Abstract

Kimberlite-sourced bentonite layers have been discovered in Late Cretaceous sedimentary drill cores located within the Buffalo Head Hills kimberlite field, north-central Alberta. Two bentonites are unambiguously differentiated from “common” intermediate to felsic volcanic-derived Alberta bentonite by having similar whole-rock geochemical composition to ultramafic rocks from the Buffalo Head Hills kimberlite field and worldwide crater-facies kimberlite. The results demonstrate that the geochemical analysis of bentonite can provide a quick, cost-effective means of testing for low-volume kimberlite volcanism. The kimberlite-sourced bentonite is associated with a cluster of Buffalo Head Hills kimberlites known as the K14 complex. The K14A kimberlite occurrence has a previously reported 206Pb/238U perovskite emplacement age of 86.8 ± 2.1 Ma. This age is compatible with early or mid-Cenomanian (∼99–96 Ma) and mid-Coniacian to Santonian (∼88–84 Ma) palynological results for mudstone underlying and bracketing the K14A and K14B kimberlites, respectively. Conversely, biostratigraphically significant palynomorphs in host rock cores bracketing the K14C kimberlite indicate emplacement during the Cenomanian or Turonian (∼96–92 Ma). U–Pb detrital zircon ages from syndepositional kimberlite-sourced bentonite directly adjacent to the K14C kimberlite contains a high frequency of young (∼99–92 Ma) zircon with a best maximum 206Pb/238U depositional age of 91.7 ± 2.9 Ma. Thus, this innovative approach may provide evidence of multiple episodes of kimberlite emplacement within or near the K14 complex.

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