CENOZOIC PERIPHERAL FORELAND BASIN DEVELOPMENT IN THE BITLIS-ZARGOS OROGEN, DUHOK, IRAQI KURDISTAN

The northwestern Zagros orogen represents the multistage collisional history associated with late Mesozoic-Cenozoic convergence of the Arabian and Eurasian continents and final closure of Neotethys. Sedimentologic, provenance, and chronostratigraphic data from the Cenozoic sedimentary rocks in the Duhok province of northern Iraq indicate the multiphase development of a peripheral foreland basin upon the Mesozoic northern Arabian passive margin platform, and provide new insights into the controls on Cenozoic basin evolution in the Iraqi proto-Zagros and Zagros systems. The Paleocene to middle Eocene Kolosh-Khurmala-Gercus sedimentary succession records the transition from deep marine to platform and non-marine siliciclastic deposition in a southward migrating foredeep, and is overlain by the middle to upper Eocene lagoonal carbonates of the Pilaspi Formation. Petrographic data and detrital zircon U-Pb and (U-Th)/He ages suggest that the Paleogene siliciclastic succession was primarily derived from a Cretaceous island arc and ophiolitic-radiolarian thrust-sheet complex that was obducted onto the northern Arabian margin and exhumed by ~75 Ma. Detrital zircon U-Pb ages also indicate detrital input from the Pan-African belt and Arabian-Nubian shield in the southwest and Triassic-Jurassic volcanics. Prior to Kolosh Fm. deposition, the Mesozoic Arabian passive-margin siliciclastic sediments in Duhok were sourced exclusively from the Pan-African and Arabian-Nubian terranes. Pronounced sea level fall at the Eocene-Oligocene transition produced a regional unconformity in northern Iraq that spans ~10-15 Myr. The middle-early Miocene (~18 Ma) is marked by paleosol and the onlap of widespread basal conglomerates upon the Oligocene unconformity followed by a shallow-marine incursion (Lower Fars). This renewed phase of basin subsidence coincides with influx of siliciclastic sediments from various Eurasian source terranes in southeastern Turkey and Iran, reflecting the onset of Arabian-Eurasian collision. A transition from marine to non-marine fluvial sedimentation of the Upper Fars and Lower Bakhtihari Fms. by ~12 Ma is coupled with diversification in Eurasian provenance signal and temporally correlates with the widespread development and uplift of the Eastern Anatolian Plateau to the north.