Contribution to the Paleozoic evolution of the recent Moesian platform

Abstract

The Paleozoic strata and in particular the Silurian and Devonian sediments of the platform are dipping at variable, not seldom, great angles (from 15-20° to 90°). Folds of different scale are observed in the drill cores. The following sedimentation discontinuities are established: between the Ordovician and the Silurian; in the Lower Devonian; within the Middle Devonian (two); beneath the Lower Carboniferous; beneath the Upper Visean; within the Lower Carboniferous (three); within the Upper Carboniferous (four); within the Permian (three). Some washouts had liquidated total some series and systems. The tectonic mobility of the region is witnessed by the great variations of the thickness (in the Carboniferous 0–3000 m, in the Permian 0–3500 m, etc.). By the facial features are proved: different depths and mobile bottoms during the Devonian, carbonate platform during the early carboniferous and alluvial plain – during the Late Tournaisian – Middle Visean, littoral sediments of the Upper Visean, subaquatic delta during the Early Carboniferous and alluvial plain – during the Late Carboniferous of Dobrudgea, proluvial remnants and conti nental basin during the Permian and a sebha in the region of Provadia. The presence of transitions in sedimentational environments of the same stratigraphic interval (Middle Devonian – Eifelian) is proved by rapid changes of conodont associations of the same age and of conodont models for bathymetric conditions. The mobility of North Bulgaria during the Paleozoic is confirmed very convincingly by the paleontological data for older sedimentary rocks positioned over younger ones in R-I Vaklino, R-120 Ograzhden, S-24 Nikola Kozlevo, R-3 Gomotarci and others. These relations can be explained only by the existence of folds and overthrusts. The driver of the mobility of the Moesian region is considered to be the movement to North (North-East?) of a Moesian terrane of Gondwanian origin - as long as it has been joined to the East-European platform during the Devonian. Later (Permian) deformations are the result of a collision with another terrane, the Balkan one, progressing from the South.