Matrix deformation and fracture network in minibasins in a foreland fold and thrust belt: The Sivas Basin, Turkey

Abstract

We use a multiscale study to investigate the strain record in the continental sandstones-filled minibasins of the Sivas Basin. Located on the central Anatolian Plateau, the Sivas basin is a foreland fold-and-thrust belt characterized in its central part by a wall and basin province in which two generations of Oligocene minibasins develop. We collected 399 oriented cores and 2504 fractures in the lower and middle members of the continental Karayün Formation from four minibasins (Emirhan, Karayün, Egribuçak and Ilkindi). Integrated analyses support several observations: (i) an early fracture set, striking NS, occurs in all minibasins. These fractures developed prior to macroscopic halokinetic structures formation (such as megaflap) and prior to minibasin tilting, during Layer Parallel Shortening (LPS). (ii) A preferential orientation of matrix texture, estimated using anisotropy of magnetic susceptibility, is related to the LPS direction only in the Emirhan minibasin. (iii) A second, younger, fracture set, oriented parallel to the tilting axes of the minibasins and to the thrust faults, developed prior to minibasin tilting or folding of minibasin edge structures (known as megaflaps, megahooks and composite halokinetic sequences). The existence of the carapace above raising salt bodies enables the propagation of the LPS deformation in response to regional shortening. However, once the carapace is broken due to the salt rise, there is no evidence of deformation at the meter and matrix scales in relation with FTB shortening affecting the wall and basin domain. The large bodies of evaporites preferentially accommodate compression in between minibasins through internal diapir squeezed. Salt bodies inhibit matrix and mesoscale deformation within the minibasins.