Transect VII begins in the East-European craton.It crosses the Scythian platform, North Dobrogea, the Stara-planina (Balkan)Range, the Srednogorie and East Rhodope. Then, it continued through the Aegean Sea, Crete, across the Eastern Mediterranean, and ends in Libya(Cyrenaika).The section crosses parts of 6 countries: Ukraina,Moldova, Romania, Bulgaria, Greece and Libya.
The team is composed of Hassan Barghathi, Christo Dabovski, Radu Dimitriu, Georgi Georgiev, Ahmed El-Hawat,Dumitriu Ioane, Haralambos Kranis, Adel Obeidi, Cheorghe Oaie, Dimitrios Papanikolaou, Antoneta Seghedi and Ivan Zagorchev. The work is coordinated by Dimitrios Papanikolaou.The Bulgarian activities are sponsored by the Bulgarian Academy of Sciences and by the Ministry of Environment and Waters under the project 204 "Geological Trans-border Sections and Itineraries".
Transect VII - Bulgaria. Tectonic/geodynamic cross section
Authors: Christo Dabovski, Ivan Zagorchev, Georgi Georgiev with the participation of Aleksander Velev
Information Sources: The sources of information are mostly bearing on the surface geology (results of geological mapping on the scale 1:25000 shown on maps on the scale 1:100000
and 1:500000; Committee of Geology. 1989-1995). The Moho discontinuity is deduced on the basis of complex gravimetric (gravity map on 1:200000) and seismic information as previously published by Petkov, Velchev and Dachev, and revised by Dachev (1988) and Boykova (2000).
The deep structure is inferred also on the basis of the deep seismic profiling along the lines Rouse-Madan-Thassos (Vol'vovskyi et al., 1992) and Ivaylovgrad-Ardino,some seismic sections and the deep borehole Pchelinovo. The deeper parts (Moho depth, lithospheric thickness) are inferred from seismological and gravimetric studies (Babuska et al., 1986; Volvovsky, 1987; Volvovsky and Starostenko, 1996).
Description of tectonostratigraphic and lithostratigraphic units: The following description (C.Dabovski, I. Zagorchev) is based mostly on Boyanov et al. (1989) and Dabovski et al. (2002). The transect crosses through the Moesian platform and the Fore-Balkan, Stara-planina (Balkan), Srednogorie and Morava-Rhodope zones. It crosses through a number of Late Alpine (Palaeogene) and Neogene-Quaternary block structures (horsts and grabens).
Description of tectonostratigraphic and lithostratigraphic units
The Moesian platform exhibits on the surface only Cretaceous and younger complexes usually buried beneath Neogene cover and Quaternary loess. The oldest sediments crossed by the boreholes belong to the Devonian. Several unconformities reflect partial uplift and erosion throughout the Mesozoic and Cenozoic history. In the basement, Devonian shales and carbonates, and (locally), Carboniferous coal-bearing formations (Dobroudzha basin) are covered by Permian red beds. The cover contains:
(a) continental Lower Triassic followed by Middle Triassic to Norian carbonates, and Carnian to Norian marine red beds;
(b) terrigenous and carbonate Jurassic, the marine transgression over the deeply eroded Triassic beginning often directly with Middle Jurassic;
(c) Upper Jurassic Lower Cretaceous carbonate sequences;
(d) Upper Cretaceous shallow-marine carbonate and terrigenous deposits, and continental or marine Palaeogene; (e) locally Badenian to Pontian Neogene marine sediments belonging to a transitional zone between the Central and Eastern Paratethys.
The Fore-Balkan is a transitional zone between the Balkan fold belt and the Moesian platform. The transitional character is indicated both by the lower degree of deformation, and by the transitional Alpine facies. In the eastern parts of the zone, the Triassic and Jurassic rocks are deeply buried beneath the Cretaceous and Palaeogene (partially) cover.
Choudnite-steni dislocation Balkan (Stara-planina) zone
The Stara-planina zone is poorly exposed along the transect. It is characterized with a north-verging thrusting and folding in pre-Late Eocene times. The zone includes pieces of units with Mid-Cretaceous and Late Cretaceous folding. The following complexes are distinguished:
(a) pre-Ordovician volcano-sedimentary complexes of island-arc and (partially) oceanic signature;
(b) Palaeozoic (Ordovician to Carboniferous) sedimentary formations intruded by Carboniferous granitoids;
(c) Permian red beds;
(d) a Triassic Peri-Tethyan sequence ending with folding and covered with unconformity by
(e) a Lower Jurassic to Kimmeridgian Peri-Tethyan sequence covered by
(f) a Callovian to Berriasian flysch and Lower Cretaceous carbonate sequence;
(g) Upper Cretaceous shallow-water carbonate sequence; (h) Danian to Middle Eocene continental and shallow-marine sediments; (i) unconformable Upper Eocene molasse.
Emine flysch, Cretaceous/Palaeocene boundary,East Balkan
East Balkan (Kotel) zone
The Kotel zone is characterized with a peculiar sequence that is considered to be of Tethyan signature, and of possible rift origin. Lower Triassic flyschoid sediments are followed by Middle Triassic carbonate of "ammonitico rosso" type, and at least three different types of Upper Triassic (Carnian to Rhaetian): reefs, marly flyschoid sequence with intraolistolites, and coarse "black flysch". Most of these facies are present as huge to gigantic exoolistolites within the Lower Jurassic flysch. The main deformation of this terrain occurred in Middle to Late Jurassic times, and the whole section is sealed by unconformable Upper Cretaceous mature sediments typical also of the Balkan zone. The whole structure of the Jurassic Matorides is reworked in the north-verging Balkanides (Stara-planina zone).
The Srednogorie zone is regarded as a volcanic island arc of Late Cretaceous age, transformed by north-verging folding and thrusting in latest Cretaceous times in an orogen, and later thrusted North over the Stara-planina zone. The following complexes are distinguished: (a) slivers and rootless bodies of ultramafic (ophiolitic?) character and mantle (or oceanic crust) origin (parts of the Precambrian Prerhodopian Supergroup); (b) principal mass of the Precambrian Prerhodopian Supergroup that represents typical continental crust of granitic composition (migmatites, gneisses, metagranites); (c) greenschist-facies formations of Palaeozoic age occurring in the Sveti-Iliya Hills; (d) granitoid plutons of Carboniferous age (determined with Rb-Sr whole-rock isochrones at 340, 320-300 and 280-240 Ma) and mixed (I-type) and continental crustal signatures; (e) Triassic and Jurassic sedimentary complexes with Peri-Tethyan (Balkanide) signature; (f) Upper Cretaceous sedimentary formations represented by coal-bearing continental to shallow-marine Cenomanian and Turonian, terrigenous to carbonate marine Coniacian, pelagic carbonates and shales, locally with radiolarites (Santonian Campanian) and Lower-Middle Maastrichthian flysch; (g) Cenomanian? to Early Maastrichthian volcanics (from pikrites and basanites to andesites and latites), in a volcano-plutonic association with gabbro to monzonites and granodiorites of mantle signature; (h) Danian conglomeratic formation of fluviolacustrine origin that contains well-rounded pebbles from all older rocks.
Lisovo syncline and Konstantinovo shear zone
The Sakar unit consists of the following complexes: (a) slivers and rootless bodies of ultramafic (ophiolitic?) character and mantle (or oceanic crust) origin (parts Botourche Group, - of the Precambrian Prerhodopian Supergroup); (b) principal mass of the Precambrian Prerhodopian Supergroup that represents typical continental crust of granitic composition (migmatites, gneisses, metagranites); (c) igneous bodies of granitic composition and Palaeozoic (including Cadomian - c. 500 Ma, Rb-Sr whole-rock isochron) and Late Cretaceous age, in most cases bearing the signature of recycled and molten older continental crust; (d) metasedimentary cover of Carboniferous?, Permian? and Triassic age that suffered a Jurassic? amphibolite-facies metamorphism. The age of the Triassic metasediments is determined with bivalves, brachiopods and conodonts. The age (123-136 Ma) of the superimposed amphibolite-facies metamorphism is determined with K-Ar studies on biotite.
The Rhodope massif is a lenticular non-homogenous body of continentalcrust. The section crosses the East-Rhodope unit. On the surface, it consists of the following principal complexes: (a) slivers and rootless bodies of ultramafic (ophiolitic?) character and mantle (or oceanic crust) origin (parts Botourche Group, - of the Precambrian Prerhodopian Supergroup);(b) principal mass of the Precambrian Prerhodopian Supergroup that represents typical continental crust of granitic composition (migmatites, gneisses,metagranites); (c) products (flysch-like sedimentary sequences, volcanogenic sequences, platform carbonates) of a Precambrian island arc (Rhodopian Supergroup); (d) igneous bodies of granitic composition and Palaeozoic and Late Cretaceous age, in most cases bearing the signature of recycled and molten older continental crust; (e) non-metamorphic sedimentary and volcanic cover (depositional unconformity over the older complexes a d and f) of Palaeogene age (and in deeper parts of the section, unroofed Palaeogene monzonites and granitoids belonging to a Palaeogene volcano-plutonic association), and sedimentary cover of Neogene age; (f) the complexes (a-d) are covered with tectonic contacts (thrusts) by Mesozoic (Triassic Jurassic) formations that belong to the Circum-Rhodope belt.