Magnetostratigraphy of Miocene–Pliocene Zagros foreland deposits in the front of the Push-e Kush Arc (Lurestan Province, Iran)

Abstract

The timing of the deformation in the Zagros Simply Folded Belt is poorly constrained because of the lack of an accurate absolute chronology of the syntectonic sedimentary sequences. The foreland basin infill at the front of the Push-e-Kush Arc is composed of fine-grained fluvial plain deposits (Agha Jari Fm.) and coarse conglomerates at the top of the section (Bakhtyari Fm.). A magnetostratigraphic study was carried out in a composite section spanning about 2800 m in order to date growth strata, and to constrain the timing of the deformation in the Mountain Front Flexure (MFF). Magnetostratigraphic correlation of the base of the Agha Jari Fm. with chron C5A yields an age of 12.8 to 12.3 Ma for this base. The transition to the conglomerates of the Bakhtyari Fm. correlates with the upper Gauss chron C2An at approximately 3 Ma. The deposition age of the top of the preserved Bakhtyari Fm. is extrapolated around the Pliocene–Pleistocene boundary. The base of the Agha Jari Fm. growth strata, and thus the beginning of the deformation in the front of the Push-e Kush Arc, is dated at 8.1–7.2 Ma. The topmost preserved Bakhtyari is folded in the NE flank of the Changuleh anticline and is unconformably overlying the SW flank of the Anaran anticline. This indicates that the tectonic deformation in the front of the Push-e-Kush Arc was active at least during 5 My. The MFF is a relatively long-lived structure active from 8.1 to 7.2 Ma to about the Pliocene–Pleistocene boundary, partly synchronous with the Changuleh anticline to the foreland. After MFF tectonic cessation, only the Changuleh anticline remained active.