GEOLOGIJA 54/1, 91-96, Ljubljana 2011 doi:10.5474/geologija.2011.007
Devonian conodonts from the Foca-Praca Paleozoic complex (Durmitor Nappe, southeastern Bosnia and Herzegovina)
Konodonti iz focansko-pracanskega paleozojskega kompleksa (durmitorski pokrov, jugovzhodna Bosna in Hercegovina)
Tea KOLAR-JURKOVŠEK1, Hazim HRVATOVIC2, Ferid SKOPLJAK3 & Bogdan JURKOVŠEK4
1 4Geoloski zavod Slovenije, Dimiceva ulica 14, SI-1000 Ljubljana; e-mail: tea.kolar@geo-zs.si, bogdan.jurkovsek@geo-zs.si, 2, 3Federalni zavod za geologiju, Ustanicka 11, 71000 Sarajevo, e-mail: zgeolbih@bih.net.ba
Prejeto / Received 15. 3. 2011; Sprejeto / Accepted 13. 4. 2011
Key words: conodonts, Devonian, CR-17 borehole, Crna Rijeka, Bosnia and Herzegovina Ključne besede: konodonti, devon, vrtina CR-17, Crna rijeka, Bosna in Hercegovina
Abstract
Conodont study of the Crna Rijeka borehole CR-17, positioned in the frontal part of the Durmitor Nappe (Foca -Praca 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 corresponding to a temperature interval from 440 °C to 720 °C.
Izvleček
Predstavljene so konodontne raziskave vrtine Crna rijeka CR-17 v čelnem delu pokrova Durmitor (paleozojski kompleks Foča - Prača, jugovzhodna Bosna in Hercegovina). Konodontna favna dokazuje spodnje-srednjo devon-sko starost, vendar je zaradi slabe stopnje ohranjenosti mogoča le določitev na stopnji rodov. Dobljeni konodontni elementi imajo visok barvni indeks (CA I = 6,5-7), ki kaže na stopnjo metamorfoze v temperaturnem intervalu od 440 °C do 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 (Basagic & 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 Foca-Praca Paleozoic
Fig. 1. Location map of the Crna Rijeka CR-17 borehole.
complex of southeastern Bosnia and Herzegovina and is positioned in the frontal part of the Durmi-tor Nappe, which tectonically overlies the Bosnia Flysch Nappe (Fig. 2).
Southeastern Bosnia and Herzegovina comprises the areas of Foca, Goražde and Praca. In the between the Foca 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; Ramovš, 1989).
Lower Devonian strata are represented by dark gray platy limestone with conodonts (Neoprionio-dus, Plectospathodus) and Upper Devonian limestone are marked by the presence of conodonts (Palmatolepis), bryozoans and crinoids (Buzaljko, 1971; Ramovš, 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 Praca thrust below Triassic formations (Kostic-Podgorska, 1958). Here, a rich fauna of corals, stromatoporoids, hydrozoans, bryozoans, brachiopods and crinoids was collected in
Lower and Middle^ Devonian limestone (Kostic-Podgorska, 1958; Zivanovic, 1963; Pantic, 1963). Some Paleozoic formations of the Foca area are of a presumed Devonian age. The thickness of the Paleozoic formations attains up to 800 m in the area (Buzaljko, 1971).
Devonian formations are overlain by Early Carboniferous flysch that is up to 1000 m thick. The flysch sediments contain ammonoids (go-niatites, orthoceratides), mollusks, gastropods, brachiopods and corals. At Podkoran, an occurrence of Early Carboniferous strata containing goniatites was studied in detail by Kittl (1904). Based on the goniatite data, Frech (1906) and Schmidt (1924) supported a Visean age of some Paleozoic formations. Podgorska (1939) published data on fauna from crinoidal limestone from the area of Praca.
Krstic et al. (1988) gave explanation of the origin for the Silurian and Devonian limestones in the Praca area of SE Bosnia considering them as allochthonous clasts and olistoliths in the Lower Carboniferous „Culm" flysch. Filipovic & Jova-novic (1994) later provided new data for age and characteristics of the same rocks in the Praca (SE
Fig. 2. Main structures of the Dinarides of Bosnia and Herzegovina (Hrvatovic, 2006): ■ - CR-17 borehole. 1. Karst Nappe, 2. Una-Dreznica-Gacko Nappe, 3. Kljuc-Radusa Nappe, 4. Mid-Bosnian Schists Mts., 5. Bosnian Flysch Nappe, 6. Durmitor Nappe, 7. Ophiolite Nappe, 8. Golija Nappe, 9. Sana-Una Nappe, 10. Sava-Vardar Nappe.
Bosnia) and Vlasenica (NE Bosnia) areas, and they interpreted them as Upper Carboniferous olistostromes connected with Asturian phase of Variscan orogenesis.
A break in sedimentation took place during the Late Carboniferous and Early Permian. The Upper Permian is represented by reddish clastics overlain by Bellerophon limestone bearing gastropods (Bellerophon) and calcareous algae (Gymnocodium). The Bellerophon limestone was first recorded by Bittner (1880) and documented later by Kittl (1904) at Han Orahovica, Katzer (1926) at Zbisce and Musici, and Kostic-Podgorska (1958) at Vi-hor, Lunji and Razbojiste. In the area of Tjenti-ste, Cadet (1966) reported finding of brachiopods, mollusks and gastropods in dark gray thick bedded limestone of Latest Permian age. In the area of the Kolina Valley, Focanska Jabuka and further towards Praca sideritic-ankeritic limestone were discovered with sulphides: pyrite, chalcopyrite, arsenopyrite, galena and antimonite. Buzaljko (1971) made a detailed stratigraphic subdivision of the Permian rocks of the Southeast Bosnia area (Fig. 3).
Conodont study
The present study is based on collections from the borehole CR 17 of Crna Rijeka and made in 2006 (Kolar-Jurkovsek & Jurkovsek, 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 Geološki 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-
M	Age	Lithology	Environments	Fossils
<100	P3	Bellerophon limestone, -	sandstone, -	gypsum, -	redish schist, -	siltstone	Shallow marine-lagoonal	Bellerophon sp., Archaeocidaris ladina, Gymnocodium sp.
			Land?	
850	P1,2	-	redish conglomerate, and quartz sandstone, -	gray schist, marble, bedded limestone, -	breccia	Shallow marine to fluvial	Naneionella, Mizzia cornuta, Globivalvulina, Tubertina sp.
100	C3	Sandstone, claystone, conglomerate, schist	Trench	Lepidodendron weltheimianum
	C2	Flysch:	Trench	Verneulites librovitchi
700	Cl	Flysch: Subgraywacke, sandstone, claystone, clayey-quartz-sericite schist, microconglomerate, massive limestone	Trench	Lepidodendron lasseni, Glyphyoceras sphaericum, Aviculopecten pra~aensis, Cyathocarinia rasliana, Chonetes, Nereites
200	D3	Bedded limestone	Marine platform	Hindeodella sp., Palmatolepsis glabra pectinata, P. rhomboidea, Belodella triangularis
450	D2	Massive reefal limestone	Marine platform	Favosites sp., Polygnathus linguiformis
200	D1	Bedded limestone, layered schist	Marine platform	Neoprioniodus bicurvatus, Plectospathodus, Panderodus unicostatus
100	S3	Massive limestone	Marine platform	Ozarkodina, Panderodus
Fig. 3. Geological description of Paleozoic strata of SE Bosnia (Hrvatovic, 2006; after Buzaljko 1971; Kulenovic, 1985).
5500 LV Scanning Electron Microscope of the Slovenian National Building and Civil Engineering Institute (ZAG Ljubljana). The conodont material is stored in the micropaleontological collection of Geological Survey of Slovenia (Geoloski zavod Slovenije) under the inventory numbers GeoZS 4072-4080, 4085.
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 Pandorinel-lina (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 CR-17 193-195 m (GeoZS 4080)
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 Neo-panderodus 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 Up-pony 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). Later, a few localities with equivalent
faunas were reported from Jezera area near Jajce in western Bosnia (Mudrenovi} et al. 1969) and from the platy limestones of SE Bosnia and Herzegovina (Kulenovi}, 1983). All faunas are characterized by the presence of Belodella. Near the village of Kolakovici in SE Bosnia, Early Devonian apparatuses of Belodella bosniensis Ramovs and B. elegans Ramovs were reconstructed that are accompanied by Ozarkodina remscheidensis (Ziegler), Ozarkodina wurmi (Bischoff & Sannemann), and Icriodus steinachensis (Al Rawi) (Ra-Mov{, 1989).
Conodont faunas of Early Devonian age are also well documented from eastern Serbia and are marked also by the presence of the genera Be-lodella and Ozarkodina (Krsti} et al. 1970, 1995; Krsti} & Sudar, 1992, 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 metamor-phism and it markedly differs from the preservation of Triassic conodonts of Bosnia and Herzegovina that show a lower CAI (Aljinovi} et al., 2006, 2011) and have lesser alteration. The comparison with observations made on conodonts of the Albanides is obvious (Schonlaub & Meqo, 1986).
Conclusions
A brief geologic overview of southeastern Bosnia and Herzegovina is presented and the results of a micropaleontological 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 presence 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.
Depth (m) Taxon	12	68	74-79	136	144/2	164	180-185	188	193-195	203
Ozarkodina sp. or Pandorinellina sp.	- - 1 ----- - -									
Neopanderodus sp. or Belodella sp.	-------- 2 -									
conodont fragments	1	-	-	-	-	-	2	3	-	1
crinoid ossicles	-	-	-	-	+	-	+	-	-	-
Fig. 4. Numerical distribution of recovered conodonts and presence of crinoids in the studied samples of the Crna Rijeka CR-17 borehole.
PLATE 1
Conodonts from the Crna Rijeka CR-17 borehole, Bosnia and Herzegovina, Early-Middle Devonian.
1	a-b Ozarkodina sp. or Pandorinellina sp. Sample CR-17 74-79 m (GeoZS 4077). a - lateral view, b - upper view.
2	a-b Neopanderodus sp. or Belodella sp. Sample CR-17 193-195 m (GeoZS 4080). a - b - lateral views.
Acknowledgements
The authors gratefully acknowledge Merlynd Nestell for reading the manuscript and making linguistic corrections, Heinz Kozur and Mike Orchard made helpful and valuable comments on the conodont part. Reviews of Sejfudin Vrabac and Milan Sudar are acknowledged. This study was partly carried out at the Geological Survey of Slovenia through the program P1-0011 financially supported by the Slovenian Research Agency. This study was also supported through the program of bilateral cooperation in science and technology in Slovenia-Bosnia and Herzegovina (2010-2011). Photographs were taken by Mateja Golez and prepared by Stanko Zakrajsek.
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