Five units were distinguished in the outcropping middle Devonian strata on the south flank of the Tindouf basin--a basal shale unit and a shale unit with intercalated thin calcareous siltstone beds and sandstone, both lower Eifelian, phosphatic limestones and shales of upper Eifelian age, fossiliferous and reef limestone and interbedded marly shale of lower Givetian age, and upper Givetian shale or siltstone alternating with biostromal limestone. Both upper and lower boundaries of the middle Devonian sequence are marked by sharp lithologic and faunal changes; in addition, there is a slight angular unconformity, not previously recognized, between the Eifelian shales and the lower Devonian beds.

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