Provenance evolution of Oligocene–Pliocene foreland deposits in the Dezful embayment to constrain Central Zagros exhumation history

Abstract

This paper presents a detailed provenance analysis of the 6.5-km thick Oligocene-Pliocene foreland succession in the north Dezful embayment in Zagros, Iran. Using petrography, geochemistry, and paleoflow analysis, we determined three provenance shifts during the exhumation of Zagros orogen. Above the Ahwaz sandstones, sourced from the Arabian craton, a sharp decrease in SiO 2 /Al 2 O 3 , Zr/Sc, Th/Sc, Th/Co and Th/Cr within the Gachsaran Fm., and the appearance of first-cycle sands derived from metamorphic and volcanic rocks at the base of Aghajari Fm., characterize the onset of exhumation, rising topography and denudation of the Zagros orogenic system during latest Oligocene and constitute the first shift. The second shift, in middle Aghajari Fm., is marked by a distinct increase in radiolarian cherts and compatible/incompatible elements, indicating the exhumation of Neo-Tethyan radiolarite-ophiolite allochthonous slices in the High Zagros Zone during Tortonian (~9 Ma). A vast number of carbonates derived from nearby growing Izeh Zone anticlines characterize the Messinian (~7 Ma) Bakhtyari conglomerates marking the third shift. In conclusion, a detailed hands-on provenance analysis of the clastic sedimentary sequences in the north Dezful embayment enabled us to determine catchment areas and shifts hitherto unstudied thus contributing to the exhumation history of the Central Zagros orogenic system.

Detrital zircon provenance record of the Zagros mountain building from the Neotethys obduction to the Arabia–Eurasia collision, NW Zagros fold–thrust belt, Kurdistan region of Iraq

“…Such a basin setting suggests that the Razak Formation could be interpreted as an early foreland basin unit, at least during the Neogene. In either case, we emphasize that both the RBS and the Razak Formation are represent the deposits of the Arabia-Eurasia early-stage collision (Khadivi et al, 2012;Koshnaw et al, 2019;Etemad-Saeed et al, 2020).…”

“…These characteristics regarding the lithology and the timing of deposition suggest that the Razak Formation could correspond to the Govanda Formation and the Merga Group of the RBS. However, unlike the RBS in the Kurdistan region of Iraq, the Razak Formation seems to be more widespread geographically from the hinterland toward the foreland, and it appears in direct contact with the Asamri (Jeribe), Gachsaran (Fatha), and Aghajari (Injana) formations (Alavi, 1994;Khadivi, 2010;Etemad-Saeed et al, 2020).…”

“…Along-strike of the Zagros suture zone toward Iran, the potential equivalent of the RBS, the Razak Formation, appears not to be preserved in the Lurestan segment, but in the Dezful and Fars segments it has been documented (James and Wynd, 1965;Alavi, 2004;Khadivi et al, 2010Khadivi et al, , 2012Vergés et al, 2019;Etemad-Saeed et al, 2020). The Razak Formation shows a lithostratigraphy and a timing of deposition that are similar to the RBS, particularly in the hinterland.…”

“…4 and 5), and the RBS deposits overlay the Paleogene and older rocks in direct contact. However in the Dezful and Fars segments of the Zagros in Iran, where the development of the Paleogene proto-Zagros fold-thrust belt is limited (Hessami et al, 2001), the Razak Formation deposits occur in direct contact with the Neogene Zagros foreland basin deposits with no documented unconformities (James and Wynd, 1965;Khadivi et al, 2010;Vergés et al, 2019;Etemad-Saeed et al, 2020). Such a basin setting suggests that the Razak Formation could be interpreted as an early foreland basin unit, at least during the Neogene.…”

“…This research aims at constraining the basin dynamics recorded by the suture zone deposits and the wedge-top units, and the convergence history of the Arabian and Eurasian continental plates based on data established with the detrital zircon U-Pb and (U-Th) / He double-dating methods. The targeted NW Zagros hinterland deposits are the Red Beds Series (potential equivalent of the Razak Formation in Iran; Etemad-Saeed et al, 2020), which is situated below the Main Zagros fault, and the proto-Zagros Tanjero (Amiran), Kolosh (Amiran), and Gercus (Kashghan) formations, in the Kurdistan region of Iraq (Fig. 1b).…”