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Sofia University, Department of Geology, 15 Tzar Osvoboditel Bd., 1504 Sofia, Bulgaria (e-mail: gigeor{at}gea.uni-sofia.bg)
The first boreholes in the Tarnovo depression, located in the central Southern Moesian platform margin zone (Bulgaria), drilled at the end of the 1970s, display intervals of unusually thin, irregular and lens-like interbedding of shales and siltstones in the Middle Jurassic succession. Their specific lithological, log and seismic features, which resemble or distinguish them from contourites, have been studied and described in detail. The depositional setting in the Tarnovo depression during the Late Aalenian-Early Bajocian was favourable for the accumulation of deeper-water sediments, influenced by bottom currents. These were deposited along the hanging walls of major growth faults, which have a decisive geodynamic importance for Early-Middle Jurassic basin evolution throughout the Southern Moesian platform margin zone. Some lithological characteristics of the studied sediments correspond to diagnostic criteria for contourites. However, some other features, such as tractive indications, thin fine-grained laminae and wavy facies alternation, are also indicative of fine-grained turbidites and/or reworked bottom-current deposits.
