Quartz arenites and laterites in the Moesian Group (Upper Triassic), northwestern Bulgaria: possible evidence for the effect of the Carnian Humid Episode

Pages: 
pp. 3-25
Sofia University “St Kliment Ohridski”, 15 Tsar Osvoboditel Blvd, 1504 Sofia, Bulgaria
Abstract: 

Quartz-rich sandstones and ironstone crusts occur in the lowermost part of the Upper Triassic Moesian Group exposed in the western Balkanides. On the basis of performed field studies, micropetrography, X-ray diffraction, and major-element chemistry, these deposits are defined as first-cycle quartz arenites and laterites, respectively. The former were deposited in an alluvial environment, while the latter developed in gravel-dominated fluvial sediments. The main control on their formation was warm to hot humid climate conditions combined with low relief, quiescent tectonic setting, mixed source area, and slow sedimentation rate. The decreasing compositional maturity of the sandstones forming the Glavatsi Member (quartz arenites→feldsarenites→litharenites), the disappearance of the lateritic crusts upwards in the continental succession, and the presence of thick overlying fluvial and playa deposits in the Komshtitsa Formation (or Chelyustnitsa Formation) reflect gradual transition from humid to subhumid climate, and then to persistent semi-arid climate regime. This irreversible trend correlates with other Upper Triassic strata deposited in the Western Tethys realm and adjacent areas. The coeval formation of quartz arenites and laterites must have been related to the most distinctive climate change during the Triassic, i.e., the global Carnian Humid Episode. The new results and interpretations appear to be the first geological record for the effect of pronounced mid-Carnian humidity reported from Eastern Europe. They also present indirect sedimentological evidence for the stratigraphical range of the Moesian Group in NW Bulgaria.

Keywords: 

first-cycle quartz arenite, laterite, tropical humid climate, Carnian Humid Episode, Moesian Group, western Balkanides

VOLUME 46 (1)/July 2017

Geological Institute, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
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Babeş-Bolyai University, RO-400084, Cluj–Napoca, Romania
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Geological Institute, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
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Babeş-Bolyai University, RO-400084, Cluj–Napoca, Romania

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
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Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria
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Comenius University, Faculty of Natural Sciences, Department of Geology and Palaeontology, Mlynská dolina G–229, Ilkovičova 6, SK–84215 Bratislava, Slovak Republic
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Slovak Academy of Sciences, Institute of Earth Sciences, Dúbravská 9, P.O. Box 106840 05, Bratislava, Slovak Republic
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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, 1113 Sofia, Bulgaria
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Geological Institute, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
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BRGM, BP 6009, 45060 Orléans cédex 2, France
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Geological Institute, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria

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