Les Séries Volcano-sédimentaires Orogéniques Néoprotérozoïques De La Basse Saoura (algérie) : Signification Géodynamique Dans La Chaîne Panafricaine

Ageological-petrological study ofPrecambriansedimentaryformationsexposed in theLower Saoura inliers has been undertaken in order to reconstruct their sedimentary environements and to compare them with similar unitsfrom NW Hoggar and Mali. Theformationsareall pre-orogenicand unconformably overlain by molassic deposits comparable with the Série Pourprée of Western Hoggar.The Sebkha el Melah graywackes (>3500 m) weredeposited in upward coarsening sequences evidencing the transition between low energy depositsdominated by theeffectsof wavesand storms (offshore or prodelta), intertidal marine deposits, and higher energy formations suggestive of a fluviatile system cutting a deltaic plain. The conformable continental volcanic complex above includescalc-alkalinelavasand pyroclasticswith geochemical signatureof shoshonites. The AdrarBled el Mass graywackes (>4000 m)are interpreted as classical turbidites similar to those from the Green Series of NW Hoggar. The turbidites were emplaced by deep marine turbiditic channels, the Bled el Mass area represemting proximal facies (continental slope) and Adrar area showing distal facies (abyssal plain) perturbated by conglomeratic lenses interpreted as deep channels. All these formations represent syn-orogenic depositsfrom an active continental margin. Such tectonicsetting sharply contrasts with the quiet cratonic to passive margin evolution of the West African Craton free of volcanic activity during the same period.