The forgotten salt basin: Sivas Basin, Turkey

Located in the center of the Anatolian Plateau in Turkey, the Tertiary Sivas Basin was built after the closure of the northern Neotethys oceanic domain from Upper Cretaceous to Pliocene times. It developed over an ophiolitic basement obducted from the north during the Late Cretaceous, initially separating the Kirshehir continental block from the Taurus microplate. During the Paleogene, the onset of the Tauride compression resulted in the development of a foreland basin within the Sivas domain, affected by north-verging thrusts reworking the foreland sequence and ophiolitic sheets. The flexural deepening of the basin resulted in the accumulation of a thick marine turbiditic succession in the foredeep area, followed by a rapid shallowing and the deposition of a thick evaporitic sequence during the late Eocene. This very special episode allowed for a second youth of the basin. Although studied for a quite long time, the Sivas Basin was indeed recently revisited as being likely the world’s finest open-air museum of salt tectonic structures. Despite huge difference with respect to known salt provinces, the Sivas basin provides outstanding outcrops of the classic geometries associated to the development of diapirs, i.e. halokinetic sequences along diapir walls, and associated stratal deformations, and more exotic structures such as bubble shaped minibasins, megaflaps and evaporites allochtonous glaciers and canopy. We will here review some of the results obtained thanks to a 5 year long project, during which the basin was dissected at the metric scale by a team including four PhD students to handle (1) the detailed mapping of a 60x30 km² domain, (2) the coupled tectono-sedimentary analysis of the central, salt-controlled area, (3) decipher the complex and recurrent story of evaporite reworking and redeposition, (4) incorporate some matrix scale observations, and eventually (5) integrate the Sivas story within the Tethyan domain evolution. More generally, this fairy tale was also an opportunity to critically review the processes of geologic knowledge acquisition, basically here the trial and error game of building a coherent story, even based on fantastic outcrops.