Abstract The West African craton is fringed along its western side by a 3000 km long orogenic belt subdivided into three separate orogens: the Bassaride (Pan-African I orogeny), Rokelide (Pan-African II orogeny) and Mauritanide (Hercynian orogeny) thrust belts. The Bassarides are cut to the north by the Mauritanides and to the south by the Rokelides but parts of this Bassaride belt are incorporated in the other two younger belts. This review presents the main geological, geophysical and geochronological results from the western side of the West African craton, collected over the past 90 years, concentrating on those from the last 15 years. Former geological investigations underlined the thin-skinned structure model within these thrust belts, whereas the geophysical results gave prominence to the major importance of block faulting resulting from the Pan-African I orogeny and its strong influence on the subsequent orogenic belt features. The geochronological data allow us to distinguish major tectonothermal events related to the Pan-African I (660–650 Ma), Pan-African II (550–530 Ma) and Hercynian (330–300 Ma and 280–270 Ma) orogenies. However, they also reveal five other tectonothermal events (at 1200–1000, 750–700, 600–580, 510–480 and 450–380 Ma), which are still very poorly understood. The 1200–1000 Ma tectonothermal event recently revealed in the northern Mauritanides may correspond to a remanent orogenic belt segment that witnessed the Grenvillian orogeny.

Abstract The Taoudéni Basin covers over 1 000 000 km 2 of the West African Craton, bounded by Pan-African orogenic belts. Four supergroups separated by craton-scale unconformities are recognized, with Neoproterozoic glaciogenic deposits occurring at the base of Supergroup 2. The Jbéliat Group occurs along a continuous, 1300-km-long, narrow belt from the Adrar region of Mauritania to the eastern limit of the Hank in Algeria and comprises thin glacial drift capped widely by periglacial polygonal structures, with more complex glacial sequences preserved in palaeo-depressions. A thicker, variously marine and continental glaciogenic succession can be found in southern parts, while fully marine, glacially influenced successions are only known from the extreme SW of the basin. The ‘triad’ sequence of diamictites overlain by barite-bearing ‘cap’ dolostones and then by green shales and/or bedded cherts (silexites) is ubiquitous and has long been used to correlate the Supergroup 1/2 boundary across the basin and into the surrounding orogenic belts. The bedded cherts commonly show a volcanic influence and are cemented by early marine calcite at their base at Adrar, Mauritania. Although fossil-based age constraints are scarce and ambiguous, regional tectonic events indicate that ‘triad’ deposition occurred between the Bassaride (665–655 Ma) and Dahomeyide (610–580 Ma) orogens. Recent U–Pb zircon studies of ignimbrite tuffs provide a minimum age for the glaciation of c. 600 Ma. Correlation of supergroup 2 glacial deposits with the c. 635 Ma end-Cryogenian (‘Marinoan’) glaciation is likely and is supported by limited carbon and strontium isotope data. Barite is commonly found within the cap carbonate and may relate to methane seepage and/or unusual oceanographic conditions after deglaciation. Several studies have attributed sequence complexity within the post-glacial succession to isostatic reequilibration. The Taoudéni Basin represents a rare Neoproterozoic example of terrestrial tillites and associated periglacial facies.

Abstract New stratigraphic, geochronological and palaeomagnetic constraints allow updates to be made to a synthesis of Neoproterozoic glacial palaeolatitudes, including modifications to some reliability estimates. The overall pattern of a Neoproterozoic climatic paradox persists: there is an abundance of tropical palaeolatitudes and near to complete absence of glaciogenic deposits demonstrably laid down between latitudes of 60° and 90°. In addition to 12 units with palaeolatitude estimates that are somewhat reliable, estimates with moderate to high reliability now include Konnarock (less than 10° from the palaeo-equator), Elatina, Rapitan, Mechum River, Grand Conglomerat (10–20°), Upper Tindir, Puga (20–30°), Nantuo, Gaskiers (30–40°) and Walsh (40–50°). Among these, Elatina, Upper Tindir and Nantuo are considered to have the highest reliability, all with estimates of low to moderate palaeolatitude. The Elatina result stems from sedimentary rocks with quantitative correction of inclination-shallowing effects, and the Upper Tindir result stems from data collected from igneous rocks that are precisely coeval with the glacial deposits. Despite continuing debate on the global character of Neoproterozoic ice ages, their pan-glacial extent (ice extending to low latitude in a low-obliquity world) is well demonstrated.

Abstract Proven Infracambrian hydrocarbon plays occur in various parts of the world, including Oman, the former Soviet Union, India, Pakistan and Australia. Organic-rich strata also occur in NW Africa, and gas shows originating from Infracambrian hydrocarbon source rocks are known from well Abolag-1 in the Mauritanian part of the Taoudenni Basin. The distribution of Infracambrian source rocks in North Africa is patchy and deposition commonly occurred in half-graben and pull-apart basins. In these intra-shelf basins, marine, organic-rich shales and limestones were deposited beneath the turbulent wave zone, away from the coarse siliciclastic Pan-African molasse detritus. On the West African Craton (including the Taoudenni Basin) organic-rich horizons were also deposited earlier, in pre- and syn-Pan-African times between 0.5 and 2 Ga (Ga is 10 9 years). The long-lasting sedimentation history in this area contrasts with that of the Pan-African regions, such as Oman, which lies in the Pan-African province of the East African Orogen, where preserved sediments are rarely older than 640 Ma. Infracambrian black phyllites in the Anti-Atlas region of Morocco were deposited on a continental slope of a short-lived ocean lying to the north of the West African Craton. Hydrocarbons generated during Infracambrian times from these deposits, however, have a low preservation potential. Infracambrian organic-rich and/or black-pyritic deposits in North Africa are proven in the Taoudenni Basin, the Anti-Atlas and the Ahnet Basin. Thick carbonate successions exist in the Taoudenni Basin, indicating deposition in areas some distance from contaminating coarse siliciclastic hinterland influx. Infracambrian strata may also occur in the Tindouf Basin. However, their deep burial and consequent early maturation history may be unfavourable for the preservation of Infracambrian-sourced hydrocarbons in this area. Local development of Infracambrian source facies may also occur in the Reggane, Ahnet, Mouydir and Iullemeden basins, as indicated by black shales in wells MKRN-1 and MKRS-1 in the Ahnet Basin. Generally, however, these basins appear to be close to the active Pan-African orogenic belt and, consequently, probably received large quantities of coarse siliciclastic sediment, largely of continental facies, which may have diluted any significant hydrocarbon source potential.