The Kanguk Formation: TOC, ?13C and sedimentology of a Late Cretaceous, organic-rich mudstone in the Sverdrup Basin, Sawtooth Range, Ellesmere Island

The Kanguk Formation is a Cenomanian-Maastrichtian organic-rich mudstone unit in the Sverdrup and Banks basins (Embry, 1991). It is >500 m thick in the basin centre on Axel Heiberg Island and thins towards the basin margins. The lower part of the Kanguk Formation consists of organic rich, papery black shales with frequent bentonite beds. Upwards the shales become siltier, less organic rich and eventually grade into the sandstones of the Paleogene Eureka Sound Group. Previous studies from the eastern basin margin describe the mudstones as organic rich (TOC up to 10%wt.), Type I-III kerogen (HI up to 550 mgS2/gTOC) and immature for oil generation (Nuñez-Betelu, 1993). Mudstones of similar age and facies are present to the west of the basin in the Beaufort Sea area, on Bylot Island (Baffin Bay) and are believed to be present offshore of the Canadian Arctic margin. Therefore the Kanguk Formation constitutes an important potential source rock along the Canadian Arctic margin. This presentation shows new data on sedimentology, TOC and ?13C in order to better understand the depositional environment and stratigraphic position of potential hydrocarbon source intervals in the Kanguk Formation.

In 2013, a 160 m thick succession of the Kanguk Formation was described and sampled at metre intervals in the Sawtooth Range, Ellesmere Island. The basal contact to the underlying deltaic sandstones of the Albian-Cenomanian Hassel Formation is sharp. The lower 0-30 m of the Kanguk Formation consist of dark shales with traces of bioturbation indicating an offshore environment below storm wave base. Between 30-80 m black, papery shales lacking bioturbation indicate deposition under anoxic seafloor conditions. Bentonites are abundant in this part of the succession but occur throughout. From 80-160 m thin, silty layers exhibiting faint cross lamination become more common. Distinct, red weathering horizons contain abundant Late Santonian to Early Campanian inoceramid shells. Near the top of the formation grain size increases rapidly. Herringbone cross stratification and mud drapes indicate a tidal environment. These beds grade into very low angle cross bedded beach sandstones and trough cross bedded sandstones with basal conglomerates and reworked red mudclasts. This indicates a rapid facies change from shoreface to fluvial deposition at the base of the Paleogene Eureka Sound Group.

The TOC data from the Sawtooth Range generally correlates with the sedimentology. It is lowest in the basal 30 m. Elevated values up to 6.2%wt. occur in the black, papery shale interval. Above 80 m, values are lower but a second, 20 m thick, organic rich interval with TOC up to 5.2%wt. is recorded. The ?¹³C also correlates with the sedimentology but is, in contrast to the TOC, most elevated in the basal 30 m. At 30 m, ?¹³C rapidly drops and then follows a generally increasing trend. Average ?¹³C is -25‰.