New data on the stratigraphy of the Middle Jurassic siliciclastic rocks from the West Balkan Mountains (West Bulgaria)

Pages: 
pp. 35-56
Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria
Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria
Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria
Department of Geology, Palaeontology and Fossil Fuels, Faculty of Geology and Geography, Sofia University “St Kliment Ohridski”, 15 Tsar Osvoboditel Blvd, 1504 Sofia, Bulgaria
Institute of Mineralogy and Crystallography, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 107, 1113 Sofia, Bulgaria
Abstract: 

The present study is a contribution to the lithostratigraphy of Middle Jurassic strata in the area of the Zimevitsa Plateau (West Balkan Mts, West Bulgaria). Based on its lithological and regional properties, the Dobravitsa Member is distinguished from the surrounding rocks of the Etropole Formation. The new member consists of alternating shales, siltstones and fine-grained sandstones. It also contains abundant siderite and calcite concretions, which are distributed in discrete stratigraphic horizons in both the mudrocks and coarser lithologies. Fossils are extremely rare. Poorly preserved ammonites and belemnites are found only. Based on several ammonite finds, the Dobravitsa Member of the Etropole Formation is assigned to a narrow stratigraphic interval of the lower Bajocian (unlimited, probably lower part of the Witchellia laeviuscula Zone). Although it has restricted lateral distribution, which is exclusively confined to its type-area, the Dobravitsa Member has a proper place in the formal Bulgarian Jurassic lithostratigraphic scheme, as it represents a discernible atypical development of the Etropole Formation in the West Balkan Mts region. Another emphasis of this study is laid on concretions from the Etropole Formation. Besides siderite and calcite concretions, a few examples of iron oxyhydroxide concretions, from localities outside the Zimevitsa Plateau area, are also described. The latter are also an atypical component of the Etropole Formation, which deserves a further special study and systematization, as it implies unknown history of this lithofacies, in both depositional and diagenetic terms.

Keywords: 

Middle Jurassic, siliciclastic rocks, stratigraphy, concretions, Bulgaria

DOI: 
10.52321/GeolBalc.51.1.35

VOLUME 51 (1)/April 2022

Institute of Earth Sciences, Ilia State University, 77 Ntsubidze Str., 0177 Tbilisi, Georgia
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Faculty of Mining and Geology, Georgian Technical University, Kostava Str., 0175 Tbilisi, Georgia
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Institute of Earth Sciences, Ilia State University, 77 Ntsubidze Str., 0177 Tbilisi, Georgia
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Faculty of Mining and Geology, Georgian Technical University, Kostava Str., 0175 Tbilisi, Georgia

Geological Institute Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria
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Geological Institute Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria

Department of Geology, Palaeontology and Fossil Fuels, Faculty of Geology and Geography, Sofia University “St Kliment Ohridski”, 15 Tsar Osvoboditel Blvd, 1504 Sofia, Bulgaria
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Geological Institute of Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria
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Department of Mineralogy, Petrology and Economic Geology, Faculty of Geology and Geography, Sofia University “St Kliment Ohridski”, 15 Tsar Osvoboditel Blvd, 1504 Sofia, Bulgaria

Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria
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Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria
|
Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria
|
Department of Geology, Palaeontology and Fossil Fuels, Faculty of Geology and Geography, Sofia University “St Kliment Ohridski”, 15 Tsar Osvoboditel Blvd, 1504 Sofia, Bulgaria
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Institute of Mineralogy and Crystallography, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 107, 1113 Sofia, Bulgaria