Quantification of the Eocene–Oligocene transition in the Zagros Foreland Basin: Palaeogeographic control on sequence architecture and tectonic signal preservation

Abstract The Eocene–Oligocene boundary was a period of major global climatic and tectonic change, yet its expression in the Zagros Foreland Basin remains controversial due to complex facies relationships and the overprint of the Pyrenean orogenic phase. This study aims to resolve this stratigraphic enigma across three key sections using an integrated multi‐proxy approach combining biostratigraphy, geochemistry and mineralogy from 670 thin sections and 30 geochemical samples. The multi‐proxy approach provides independent, cross‐validated lines of evidence for interpreting depositional environments and sequence boundaries, moving beyond correlation based on lithostratigraphy alone. Results delineate two distinct boundary expressions. In the interior Fars, an erosional unconformity separates the Lutetian Orbitolites complanatus ‐ Coskinolina roberti ‐ Rhapydionina liburnica zone of the Jahrum Formation from the Rupelian Nummulites vascus ‐ N. fichteli zone of the Asmari Formation. In coastal Fars, a continuous transition is marked by the Late Eocene Turborotalia cerroazulensis ‐ Hantkenina zone of the Pabdeh Formation grading into the Rupelian Asmari. Geochemical data validate these models: the Pabdeh Formation shows high CaO and Sr. with low Al 2 O 3 , indicating a pelagic setting, while the Jahrum Formation has higher terrigenous proxies. SEM‐EDS confirms syngenetic dolomitisation in the interior platform and pyrite framboids in the basinal Pabdeh, indicating anoxia. A Monte Carlo sensitivity analysis confirms 97.3% confidence for the unconformity and 89.4% for the conformable interpretation. This work quantitatively demonstrates that a paleobathymetric gradient was the dominant control on sequence architecture, effectively neutralising the Pyrenean tectonic signal in deeper basinal settings. This framework provides a predictive model for stratigraphic correlation in foreland basins globally.