In this paper, we focus on the sedimentology and tectonic controls on the formation of cherty ironstone hosted in the Early Eocene Naqb Formation exposed in the northern part of the Bahariya Depression (Egypt). This rock unit (up to 13 m thick) is composed of two carbonate sequences separated by a paleokarstic surface. The Naqb Formation was deposited on a shallow-water platform with intertidal, shallow subtidal and oolitic shoal facies. Dominant organisms in these environments comprise larger benthic foraminifera (nummulites, alveolinids, miliolids, orbitolites), dasycladacean algae, mollusk shells and some echinoids whereas the nonskeletal grains are mostly of ooids, oncoids and pelloids. The two carbonate sequences have undergone extensive diagenetic processes, the most important of which are the karstification, dolomitization, silicification, barite formation and Fe/Mn accumulation.