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Tectonics of the Western Black Sea back-arc basin as reveled by the architecture of its sedimentary fill

Abstract

Architecture of the sedimentary basin fill is the reflection of the tectonic processes that created, enlarged and subsequent close the sedimentary basin. Depicting the geometry and litho-stratrigraphy of the basin fill can provide useful insights for the tectonic evolution of both the basin and the adjacent orogen where the direct observation is hamper by uplift and erosion, such as in the case of back-arcs domains.

Back-arc basin evolution is driven by processes active at the main subduction zone typically assuming the transition from an extensional back-arc, during the roll-back of a mature slab, to a contractional basin, during high-strain collisional processes. An similar type of transition is observed in the Black Sea Basin, from an extensional domain during Cretaceous-Early Plaeogene as an consequence of the roll-back associated with the N-ward subduction of Neothetys under the Rhodope-Pontides Arc, and was gradually inverted during Late Paleogene-Pliocene times after the collision between Pontides and Taurides continental units.

The Cretaceous-Paleogene extension resemble in an series of graben, tilted block and prograding passive margin like structures, with associate wedge shape geometry of the syn-extensional sediments. These deposits are younger in age towards the basin center, demonstrating the migration of extension from basin margin, offshore Romania-Ukraine shelf in the North and onshore Pontides in the South, towards basin center, offshore Bulgaria and Turkey. These extensional geometry plays and important role in the subsequent inversion, which transform the Black Sea into an compressional back-arc basin.

The shortening started during late Eocene gradually affected all areas of the Western Black Sea Basin during Oligocene and Pliocene times as reveled by syn-tectonic sedimentation, on its western margin. In terms of sediments lithology this marks an shift form carbonatic passive margin to and clastic “foreland” like sedimentation, such as in the case of Kamkya (Late Eocene-Lower Miocene) and Histria (Oligocene-Upper Miocene) depressions. The mechanism of this generalized inversion is the transmission of strain from the collision recorded in the Pontides-Balkanides orogens into the back-arc basin.

The architecture of the “anomalous” thick uppermost Miocene-Pliocene sedimentary pile on the north-western part of the basin, is the result of the combine far field effect of the tectonic process taking place into the Carpathian Orogen, and the continuous subsidence in the Western Black Sea center.