The age of the brachiopod limestones from Guča , western Serbia

The asymmetric rhynchonellide brachiopod Cyclothyris? globata (ARNAUD, 1877) has a large distribution in the Coniacian, Santonian and Campanian outcrops of the western Tethys. The species has also been identified in Guča, (Vardar Zone, western Serbia), where it occurs together with the capillate terebratuloid “Terebratula” sp. (gen. et sp. nov.). In addition to Serbia, this brachiopod association is found in many localities of northeastern Bulgaria (Shumen Formation). In older literature, in Romania and Bulgaria, “Terebratula” sp. (gen. et sp. nov.) was confused with the Late Maastrichtian Terebratulina striata (WAHLENBERG, 1821). The present microfaunal study based on planktonic foraminifera showed that the age of the beds with Cyclothyris? globata and “Terebratula” sp. (gen. et sp. nov.) in Guča may be dated as Lowermost Campanian, i.e., the Santonian/Campanian boundary.


Introduction
A brachiopod assemblage of two species, i.e., Cyclothyris?globata (ARNAUD) and "Terebratula" sp.(gen. et sp. nov.), was found in the Upper Cretaceous succession at the Dupljaj Stream, near Guča, in the Bjelica Belt of the Vardar Zone (western Serbia) (Fig. 1).The occurrences in ex-Yugoslavia of Cyclothyris?globata, which is common in several Coniacian--Campanian outcrops along the northern and southern Tethyan margins and in central Tethyan domains, were described and dated as Campanian by RADULO-VIĆ & MOTCHUROVA-DEKOVA (2002).In several localities of the Vardar Zone (Guča, western Serbia) and the Balkans (the Shumen Formation, northern Bulgaria), C.? globata was found in assemblages with the capillate "Terebratula" sp.(gen. et sp. nov.), which previously was misidentified with the Late Maastrichtian Terebratulina striata (WAHLENBERG).The age of the brachiopod association from Guča, based on the The age of the brachiopod limestones from Guča, western Serbia RAJKA RADOIČIĆ 1 , VLADAN RADULOVIĆ 2 , DRAGOMAN RABRENOVIĆ 3 & BARBARA RADULOVIĆ 2 abundance of microfossils, is updated herein.It is documented by the evidence of a rich association of benthic and planktonic foraminifera.The sequence of deposits bearing brachiopods evolved from a shallow marine environment weakly influenced by open sea into true hemipelagic calcisphere-globotruncanid deposits of the lower ramp-transition to a shallow basinal environment.

Geological setting
The Cretaceous succession, according to ĆIRIĆ (1958), is formed of Senonian limestones and clastics transgressive and unconformable over different units of the Paleozoic complex.The author used abundant mollusks, mainly rudists, then corals and brachiopods, to document the Santonian, Campanian and Maastrichtian ages of the deposits; the latter also rich in large foraminifera -loftusiae and orbitoids.
Micropaleontological examinations and research of the rudist fauna during the geological mapping for the Sheet Čačak on the scale 1:100 000 documented the presence of the Coniacian and Turonian.Transgression in the present-day Dragačevo area started in the Albian, according to unpublished information (RR).Successive phases of the transgression evolved in the latest Cenomanian?-EarlyTuronian (following the Late Cenomanian event), in the Santonian and in Maastrichtian, when sea advanced over most of the area.
Albian deposits, precisely limestones bearing Hemicyclammina sigali MAYNC, are known only from the NE Kravarica Belt, under the Lower Cenomanian limestones with Ovalveolina sp, Murgeina apula (LU-PERTO SINNI), Pseudolituonella reicheli MARIE, Chrysalidina gradata D'ORBIGNY, Pseudorhipidionina casertana (DE CASTRO) etc.A layer containing brachiopods, which is the subject of this note, was found in a minor exposure of the Bjelica Belt near Guča.The Cretaceous limestones and clastic preflysch succession of Bjelica were deposited during the Santonian, Campanian and Maastrichtian, whereas the age of the flysch (based on the nautilid Hercoglossa cf.danica) is Maastrichtian-Danian (ĆIRIĆ 1958).According to the authors of the geological map, massive marly limestones and partly marls in the Bjelica Belt are designated in the Middle Campanian only, while the flysch sedimentation in the belt, and in the entire Dragačevo expanse, excluding Jelica II, began (unsubstantiated!) much earlier, in the Late Campanian (BR-KOVIĆ et al. 1978, Fig. 4).The presence of Maastrichtian limestones with rudists, loftusiae and orbitoids, well known from the publications on Dragačevo, has been unjustly and inexcusably neglected (first information on the Maastrichtian limestones was given by V. PETKOVIĆ 1909;in ĆIRIĆ 1958).
Observation on the Cretaceous of Jelica Mt. followed by an Explanatory Text for the Geological Map, Sheet Čačak on the Scale 1:100 000 The Cretaceous of Jelica Mt. is designated on the geological map in two belts of different developments: Jelica I (assigned to the Inner Dinarides) with a succession similar to the Bjelica Belt, and Jelica II (assigned to the Vardar Zone) with only a Middle Campanian Diabase-Chert Formation present (BRKO-VIĆ et al. 1978, Fig. 4).
Why the (Jurassic) Diabase-Chert Formation was dated Campanian and what kind of deposits were developed there are the questions answered in the controversial text "Senonian of the Vardar Zone", as follows (translation from Serbian): "Senonian rocks in the Vardar Zone are represented by a particular Diabase-Chert Formation.They form a narrow, discontinuous belt along the Jelica Range, in a zone of intensive structural deformation, thereby in structural unconformity with adjacent units" "These rocks are rudistid in character (sic!) in a chaotic arrangement of units of ill-defined beds.The rock constituents are knots of different rocks chiefly in an arenite-silt matrix.Some areas in the breccioid mass differ in the composition and size of the knots and in the cementing material.The Jelica Range is built of breccia composed only of diabase fragments, with even the binder being finegrained diabase breccia.The rocks in the western Jelica Range are sedimentary, subordinately mafite and ultramafite.In relation to the attitude of different units and their structures, these breccioids are likely an ophiolite mélange of olistostrome origin." (p. 36).
What the mapping researchers observed in the field was obviously tectonite, a chaotic unit or ophiolite mélange, by no means a Diabase-Chert Formation, which was only one component of a major tectonic event during the Campanian.Lamentably, the authors of the map uncritically accepted then the prevailing interpretation of M. N. DIMITRIJEVIĆ & M. D. DIMITRI-JEVIĆ (1973, pp. 228, 230) that the Diabase-Chert Formation was a "typical olistostrome mélange", given "Cretaceous age" on Jelica.
Jelica II is a part of the known tectonic Rujevac-Veliki Majdan Zone in western Serbia (ĆIRIĆ 1996;RADOIČIĆ 1997).Based on planktonic foraminifera from some minor masses and blocks of the Jelica II Belt, the newest sediment is dated Early Campanian, the same as the Rujevac-Veliki Majdan ending in Kosovo.
Not infrequently, differentiation is not made between tectonites s.str., particularly those of higher order of magnitude and post-tectonic sedimentation processes (there are, of course, specific relationships).Concerning the ophiolite mélange -tectonite, it depends on the mechanical properties of the rocks, crushed and broken in strong tectonic events, which were sufficiently plastic to include more compact components.In the given terrains, it is mostly the Diabase-Chert Formation.

Microbiostratigraphy
Upper Cretaceous rocks of the Bjelica Belt in the Dupljaj Potok near Guča are known from the finds of brchiopods.Basal terrigenous deposits of the Bjelica Belt pass into carbonate rocks (sandstone-calcareous sandstone-sandy to silty limestone) unexposed in the Dupljaj Potok.Neither of the oldest carbonate rocks is uncovered sufficiently for observation of the stratification.For detailed stratigraphical dating of the brachiopods, six samples (VR 101 through VR 106) were collected for micropaleontological examination from 10-12 meters of the stratigraphic column, viz.: -The lowermost 2 m of the observed calcareous sandstone (sample VR 101) contains an abundance of coarse agglutinated foraminifer Hemicyclammina chalmasi (SCHLUMBERGER), few other benthic foraminifers: Pararotalia minimalis HOFKER, Nummofallotia cretacea (SCHLUMBERGER), Goupillaudina sp., miliolids and a few planktonic microfossils -Heterochelix sp. and calcispheres.Sparse fragments of corallinacean algae and mollusks are also found.(Pl. 1,Pl. 3,Fig. 9;Pl. 6,Figs. 1,11).
Shell of medium size (L min 17.7 mm; L max , 26.7 mm), generally with subtriangular outline, or transverselyoval, always with a twisted asymmetrical anterior commissure.The dorsal valve is usually more convex than the ventral valve.Greatest width at the anterior The age of the brachiopod limestones from Guča, western Serbia third, maximum thickness at midvalve.The lateral commissure straight.Beak massive, suberect to nearly straight with sharp and short beak ridges.Squama and glotta developed.The apical angle ranges between 72° and 96°.Foramen rounded, circular, relatively large, hypothyrid to submesothyrid, slightly labiate.The interarea small, concave.Each valve is ornamented with 24 to 36 simple ribs, which anteriorly become stronger and sharper.
Remarks.Specimens of supposedly the same species from Romania and Bulgaria (northern margin of Tethys) were confused with Terebratulina striata (WAHLENBERG, 1821), known from the Late Maastrichtian of Sweden (Epicontinental Sea).A preliminary research of the internal morphology of this new form by V. RADULOVIĆ and N. MOTCHUROVA-DEKOVA on Bulgarian specimens reveals a terebratuloid loop.This feature clearly distinguishes this taxon from T. striata that has a ring-like loop; this feature places them in two different families.The capillate ornamentation of the shell of the new form makes it similar to Capillithyris capillata (D'ARCHIAC 1847), known from the Albian and Cenomanian of western Europe (Belgium, England, Poland and the Ukraine).However, the Serbian terebratuloid differs in having straight capillae (in C. capillata the capillae are waving and intersected by concentric growth lines.Internally, it is distinguished from the latter in having much reduced hinge plates.
This new capillate terebratuloid brachiopod will be officially described elsewhere by a different coauthorship board.Its preliminary description is proposed here with the kind permission of the colleagues N. MOTCHUROVA-DEKOVA and E. SIMON.

Discussion
Hemicylammina chalmasi, a large agglutinated foraminifer, is known from the Coniacian-Late Santonian of the Spanish Pyrenees (CORNELLA 1977;CAUS et al. 1981), from the Late Turonian or Early Campanian of the Northern Calcareous Alps (SCHLA-GINTWEIT & WAGREICH 2004) and from the Campanian of the Vardar Zone in Serbia.The Campanian age of Hemicyclammina chalmasi is based on planktonic foraminifera in the limestone with planktonic and benthic foraminifera (POLAVDER 2003).The abundance of Hemicyclammina chalmasi in bed VR101 is the acme of this species or, more probably the paracme, because extreme scarcity of specimens in the limestone with brachiopods (VR102) can be interpreted as their last occurrence.Other benthic foraminifera in bed VR102 have a larger stratigraphic distribution -the Coniacian to the Campanian.
Prevailing planktonic foraminifera in sample VR102 are two keeled species distributed in both the asymetrica and elevata zones, some of them earlier, in the concavata Zone.Species of the genus Dicarinella were not found in the five thin sections, whereas, in the overlying hemipelagic-pelagic silty limestone, Dicarinella asymetrica and Marginotruncana coronata were present in the sample VR103.Both species totally disappeared in the Lowermost/Lower Campanian (PREMOLI-SILVA & VERGA 2004, p.45).This leads to the conclusion that the layer containing brachiopods was the basal bed of the Campanian that marked the Santonian/Campanian boundary.
A few benthic macroforaminiferal specimens of Navarella joaquini were found in the samples VR103 and 104.This species is described by CIRY & RAT (1951) from the Maastrichtian of the Spanish Pyrenees, then cited also from the Maastrichtian of the Suisse Alps, from Scaglia rossa of the Veronese in Italy, in the Pyrenees and France (SAMPÒ 1972).In the Western Aquitaine, the species was found in the Campanian (RIBIS 1965fide SAMPÒ 1972).The hemipelagic limestone of the sample VR104, beside Navarella, bears another macroforaminifer Tekkeina anatoliensis FARINACCI & YENIAY, a species described from the Santonian of Susus Dag in the Western Pontides, Turkey.The Santonian age was confirmed by the planktonic foraminiferal association with Dicarinella concavata (BROTZEN).In the type locality, the species ends at an unconformable boundary (a gap between the Santonian and Late Campanian), and is absent in the Upper Campanian (FARINACCI & YENAIY 1994).
It follows from the above that Tekkeina anatoliensis is distributed in Santonian and Lower Campanian hemipelagic-pelagic deposits.

Conclusions
The researched stratigraphic sequences of Dupljaj Potok, based on micropaleontological contains, is dated as Latest Santonian and Early Campanian.The bed with brachiopods marks the boundary between the Santonian and the Campanian and is included in the basal Campanian.
Cyclothyris? globata is a species of large geographical distribution, known from the Northern and Southern Tethyan margins and the Central Tethys.The species occurs in the stratigraphic interval from Coniacian to Campanian.In western Serbia, it is found at Guča (Bjelica Belt, the Vardar Zone) in association with the capillate "Terebratula" sp.(gen.et sp.nov.).The association is also known from the uppermost Santonian of northeastern Bulgaria (Shumen Formation).
According to the obtained data, a part of the Bjelica Cretaceous Belt, during the Latest Santonian and Early Campanian, evolved gradually from a shallow marine environment weakly influenced by open sea (few planktonic foraminifera in Hemicyclammina chalmasi carbonate sandstone) to hemipelagic with mixed benthic and planktonic foraminifers and brachiopods into true hemipelagic calcisphere-globotruncanid deposits on a lower ramp-transition to shallow basinal environment.Information on the development of facies (ĆIRIĆ 1958;BRKOVIĆ et al. 1978) indicates subsidence of the Cretaceous Dragačevo Unit in the Bjelica Belt, which continued to the Maastrichtian or even into the Danian.
Scale bar = 0.2 mm for all figures.
Scale for = 0.2 mm for all figures.