Is the Black Sea really a back-arc basin?

The Black Sea is traditionally thought to be a back-arc basin with active rifting beginning in the middle Cretaceous. As to the magmatic arc associated with the southern margin of the basin, however, there are many open-ended questions regarding the nature, age of the arc, and even the polarity of subduction associated with the arc. Also, many models attempt to explain the formation of the Black Sea Basin in terms of geodynamic models of modern back-arc basin formation, in which extension is driven by slab roll-back. The age of rifting in the Western Black Sea (WBS) basin is still an unresolved issue. Whereas some suggested an Early to middle Cretaceous age (i.e., Barremian to Cenomanian) for the opening, others prefer a younger, Late Cretaceous age for the rifting, such as Turonian to Santonian, or Cenomanian to Santonian. Yet others recently described an unusually long rifting phase from the Barremian to the Santonian. The stratigraphic record of rifting on the conjugate margins of the WBS basin is markedly different. On the Turkish side, in the Pontides, a significant part of the synrift strata is missing either by erosion or by nondeposition. This is attributed to either uplift/erosion on a rift-shoulder, or to uplift/erosion due to collision to the south of the Central Pontides during Cenomanian-Coniacian times. On the conjugate Bulgarian, Romanian, and Ukrainian margin, the stratigraphic record of the Black Sea rifting is much more complete, indicating separate extensional periods for the Aptian-Albian, Cenomanian-Coniacian, and the Santonian-Campanian. The opening of the WBS Basin can be explained by asymmetric rifting at the southern margin of the European plate without invoking back-arc extension, at least for the first, wide-rift style phase of rifting during the Aptian-Albian. The subsequent Turonian-Coniacian narrow-rift style phase of rifting of the WBS basin may have been driven by subduction roll-back associated with the Pontides. Therefore only the extensional phase during the Cenomanian/Turonian to Coniacian(?) could be considered as a synrift opening period for a truly back-arc basin. The subsequent prolonged postrift subsidence is punctuated by arc volcanism along the southern margin of the WBS basin during the Campanian.