Microfacies characteristics of carbonate cobble from Campanian of Slovenj Gradec ( Slovenia ) : implications for determining the Fleuryana adriatica De Castro , Drobne and Guši ć paleoniche and extending the biostratigraphic range in the Tethyan realm

A carbonate cobble was collected in a creek near Slovenj Gradec (Slovenia). It comprises Trochactaeon gastropods as well as foraminifera Fleuryana adriatica and Cuneolina ketini from a subtidal environment with agglutinated and porcelaneous benthic foraminifera. Packstone-grainstone of the structural type contains the abovementioned foraminiferal taxa, which are previously undetermined in this part of the Upper Cretaceous Tethyan realm. Stratigraphic data from this area, together with the determined microfossil assemblage of the carbonate cobble, indicate the upper part of Lower Campanian age, implying an extension of the F. adriatica and C. ketini stratigraphic range. The paleoniche within the Tethyan realm in which F. adriatica thrive is the shallowest part of the subtidal, close to peritidal conditions. It was developed on a relatively harder substrate that resulted from a laterally more pronounced paleorelief which enabled the shifting of hyaline benthic foraminifers towards the shallowest part of the subtidal. Their paleoniche is laterally absent from protected paleoenvironments with soft muddy substrate and a relatively high carbonate sedimentation rate, colonized with elevator rudists, as well as from relatively higher water energy paleoenvironments with completely hard grainstone-


Introduction
Near the Upper Cretaceous Slovenj Gradec locality, carbonate cobble rich in Gosau-type gastropod fauna (see Figure 1) was collected from a creek during previous eld investigations (Moro et al., 2016).In a paper by Mikuž et al. (2012), typical Gosau gastropods Trochactaeon cf.goldfussi (d`Orbigny) and Trochactaeon giganteus (Sowerby) were determined.To determine microfacies characteristics, a single thin section was also made from the carbonate cobble with trochactaeons.Within the agglutinated-porcelaneous foraminiferal assemblage, Fleuryana adriatica De Castro, Drobne, and Guši was determined, biostratigraphically important for the Upper Campanian to Late Maastrictian (De Castro et al. 1994;Veli 2007;Fleury, 2014;Solak et al., 2017).Determination of F. adriatica suggests a younger age of the eroded carbonate cobble compared with the nearby Slovenj Gradec succession, which has a chronostratigraphic age of the upper part of the Lower Campanian (Moro et al., 2016).Considering the other Gosau-type sedimentary successions where Campanian acteonelloids always lie below rudists bearing limestones (Sanders and Baron Szabo, 1997;Kollmann, 2014), the bistratigraphical range of F. adriatica (Upper Campanian to Late Maastrichtian) (Fleury, 2014;Solak et al. 2017) needs to be reconsidered.
Latest Jurassic to Early Cretaceous orogen convergence (Marton et al., 2017) was thrusted in the investigated area, which was overridden by a nappes system.Subsequently, large parts of the orogen were uplifted and subareally eroded (Ratschbacher et al., 1989, Sanders et al., 2004).A characteristic of the Late Cretaceous tectonics of the Alpine-Carpathian-Pannonian part of the Tethyan realm is the synchronous formation of Gosau-type sinsedimentary basins.Initial subsidence from Cenomanian to Campanian times within Gosautype basins is associated with the development of a uvial-lacustrine to shallow marine environment and the deposition of conglomerates, coal-bearing marls, siliciclastics rich in corals and acteonelloid gastropods and rudist limestones on the top of the succession (Willingshofer et al., 1999).As a result of the oblique orogenic convergence, the abovementioned deposits were mainly This paper aims to resolve the question of the stratigraphical disparity between the carbonate cobble and the Slovenj Gradec succession, as well as to determine the extension of the biostratigraphical range and paleoecological niche of the Fleuryana adriatica microfossil association for the Tethyan realm.

Geological background of Fleuryana adriatica and the associated microfossil assemblage
Upper Cretaceous Tethyan localities with ndings of F. adriatica and associated microfossils are rare, and research studies range from the description of a new species and determination of associated microfossils to paleoenvironmental reconstructions and chronostratigraphical determinations.

Methods
Thin-section analyses of the limestone cobble as well as the Slovenj Gradec succession include textures and skeletal components and biostratigraphic characteristics.Visual percentage charts were used to estimate the relative abundance of grains (Baccelle and Bosellini, 1965;in Flügel, 2004), and emphasize any differences in microfacies of the carbonate cobble as well as microfacies differences between the cobble and the Slovenj Gradec

Microfacies characteristics and chronostratigraphy of the carbonate cobble
The studied cobble is entirely composed of carbonate, with dimensions 20x10 cm.At the macroscopic level, it shows a uniform texture without any visible structure.

Microfacies characteristics of the Slovenj Gradec succession
The carbonate facies of the Slovenj Gradec succession are packstone-grainstone and oatstone-rudstone, with both lithotypes distributed randomly throughout the succession.Completely preserved macrofossils are rare and consist of small radiolitid individuals up to 4 cm in height and 0.8 cm in diameter in the succession's lower part.Thin sections, 28 in total, reveal shallow-water non-skeletal and skeletal particles, including peloids, benthic foraminifers, and fragments of macrofossils.Within the packstone-grainstone, the estimated frequency of bioclasts is 2.5 to 20%, where fragments of macrofossils are present with a frequency of 5 to 20%, while microfossils are present with a frequency of up to 2.5%, with a random domination of miliolids or cuneolinas and rare dicyclinids.Other microfossils (such as small nezzazatinellids, Accordiella conica, Calveziconus cf.lecalvezae, Dictyopsella kiliani and previously undetermined Nezzazatinella sp.) are present in small numbers, from 1 to 4 specimens.Within the oatstone-rudstone variates, the estimated frequency of bioclasts, rarely lithoclasts, is between 50 and 60%.Fragments of radiolitids predominate while microfossils are present with a small number of miliolids and nezazzatids.
Besides the type of substrate, salinity, turbidity, and nutrient supply could also be controlling factors for the macro and microfauna of the Upper Cretaceous Tethyan realm with subtropical conditions (Camoin et al., 1993)

Conclusions
The following conclusions may be drawn based on the microfacies analysis of the cobble from Slovenj Gradec, as well as the correlation with other localities comprising F. adriatica and associated microfossils within the Tethyan realm.
1.The paleoniche in which F. adriatica thrive is the shallowest part of the subtidal, close to peritidal conditions.The relatively harder substrate is a result of the laterally more pronounced paleorelief.It is rare and narrow, resulting from the shifting of hard grainstone-rudstone substrate with hyaline benthic foraminifers towards the shallowest part of the subtidal.Moreover, it is laterally absent from protected paleoenvironments with soft muddy substrate and relatively high carbonate sedimentation rate, as well as from relatively higher water energy, more open paleoenvironments with hard grainstone-rudstone substrate.
2. According to the benthic microfossils and determined chronostratigraphic range of nearby successions (obtained by previous investigations), the regional biostratigraphic range of F. adriatica and C. ketini could be extended to the upper part of the Lower Campanian (80.5 Ma).Incorporated in rudist biozones and together with the ranges of other stratigraphically important foraminifers, these extended ranges could be useful in cases where fossil remnants of rudists are laterally absent.
the Maastrichtian of the Latium area (Italy) (Chiocchini and Mancinelli, 2001), F. adriatica occurs within a vertical exchange of laminated dolomites and partly dolomitized mudstones/wackestones of "Discorbidae e Miliolidae biozone" (Chiocchini and Mancinelli, 2001; Chiocchini et al., 2012).Associated microfossils are mostly composed of Ostracoda, Miliolidae, and Charophyta, while Laf tteina marsicana Farinacci, Fleuryana adriatica De Castro Drobne and Guši and Rhapydionina liburnica Stache are present only in the upper part of the unit.The biostratigraphic age is determined as the uppermost Maastrichtian.

Figure 1 .
Figure 1.Photographs (above, below and from the side) of the carbonate cobble