Lithic geochemistry of the Claggett marine cyclothem in south- central Saskatchewan

Sediments of the Lea Park Formation in south-central Saskatchewan were deposited in the Claggett sea during the Late Cretaceous (Campanian) Claggett marine cycle. Rocks of the Lea Park Formation have remained virtually unaffected by diagenetic alteration; hence, variations in mineralogical and chemical compositions result primarily from changes in the source of detritus. Quartz, feldspar, discrete illite, kaolinite, and chlorite were derived from weathering of the western highlands, whereas illite-smectite (I-S), the dominant clay phase, originated from volcanic ash. Changes in the proportions of these minerals suggest a large-scale volcanic episode during deposition of the Lea Park sediments, an episode that affected not only the detritus delivered to the seaway but also the chemical and isotopic compositions of the sea water itself. The similarity between the mineralogical composition of the Lea Park Formation in Canada and that of the coeval lower part of the Pierre Shale in the United States indicates that volcanic ash was an important detrital source for both formations. -from Authors