Authors: Violeta Gajić, Milena Dunčić, Ana Mladenović, Dejan Prelević

Abstract:
In the central part of North Macedonia, in the area of the Klepa Mts., Upper Cretaceous sedimentary formations have been studied. Based on sedimentological, micropaleontological and biostratigraphical investigations of samples from both the east and west side of the Klepa Mts., sedimentary rocks of the Campanian-Maastrichtian age are determined. During the latest Cretaceous, this area was dominated by the sedimentation of dominantly carbonate rocks with variable amounts of clastic components. From the tectonic point of view, investigated area belongs to the contact zone between the Adriatic microplate (on the west) and the Eurasian margin (on the east). This contact zone is represented by a relatively wide area, that evolved in the form of tectonically active sedimentary basins due to a convergence between the aforementioned tectonic plates. However, the nature of this contact zone, also known as the Sava-Vardar zone, which extends along the central part of the Balkan Peninsula, is still a matter of debate. The traditional view explains the Sava – Vardar zone as the remnant of the Late Cretaceous oceanic domain, which subducted under the Eurasian plate and initiated the formation of the Banat-Timok-Srednjegornje volcanic arc. Nevertheless, based on the study of several Upper Cretaceous basaltic occurrences within the Sava-Vardar zone, it is concluded that they are of an intraplate origin. Following that, if we assume that this traditional point of view for the contact zone is true, these basalts should be interpreted as being formed in the forearc region. Alternatively, if these basaltic occurrences are of intracontinental origin, they can be interpreted as being formed in the area of a diffuse tectonic zone between the Adriatic microplate and the Eurasian plate, that was suitable for the formation of pull-apart basins. Investigated carbonate rocks are represented by reddish, locally pinkish, or grey micritic limestones and marly limestones. They can be found in the form of laminated platy layers, showing horizontal, tilted lamination or convolution. All lithotypes are characterized by abundant allochems of biogenic origin, so they can be defined as bioclastic carbonate rocks. The carbonate rocks are characterized by variable content of clastic material, originating from the shallower parts of the basin, and transported by turbiditic flows. Because of that, they can structurally be interpreted as calcarenites and calcilutites. In the investigated hemipelagic limestones of the Klepa Mts., a very rich association of microfossils is defined. Planktonic foraminifers dominate, but also calcified radiolarians, as well as microplankton in the form of calcisphere and different benthonic foraminifers are present. The association of planktonic foraminifers is dominantly presented by globotruncana, as typical representatives of a complex morphological group and intermediary morphological group related to the complex morphotype. This microfossil association of planktonic foraminifers indicate the late Campanian – early Maastrichtian age of the investigated limestones. A study of lithological and stratigraphical characteristics on the field, as well as the determination of a very rich association of the Upper Cretaceous fossils, indicate constant sedimentation from the late Campanian to early Maastrichtian time in the area of the Klepa Mts. Palaeoecological characteristics of the determined association of planktonic foraminifers indicate relatively deep sedimentation (~300 m) of the studied limestones, with periodical changes in bathymetry. Globotruncana species belonging to the bathypelagic areas are dominant. Small shapes represented by hedbergelama, heteroheliksima, globigerineloidesima or globotruncanelama, belong to epipelagic areas. Small benthic species belonging to groups of lagenida, gavelinelida or rotalida, represent species from the central or external part of the shelf up to bathyal areas..