ASYMMETRIC ZONATION OF A THICK ORDOVICIAN K-BENTONITE BED AT KINNEKULLE-SWEDEN

The clay fraction of a K-bentonite at Kinnekulle in southwestern Sweden has been studied by X-ray powder diffraction, chemical analyses, and cation-exchange capacity determinations. Previous investigations of the upper half of this bed (B-bed) have shown the clay mineral to be illite/smectite (I/S), containing about 50% illite layers at the center of the bed and 65% illite layers at the upper contact. New data on six samples from the lower part of the bed show no zonation, the I/S containing about 50% illite layers in all samples. The bentonite occurs in limestones and shales overlying a 40-m-thick limestone bed and is overlain by limestones, marls, and shales, which in turn are overlain by a 40-m-thick diabase. The limestones are silicified in contact with the bentonite, particularly beneath the B-bed.