TERMINAL LATE CRETACEOUS REGRESSION ON THE SOUTHEAST MARGIN OF THE SVERDRUP BASIN: SHALE AND BENTONITE PETROLOGY OF THE UPPER KANGUK FORMATION, DEVON ISLAND, NUNAVUT

Over 200 m of interbedded, fossiliferous shales and glauconitic sandstones of the upper Kanguk Formation, Devon Island, Nunavut, record the terminal Late Cretaceous regression of the Boreal Sea from the southeastern margin of the Sverdrup Basin. These marine to nearshore marine sediments are capped with marginal marine to non-marine shales and sandstones and host two distinct suites of bentonites. Terrestrial palynomorphs recovered from marginal marine shales overlying the uppermost bentonite constrain the minimum age of these sediments to the Late Campanian at 72-73 Ma.

Preliminary geochemical data indicate a peralkaline magmatic source of continental affinity for the bentonites and shales. Primary geochemical signatures of sandstone samples likely are obscured by glauconitization and phosphatization, but high Fe and K abundances are consistent with shale and bentonite data. Bentonite chemistry is bimodal with Ti-rich and Zr-poor and Ti-poor, Zr-rich compositions as well as high and low K abundances. X-ray diffraction analysis of clay separates indicates that saponite is the dominant clay mineral component. Many of the bentonite samples contain a significant quantity of x-ray amorphous volcanic glass. Shale bulk chemical and mineralogical data suggest that ash is a significant shale component.

The occurrence of significant quantities of Late Campanian ash in a regressive sedimentary sequence points to continuing tectonic activity in the high eastern Arctic. The inferred age of these sediments and associated volcanism implicate the Hanson Point volcanics of northeastern Ellesmere Island as a likely source of the bentonite, but the North Greenland and Svalbard large igneous provinces are also potential polar sources. Extrabasinal sources of ash similar to those of the Western Interior cannot be excluded. The regression recorded in Upper Kanguk sediments is apparently coeval with uplift to the northeast of Devon Island and the onset of the Eurekan Orogeny, and signals the transformation of the Cretaceous marine Sverdrup Basin to an alluvial coastal plain.