Are there Middle Jurassic contourites in the Tarnovo depression (Southern Moesian platform margin)?
George Georgiev, Nikola Botoucharov, 2007. "Are there Middle Jurassic contourites in the Tarnovo depression (Southern Moesian platform margin)?", Economic and Palaeoceanographic Significance of Contourite Deposits, A. R. Viana, M. Rebesco
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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.
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There has lately been a growth in the number and level of studies of contourite deposits. Most recent studies of contourites have two major lines of interest. One, propelled by the oil industry's continuous move into increasingly deep waters, concerns their economic significance. The other involves the stratigraphic/palaeoceanographic record of ocean circulation changes imprinted on contourite deposits that can be a key to understanding better the climate-ocean connection. The application of many different theoretical, experimental and empirical resources provided by geophysics, sedimentology, geochemistry, petrology, scale modeling and field geology are used in the 16 papers of this volume, proposing answers to those two main aspects. The papers are subdivided into two major categories (economic interest and stratigraphic/palaeoceanographic significance), with case studies ranging from well-documented drifts to new examples of modern and fossil series, involving a large diversity of geographic and physiographic scenarios worldwide.