Glauconite and phosphate peloids in Mesozoic carbonate sediments (Eastern Subbetic Zone, Betic Cordilleras, SE Spain)

AB STRACT: Glauconite and Ca phosphate peloids occur in Jurassic and Cretaceous bioclastic carbonate rocks from pelagic swell sequences of the Algayat-Crevillente Unit (Subbetic Zone). The size and morphology of the peloids are controlled by the bioclasts. The glauconite in both stratigraphic positions is K rich (>0.69 atoms p.f.u.) and shows well-defined 10 AÊ lattice fringes. Poorly crystalline areas with a composition of Fe-smectite are found within the peloids, indicating the nature of the glauconitic precursor. This precursor would be formed in the shielded microenvironments of the bioclast and later transformed to glauconite by equilibration of peloids with sea water that culminated with the crystallization of a phosphatic phase. The greater presence of smectite areas in the Jurassic peloids and the lower K contents (0.69 ­ 0.81) of these glauconites, compared with the Cretaceous glauconites (0.81 ­ 0.89) can be explained by the calcitic early diagenetic cementation which stopped the process of glauconitization.