Biostratigraphy and paleoenvironments of post-rift sedimentation in the Upper Cretaceous basin of the Timok Magmatic Complex (Serbian Carpathians)

The Timok Magmatic Complex (TMC) represents a segment of the wider Apuseni–Banat–Timok–Srednogorie (ABTS) Late Cretaceous magmatic belt, formed in response to the roll-back of the Neotethys slab beneath the Carpatho-Balkanides orogen in SE Europe. The TMC basin comprises Upper Cretaceous volcano-sedimentary sequences structurally incorporated within the Getic nappe system of the Serbian Carpathians. The evolution of the TMC basin was governed by Albian–Cenomanian to Turonian–Campanian E–W- to NE–SW-oriented extension associated with syn-tectonic calc-alkaline magmatism (~88–76 Ma). The post-rift stage of the basin evolution is characterized by Campanian–Maastrichtian shallow-marine carbonate sedimentation and regressive molasse deposits. The shallow-marine sediments, generally known as the “Vrbovac Beds”, were investigated at two localities in the southern part of the TMC basin. The lower parts of the Vrbovac Beds consist of coarse-grained carbonate breccia containing fragments of andesitic volcanites, corresponding to the final magmatic episode in the TMC basin. The upper parts comprise a succession of clastites and carbonates with diverse associations of rudists, gastropods, corals, and macroforaminifera. Carbonates are predominantly calcarenites, calcrudites, and biomicrites, whereas the clastic sediments include fine- to coarse-grained sandstones, marlstones, and shales. At the Bačevica locality, fossiliferous horizons are poorly exposed and two levels are recognized. The first level consists of loosely cemented limestone blocks with a diverse shallow-marine assemblage dominated by large rudists (Pironaea), gastropods (Trochactaeon giganteus Sowerby), and solitary corals (Cunnolites). Due to the weak cementation, material from this horizon is partly reworked and incorporated into second fossiliferous horizon, which is characterized by a rudist-dominated assemblage with Vaccinites loftusi, Radiolites sp., Pseudopolyconites sp., and Laperousia sp. In contrast, the Dubrava locality succession is subhorizontal and thin-bedded and well-preserved rudist in growth position indicate an autochthonous position. The rudist assemblage is comparable to that at Bačevica, and dominated by Vaccinites loftusi, Radiolites angeoides, and Pseudopolyconites sp., but lacks Pironaea. Cunnolites and large Trochactaeon specimens. During the Campanian–Maastrichtian, rudists and associated shallow-marine fauna inhabited depositional environments along the margins of the active andesitic Timok volcanic complex. The infill of rudist shells consists of siliciclastic material (quartz and clay minerals), indicating terrigenous input and deposition in clastic influenced environment. The studied sections record a transition from relatively high-energy depositional conditions at Bačevica to more stable environmental settings at Dubrava. Rudist habitats stretched from protected and open-marine parts of platforms to shelf margins where they produced large amounts of bioclastic rudist sands as observed at Bačevica.                                                                 

By linking stratigraphic, sedimentological, and tectonic observations, this study provides new constraints on the late evolutionary stages of the Upper Cretaceous TMC basin.

Keywords: biostratigraphy; sedimentology; paleoenvironments; Timok Magmatic Complex; Serbian Carpathians