Trans-border ( east Serbia / west Bulgaria ) correlation of the Jurassic sediments : main Jurassic paleogeographic units

In the region across the Serbian/Bulgarian state border, there are individualized 5 Jurassic paleogeographic units (from West to East): (1) the Thracian Massif Unit without Jurassic sediments; (2) the Lu`nica-Koniavo Unit – partially with Liassic in Grsten facies and with deep water Middle Callovian–Kimmeridgian (p. p.) sediments of the type “ammonitico rosso”, and Upper Kimmeridgian–Tithonian siliciclastics flysch; (3) The Getic Unit subdivided into two subunits – the Western Getic Sub-Uni – without Lower Jurassic sediments and the Eastern Getic Sub-Unit with Lower Jurassic continental and marine sediments, which are followed in both sub-units by carbonate platform limestones (type Stramberk); (4) the Infra (Sub)-Getic Unit – with relatively deep water Liassic and Dogger sediments (the Dogger – of type “black shales with Bossitra alpina”) and Middle Callovian–Tithonian – of type “ammonitico rosso”; (5) the Danubian Unit – with shallow water Liassic, Dogger and Malm (Miro~–Vr{ka ^uka Zone, deep water Dogger and Malm (Donjomilanova~ko–Novokoritska Zone).


Introduction
During the Springer of 2005, a Serbian-Bulgarian team commenced bilateral research with the aim of making an effort to unify the views of Bulgarian and the Serbian geologists concerning the geology of the Jurassic on both sides of the Bulgarian/Serbian border.For the beginning, an attempt will be made to unify our opinions on the main paleogeographic units and subsequently new research on the lithostratigraphy and the correlation of Jurassic sediments from both side of the border will be performed.
During the Jurassic, from the Romanian Carpathians, the following main paleogeographic units can be prolonged in eastern Serbia: Thracian Massif Unit, Lu`nica-Koniavo Unit, Getic, Infra (Sub)-Getic, Danubian.They are more or less accepted by the Serbian geologists, but are not used in Bulgaria.These units, which are strictly paleogeographic and differ from the present day tectonic units, have a bipartite structure, built of two ensembles of beds -lower (the Lower Jurassic up to the Lower Callovian) and upper (the Middle Callovian-Tithonian). From the differences in these two parts, the main paleogeographic units in the studied region were reconstructed.
The Thracian Massif Unit (Fig. 1) The name Thracian Massif Unit is used for the paleogeographic unit which unifies the Rhodope Massif, the Serbo-Macedonian Massif and the Srbsko-Makedonska Masa (DIMITRIJEVI], 1992), etc.During the Jurassic, the Thracian Massif Unit played the role of source area and was never covered by sea water, and hence there are not marine sediments on it.For this unit (ANDJELKOVI] et al., 1996) used the name of Moravska Zone., 1996) as the tectonic structure Lu`ni~ka nappe (K-I) of the Karpatikum.In Bulgaria (TCHOUMAT-CHENCO, 2002) the name Jurassic Kraishtides is used for this unit.To avoid discordance between the meaning included by the different authors, the most neutral term of Lu`nica-Koniavo Unit is used here.

KRSTI], 2003
).In the Bulgarian literature, this paleogeographic unit is known as Dragoman Jurassic Horst (SAPUNOV et al., 1985).As a Jurassic paleogegraphic unit, the Getic finished in the region south of the town of Pernik on Bulgarian territory, where it is "cut" by the Thracian Massif Unit (its Rhodope part).
More uniform for the Getic Unit is the upper part (beds), which consist of Callovian-Upper Jurassic-Lower Cretaceous thick bedded carbonate platform limestones, in many places with coral reefs.However the lower part -the Jurassic sediments lying below these thick bedded bioclastic limestones is different in different parts of the Getic Unit.This permited the division of the Getic Unit into two sub-units: the Western Getic Sub-Unit with Middle Jurassic marine sediments and the Eastern Getic Sub-Unit with Lower and Middle Jurassic in the lower part.

The Western Getic Sub-Unit (Figs. 1, 2)
The Western-Getic Sub-Unit is situated to the East of the Lu`nica-Koniavo Unit.It is structured by two parts.The lower part is built up of Middle Jurassic shallow water sandstones and sandy and bioclastic limestones, which lie locally on continental Lower Juras-Fig.2. Stratigraphical section across the main Jurassic paleogeographic units in south-eastern Serbia and western Bulgaria.1, Continental clays and sandstones (Gresten facies); 2, sandstones; 3, black shales; 4, sandy and bioclastic limestones; 5, micritic limestones; 6, micritic limestones with chert concretions; 7, nodular and lithoclastic limestones (type "ammonitico rosso"); 8, thick bedded limestones (type "Stramberk"); 9, flysch type alternation of sandstone and clay; 10, interval with submarine break in the sedimentation; 11, interval with aerial break in the sedimentation (dry land conditions); 12, stratigraphic boundaries: a, transgressive; b, connected with submarine break in the sedimentation.sic clays and sandstones of Gresten facies.The upper part is built up of relatively thick bedded carbonate platform limestones, in the lower part with concretions of white chert and in the upper part by chert-free thick bedded shallow water bioclastic limestones.

The Eastern Getic Sub-Unit (Figs. 1, 2)
The characteristic for this paleogeographic unit (e.g. the section of Berende Izvor in western Bulgaria) is the presence of Lower Jurassic sediments upwards from the base: continental clay and sandstones, marine sandstones, bioclastic limestones and marls, interbedded by clayey limestones, and of Middle Jurassic black shales with Bositra alpina (facies well known in the Alps), followed by clayey limestones and marls, caped by a thin bed of sandy, crinoidal limestones.To West (e.g.near the town Slivnitsa), the Liassic is represented by irony red limestones, and the Dogger by sandstones and bioclastic limestones, similar to those in the Western Getic Sub-Unit.The upper parts are also similar to those of the Western Getic Sub-Unit -thick bedded limestones, in the base with concretions of white chert, and capped by chert free limestones.These sediments build the VidliM ountain in Serbia and are individualized as VidliS cale (KRAÜTNER & KRSTI], 2003), or Vidli~ka nappe (K-VII) (ANDJELKOVI] et al., 1996).In Bulgaria it is part of the Dragoman paleo-horst (SAPUNOV et al., 1985).