Early radioisotopic age constraints on the Campanian formations of your WIB consisted of K–Ar analyses of biotite and feldspar from interbedded bentonites115,116, with assumed uncertainties around the order of ± five%, and these analyses are not mentioned more here. Biotite ages, in particular, are viewed as of questionable accuracy by https://www.generationgenius.com/videolessons/fossil-record-video-for-kids/