Abstract
Uppermost Cretaceous–Eocene series of the Marrakech High Atlas consist of alternations of marl, dolomite, limestone, gypsum and phosphatic beds. The rocks were deposited in a shallow, coastal marginal basin characterised by rapid changes in salinity. Palygorskite occurs as interwoven fibrous mats forming fine laminae and as coatings and pore-filling, and pore-bridging cements in dolomitic marls. This textural evidence suggests a direct chemical precipitation, mostly post-dating dolomitization. A magnesium concentration in presence of dolomite was sufficient for palygorskite precipitation; the necessary Si and Al were derived by dissolution of silicates under alkaline conditions. The maximum development of palygorskite was near the top of the upper sedimentary system, which was deposited during a marine transgression.
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