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Regional Structure of the Western Black Sea Basin: Map-view Kinematics

Abstract

The opening of the Black Sea Basin appears far from being reasonably resolved. Various kinematic elements on the conjugate margins of the Western Black Sea, i.e. the Bulgarian, Romanian and Ukrainian margin in the NW versus the Turkish margin in the SE, appear to be a key in constraining the opening geometry of the basin. For example, the pre-rift structural fabric of the Romanian margin, well-known from the nearby onshore, has not been systematically followed into the deepwater part of the basin. In this study, the Capidava-Ovidiu Fault separating the Moesian Platform from Central Dobrogea is interpreted to dissect the Polshkov High in the deepwater part of the basin. The Polshkov High is a system of large syn-rift fault blocks located just basinward from a major breakaway normal fault trend. The Polshkov High trend has several structural culminations displaying contrasting extension polarity and fault spacing frequency. The along-strike change in the syn-rift structural pattern of the Bulgarian-Romanian margin, reflecting contrasting crustal rheologies inherited from pre-rift deformational episodes, should find its counterpart on the conjugate Turkish margin. A pronounced change in the structural trends in the Eregli Embayment is considered as the expression of a structural feature corresponding to the Capidava-Ovidiu fault system on the Turkish margin. Regional-scale correlation of 2D reflection seismic and well data and a critical review of the relevant onshore geology provided corresponding elements to constrain the kinematics of the basin opening. If the European margin is fixed in a kinematic reconstruction, the clockwise opening of the rift basin occurred along NW-SE trending transform faults around an Euler rotation pole positioned to the SW of the present Black Sea. The more prominent rotational element in the opening of the Western Black Sea basin, as opposed to the existing kinematic models is also supported by the broadly triangular shape of the oceanic crust imaged on recently acquired long-offset (10+ km) reflection seismic data. Contrary to previous models, with an Euler pole close to the SW corner of the Black Sea and using the well-defined, slightly curved southwestern edge of the Andrusov High and the Arkangelsky Ridge as a transform margin of the opening basin, we have not found a space problem in the map-view reconstruction of the basin opening.