Sedimentological and geochemical interpretation of a transgressive sequence: The late Cretaceous Qahlah formation in the Western Oman Mountains, United Arab Emirates

The stratigraphic and palaeogeomorphologic conditions of the Qahlah Formation deposition in the United Arab Emirates are related to the geotectonic evolution of the western Oman Mountains during the Late Cretaceous. The Qahlah Formation ranges from a few metres to more than 70 m in thickness. It is the first sedimentary deposit to onlap the obducted Semail ophiolite, which was subjected to extensive weathering in a tropical environment during the Maastrichtian. Erosion accompanied the transgression of the Maastrichtian sea across the region. The sedimentary sequence can be divided into four facies: ophiolitic breccia, ophiolitic conglomerate, lateritic ferruginous siltstone and lithic sandstone. These sediments were probably formed in a shallow-marine to beach setting adjacent to a retreating cliff line of the ophiolite. A comparative analysis of the principal chemical and mineralogical components of the different facies indicates a genetic relationship between them. The nickel content (0.85-1-1.16 wt%) in the laterite facies is of economic interest as a low-grade ore provided that larger reserves can be identified.