Petrological and geochemical constraints on provenance, paleoweathering, and tectonic setting of the Cambro-Ordovician Khabour Formation, western and northern Iraq

Petrographic descriptions and point counting data, supported by SEM analysis, are presented for 89 sandstone samples of the Khabour Formation from the Khabour, Ora, Chalki Nasara, and Chia Zinnar outcrop sections in northern Iraq. These are compared with previously published data for subsurface samples from the Akkas-1 and Akkas-3 wells in western Iraq. Petrographic observations revealed that sublitharenites and subarkoses form the main sandstone types and may suggest a granitic source region with minor input from metamorphosed sediments. This is supported by the geochemical analysis gained from 66 sandstone samples. Chemical Index of Alteration (CIA) and Index of Chemical Variability (ICV) values along with A-CN-K trends, and Th/U versus Th relationships suggest moderate weathering and humid climatic conditions in the source area. The paleoclimate geochemical proxies are supported by clay mineral associations revealed by XRD and SEM data. Up-section trends in Rb/Sr values imply that humid and dry conditions prevailed during the deposition of the Khabour succession. The Khabour Formation sandstones were deposited in a passive margin setting; however, their ultimate origin is likely to be recycled orogen and continental block provenances with stable craton sources and with uplifting in the basement complexes