Tectono-sedimentary evolution of the Dehdasht structural basin (Central Zagros, Iran)

Abstract

This paper deals with the tectono-sedimentary evolution of the Dehdasht Basin, located at the boundary between the Izeh Zone and the Dezful Embayment, in the Central Zagros. The structural evolution of the basin is closely related to the coeval sedimentation of Neogene Fars Group foreland basin deposits. The analysis of five geological cross-sections reveals the interaction between tectonics, Gachsaran Formation diapirism and coeval sedimentation as well as the influence of hidden basement-involved faults. The great thickness of the Miocene Gachsaran evaporites contributes to the internal structure of the Dehdasht Basin as well as decouples the Competent Group structure at depth from the Passive Group structure cropping out at surface. The basin forms a synclinorium limited by high amplitude NW-SE trending anticlines filled with Neogene deposits. Its internal structure is characterized by relatively thin growth synclines-minibasins separated by Gachsaran diapiric ridges formed under a combination of shortening and diapirism. The amount of shortening across the basin ranges between 7.5 and 13.1 km (16–24%) whereas the restored preserved thickness of Gachsaran evaporites increases southeastwards from 2 to 2.85 km. This high thickness is interpreted as partly accumulated by gravity gliding from the rising surrounding anticlines. Observed changes in structural relief across and along the Dehdasht Basin suggests its development above an array of hidden and linked basement faults including segments of the Mountain Frontal Flexure with NW-SE Zagros trend under the northern and southern boundary anticlines and a transfer fault with N-S Arabian trends at the SE border. The observed structural variations both along-strike and across the Dehdasht Basin at a local scale are similar to those already found at larger scales along the major Kazerun Fault Zone.