Ironstone deposits hosted in Eocene carbonates from Bahariya (Egypt)—New perspective on cherty ironstone occurrences

Nummulite biostratigraphy of the Eocene succession in the Bahariya Depression, Egypt: Implications for timing of iron mineralization

“…This was clearly demonstrated by Afify et al (2015b) for the dolostones of the Naqb Formation. Moreover, recognition of replacement and/or cementation of the carbonate deposits of the Qazzun and El Hamra formations by the same assemblage of FeeMn minerals strongly suggests that the whole set of Eocene deposits were affected by a unique hydrothermal event sourcing iron-rich fluids.…”

“…Likewise, the ironstone succession is formed of two sequences (Fig. 6A), where the Fe-Mniron-rich rocks show clear evidence for replacement and/or cementation of the carbonate fabrics by FeeMn minerals (Afify et al, 2015b). Some unaltered thin clay/marl beds occur intercalated with the ironstone rocks ( Fig.…”

“…Interpretation: The carbonate deposits of the Naqb Formation were accumulated in shallow depositional environments, from shallow subtidal to intertidal-supratidal (Afify et al, 2015b). The low diversity of fossil assemblages (e.g., nummulitids, alveolinids, textulariids, and dasycladacean algae) in the lower sequence could be interpreted as characteristic of oligophotic inner-to mid-ramp environments, preferably at water depth ranging from 40 to 80 m (Hottinger, 1997;Beavington-Penney and Racey, 2004) with random scatter of nutrients where the nummulitids preferred lower nutrient levels (Bassi et al, 2013).…”

“…The association of nummulitids and alveolinids characterizes the shoals and banks of inner-ramp settings (Buxton and Pedley, 1989). In contrast, abundance of evaporite pseudomorphs, scarcity of fossils and calcretization in the upper sequence are indicative of high salinity, very shallow and calm conditions in intertidal-supratidal environments disturbed by current action (Warren, 2006;Ortí, 2010;Afify et al, 2015b).…”

“…iron oxyhydroxides, quartz, manganese minerals, apatite, dolomite, clay minerals, and sulfate minerals (Afify et al, 2015b). Goethite and hematite are the main iron-bearing minerals.…”