Facies analysis and sequence stratigraphy of neoproterozoic Platform deposits in Adrar of Mauritania, Taoudeni basin, West Africa

Abstract

The Neoproterozoic and Palaeozoic Taoudeni basin forms the flat-lying and unmetamorphosed sedimentary cover of the West African Craton. In the western part of this basin, the Char Group and the lower part of the Atar Group make up a 400-m-thick Neoproterozoic siliciclastic succession which rests on the Palaeoproterozoic metamorphic and granitic basement. Five erosional bounding surfaces of regional extent have been identified in this succession. These surfaces separate five stratigraphic units with lithofacies associations ranging from fluvial to coastal and fluvial-, tide-, or wave-dominated shallow marine deposits. Owing to their regional extent and their position within the succession, the erosive bounding surfaces correspond to relative sea-level falls, and accordingly the five stratigraphic units they bound represent allocyclic transgressive-regressive depositional sequences (S 1 -S 5 ). Changes in the nature of the deposits forming the transgressive-regressive cycles reflect landward or seaward shifts of the stacked sequences. These successive relative sea-level changes are related to the reactivation of basement faults and tilting during rifting of the Pan-Afro-Brasiliano supercontinent 1000 m.y. ago. The stromatolite bearing carbonate-shale sequences which form the rest of the Atar Group mark the onset of a quiet period of homogeneous subsidence contemporaneous with the Pan-African I oceanization 800-700 m.y. ago.

Geochemistry areas and sample sites, and multielement and single element geochemistry maps of Mauritania (phase V, deliverable 58)

“…Below the unconformity is a Mesoproterozoic paleosol developed on deformed granitoids of the Complexe d'Amsaga. Benan and Deynoux (1998) interpreted a shoreface depositional facies for this lowest part of the Groupe de Char section.…”

“…The Groupe de Char rests unconformably on Archean and Paleoproterozoic basement rocks along the northwestern and northern edge of the basin. It mainly consists of sandstone and conglomerate and is about 300 m thick (Benan and Deynoux, 1998). It was long assigned an age near the Mesoproterozoic-Neoproterozoic boundary based on an Rb-Sr age of 998±34 Ma from matrix clays (Clauer and others, 1982).…”

Revised stratigraphic framework for the lower Anti-Atlas Supergroup based on U–Pb geochronology of magmatic and detrital zircons (Zenaga and Bou Azzer-El Graara inliers, Anti-Atlas Belt, Morocco)

“…The lower part of the sedimentary fill of the Taoudeni Basin, the Hodh Supergroup (Super-groupe du Hodh), is subdivided into the three unconformity-bound groups: the Char, Atar, and de l'Assabet el Hassiane (Moussine-Pouchkine and Bertrand-Sarfati, 1997;Benan and Deynoux, 1998). The mixed carbonate-siliclastic Char Group was deposited in a fault-bounded, compartmentalized basin developed on the deeply weathered Eburnean basement with aeolean and fluvial redbeds grading upsection to tidally influenced, marine siliciclastic and carbonate deposits with some evidence (halite pseudomorphs, mudcracks and mudchips, dessication cracks) for warm and arid climate.…”

Reinterpreting a Proterozoic Enigma:Conophyton‐JacutophytonStromatolites of the Mesoproterozoic Atar Group, Mauritania

“…Potentially correlative and similarly subdivided strata are also exposed in the Hoggar uplift of Algeria Bertrand-Sarfati et al, 1991Moussine-Pouchkine & Bertrand-Sarfati, 1997) and in several poorly studied exposures in the southern Taoudeni Basin (Bertrand-Sarfati & Moussine-Pouchkine, 1983;Bertrand-Sarfati et al, 1987). At the base of the succession, coarse-to fi ne-grained siliciclastic strata and subordinate carbonates of the Char Group are preserved as erosional remnants in cratonal depressions and represent initial mantling of the craton by fl uvial, coastal aeolian and shallow-marine deposits (Benan & Deynoux, 1988). In contrast to the Char Group, fi ne-grained siliciclastic strata, stromatolite-bearing carbonate and minor evaporitic strata (Goodman & Kah, 2004) of the Atar Group represent craton-wide fl ooding and deposition in predominantly shallow marine environments .…”