Rare-earth elements as tracers of the genetic relationship between smectite and palygorskite in marine phosphorites

Detrital smectite in a sandy claystone and a phosphorite, and authigenic palygorskite in a dolomitic marl and a porcellanite from Cretaceous-Tertiary phosphorite deposits of the Ganntour Basin (Morocco) were purified using cation exchange resin, leached with dilute acid, and analysed for the contents and distribution patterns of their REE before and after acid treatment. The normalized patterns confirm a detrital origin for the smectite in the sandy claystone, whereas the origin of the smectite from the phosphorite is obscured by the addition of REE from the phosphogenic environment. The normalized REE patterns of the palygorskite suggest formation in non-oxidizing restricted environments. The Al2O3/Sigma REE ratio of the two clay types suggests formation of diagenetic palygorskite (and mixed-layer illite-smectite) from AI-bearing detrital smectite by a dissolution-crystallization process.