Microfacies analysis of Wadi Waqb member (Miocene) in Wadi Aynunah, Northwest of Saudi Arabia

Easier access to most of spectacular sedimentological features of Midyan region along the northern coast of Red Sea has enabled a more detailed examination of the Miocene succession that could not have been possible except from deep subsurface drilling. The Wadi Waqb member of Jabal Kibrit Formation hosted the Wadi Waqb reservoir in this region. In this study the microfacies of the exposed discontinuous fringing rhodolith and coral reef complex of Wadi Waqb member that seated unconformably on steep cliffs of granitic basement are investigated. Four microfacies were recognized as follows: MF-1) Quartz-peloid packstone and Red algal bioclastic boundstone, MF-2) Bioturbated rhodophyte-bioclastic grainstone, MF-3) Calc-allochemic sandstone, and MF-4) Intraclastic wackestone. Microfacies 1 and 2 are considered to be deposited at the upper and mid reef front. The depositional environment of the MF-3 is considered to have occurred in periodical flash floods and microfacies 4 is considered to be a lower reef front deposit. Careful microfacies analysis of mixed reefal carbonate and siliciclastic deposits provides a better understanding of how and why carbonate microfacies develop.