The origin of the Lower Jurassic Cleveland Ironstone Formation of North-East England: evidence from portable gamma-ray spectrometry

Abstract

Summary The distribution of K, U and Th in the Cleveland Ironstone Formation, measured by gamma-ray spectrometry, is found to be useful in investigating the origin of oolitic ironstones. The oolitic ironstone seams are enriched in Th and depleted in K relative to the interbedded mudstones which show a close correlation between Th and K. The enrichment of Th in the ironstone seams represents a primary depositional rather than a diagenetic process, and the Th-enriched material must have been transported to the site of ironstone deposition from elsewhere. The values of Th (20–45 ppm) and the Th/K ratios (20–100) recorded in the ironstone seams are consistent with the original Th-enriched material being kaolinitic/bauxitic clay from a lateritic weathering source.