Characteristic features and structural evolution of a post collisional basin: The Sivas Basin, Central Anatolia, Turkey

摘要

The ENE-SSW trending Sivas Basin is located at the easternmost wedge-like tip of the Central Anatolian Block and exhibits characteristics of two other basins, one in west-central Anatolia and the other in eastern Anatolia. The Sivas Basin started to form within a collisional mosaic during Maastrichtian time with the Pre-Maastrichtian basement, the latter composed of continental metamorphic rocks, Jurassic-Lower Cretaceous platform carbonates of the Tauride Belt, and ophiolites and ophiolitic melange derived from closure of the northern branch of Neo-Tethys. Similar Tertiary basins were developed on comparable collisional mosaics in other parts of Anatolia. The Sivas Basin is asymmetrical in both the longitudinal and transversal directions. Its infill is dominated by a thick Maastrichtian-Tertiary shallow marine-continental succession resting unconformably on Pre-Maastrichtian basement rocks and dissected into several subbasins. This infill consists of post-collisional deposits which overlie paleotectonic units unconformably and each subbasin is bounded by northeast-southwest trending oblique-slip faults exhibiting dominant strike-slip. The subbasins are characterized by contrasting stratigraphic successions, although all are composed of interstratified continental and shallow-marine facies. Both the northern and southern margins of the subbasins include Upper Eocene olistostromes containing mega-blocks of varied origin. The latter are sourced in paleotectonic units and were reworked in a shallow-marine depositional setting. The fill of the middle subbasins exhibits strong vertical and lateral facies changes, characterized by local and regional unconformities and includes continental to shallow-marine volcanic rocks. This basin was deformed under north-south-directed compression during Late Pliocene-Quaternary times during the neotectonic phase of deformation. This deformation divided the basin into new, small-scale, mainly pull-apart subbasins including those at Imranli, Ishani, Altinyayla and Sarkisla. From stratigraphic and structural correlations, a post collisional intra-continental basin model for the Sivas Basin is preferred.