2.a. Overview of major tectonic units of the Dinarides

Ophiolite massifs in the Central Dinarides represent dismembered portions of a large ophiolite thrust sheet, associated with an underlying tectono-sedimentary mélange, that was obducted onto the eastern margin of the Adriatic Plate at the Jurassic–Cretaceous transition (Bernoulli & Laubscher, Reference Bernoulli and Laubscher1972; Schmid et al. Reference Schmid, Bernoulli, Fügenschuh, Matenco, Schefer, Schuster, Tischler and Ustaszewski2008; Chiari et al. Reference Chiari, Djerić, Garfagnoli, Hrvatović, Krstić, Levi, Malasoma, Marroni, Menna, Nirta, Pandolfi, Principi, Saccani, Stojadinović and Trivić2011; Ferrière et al. Reference Ferrière, Chanier and Ditbanjong2012; Nirta et al. Reference Nirta, Moratti, Piccardi, Montanari, Carras, Catanzariti, Chiari and Marcucci2018). Today, these ophiolite massifs are arranged along two subparallel, meridian-trending belts extending from Greece to the Pannonian Basin: the Eastern Vardar ophiolites (i.e. the ophiolites tectonically emplaced eastward above parts of the European margin) and the Western Vardar ophiolites (i.e. the ophiolites obducted westward above the Adria margin; Schmid et al. Reference Schmid, Bernoulli, Fügenschuh, Matenco, Schefer, Schuster, Tischler and Ustaszewski2008). In the Dinarides the two belts are separated by the Sava suture zone (Ustaszewski et al. Reference Ustaszewski, Kounov, Schmid, Schaltegger, Krenn, Frank and Fügenschuh2010), whereas to the south the limit mostly coincides with an intervening continental mega-unit known as the Pelagonian in Greece and Korabi in Albania (Fig. 1). In Serbia the Pelagonian–Korabi continental unit continues in the Drina–Ivanjica Unit. A long-standing and unsolved dispute exists among authors who consider the Pelagonian–Korabi–Drina–Ivanjica Mega-Unit as a microcontinent separating, during the Mesozoic period, two distinct oceanic basins (the Pindos ‘Ocean’ to the west and the Maliac–Vardar Ocean to the east: Robertson & Karamata, Reference Robertson and Karamata1994; Karamata et al. Reference Karamata, Olujić, Protić, Milovanović, Vujnović, Popević, Memović, Radovanović, Resimić-Sarić, Karamata and Janković2000; Robertson & Shallo, Reference Robertson and Shallo2000; Dimitrijević, Reference Dimitrijević2001; Stampfli & Borel, Reference Stampfli, Borel, Cavazza, Roure, Spakman, Stampfli and Ziegler2004) and those who regard this mega-unit as the easternmost rim of the Adriatic Plate located to the east of a unique oceanic basin (i.e. the Maliac–Vardar Ocean: Ferrière, Reference Ferrière1982; Pamić et al. Reference Pamić, Gušić and Jelaska1998; Bortolotti et al. Reference Bortolotti, Marroni, Pandolfi, Principi, Dilek, Ogawa, Bortolotti and Spadea2005; Schmid et al. Reference Schmid, Bernoulli, Fügenschuh, Matenco, Schefer, Schuster, Tischler and Ustaszewski2008, Reference Schmid, Fügenschuh, Kounov, Maţenco, Nievergelt, Oberhänsli, Pleuger, Schefer, Schuster, Tomljenović, Ustaszewski and van Hinsbergend2020; Chiari et al. Reference Chiari, Djerić, Garfagnoli, Hrvatović, Krstić, Levi, Malasoma, Marroni, Menna, Nirta, Pandolfi, Principi, Saccani, Stojadinović and Trivić2011; Gawlick et al. Reference Gawlick, Missoni, Suzuki, Lein, Sudar and Jovanović2016).

Fig. 1. Tectonic sketch map of the Dinaric–Hellenic orogenic belt with simplified tectonic subdivision (modified after Schmid et al. Reference Schmid, Bernoulli, Fügenschuh, Matenco, Schefer, Schuster, Tischler and Ustaszewski2008) and distribution of the main ophiolitic massifs (in solid black). a – Krivaja–Konjuh; b – Zlatibor; c – Maljen; d – Ibar; e – Mirdita; f – South Albania; g – Pindos; h – Vourinos; i – Koziakas; j – Guevgueli; k – Almopias; l – Othrys; m – Iti; n – Kallidromon; o – Euboea; p – Argolis.

Here, we adopt a geotectonic scheme that considers the ophiolite massifs presently preserved in the Central Dinarides as pertaining to a single oceanic basin (Chiari et al. Reference Chiari, Djerić, Garfagnoli, Hrvatović, Krstić, Levi, Malasoma, Marroni, Menna, Nirta, Pandolfi, Principi, Saccani, Stojadinović and Trivić2011; Cvetković et al. Reference Cvetković, Prelević, Schmid and Papić2016; Gawlick et al. Reference Gawlick, Sudar, Missoni, Suzuki, Lein and Jovanović2017b; Schmid et al. Reference Schmid, Fügenschuh, Kounov, Maţenco, Nievergelt, Oberhänsli, Pleuger, Schefer, Schuster, Tomljenović, Ustaszewski and van Hinsbergend2020). From west to east the tectonic units are arranged as the Deformed Adriatic Zone (including the Budva–Cukali Zone, the Dalmatian Zone and the High Karst, Pre-karst and East Bosnian–Durmitor units; Aubouin et al. Reference Aubouin, Blanchet, Cadet, Celet, Charvet, Chorowicz, Cousin and Rampnoux1970; Schmid et al. Reference Schmid, Bernoulli, Fügenschuh, Matenco, Schefer, Schuster, Tischler and Ustaszewski2008), the Western Vardar ophiolitic unit (WVO; Dinaric Ophiolite Belt of Pamić et al. Reference Pamić, Tomljenović and Balen2002 and Chiari et al. Reference Chiari, Djerić, Garfagnoli, Hrvatović, Krstić, Levi, Malasoma, Marroni, Menna, Nirta, Pandolfi, Principi, Saccani, Stojadinović and Trivić2011), the continental-derived Drina–Ivanjica Unit, the Eastern Vardar ophiolitic unit (EVO; Vardar Ophiolite Belt of Chiari et al. Reference Chiari, Djerić, Garfagnoli, Hrvatović, Krstić, Levi, Malasoma, Marroni, Menna, Nirta, Pandolfi, Principi, Saccani, Stojadinović and Trivić2011), and the Serbo-Macedonian–Rhodope Massif, generally considered to be the metamorphosed and deformed margin of the Eurasian Plate (Burg, Reference Burg, Skourtsos and Lister2012; Bonev et al. Reference Bonev, Marchev, Moritz and Collings2015; Fig. 1). The East Bosnian–Durmitor and Drina–Ivanjica units share a very similar stratigraphic succession including a pre-Carboniferous basement unconformably overlain by upper Palaeozoic deposits, Triassic siliciclastic rocks and carbonates, Upper Triassic – Lower Jurassic platform carbonates and finally by Lower–Upper Jurassic deep-water carbonates and radiolarites (Dimitrijević, Reference Dimitrijević1997; Karamata, Reference Karamata, Robertson and Mountrakis2006; Djerić et al. Reference Djerić, Gerzina and Schmid2007; Chiari et al. Reference Chiari, Djerić, Garfagnoli, Hrvatović, Krstić, Levi, Malasoma, Marroni, Menna, Nirta, Pandolfi, Principi, Saccani, Stojadinović and Trivić2011). These similarities and their common structural position below the WVO are in accordance with a common palaeogeographic position on the easternmost tip of the Adriatic continental margin. In western Serbia, the ophiolitic massifs of the WVO (mainly represented by the Zlatibor and the Maljen massifs) have exactly the same geological features and therefore are considered to have had physical continuity, which was disrupted during exhumation of the Drina–Ivanjica Unit (Chiari et al. Reference Chiari, Djerić, Garfagnoli, Hrvatović, Krstić, Levi, Malasoma, Marroni, Menna, Nirta, Pandolfi, Principi, Saccani, Stojadinović and Trivić2011; Porkolab et al. Reference Porkolab, Köver, Benko, Heja, Fialowski, Soos, Gerzina Spajić, Đerić and Fodor2019). Finally, the more internal Adria-derived unit is represented by the Jadar–Kopaonik Unit, consisting of a Palaeozoic metasedimentary succession overlain by a Middle Permian to Lower–Middle Triassic shallow-water clastic–carbonate sedimentary succession (Robertson et al. Reference Robertson, Karamata, Šarić, Robertson, Karamata and Šarić2009) passing into Middle Triassic to Jurassic hemipelagic and distal turbiditic carbonates and radiolarites (Schefer et al. Reference Schefer, Egli, Missoni, Bernoulli, Fügenschuh, Gawlick, Jovanović, Krystin, Lein, Schmid and Sudar2010b). These successions are considered to be part of the distal part of the Adria passive margin facing the northern branch of the Neotethys (Schefer et al. Reference Schefer, Egli, Missoni, Bernoulli, Fügenschuh, Gawlick, Jovanović, Krystin, Lein, Schmid and Sudar2010b; Gawlick et al. Reference Gawlick, Sudar, Missoni, Suzuki, Lein and Jovanović2017b).

The tectonic evolution in the internal (eastern) part of the Central Dinaric orogenic belt began in Middle Jurassic time and was marked by three major geodynamic events: (1) Middle Jurassic intraoceanic subduction that led to the formation of high temperature – low pressure (HT–LP) metamorphism in the hanging wall (amphibolite sole; Lanphere et al. Reference Lanphere, Coleman, Karamata and Pamić1975; Okrusch et al. Reference Okrusch, Seidel, Kreuzer and Harre1978; Dimo-Lahitte et al. Reference Dimo-Lahitte, Monié and Vergély2001; Borojević Šoštarić et al. Reference Borojević Šoštarić, Palinkaš, Neubauer, Cvetković, Bernroider and Genser2014); (2) Late Jurassic/Early Cretaceous obduction of the oceanic lithosphere onto the eastern Adriatic continental margin; and (3) Late Cretaceous–Palaeogene collision of the Eurasian Plate with the Adriatic Plate (Ustaszewski et al. Reference Ustaszewski, Kounov, Schmid, Schaltegger, Krenn, Frank and Fügenschuh2010). In the external part of the orogen, bauxite and lateritic horizons and widespread karst depressions, possibly related to uplift, emersion and erosion of portions of the Adria carbonate platform during latest Jurassic time, were the first indicators of plate convergence in the proximal continental domain (Carras & Tselepidis, Reference Carras, Tselepidis, Solakius and Kati2001; Vlahović et al. Reference Vlahović, Tišljar, Velić and Matičec2005).

2.b. Outline of the syn- and post-obduction depositional sequences in the Dinaric–Hellenic orogen

In the internal (eastern) part of the Dinaric–Hellenic orogenic system, the units deformed during the Late Jurassic – Early Cretaceous tectonic phase are unconformably overlain by the widespread Cretaceous transgression successions (Radoičić, Reference Radoičić1995; Photiades et al. Reference Photiades, Carras, Bortolotti, Fazzuoli and Principi2007; Fazzuoli et al. Reference Fazzuoli, Menna, Nirta, Carras and Principi2008). These sediments are known throughout the entire Dinaric–Hellenic orogen alternatively as ‘overstepping sediments’, ‘Gosau-type deposits’, ‘deposits of the Cretaceous transgression’, ‘post-obduction sedimentary cover’ and the ‘Mesoautochthonous Complex’ (Jacobshagen, Reference Jacobshagen1986; Willingshofer et al. Reference Willingshofer, Neubauer and Cloetingh1999; Hrvatović, Reference Hrvatović2006; Photiades et al. Reference Photiades, Carras, Bortolotti, Fazzuoli and Principi2007; Fazzuoli et al. Reference Fazzuoli, Menna, Nirta, Carras and Principi2008; Schmid et al. Reference Schmid, Bernoulli, Fügenschuh, Matenco, Schefer, Schuster, Tischler and Ustaszewski2008; Schuller et al. Reference Schuller, Frisch, Danisik, Dunkl and Melinte2009; Nirta et al. Reference Nirta, Moratti, Piccardi, Montanari, Carras, Catanzariti, Chiari and Marcucci2018). They are made up of terrestrial, transitional and shallow-marine coarse-grained clastic sedimentary rocks and of marine fine-grained clastic sediments and carbonates. The composition of the clastic deposits directly depends on the lithology of the underlying or adjacent substratum. These deposits presently crop out over areas of varying extension (Fig. 2), from several hundred kilometre wide continuous successions to small-scale slices occurring as tectonic chunks or olistoliths inside tectonic mélanges. These transgressive deposits form a roughly N–S-trending stripe in the internal (eastern) part of the orogen, extending from southern Greece (Argolis; Bortolotti et al. Reference Bortolotti, Carras, Chiari, Fazzuoli, Marcucci, Photiades and Principi2003) to at least southwestern Serbia (Bortolotti et al. Reference Bortolotti, Ficcarelli, Manetti, Passerini, Pirini-Radrizzani and Torre1971; Pejović & Radoičić, Reference Pejović and Radoičić1971; Sladic-Trifunovic, Reference Sladic-Trifunovic1998), through central and northern Greece (Carras et al. Reference Carras, Fazzuoli and Photiades2004; Photiades et al. Reference Photiades, Carras, Bortolotti, Fazzuoli and Principi2007), Albania (Gawlick et al. Reference Gawlick, Frisch, Hoxha, Dumitrica, Krystyn, Lein, Missoni and Schlagintweit2008) and North Macedonia. The bedrock of these deposits consists both of oceanic crust and continental margin units. The ophiolites show evidence of emergence with the formation of rather high reliefs that underwent erosion and pedogenesis (Photiades et al. Reference Photiades, Carras, Bortolotti, Fazzuoli and Principi2007; Fazzuoli et al. Reference Fazzuoli, Menna, Nirta, Carras and Principi2008). The basal portions of these successions, commonly clastic, are usually devoid of datable fossils, and biostratigraphic age determinations are only possible in the overlying marine deposits. The oldest fossiliferous deposits are generally Aptian to Cenomanian: Mokra Gora (Pejović & Radoičić, Reference Pejović and Radoičić1971); Mirdita, northern Albania (Schlagintweit et al. Reference Schlagintweit, Gawlick, Lein, Missoni and Hoxha2012); Argolis Peninsula, Greece (Bortolotti et al. Reference Bortolotti, Carras, Chiari, Fazzuoli, Marcucci, Photiades and Principi2003); and Vourinos and Vermion massifs, Greece (Carras et al. Reference Carras, Fazzuoli and Photiades2004; Photiades et al. Reference Photiades, Carras, Bortolotti, Fazzuoli and Principi2007).

Fig. 2. Simplified tectonic map of western Serbia and eastern Bosnia (location in Fig. 1). Redrawn after the Geological Map of Yugoslavia at scale 1:500.000 (Federal Geological Survey of SRF Yugoslavia, 1970), Schmid et al. (Reference Schmid, Bernoulli, Fügenschuh, Matenco, Schefer, Schuster, Tischler and Ustaszewski2008) and Chiari et al. (Reference Chiari, Djerić, Garfagnoli, Hrvatović, Krstić, Levi, Malasoma, Marroni, Menna, Nirta, Pandolfi, Principi, Saccani, Stojadinović and Trivić2011).

Owing to the nature of their bedrock, stratigraphic age and geological characteristics, the post-orogenic Cretaceous deposits cropping out in the Zlatibor–Malijen areas (western Serbia) were assigned by Chiari et al. (Reference Chiari, Djerić, Garfagnoli, Hrvatović, Krstić, Levi, Malasoma, Marroni, Menna, Nirta, Pandolfi, Principi, Saccani, Stojadinović and Trivić2011) to three main informal groups: the Mokra Gora Group (the type section of which is described here); Kosjerić Group (Cenomanian–Turonian, Radoičić & Schlagintweit, Reference Radoičić and Schlagintweit2007); and Guča Group (Campanian, Radoičić et al. Reference Radoičić, Radulović, Rabrenović and Radulović2010; Chiari et al. Reference Chiari, Djerić, Garfagnoli, Hrvatović, Krstić, Levi, Malasoma, Marroni, Menna, Nirta, Pandolfi, Principi, Saccani, Stojadinović and Trivić2011). The Mokra Gora Group is lying on top of the ophiolites, the Kosjerić Group is overlying both ocean-derived and continental-derived rocks, and the Guča Group exclusively covers continental units (i.e. the Drina–Ivanjica Unit) (Fig. 3).

Fig. 3. Schematic geological cross-sections showing relationships between the Cretaceous deposits and their substratum. The geographic locations of the cross-sections are indicated in Figure 2. Age of the tectonic activity along the main structural features: J₃ – Late Jurassic; Cr₂ – Late Cretaceous; P – Palaeogene.

Older sedimentary successions are reported to stratigraphically rest above the ophiolite along the Dinaric–Hellenic chain. In the Žepče–Zavidovići–Maglaj area (Bosnia and Herzegovina; Fig. 2), the ophiolites are covered by a coarse-grained flysch succession containing shallow-water limestone clasts and blocks with a Tithonian–Berriasian fauna and ophiolite- and continent-derived clasts including Upper Permian granite, which passes upwards into a succession consisting of bioclastic limestones, calcareous breccia and pelagic limestones of early Albian to late Santonian age (Jovanović, Reference Jovanović1961; Blanchet et al. Reference Blanchet, Durand Delga, Moullade and Sigal1970; Hrvatović, Reference Hrvatović2006). These deposits, known in the literature as the ‘Pogari Series’ (Jovanović, Reference Jovanović1961), ‘Série de Maglaj’ (Blanchet et al. Reference Blanchet, Durand Delga, Moullade and Sigal1970) or ‘Pogari Formation’ (Hrvatović, Reference Hrvatović2006), are here renamed as the ‘Pogari Group’ in order to account for their complex lithostratigraphic, chronostratigraphic and environmental evolution. A similar stratigraphic position characterizes the Tithonian–upper Valanginian deposits of the ophiolite-bearing Firza flysch exposed in northern Albania (Gardin et al. Reference Gardin, Kici, Marroni, Mustafa, Pandolfi, Pirdini and Xhomo1996) containing a lower member characterized by abundant platform carbonate clasts of ?Kimmeridgian–Tithonian age (Kurbnesh Formation of Schlagintweit et al. Reference Schlagintweit, Gawlick, Missoni, Hoxha, Lein and Frisch2008). The Firza flysch and adjacent ophiolites and mélange were later unconformably covered by upper Berriasian–Valanginian Munella platform carbonates (Gawlick et al. Reference Gawlick, Frisch, Hoxha, Dumitrica, Krystyn, Lein, Missoni and Schlagintweit2008), probably deposited above the obducting ophiolites, and were then deformed and partly dismantled during the last stages of obduction tectonics (Peza & Marku, Reference Peza and Marku2002; Schlagintweit et al. Reference Schlagintweit, Gawlick, Lein, Missoni and Hoxha2012). Finally, the Firza flysch and Munella carbonates were unconformably covered by shallow-water limestones starting in early Aptian time (Mali i Shenjtit Platform; Schlagintweit et al. Reference Schlagintweit, Gawlick, Lein, Missoni and Hoxha2012).

As terrestrial to shallow-marine sedimentation resumed above the ophiolites, turbiditic deposition took place in front of the ophiolite thrust sheet in the pro-wedge flexural basins formed as a consequence of the nappe stacking following the ophiolite obduction. The older flysch deposits on the flexured continental margin are Tithonian–Berriasian in age and are discontinuously exposed along the whole Dinaric–Hellenic chain. They are named the Boeotian flysch in Greece (Clément, Reference Clément1971; Nirta et al. Reference Nirta, Moratti, Piccardi, Montanari, Catanzariti, Carras and Papini2015), whereas in the Central Dinarides they are known as the Bosnian flysch (Blanchet, Reference Blanchet1966). The latter crops out along a NW–SE-aligned thrust sheet known as the Pre-karst Unit (Schmid et al. Reference Schmid, Bernoulli, Fügenschuh, Matenco, Schefer, Schuster, Tischler and Ustaszewski2008 with references) that is lying below the East Bosnian–Durmitor Unit, which in turn is overlain by the Western Vardar ophiolites (Charvet, Reference Charvet1978). The Bosnian flysch consists of a lower lithostratigraphic unit, mostly reported as Tithonian to Valanginian (Blanchet, Reference Blanchet1966, Reference Blanchet1968; Charvet, Reference Charvet1967; Cadet, Reference Cadet1968; Rampnoux, Reference Rampnoux1969) and up to Aptian in age (Cadet & Sigal, Reference Cadet and Sigal1969; Charvet, Reference Charvet1978; Mikes et al. Reference Mikes, Christ, Petri, Dunkl, Frei, Baldi-Beke, Reitner, Wemmer, Hrvatović and von Eynatten2008), that is mainly composed of siliciclastic deposits (Vranduk Formation) followed upwards by lower Albian to Maastrichtian carbonate-dominated clastic deposits of the Ugar Formation (Mikes et al. Reference Mikes, Christ, Petri, Dunkl, Frei, Baldi-Beke, Reitner, Wemmer, Hrvatović and von Eynatten2008 with references). According to Mikes et al. (Reference Mikes, Christ, Petri, Dunkl, Frei, Baldi-Beke, Reitner, Wemmer, Hrvatović and von Eynatten2008), the upper part of the Vranduk Fm is at least Aptian in age. According to several authors (Dimitrijević, Reference Dimitrijević1982; Csontos et al. Reference Csontos, Gerzina, Hrvatović, Schmid and Tomljenović2003; Schmid et al. Reference Schmid, Bernoulli, Fügenschuh, Matenco, Schefer, Schuster, Tischler and Ustaszewski2008), sedimentation of the Ugar Fm started upon the deformed Vranduk Fm above an unconformity surface, suggesting deformation and involvement of the Vranduk Fm in the advancing thrust stack before early Albian time.

Provenance studies of the Vranduk Fm suggest sediment feeding from the obducted ophiolites, granitoids, eroding continental areas, reefs and different environments in a Urgonian-type carbonate platform facies, which existed only since late Barremian time (Mikes et al. Reference Mikes, Christ, Petri, Dunkl, Frei, Baldi-Beke, Reitner, Wemmer, Hrvatović and von Eynatten2008). A similar provenance configuration characterizes the basal clastic succession of the Pogari Group (Blanchet et al. Reference Blanchet, Durand Delga, Moullade and Sigal1970), whereas a clearly different shedding scenario marks the transition to the Upper Cretaceous Ugar Fm, with increasing detrital inputs from carbonate rocks and a drastic decrease of siliciclastic material, in particular Cr-spinel grains (Mikes et al. Reference Mikes, Christ, Petri, Dunkl, Frei, Baldi-Beke, Reitner, Wemmer, Hrvatović and von Eynatten2008). The occurrence of abundant quartz and metamorphic lithic fragments inside the Vranduk Fm suggests the existence of an Early Cretaceous source area where continental basement was exposed. Zircon fission track (ZFT) analyses of the siliciclastic detritus from the Vranduk Fm provide evidence of an Aptian cooling age (averaging 120 Ma) for the source area (Mikes et al. Reference Mikes, Christ, Petri, Dunkl, Frei, Baldi-Beke, Reitner, Wemmer, Hrvatović and von Eynatten2008), which points to the presence of exhumed portions of continental margin units of the Adriatic Plate soon after the end of the obduction tectonic processes. This age compares well with similar cooling ages from Lower Cretaceous foredeep deposits in the Zagreb region (122 ± 45 ZFT age from the Aptian–Albian Bistra Formation; Lužar-Oberiter et al. Reference Lužar-Oberiter, Mikes, Dunkl, Babić and Eynatten2012) and from a low-grade metamorphic unit of the Drina–Ivanjica Unit (139–129 Ma K–Ar age, Milovanović, Reference Milovanović1984). For this latter unit, an early phase of deformation (Tithonian–Valanginian; 150–135 Ma K–Ar age), coeval with the W-directed obduction event, was reported by Porkolab et al. (Reference Porkolab, Köver, Benko, Heja, Fialowski, Soos, Gerzina Spajić, Đerić and Fodor2019). Moreover, the continental clastic deposits of pre-Cenomanian age resting unconformably on the Drina–Ivanjica Palaeozoic rocks contain abundant lithoclasts of Triassic and Jurassic carbonate as well as quartz and metamorphic rock fragments (Kosjerić Group of Chiari et al. Reference Chiari, Djerić, Garfagnoli, Hrvatović, Krstić, Levi, Malasoma, Marroni, Menna, Nirta, Pandolfi, Principi, Saccani, Stojadinović and Trivić2011). This strongly suggests that the Mesozoic cover of the internal sectors of the imbricated Adriatic margin was tectonically removed and the Palaeozoic basement exhumed and exposed to subaerial erosion during Early Cretaceous time.

Here the sedimentary evolution of the Mokra Gora Group has been analysed in detail in its type area in the Zlatibor Massif and in key outcrops located on the Maljen massif. Supplementary investigations have also been performed in key sections pertaining to the Kosjerić and Guča groups. The results were then compared with the sedimentary evolution of partly coeval shallow-water to pelagic deposits (Pogari Group and Bosnian flysch) and with the evolution of the AdCP.

3.a. Mokra Gora Group in the Zlatibor and Maljen ophiolitic massifs

A detailed reconstruction of the Mokra Gora Group succession was possible only for the deposits exposed above the Zlatibor ophiolites, while a schematic lithostratigraphic reconstruction was done in the scattered outcrops located above the Maljen ophiolites.

Several authors have studied the Mokra Gora succession in the Zlatibor Mountains, identifying lithostratigraphic units that sometimes refer to non-synchronous and incomparable sedimentary packages (Loczy, Reference Loczy1924; Milovanović, Reference Milovanović1933; Drakulić & Dedić, Reference Drakulić and Dedić1963; Fotić, Reference Fotić1962). Generally, three main lithostratigraphic units have been differentiated: (1) a basal clastic unit unconformably lying on weathered serpentinite; (2) an intermediate hemipelagic marly limestone unit; and (3) an upper shallow-water massive reef limestone unit with an abundant rudist fauna (Radoičič, Reference Radoičić1984).

The lithostratigraphic column of the Mokra Gora Group in the Zlatibor area is a composite and results from four partial stratigraphic sections measured and sampled in the valley of the Kamišna creek, a tributary of the Beli Rzav River, near the border with Bosnia and Herzegovina (Mokra Gora area). Supplementary observations on the lowermost part of the succession were made in the close-by village of Vardište (Bosnia and Herzegovina) (Fig. 4a). The Mokra Gora sedimentary succession is weakly affected by tectonic deformation that is mainly represented by large open folds and interstratal slip. A kilometre-sized open fold trending WSW–ENE and gently plunging to the WSW represents the main tectonic structure.

Fig. 4. (a) Geological map of the Kotroman–Vardište area (~5 km southwest of Mokra Gora village) with location of the studied stratigraphic sections. (b) Sketch of the measured sections within the Mokra Gora Group.

The lithostratigraphic column was reconstructed through the recognition of key strata and intervals. The lithological and sedimentological features of the Mokra Gora succession reflect two deepening–shallowing cycles, named Unit A and Unit B, topped by shallow-marine rudist-bearing carbonates (Unit C). A detailed study was performed in the A and B units while the C unit was not studied. The measured thickness of units A and B is more than 400 m (Fig. 4).

The lower portion of the succession was measured at Vardište, a little village north of the railway station (section 1; 43° 45′ 40.0″ N 19° 27′ 29.1″ E – same outcrops studied by Bortolotti et al. Reference Bortolotti, Ficcarelli, Manetti, Passerini, Pirini-Radrizzani and Torre1971) and in the vicinity of Kotroman village (section 2: 43° 46′ 01.0″ N 19° 28′ 07.2″ E; section 3: 43° 46′ 05.0″ N 19° 28′ 22.4″ E); the middle and upper portions of the succession were studied on the eastern flank of Tusto Brdo (section 4: 43° 46′ 37.1″ N 19° 28′ 36.2″ E) and on the southern slope of Ograđenica Hill (section 5: 43° 46′ 59.9″ N 19° 28′ 54.5″ E) and south of Kotroman village (section 2b: 43° 46′ 06.6″ N 19° 27′ 54.6″ E) (Fig. 4). Previous detailed lithostratigraphic studies were performed only on the Vardište section by Bortolotti et al. (Reference Bortolotti, Ficcarelli, Manetti, Passerini, Pirini-Radrizzani and Torre1971). Other studies focused on a general description of the main lithostratigraphic units and their respective biostratigraphic assemblages and gave no precise stratigraphic location for the samples collected and studied (Pejović & Radoičić, Reference Pejović and Radoičić1971; Banjac et al. Reference Banjac, Bandel and Kiel2007, Reference Banjac, Jovanović, Dulić and Ljubović-Obradović2008; Radoičić & Schlagintweit, Reference Radoičić and Schlagintweit2007). As a consequence, in some cases it was impossible to make a reliable correlation of the biostratigraphic data, especially in the lower portion of the succession, as previous workers recognized the presence of only one deepening–shallowing cycle. The majority of workers studied single outcrops located north of Kotroman (section 3; Banjac et al. Reference Banjac, Bandel and Kiel2007) and north of Mokra Gora village (Pejović & Radoičić, Reference Pejović and Radoičić1971; Radoičić & Schlagintweit, Reference Radoičić and Schlagintweit2007), which are representative of Unit B only.

3.a.1. Basement

The basement of the Mokra Gora succession is represented by serpentinites belonging to the Zlatibor ophiolitic massif. The topmost portion of the serpentinites is fractured and strongly weathered and shows a reddish colour from diffuse iron oxides. The serpentinites are topped by a discontinuous level of laterite and then by a decimetre-thick horizon of siliceous duricrust (silcrete). This is a massive quartz-rich layer with diffuse Fe-oxides that homogeneously covers the weathering profiles on the top of the serpentinites. The upper surface of the silcrete horizon has a globular appearance suggesting that the silcrete is originated from the coalescence of several bulbous silcrete masses (Fig. 5). At the microscopic scale, the silcrete consists of amorphous silica particles cementing sub-millimetric to centimetric clasts of deeply weathered minerals coming from the underlying serpentinite basement (Bortolotti et al. Reference Bortolotti, Ficcarelli, Manetti, Passerini, Pirini-Radrizzani and Torre1971). The main feature of the weathered horizon and the association with silcrete and laterite suggests the prolonged exposure of the serpentinites to a subaerial environment in a warm and humid climatic regime (Summerfield, Reference Summerfield1983).

Fig. 5. (a) Silcrete horizon lying above the weathered serpentinite (Kotroman area, base of section 2a in Fig. 4). Pen for scale is ~14 cm long. (b) Bulbous silcrete occurrences within the shale and silty layers of subunit B1 (Kotroman area, see Figs 4 and 6 for location). Hammer for scale is 33 cm long.

3.a.2. Unit A

The stratigraphic section was measured and sampled along the Šargan Eight Railway on the right side of the Šarganišica Creek. Additional observations were made in the Vardište area. The total thickness of the unit is ~60 m. Based on lithological differences, Unit A was subdivided into four subunits (subunits A1, A2, A3 and A4).

3.a.2.a. Subunit A1

This subunit is made up of metre-thick conglomerates alternating with subordinate coarse- to fine-grained litharenitic (mostly ophiolite-derived clasts) sandstones and siltstones (Figs 6, 7a). The conglomeratic horizons are sometimes channelized and show crude clast imbrication. The silty horizons are laterally continuous at the outcrop scale and are massive or characterized by plane-parallel laminations. The sandy levels are characterized by cross-stratification; they are discontinuous and sometimes show pinch-out terminations. All the deposits of this subunit are dark red in colour. Clasts from the conglomerates, consisting mostly of serpentinites with a few basalts and cherts, exhibit a provenance from the ophiolitic substratum. Their size varies from 2 cm to 20 cm, they are well rounded to sub-rounded and they are often silicified and/or replaced by limonite alteration. The replacement of the host sediments by silica is so strong that, in some cases, it leads to the formation of layers of decimetre-thick silcrete. Laterite deposits consisting of poorly sorted litharenites with a ferruginous matrix are present in decimetre-thick pockets in the lower portion of the subunit, sometimes hosting concentrations of spherules of Fe–Ni oxides (oolitic iron; Fotić, Reference Fotić1962). Widespread Fe-oxides give this subunit a dark red colour. The thickness of subunit A1, as measured in the Vardište section, is ~20 m (section 1, Figs 4, 6). The transition to subunit A2 is marked by the disappearance of the conglomeratic levels. Overall, the subunit is arranged in a fining-upward and thinning-upward succession.

Fig. 6. Lithostratigraphic composite column of the lower part of the Mokra Gora Group in the type area. See Figure 4 for locations. FS – flooding surface.

Fig. 7. Key outcrop photographs of the Mokra Gora Group. (a) Basal conglomerates and sandstones of subunit A1; Vardište area 43° 43′ 56″ N; 19° 27′ 53″ E. (b) Transition between subunits A2 and A3 along stratigraphic column 2a; see Figure 4 for location. (c, d) Transitions between units A and B and between subunits B1 and B2, respectively, Užice–Višegrad road-cut near Kotroman village (lithostratigraphic column 3 in Fig. 4). (e) Marlstone and limestone succession characterizing subunit B3 (lithostratigraphic column 2b in Fig. 4). (f) Uppermost portion of Unit B and contact with massive limestones of Unit C, Ograđenica Hill (lithostratigraphic column 5 in Fig. 4).

The lithofacies association of subunit A1 can be related to a high-energy fluvial environment, probably with braided channels, in a warm and humid climate.

3.a.2.b. Subunit A2

Subunit A2 consists of massive decimetre-thick to metre-thick beds of ophiolitic sandstones and siltstones alternating with centimetre- to decimetre-thick massive shales. The coarse-grained sandstones show a faint cross-lamination. Microconglomeratic centimetre-thick lenticular pockets are scattered in the siltstone levels. Rare decimetre-thick silcrete horizons are also present. Rock fragments are angular and contain alterations of minerals, mainly chlorite, relics of olivine and pyroxene and opaque heavy minerals (magnetite, spinel, etc.) floating in a haematitic–goethitic detrital matrix. Sub-spherical ferruginous nodules, probably derived from laterite crusts, are also present and in some cases are surrounded by a thin film of authigenic quartz. In the uppermost half-metre of the subunit a lithic–carbonatic sandstone occurs with scattered recrystallized bioclasts and mixed micritic/detrital matrix. The thickness of this subunit measured in the Vardište and Kotroman sections is nearly 25 m (sections 1 and 2a, Figs 4, 6).

This subunit depicts a fining-upward and thinning-upward succession. It is interpreted to have originated from fluvial environments, probably meandering streams, in a warm and humid climate.

3.a.2.c. Subunit A3

The shift from subunit A2 to A3 is marked by the appearance of the first marly layer (Fig. 7b). The lower portion of subunit A3 is represented by marlstones alternating with centimetre- and decimetre-thick beds of nodular bioclastic limestones (mudstones, wackestones and packstones) and a few centimetre-thick red-coloured ophiolite-bearing sandstones. Bioturbation is common. The nodular limestones probably derive from the interference between bioturbation and differential dissolution/cementation, as suggested by the occurrence of dissolution seams made up of clay minerals and opaque oxides.

In an upward direction the ophiolite-derived fragments progressively decrease and the succession is characterized by well-bedded decimetre-thick (max. 50 cm) bioclastic mudstones to packstones, and locally rudstones/floatstones, regularly alternating with marlstones and siltstones. Accumulations of bivalves and gastropods are scattered in the subunit. The thickness of this subunit measured in the Kotroman sections is 10 m (section 2a, Fig. 6).

The bioclastic wackestones and mudstones suggest lagoonal and marine subtidal environments of the inner ramp (sensu Burchette & Wright, Reference Burchette and Wright1992). The bioclastic floatstones and rudstones were likely deposited during storm events (tempestites).

3.a.2.d. Subunit A4

The transition from subunit A3 to A4 is marked by an abrupt decrease in thickness and frequency of the decimetre-thick limestone beds and an increase in the marly portion. Subunit A4 consists of decimetre-thick beds of fossiliferous marlstones regularly alternating with centimetre- to decimetre-thick beds of nodular bioclastic packstones/floatstones passing upwards to decimetre-thick beds of packstones and, finally, to decimetre-thick coarse- to fine-grained ophiolite-bearing sandstones. Reworked layers of bioclastic packstones/rudstones with variable amounts of ophiolite-derived clasts are common in the upper portion of the subunit. Generally, the high amount of the clastic input is marked by a dark red colouring. Fenestral porosity, associated with organic decay and other syn-sedimentary processes, is locally common. The subunit represents a coarsening- and thickening-upward succession. The transition to Unit B happens through the progressive increase of terrigenous layers and the decrease of carbonates until their complete disappearance. The thickness of this subunit measured in the Kotroman sections is 8 m (section 2a, Fig. 6).

Subunit A4 was deposited in a mixed carbonate–clastic inner-ramp environment. The progressive upward increase of extrabasinal rock fragments and storm beds indicates a shallowing-upward trend.

3.a.4. Unit C

Unit C consists of massive to metre-thick bedded rudist lithosomes and bioclastic deposits. The exposure of the basal contact in Ograđenica Hill shows evidence of a slight angular unconformity at the contact with Unit B (Fig. 7f). The exposed thickness of this unit is ~70 m and could be subdivided into a lower part made up of massive limestones (~20 m thick) and an upper part of well-bedded limestones (~50 m thick).

This unit was deposited in a shallow-water environment. Olujić et al. (Reference Olujić, Pamić and Kapeler1987) reported, albeit poorly constrained, another transition to basinal environments in post-Santonian time.

Another significant succession pertaining to the Mokra Gora Group crops out in a more internal position on top of the ophiolites of the Maljen massif between Struganik and Ba villages (Figs 2, 3; see geological map in Chiari et al. Reference Chiari, Djerić, Garfagnoli, Hrvatović, Krstić, Levi, Malasoma, Marroni, Menna, Nirta, Pandolfi, Principi, Saccani, Stojadinović and Trivić2011). In this succession only one transgressive cycle is recognized, and the deepening-upward trend is constant from Cenomanian to early Campanian times.

The succession here starts with ophiolite-bearing conglomerates and sandstones of continental to littoral origin that rapidly pass upwards into a marl–limestone succession with interbedded calcarenites representing inner- to mid-ramp environments. Samples collected from marly levels yield only poorly preserved nannofossils. However, the absence of the marker Micula decussata and the presence of Eiffellithus turriseiffelii and Corollithion kennedyi proposes an age range of late middle Cenomanian (upper CC9 – lower CC10 zones of Sissingh, Reference Sissingh1977) to late Coniacian (CC14 Zone of Sissingh). Yet, the Turonian age of the overlying lithofacies constrains the age of this shallow-marine marl–calcarenite succession to the middle Cenomanian–Turonian.

The succession evolves upwards into more open-marine deposits (outer-ramp to basinal environment) with sedimentation of platy limestones alternating with marlstones and fine-grained calcarenites of Turonian age (Filipović et al. Reference Filipović, Marković, Pavlović, Rodin and Marković1978). Finally, the succession passes into a basinal flysch consisting of low-density turbidite deposits (calcareous sandstones and calcirudites) and cherty limestones of Coniacian–Santonian age (Djerić et al. Reference Djerić, Gerzina, Gajić and Vasić2009; Vishnevskaya et al. Reference Vishnevskaya, Djerić and Zakariadze2009; Bragina et al. Reference Bragina, Bragin, Djerić and Gajić2014). Towards the Santonian portion of the succession, slumping layers and other syn-sedimentary deformations became common (Fig. 8a).

Fig. 8. Outcrop photographs of the Mokra Gora, Guča and Kosjerić groups and of the Ljig flysch. (a) Slumped layer of calcarenite with cherty lenses in the upper portion of the Mokra Gora Group (Coniacian–Santonian), near Struganik village (Maljen massif area). (b) Fluvial conglomerates of the basal succession of the Kosjerić Group unconformably overlying the Drina–Ivanjica Palaeozoic phyllites, south of Kosjerić village. (c) Middle Turonian rudist-bearing reefal limestones, Kosjerić area; quarry cliff is ~40 m height. (d) Unconformable stratigraphic contact of the basal clastic succession of the Guča Group above the Palaeozoic phyllites of the Drina–Ivanjica Unit, Guča area. (e) Marly chaotic unit in the basal Guča Group with widespread centimetre- to decimetre-thick metamorphic clasts from the Drina–Ivanjica Unit; Phy – phyllite. Hammer for scale is 33 cm long. (f) Thick-bedded turbidite strata of the Ljig flysch (road-cut 2 km south of Ljig, see Fig. 2).

In the Struganik–Ba area, the Mokra Gora Group is overthrust by siliciclastic flysch of middle Campanian–Maastrichtian age (Ljig flysch; Dimitrijević & Dimitrijević, Reference Dimitrijević, Dimitrijević, Dimitrijević and Dimitrijević1987; Chiari et al. Reference Chiari, Djerić, Garfagnoli, Hrvatović, Krstić, Levi, Malasoma, Marroni, Menna, Nirta, Pandolfi, Principi, Saccani, Stojadinović and Trivić2011). This tectonic superposition is sealed, and thus postdated, by the Cenozoic intrusion of the Ba–Slavkovica quartz latites (Schefer et al. Reference Schefer, Cvetković, Fügenschuh, Kounov, Ovtcharova, Schaltegger and Schmid2010a; Chiari et al. Reference Chiari, Djerić, Garfagnoli, Hrvatović, Krstić, Levi, Malasoma, Marroni, Menna, Nirta, Pandolfi, Principi, Saccani, Stojadinović and Trivić2011).

3.b. Kosjerić Group

The Kosjerić Group (Chiari et al. Reference Chiari, Djerić, Garfagnoli, Hrvatović, Krstić, Levi, Malasoma, Marroni, Menna, Nirta, Pandolfi, Principi, Saccani, Stojadinović and Trivić2011) consists of a continental to transitional clastic unit passing upwards into bedded shallow-marine carbonates. The clastic unit is mainly composed of quartz pebbles and low-grade metamorphic clasts derived from subaerial erosion of the Palaeozoic formations located on the eastern flank of the Drina–Ivanjica Unit. Also, rare metre-sized slide blocks of shallow-water carbonates of presumably Triassic age were observed within the basal clastic unit (Kosjerić area). The contact with the underlying Drina–Ivanjica Unit and the ophiolite thrust sheets is marked by an angular unconformity (Fig. 8b).

The shallow-marine limestones gradually pass into a middle Turonian – lower Campanian marly basinal succession (Mojsilović et al. Reference Mojsilović, Baklajić, Đoković and Avramović1978; Radoičić & Schlagintweit, Reference Radoičić and Schlagintweit2007). A middle Turonian age was reported for an episode of shallow-water sedimentation characterized by massive reefal bioconstructions with abundant rudists, which is possibly heteropic with the basinal succession (Mojsilović et al. Reference Mojsilović, Baklajić, Đoković and Avramović1978). These typically reddish deposits are always bounded by tectonic contacts that hamper the recognition of the original stratigraphic relationships with the other lithofacies (Fig. 8c).

3.c. Guča Group

The Guča Group is represented by a basal formation characterized by littoral to slope clastic deposits unconformably lying above the Palaeozoic formations of the Drina–Ivanjica Unit (Fig. 8d) and partly above the pelagic sediments of the Kosjerić Group. The clasts in the basal succession are mainly represented by well-rounded quartz pebbles, phyllites and other low-grade metamorphic rocks along with lower amounts of dark grey limestones of possibly Triassic age. The basal clastic sediments pass upwards to shallow-marine carbonates that start with well-bedded limestones and calcarenites turning upwards into sporadic rudist-bearing massive limestones. The successive drowning of the carbonate platform is marked by deposition of thin-bedded calcareous litharenites interlayered with frequent slumps and debris flow deposits derived from the eroding Drina–Ivanjica formations (pre-flysch facies; Fig. 8e). Finally, basinal sedimentation is indicated by thick-bedded turbidite strata with arkose to lithic arkose composition. These turbidites stretch in a NNW–SSE direction from the Lučani area to the north, to the Majden area (North Macedonia) to the south and are known as the Kosovska–Mitrovica flysch (Dimitrijević & Dimitrijević, Reference Dimitrijević, Dimitrijević, Dimitrijević and Dimitrijević1987).

The Kosovska–Mitrovica flysch shares a similar age and petrographic composition with the Ljig flysch overthrusting the Mokra Gora Group to the south of the Maljen ophiolitic massif (Fig. 8f). In turn, Chiari et al. (Reference Chiari, Djerić, Garfagnoli, Hrvatović, Krstić, Levi, Malasoma, Marroni, Menna, Nirta, Pandolfi, Principi, Saccani, Stojadinović and Trivić2011) pointed out a correlation between the Ljig flysch and the Brus flysch partly corresponding to the Paraflysch Unit of Dimitrijević & Dimitrijević (Reference Dimitrijević and Dimitrijević2009) cropping out in the EVO and topping the structural pile in the Kopaonik area.

4.a. Material and methods

A total of 89 samples were collected in the Mokra Gora (67 samples), Kosjerić (5 samples) and Guča (17 samples) groups and studied for microfossil content after preparation of one thin-section for each sample. The sampling in the Mokra Gora Group in the Zlatibor area was taken every 1 m, on average, in the limestones of Unit A and every 5 m, on average, in Unit B. The sampling in the Kosjerić and Guča groups was scattered in different sections representative of their basal portions, just above the basal unconformity surfaces, and at the transition with the flysch sedimentation.

Scattered samples for the study of nannofossil assemblages were collected in the Mokra Gora Group, both in the Zlatibor (11 samples) and Maljen (6 samples) sections. The biozonations adopted for dating the calcareous nannofossil assemblages use the CC zones of Sissingh (Reference Sissingh1977). For each sample, the presence and abundance of each species was evaluated every 200 fields of observation (FOV).

Macrofossils (bivalves and gastropods) from the Mokra Gora succession sampled in the Zlatibor area were sampled from distinct levels, corresponding to individual beds or a series of a few beds, and prepared in the laboratory before taxonomic identifications. The samples of molluscs studied by Bortolotti et al. (Reference Bortolotti, Ficcarelli, Manetti, Passerini, Pirini-Radrizzani and Torre1971) are re-studied and revised herein.

4.b. Mokra Gora Group

The first studies of the Mokra Gora succession in the type area (Žujović, Reference Žujović1893; Petković, Reference Petkovic1925; Ampferer, Reference Amferer1928; Milovanović, Reference Milovanović1933) pointed to a latest Cretaceous age based on hippuritid bivalves and abundant fossil gastropod associations. Loczy (Reference Loczy1924), based on ammonites, was the first to recognize older ages for the lower part of the succession (Cenomanian–Turonian). Bortolotti et al. (Reference Bortolotti, Ficcarelli, Manetti, Passerini, Pirini-Radrizzani and Torre1971) studied the Vardište section and indicated a Late Jurassic age for the lower part of the succession (Unit A). Pejović & Radoičić (Reference Pejović and Radoičić1971) and Radoičić (Reference Radoičić1984) placed the lower part of the Mokra Gora succession (Unit B) as older than Cenomanian, and indicated a late Turonian to latest Cretaceous age for the upper part represented by massive limestones with hippuritids and gastropods (Unit C). Banjac (Reference Banjac1994a,b, Reference Banjac2000) and Banjac et al. (Reference Banjac, Bandel and Kiel2007, Reference Banjac, Jovanović, Dulić and Ljubović-Obradović2008) described Albian–Cenomanian mollusc faunas from the lower part of the succession. The same age was confirmed by I. Dulić (unpub. Ph.D. thesis, Univ. Belgrade, 2003) based on associations of palynomorphs. Finally, Radoičić & Schlagintweit (Reference Radoičić and Schlagintweit2007) erected the new dasycladalean species Neomeris mokragorensis from the Albian of the Mokra Gora succession and the Albian–Santonian of other localities.

In general, the previous investigations recognized only one regression–transgression cycle, and most of the time the analysed samples are not clearly located on a lithostratigraphic column. This hampered the unambiguous correlation with the results of this study. Comparison with previous biostratigraphic data was made only when the lithostratigraphic position within the succession was clearly indicated.

4.b.1. Unit A

No fossils were detected in subunit A1, whereas the poor preservation of bioclasts in subunit A2 hampered any age determination.

Fossils in subunit A3 are represented by the dasycladalean alga Salpingoporella dinarica Radoičić and Salpingoporella hasi Conrad, Radoičić & Rey, Rivulariaceae algae, the benthic foraminifers Hemicyclammina sigali Maync and Spiroloculina sp., and a moderately diverse assemblage of bivalves and gastropods (Fig. 9).

Fig. 9. Thin-section photographs of microfossils in subunits A3–A4. (a, b) Salpingoporella dinarica Radoičić, sample MK7. (c) Hemicyclammina sigali Maync, sample MK_c. (d) Hemicyclammina sigali Maync, sample MK9. (e, g) Salpingoporella hasi Conrad, Radoičić & Rey, sample MK20. (f, j) Salpingoporella hasi Conrad, Radoičić & Rey, sample MK14. (h) Spiroloculina sp., sample MK9. (i) Undetermined foraminifer, sample MK9. Scale bar = 500 μm for all figures.

The range of S. dinarica is Berriasian to Albian with its acme in the Aptian, and the range of S. hasi is Aptian to Cenomanian (Carras et al. Reference Carras, Conrad and Radoičić2006). H. sigali is usually known from the Albian–Cenomanian (Sartorio & Venturini, Reference Sartorio and Venturini1988), but was originally reported from the Aptian–Cenomanian (Maync, Reference Maync1953; Loeblich & Tappan, Reference Loeblich and Tappan1988), while Hosseini et al. (Reference Hosseini, Conrad, Clavel and Carras2016) reported it from the Barremian of the Zagros Mountains (Iran). In addition, considering that the first occurrence of Neomeris mokragorensis Radoičić & Schlagintweit in the studied succession takes place 30 m upwards, in the lower part of subunit B3, and its range in Mokra Gora is middle–late Albian (Radoičić & Schlagintweit, Reference Radoičić and Schlagintweit2007), the age of subunit A3 can be attributed to the late Aptian. This dating agrees with the statement of Radoičić & Schlagintweit (Reference Radoičić and Schlagintweit2007) that ‘a latest Aptian age of the lowermost beds cannot be excluded’. Our data strengthen the presence of the Aptian, mainly because of the presence of S. dinarica, a species strongly present in the Aptian of the Dinarides–Hellenides.

This age assignment is compatible with the benthic mollusc fauna of subunit A3, although it should be kept in mind that the longevity of the Mesozoic bivalve and gastropod species commonly spans distinctly more than a single stage, and even more so for genera. The molluscan fauna, as revised herein (Fig. 11), is dominated by various oysters (Amphidonte sp., Gyrostrea sp. and Flemingostreini gen. et sp. indet.), the bivalves Eomiodon sp. and Brachidontes sasykensis Romanov, and the gastropods Bicarinella bicarinata (Pchelintsev) and Pseudonerinea sp. While Amphidonte and Gyrostrea are typical Cretaceous oyster genera, Brachidontes sasykensis has been reported from the Barremian of the Dniester–Prut region (Romanov, Reference Romanov1976) and Bicarinella bicarinata from the Albian–Cenomanian of Mokra Gora (Banjac et al. Reference Banjac, Bandel and Kiel2007). A Late Jurassic age of subunit A3, as inferred by Bortolotti et al. (Reference Bortolotti, Ficcarelli, Manetti, Passerini, Pirini-Radrizzani and Torre1971), is no longer maintained according to our updated determinations.

Fossils in subunit A4 are represented by the dasycladalean alga Salpingoporella hasi, algae Solenoporaceae (Parachaetetes?) and Corallinaceae (Archaeolithothamnium?), and gastropods and bivalves. Because of the position, the age interval in which this subunit was deposited could be late Aptian to early Albian.

4.b.2. Unit B

Subunit B1 is barren of fossils. Subunit B2 yielded microfacies with no significant fossils, such as various benthonic foraminifers, Rivulariaceae algae, thick and thin bivalves, gastropods, ostracods and encrusters.

The lower part of subunit B3 yielded microfacies containing Neomeris mokragorensis, Salpingoporella hasi, Hemicyclammina sigali, Bacinella sp., rudist fragments, gastropods, ostracods and charophytes (Fig. 10). Pejović & Radoičić (Reference Pejović and Radoičić1971) recognized in this subunit Salpingoporella urladanasi Conrad, Peybernès & Radoičić, Bacinella sterni Radoičić and the benthic foraminifer Nezzazatinella cf. picardi (Henson). As mentioned above for subunit A3, the range of Neomeris mokragorensis in this area is middle–late Albian (Radoičić & Schlagintweit, Reference Radoičić and Schlagintweit2007). So, the lower part of subunit B3 can be considered to be middle Albian. This dating does not contrast with the ranges of the other species mentioned.

Fig. 10. Thin-section photographs of microfossils in subunit B3. (a) Neomeris mokragorensis Radoičić & Schlagintweit, sample MK35. (b, c) Neomeris mokragorensis Radoičić & Schlagintweit, sample MK30 (c detail of b). (d) Hemicyclammina cf. sigali Maync, sample MK29. (e) Hemicyclammina cf. sigali Maync, sample MK31. (f) Hemicyclammina cf. sigali Maync, sample MK33. (g) Hemicyclammina sigali Maync, sample MK51. Scale bars = 300 μm.

In the lower part of subunit B3, gastropods occur in abundance, and although they are mostly poorly preserved, we could identify the species Bicarinella bicarinata, Cassiope kotromanensis (Banjac, Bandel & Kiel) and Paraglauconia lujani (de Verneuil & Collomb) with certainty (Fig. 11). The age of these gastropod species is given as Albian–Cenomanian by Banjac et al. (Reference Banjac, Bandel and Kiel2007). The bivalves Brachidontes sasykensis and Eomiodon sp., already mentioned for subunit A3, also occur in the lower part of subunit B3 in addition to oysters (Flemingostreidae gen. et sp. indet. and Curvostreini gen. et. sp. indet.) and locally abundant ‘Anomia’ sp. (Fig. 11).

Fig. 11. Characteristic bivalves and gastropods from the Cretaceous of the Mokra Gora succession, western Serbia. (a) Brachidontes sasykensis Romanov, Reference Romanov1976, subunit A3, external view of right valve. (b) Brachidontes sasykensis Romanov, Reference Romanov1976, subunit A3, external view of left valve. (c) Gyrostrea sp., subunit A3; (c₁) external view of left valve, (c₂) external view of right valve. (d) Gyrostrea sp., subunit A3; (d₁) external view of left valve, (d₂) internal view of left valve. (e) Flemingostreini gen. et sp. indet., subunit A3; (e₁) external view of right valve, (e₂) internal view of right valve. (f) Flemingostreini gen. et sp. indet., subunit A3; (f₁) external view of right valve encrusted by left valves of Amphidonte sp., (f₂) internal view of right valve. (g) Amphidonte sp., subunit A3; (g₁) external view of right valve, (g₂) internal view of right valve. (h) Curvostreini gen. et sp. indet., subunit B3; (h₁) external view of right valve, (h₂) internal view of right valve. (i) Flemingostreidae gen. et sp. indet., subunit B3; (i₁) external view of right valve, (i₂) internal view of right valve. (j) Rock sample with several specimens of ‘Anomia’ sp. and poorly preserved Brachidontes and gastropod, subunit B3. (k) ‘Anomia’ sp., subunit B3 (same slab as in (j)). (l) ‘Anomia’ sp., subunit B3. (m) Eomiodon sp., subunit A3, external view of left valve. (n) Eomiodon sp., subunit A3, external view of right valve. (o) Eomiodon? sp., subunit B3; (o₁) external view of left valve, (o₂) external view of right valve. (p) Bicarinella bicarinata (Pchelintsev, Reference Pchelintsev1953), subunit B3; (p₁) adapertural view, (p₂) apertural view. (q) Bicarinella bicarinata (Pchelintsev, Reference Pchelintsev1953), subunit A3. (r) Cassiope kotromanensis (Banjac, Bandel & Kiel, Reference Banjac, Bandel and Kiel2007), subunit B3. (s) Cassiope kotromanensis (Banjac, Bandel & Kiel, Reference Banjac, Bandel and Kiel2007), subunit B3, adapertural view. (t) Paraglauconia lujani (de Verneuil & Collomb, Reference Verneuil and Collomb1853), subunit B3. (u) Paraglauconia lujani (de Verneuil and Collomb, Reference Verneuil and Collomb1853), subunit B3. (v) Pseudonerinea sp., subunit A3, polished section. Length of scale bars = 1 cm.

The upper part of subunit B3 is characterized by Hemicyclammina sigali, S. hasi, N. mokragorensis and Aeolisaccus sp. Radoičić & Schlagintweit (Reference Radoičić and Schlagintweit2007), among others, also recognized Ovalveolina maccagnoae De Castro, Atopochara trivolvis Peck, Charophyta gyrogonites, Pseudorhapydionina laurinensis (De Castro), Charentia cuvilleri Neumann, Cuneolina sp. and oysters. This fossil assemblage and its position suggests a middle Albian – earliest Cenomanian age for this part, in agreement with these authors.

Nannofossil assemblages from subunit B4 and the lower part of subunit B5 reported by Chiari et al. (Reference Chiari, Djerić, Garfagnoli, Hrvatović, Krstić, Levi, Malasoma, Marroni, Menna, Nirta, Pandolfi, Principi, Saccani, Stojadinović and Trivić2011) indicate an age no older than late Albian and no younger than late Coniacian. However, the presence of Pithonella ovalis (Kaufmann) in samples collected in subunit B4 and of S. cf. hasi up to the middle part of subunit B5 suggests that the age of subunits B4 and B5 is still within the late Albian–Cenomanian time span.

According to Radoičić & Schlagintweit (Reference Radoičić and Schlagintweit2007), subunit B6 is characterized by rare and poorly preserved ammonites, echinoderms, foraminifers (Hedbergella sp.) and other planktonic organisms (Pithonella sp.), resedimented fragments of rudists, other molluscs and halimedacean algae. Loczy (Reference Loczy1924) attributed a Cenomanian–Turonian age to this subunit.

4.c. Kosjerić Group

The lowermost portion of the shallow-marine limestones was sampled in the Kosjerić area some metres above the contact with the Palaeozoic formations of the Drina–Ivanjica Unit, giving a late Cenomanian age (Pseudolituonella reicheli Marie, Cuneolina pavonia D’Orbigny, Broeckina (Pastrikella) balcanica Cherchi, Radoičić & Schroeder, Vidalina radoicicae Cherchi & Schroeder, Chrysalidina gradata D’Orbigny and Heteroporella lepina Praturlon).

West of the Zlatibor Massif (near Ravni Village) some isolated outcrops of the Kosjerić Group seal the contact between the ophiolitic mélange and kilometre-sized slices of Triassic carbonates embedded in it (Sirogojno carbonate–clastic mélange of Missoni et al. Reference Missoni, Gawlick, Sudar, Jovanović and Lein2012). Samples from the basal portion of the carbonate unit confirm a late Cenomanian age (Chrysalidina gradata D’Orbigny, Cuneolina pavonia D’Orbigny, Minouxia cf. lobata Gendrot, Pseudonummoloculina heimi (Bonet), Pseudolituonella reicheli Marie and Pseudorhapydionina dubia (De Castro)). Radoičić & Schlagintweit (Reference Radoičić and Schlagintweit2007) and Dimitrijević et al. (Reference Dimitrijević, Ljubović-Obradović and Dimitrijević1996) attributed a similar age (Cenomanian–Turonian p.p.) to the shallow-water carbonates of the Kosjerić and Ravni areas.

4.d. Guča Group

Radoičić et al. (Reference Radoičić, Radulović, Rabrenović and Radulović2010) reported an earliest Campanian age for the base of the shallow-marine carbonate member.

We studied in detail two sections located between Lučani and Guča villages (western Serbia) (Fig. 12). In these sections, 1–2 m of continental to littoral conglomerates rapidly passes upwards to distal ramp calcarenites and limestones and finally to basinal turbidites. The microfacies content consists of Moncharmontia apenninica (De Castro), Murgeina apula (Luperto Sinni), Orbitoides media (D’Archiac), Orbitoides apiculata Schlumberger, Siderolites calcitrapoides Lamarck, Hemicyclammina chalmasi (Schlumberger), Sulcoperculina sp., Goupillaudina sp., Minouxia sp., Globotruncana linneiana (D’Orbigny), ‘Stomiosphaera’ sphaerica (Kaufmann), biserial Heterohelicidae and Archaeolithothamnium sp., and allows the attribution of the carbonate members to the Campanian–Maastrichtian. Based on nannofossil assemblages sampled in the same section, Chiari et al. (Reference Chiari, Djerić, Garfagnoli, Hrvatović, Krstić, Levi, Malasoma, Marroni, Menna, Nirta, Pandolfi, Principi, Saccani, Stojadinović and Trivić2011) attributed a middle to late Campanian age to the pre-flysch facies of the succession. The comparison of these data allows the attribution of a late Campanian age to the continental to shallow-marine deposits of the Guča Group, whereas the Kosovska–Mitrovica flysch spans from the Maastrichtian to the Danian (ćirić, Reference Ćirić1958).

Fig. 12. Measured and sampled sections of the Guča successions in the type area. Geological map from Chiari et al. (Reference Chiari, Djerić, Garfagnoli, Hrvatović, Krstić, Levi, Malasoma, Marroni, Menna, Nirta, Pandolfi, Principi, Saccani, Stojadinović and Trivić2011).