Variation of structural style and basin evolution in the central Zagros (Izeh zone and Dezful Embayment), Iran

Abstract

Structural style, and its relationship to sedimentary facies and the evolution of sedimentary depocenters since Late Cretaceous times have been studied, on the basis of one regional balanced transect and several updated isopach maps, in the Izeh zone and the Dezful Embayment, central Zagros. This study relies on fieldwork data, existing geological maps, seismic data and well information. A new structural classification for part of the Zagros sedimentary cover is presented to highlight the different mechanical behavior of the formations in the stratigraphic column. It shows the existence of several local decollement levels activated during folding. These decollement levels separate lithotectonic units, which accommodate shortening in different ways. The Lower Paleozoic is the basal decollement level throughout the studied area. Triassic evaporites, Albian shales, Eocene marls and Miocene evaporites can act as intermediate decollement levels, and present variable facies in the Central Zagros. Lateral facies and thickness variations, the sedimentary overburden and the close relationship with inherited fault patterns influenced the wavelength, amplitude and style of folding in the study area. Furthermore, surface structures do not necessarily coincide with deeper objectives where these disharmonic levels are involved in folding. The evolution of sedimentary depocenters from the Late Cretaceous (obduction episode) until early Miocene collision is described, based on updated isopach maps and tectonic subsidence curves. This analysis shows continuous compression and movements along N–S and NW–SE trending faults in the Zagros basement which predate the Neogene Zagros folding and influence sedimentation history. It also indicates a southwestward migration of the depocenters through time, in addition to the basement involvement below some folds during the Zagros orogeny.