Devonian stratigraphy, correlations and basin development in the Balkan Terrane, western Bulgaria

Devonian sediments in western Bulgaria occur in three specific Alpine tectonic units: the Svoge, Lyubasha-Golo bardo and Morava units. In the Svoge and Lyubasha-Golo bardo units, purely siliciclastic Lower and Middle Devonian rocks occur, whereas in the Morava Unit the Lower and Middle Devonian are represented by clayey limestones, shales and lydites. Stratigraphically important Lower Devonian fossils in the Svoge and Lyubasha-Golo bardo units include graptolites and tentaculitids, whereas in the Morava Unit, they include conodonts, graptolites, tentaculitids and plant macrofossils. The Lower Devonian in the Svoge and Lyubasha-Golo bardo units was deposited in a basinal facies setting, whereas the Lower Devonian in the Morava Unit represents an open shelf environment. From the Givetian until the end of the Devonian, a uniform deep basin developed throughout the Balkan Terrane, in which thick turbiditic succession was deposited. The Devonian sediments of the Balkan Terrane represent a continuation of marine development on the passive margin of peri-Gondwana and record the final pre-Variscan stage of basin evolution related to the closure of the Rheic Ocean. During the Early Carboniferous, the Lower Palaeozoic sediments of the Balkan Terrane were affected by the Variscan orogeny and covered by Upper Carboniferous and Permian continental molasse sediments.