Early radioisotopic age constraints to the Campanian formations with the WIB consisted of K–Ar analyses of biotite and feldspar from interbedded bentonites115,116, with assumed uncertainties around the buy of ± 5%, and these analyses aren't mentioned further more below. Biotite ages, specifically, are deemed of questionable accuracy by modern benchmarks https://bookmarklethq.com/story13233768/new-step-by-step-map-for-what-is-the-fossil-record