LATE CRETACEOUS TO PALEOCENE OROCLINAL BENDING IN THE CENTRAL PONTIDES (TURKEY)

The Turkish Pontide fold-and-thrust belt formed since the Paleozoic and is an important element in the Africa-Eurasia convergence and the resulting closure of the Neo-Tethys ocean. It has a peculiar arc-shaped geometry in its central part, along the Black Sea coast, which may have resulted from oroclinal bending. We have determined the vertical-axis rotation history of this area using paleomagnetism on Cretaceous to Eocene rocks from 47 sites and critically analyzed previously published data. We applied the same reliability criteria to all data.

Our results show that late Cretaceous sites have clockwise and counterclockwise rotations perpendicular to the structural trend in the central Pontides. In the eastern Pontides, they show only local rotations. Paleocene to Eocene rocks in the central and eastern Pontides show no rotation. We conclude that the central Pontide northward arc shaped geometry results from oroclinal bending in latest Cretaceous to earliest Paleocene times. The timing and scale of geological processes that occurred in the region make it likely that orocline formation resulted from Neo-Tethys closure between the Pontides and the metamorphic promontory of the Anatolide-Tauride Block.

Earlier studies on the southerly located Çankýrý Basin reveal that clockwise and counterclockwise rotations occurred in Eocene-Oligocene times. This implies that the entire region underwent continuous deformation from the late Cretaceous to the Eocene, caused by convergence of the Pontides and the Anatolide-Tauride block, with a southward moving deformation front. Deformation was first localized in the northern part of the central Pontides until the Paleocene, resulting in oroclinal bending, and from at least Eocene times it shifted toward the Çankýrý Basin region.