They came from near and far: altered volcanic ash layers within the Late Cretaceous Kanguk Formation, Sverdrup Basin

The mudstone-dominated Late Cretaceous Kanguk Formation of the Sverdrup Basin, Canadian Arctic, contains numerous diagenetically altered volcanic ash layers (bentonites) that provide a record of Late Cretaceous volcanism within the High Arctic. Eleven bentonites were sampled from an outcrop section in the Sawtooth Range, Ellesmere Island. Five of the sampled bentonites were analysed for combined zircon U-Pb age and Hf isotopes. All of the bentonite samples collected were analysed for whole-rock geochemistry.

Two distinct types of bentonite are identified from the whole-rock trace element geochemistry and zircon Hf isotope data. (1) Nine decimetre-thick peralkaline rhyolitic to trachytic bentonites occur distributed through the late Turonian to early Campanian (c. 92-82 Ma) outcrop section. These bentonites originated from mildly alkaline magmas with limited crustal contamination that were likely erupted in an intra-plate tectonic setting. The considerable thickness of many of these bentonites suggests that the volcanic centres were proximal to the Sverdrup Basin. Local volcanism associated with the High Arctic Large Igneous Province (HALIP) is the inferred source of these bentonites. (2) Two thinner, centimetre-thick, sub-alkaline, dacitic to rhyolitic bentonites of late Turonian to early Coniacian age (c. 90-88 Ma) were also identified. The geochemistry and isotope data from these bentonites support a parent magma with a greater degree of crustal contamination that was erupted from volcanoes within an active continental margin tectonic setting. The lack of nearby potential sources of sub-alkaline magmatism, together with the thinner bed thickness of the sub-alkaline bentonites and small size of euhedral zircons, are consistent with a more distal source area. The age and geochemistry of these two sub-alkaline bentonites correlate with an interval of intense volcanism in the Okhotsk-Chukotka Volcanic Belt (OCVB), Russia. Consequently, during late Turonian to early Coniacian times intense volcanism within the OCVB may have resulted in widespread volcanic ash dispersal across Arctic Alaska and Canada, reaching as far east as the Sverdrup Basin.