Unravelling Tectono‐Eustatic Dynamics in Jurassic Mixed Siliciclastic–Carbonate Systems: A Benthic Foraminiferal Record From the Binalud Tethyan Gateway, <scp>NE</scp> Iran

ABSTRACT Fossil benthic foraminifera are essential proxies of Jurassic marine environmental change, yet their distribution and palaeoecological significance across northeastern Iran remain insufficiently understood. This study presents a detailed, high‐resolution quantitative investigation of Middle‐Upper Jurassic (Bajocian‐mid Tithonian) benthic foraminiferal assemblages from the Dalichai Formation recorded at the Baqi section of the Binalud Mountains. The analysis integrates foraminiferal data with microfacies characteristics to reconstruct palaeoenvironmental evolution and relative sea‐level history within the northern Tethyan margin. Fifty species representing twenty‐seven genera and organised into twelve foraminiferal morphogroups were identified, defining seven successive ecostratigraphic intervals (A‐G) that mark distinct ecological and depositional stages. Interval A (Bajocian) represents a shallow‐neritic, reduced‐salinity environment dominated by agglutinated taxa. Interval B, a red‐shale bed at the Bajocian‐Bathonian boundary, corresponding to the Ammonitico Rosso facies, records a rapid transgressive pulse linked to early rifting. Interval C and D (Bathonian–lower Oxfordian) capture maximum deepening, with pelagic and gravity‐flow deposits associated with horst‐and‐graben formation and an abrupt diversity decline. Interval E (upper Oxfordian‐lower Kimmeridgian) reflects partial shallowing and renewed agglutinated dominance. Interval F (Kimmeridgian) demonstrates open‐marine, oxygen‐rich conditions with abundant calcareous epifauna. And Interval G (upper Kimmeridgian‐mid Tithonian) indicates progressive shallowing and enhanced siliciclastic delivery. The reconstructed sea‐level curve reveals a major transgression from the Bajocian to early Oxfordian and regression from the Kimmeridgian to Tithonian, broadly conforming to global eustatic trends but punctuated by tectonically induced fluctuations. This integrated approach refines our understanding of Jurassic sequence development in the Binalud Basin and underscores the ecological response of benthic foraminiferal communities to coupled eustatic and tectonic controls within the marginal Tethyan system.