24 AFRICA/North African Phanerozoic from the Triassic-Cretaceous sediments Ore deposition occurred when these metal-bearing solutions mixed with microbially reduced sulphate solutions that were associated with the organic carbon of the Cenomanian-Turonian strata Due to the generally high sea-level, the marine Upper Cretaceous in North Africa is dominated by calcareous lithologies, namely dolomites/limestones, chalks, and marls (Figure 11) Lateral and vertical facies distributions are strongly related to sea-level changes of various orders as well as to the changing structural relief associated with Late Cretaceous syndepositional compression Great variations in thickness and facies as well as onlap features, for example, are developed around the domal anticlines of the Syrian Arc Foldbelt in Sinai and within rift grabens of the Sirt Basin (N Libya) The Campanian–Maastrichtian was characterised by very high sea-level, resulting in a widespread distribution of hemipelagic deposits, such as chalks and marls These deposits often contain abundant foraminiferal faunas and calcareous nannofossil floras, which allow high-resolution biostratigraphic and palaeoecological studies in these horizons As on the Arabian Peninsula, the Santonian–Maastrichtian interval in North Africa contains significant amounts of phosphorites, which are mined in, for example, Morocco/Western Sahara and Abu Tartour (Western Desert), making North Africa one of the world’s largest producers of phosphate (see Sedimentary Rocks: Phosphates) In places, the Campanian–Maastrichtian contains organic-rich intervals with total organic carbon contents of up to 16%, for example, in the Moroccan Tarfaya Basin and Atlas Gulf area, the Libyan Sirt Basin and the Egyptian southern Western Desert, Red Sea Coast and Gulf of Suez (Figure 9) Notably, Figure 11 Contact between chalky limestones of the Early Eocene Bou Dabbous Formation (reddish) and the underlying Campanian Maastrichtian Abiod Formation (bluish) (Ain Rahma Quarry, Gulf of Hammamet area, Tunisia) Algeria, Tunisia, and West Libya are dominated by organically lean deposition during this time Campanian–Maastrichtian black shales form important hydrocarbon source rocks in the Sirt Basin and the Gulf of Suez Palaeogene Sea-level during most of the Paleocene–Eocene remained high resulting in deposition over wide areas (Egypt: Dakhla and Esna Shale) of hemipelagic marls and chalks that are rich in planktonic foraminifera A sea-level fall occurred during the mid-Paleocene, resulting in the formation of a short-lived carbonate interbed (‘Tarawan Chalk’) in parts of Egypt Within the Eocene, the facies typically changes here to hard dolomitic limestones with abundant chert nodules (‘Thebes Limestone’) A similar Palaeogene facies development can also be found in parts of northern Libya and Tunisia The Eocene in Egypt, Libya, Tunisia, and Algeria includes nummulitic limestones up to several 100 metres thick, which were deposited in carbonate ramp settings The unit forms major hydrocarbon reservoirs in offshore Libya and Tunisia Well-exposed and continuous exposures occur in Jabal al Akhdar (Cyrenaica), where the nummulite body’s geometry can best be studied (Figure 12) Notably, the Giza pyramids in Cairo are built from Eocene nummulite limestone The Eocene hydrocarbon play in the offshore of Tunisia is sourced by dark-brown marl and mudstone of the lower Eocene Bou Dabbous Formation The unit contains type I and II kerogen and ranges in thickness from 50 to 300 m Neogene and Quaternary Marine conditions during the Miocene were again restricted to the northernmost margin of North Africa Figure 12 High energy nummulitic bank facies, Darnah Forma tion, Middle to Late Eocene, West Darnah Roadcut, Jebel Akhdar (Cyrenaica, Libya)