The major, trace and rare earth element geochemistry of glauconites from the early Cretaceous Kurnub Group of Jordan

The major, trace and REE geochemistry of glauconites (as members of the trioctahedral micas) from the early Cretaceous Kurnub Group of Jordan are discussed. The investigated glauconites, with 7.1 to 9.2 % K2O, are ranked as evolved to highly evolved as defined by Odin and Matter (1981). Al2O3 contents show a significant inverse relationship with K2O and Fe2O3. The trace element contents show a broad range of variation in contrast to the major elements and a consistent relationship with major elements is lacking. The studied glauconites show a very wide range in the total amount of REE (∑REE = 4.5 to 564.5 ppm). Two distinct groups have been differentiated accord-ingly: I. REE-poor group with ∑REE < 15 ppm and with a weak to moderate LREE/HREE fractionation (1.2 to 8.2); II. REE- rich group with ∑REE up to 565 ppm and with moderately to highly fractionated chondrite-normalized patterns (LREE/HREE ratios 3.5 to 64). The group I glauconites are set in an arena-ceous (detrital quartz) dolomitic matrix while group II glauconites are embedded in a mudstone or marlstone or has an argillaceous matrix. The REE abundances are therefore lithologically rather than regionally controlled. When normalized to NASC the investigated glauconites display the distinctive hat-shaped pattern reported for other authigenic minerals of marine origin. The calculated Ce anomaly indicates the forma