Kinematics of back‐arc inversion of the Western Black Sea Basin

Abstract

[1] 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 retreat of a mature slab, to a contractional basin, during high-strain collisional processes. Such a transition is observed in the Black Sea, where the accurate quantification of shortening effects is hampered by the kinematically unclear geometries of Cenozoic inversion. By means of seismic profiles interpretation, quantified deformation features and associated syn-tectonic geometries on the Romanian offshore, this study demonstrates that uplifted areas, observed by exploration studies, form a coherent thick-skinned thrust system with N-ward vergence. Thrusting inverted an existing geometry made up by successive grabens that were inherited from the Cretaceous extensional evolution. The shortening started during late Eocene times and gradually affected all areas of the Western Black Sea Basin during Oligocene and Miocene times, deformation being coherently correlated across its western margin. The mechanism of this generalized inversion is the transmission of stresses during the collision recorded in the Pontides-Balkanides system. Syn-tectonic sedimentation in the Western Black Sea demonstrates that this process was continuous and took place through the onset of gradual shortening migrating northward. Although the total amount of shortening is roughly constant in an E-W direction, individual thrusts have variable offsets, deformation being transferred between structures located at distance across the strike of the system. The Black Sea example demonstrates that the vergence and offset of thrusts can change rapidly along the strike of such a compressional back-arc system. This generates apparently contrasting geometries that accommodate the same orogenic shortening.

Geometry and Cenozoic evolution of the Crimean fold-thrust belt from cross-section balancing and kinematic forward modeling

“…The thin-skinned Sorokin accretionary wedge and the thick-skinned Crimean dome each yielded ~12 km of shortening. The total value, ~24 km, is higher than the one obtained by [Munteanu et al, 2011] for the northern Western BlackSea basin (see blue section line in Fig. 1, b); they estimated ~16 km of shortening during the late Middle Eocene-Pliocene.…”

“…There, thrusting inverted the Cretaceous rift margin of the Odessa shelf, causing ≤16 km shortening (Fig. 1, b) [Munteanu et al, 2011].…”

Cross-sectional anatomy and geodynamic evolution of the Central Pontide orogenic belt (northern Turkey)

“…Its doubly vergent geometry mainly resulted from the inversion of normal faults. Similar structural inversions seem to be common along the margins of the western Black Sea Basin during the Eocene-Miocene times, as suggested by seismic lines interpretations offshore Crimea and Romania (Khriachtchevskaia et al 2010;Munteanu et al 2011). In Turkey, our paleostress analysis, structural analyses and new stratigraphic ages provide new information on the timing and signification of the normal faulting and structural inversion events.…”

Petroleum geology of the Black Sea: introduction

“…Insights into the Cretaceous rift history of the Western Black Sea can be gained from an analysis of the successions in onshore and offshore Romania (Munteanu et al 2011;Krezsek et al 2017). Initial rifting occurred during the Aptian with the deposition of fluvial and lacustrine clastic successions and local marine carbonates.…”

“…Synrift sediments form reservoirs on the Romanian shelf (e.g. Lebada, Midia) where traps are created by Eocene inversion (Munteanu et al 2011) and, consequently, juxtaposition with Maykop Suite equivalent source rocks Cranganu & Saramet 2011). Synrift sandstones may be present in faulted culminations on the Shatsky and Andrusov ridges, and provide an alternative objective to the pre-rift carbonates currently targeted at Maria.…”