The Late Alpine superimposed depressions in thе south-eastern part of the Balkan peninsula are structures of collisional-collapse type. They play a role of neoautochton which overlays a highly disintegrated Middle and Late Alpine orogen of collage-accretional character. It is represented by the Sredna Gora and Rhodope superunits. The superimposed depressions are of Palaeogene-Neogene age and are elements of a separate tectonic entity (Maritsa superimposed graben system) within the boundaries of the Balkanides-Anatolian segment of the Alpine mobile belt. The following three wide depressions on South Bulgarian territory are characterized in this paper: Upper Thrace Depression (UTD), East Rhodope Depression (ERD) and the East Thrace Depression (ETD). The Tertiary evolution of each depression is characterised by three up to five destructive stages. The Late Eocene and Oligocene stages are accompanied by an active polycyclic or monophase magmatism mostly represented by intermediate to acid volcanics. Ca-alkaline, subalkaline and alkaline magmas are distinguished. Basic volcanics of toleiitic, subalkaline to alkaline composition are rare. During the stages outlined, phenomena of compression or extension with exhumation are recorded. A number of important faults and fault zones formed during those stages, some of them being now represented by dike bundles. Essential overthrustings took place only along some faults of late Laramian and Savian age.
The Padala Formation represents the sedimentary filling of the Padala graben. It is built up mostly of polymictic breccia and conglomerate interbedded with thin sandstone beds containing coalefied plant debris and thin coal lenses. The formation is of Palaeogene age. The Padala Formation belonged to a larger Palaeogene basin, and was situated close to the source area of the terrigeneous material.
Volcanic rocks from the Eastern Rhodopes depression near to Bulgarian-Greek border are investigated. Six samples of basic altered rocks from 4 dykes and 2 larger bodies located into Kapinovo graben and Kushla volcano-tectonic structure are characterized. The K-Ar age of the basic dykes and small bodies is (31-32.5)±1.3 Ma and they are referred to the Early Oligocene (Rupelian). The time-span of the formation of the dykes corresponds as a whole to the time-span of the paroxismal volcanic events in the East Rhodope Volcanic Area.
Аn Algal detritus which is the basic rock-forming material is established in the organogeneous limestones among the coarse-terrigenous deposits of the Кrumovgrad Group of the Mandritsa depression to the South of Ivaylovgrad along the Kostilkovska river valley. А various foraminiferаl assemblage is found in these rocks consisting mainly of the representatives of the families of Lagenidae, Discorbidae, Miliolidae, Textulariidae, Rotaliidae, Acervulinidae, Linderinidae. These bioassociations аrе typical of the reef (marine shallow-depth) facies. They contain most of the bioelements of the co-assemblages of the intraplatfоrm facies of the Paleocene and the Early uр to Middle Еосеnе basins of the South Tethys. Furthermore, they аrе analogous to the assemblages described in the Upper Раleocene of the West Carpathians and the Middle and Upреr Paleocene in the Dinarides. Following these соmраrisons, the age of the coarse-clastic deposits along the Коstilkovo river valley could bе referred to the span Upper Paleocene - Middle Еосеnе. Thus, the presence of marine Lower Paleogene sediments is proven also in the West part of the East Thracian depression.
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