Tectonostratigraphy and thrust tectonics of the central and eastern parts of the sivas tertiary basin, turkey
The Sivas Tertiary Basin is one of the central Anatolian basins that formed over the collision zone between the Pontides and the Anatolide-Tauride belts. The basin, which is floored by southerly obducted Neotethyan ophiolite sheets onto the Taurides during the Late Cretaceous time interval, occupies a key position in the sedimentary record of the continental collision processes. The central and easternmost parts of the Sivas Basin around the Hafik (Sivas) and Kemah (Erzincan) regions have been studied with respect to tectonostratigraphy, tectonic style, and kinematics. The tectonic style of the Sivas Basin is characterized mainly by polyphase thrust systems developed along a regional NNW-SSE shortening direction. The general transport directions are oriented toward the south and southeast. However, N-vergent thrust development in the late Oligocene and late Pliocene-Quaternary epochs occurred in the central part of the Sivas Basin where thrust propagation is controlled mainly by a decollement surface at the bottom of an Oligocene gypsum mass in the Hafik Formation. In the eastern part of the basin, thrust propagation is controlled by several decollement surfaces in the basin sequences. This study demonstrates that the central and eastern parts of the Sivas Basin experienced significant shortening, involving both basin deposits and basement. This contraction has been largely underestimated by previous studies, and the eastward-narrowing geometry of the basin can be related to an increasing amount of contraction toward the east. The age of thick gypsum-rich formations, previously attributed to the late Miocene, is now restricted to the Oligocene by consideration of both the stratigraphic relationships with lower Miocene shallow-marine formations and the geometry of the thrust systems. © 1996 Taylor & Francis Group, LLC.