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 Fo rmation deposition in the United Arab Emirates are related to the geot ectonic evolution of the western Oman Mountains during the Late Cretac eous. The Qahlah Formation ranges from a few metres to more than 70 m in thickness. It is the first sedimentary deposit to onlap the obducte d Semail ophiolite, which was subjected to extensive weathering in a t ropical environment during the Maastrichtian. Erosion accompanied the transgression of the Maastrichtian sea across the region. The sediment ary sequence can be divided into four facies: ophiolitic breccia, ophi olitic conglomerate, lateritic ferruginous siltstone and lithic sandst one. These sediments were probably formed in a shallow-marine to beach setting adjacent to a retreating cliff line of the ophiolite. A compa rative 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 ec onomic interest as a low-grade ore provided that larger reserves can b e identified.