were composite samples embracing over three to six meters of the borehole in order to obtain positive results. A standard technique for conodont extraction was applied by use of acetic acid and then heavy liquid separation. The samples were dissolved at the Geolo{ki zavod Slovenije / Geological Survey of Slovenia.
Out of the 10 examined samples from the investigated interval, six samples were productive for conodonts. However, conodont yields are rather low (Fig. 4). The obtained elements are largely fragmented. An identification at a generic level is possible only due to poor state of preservation. The conodont elements recovered have a high Color Alteration Index (CAI = 6.5-7) indicating a degree of metamorphism corresponding to a temperature interval from 440 °C to 720 °C (rejeBian et al., 1987).
Most of the forms are identerminable and only the elements of the two samples (CR 74-79 m and CR-17 193-195 m) enable comparison with Early-Middle Devonian taxa.

Materials and methods
Photographs of all illustrated conodont elements presented herein were taken on the JSM-

Sample CR-17 74-79 m (GeoZS 4077)
A single element was recovered from this sample. It is a spathognathodiform element (Pl. 1, Fig. 1) but the upper part of the denticles is broken away but it appears to represent an Early-Middle Devonian species of Ozarkodina or Pandorinellina (roBison, 1981;suttner 2007). However, the form also has certain similarities to Ozarkodina pandora Murphy, Matti & Walliser, an important Lockhovian datum (MurPhy et al., 1981).
Sample  The sample yielded two fragments of coniform elements with distinct longitudinal striation, yet partly etched (Pl. 1, Fig. 2). The specimens are marked by fine striation characteristic for Neopanderodus that ranges from the Lower to the Middle Devonian (roBison, 1981). Nevertheless, the specimens can be compared with Belodella striata Kozur, the only belodellid representative with fine striated ornamentation. This species was first described from the basal Pragian of the Uppony Mts. in Hungary (kozur, 1984).

Remarks on the Early-Middle Devonian conodont faunas of Bosnia and Herzegovina
The first Lower Devonian conodont faunas in Bosnia were described from the Dvor na Uni area on the Croatian-Bosnian border (\ur|anovi}, 1968, 1973 (krsti} et al. 1970, 1995krsti} & suDar, 1992krsti} & suDar, , 1994. The studied conodonts are strongly affected by metamorphism as indicated by a high CAI. Furthermore, most recovered conodonts are fragmented, corroded and recrystallized. This state of preservation is a result of the regional metamorphism and it markedly differs from the preservation of Triassic conodonts of Bosnia and Herzegovina that show a lower CAI (aljinovi} et al., 2006CAI (aljinovi} et al., , 2011 and have lesser alteration. The comparison with observations made on conodonts of the Albanides is ob vious (schönlauB & Meço, 1986).

Conclusions
A brief geologic overview of southeastern Bo snia and Herzegovina is presented and the results of a micropale ontological study carried out in the Crna Rijeka are documented herein. Conodonts were recovered from the Paleozoic strata of the CR-17 borehole. The scant conodont fauna indicates an Early-Middle Devonian age of the studied interval. The pre sence of conodonts in the tectonized carbonate facies is of significant importance for further study. The obtained results provide a reliable basis for a detailed biostratigraphic study aiming at a precise time assignment of the studied Devonian strata.