PLIO-PLEISTOCENE GLACIAL GEOLOGY OF THE SMOKING HILLS, NORTHWESTERN ARCTIC CANADA

The glacial geological record of Smoking Hills, situated along the northwest coastal mainland of arctic Canada (69°13’N; 127°03’W) was first described in the late 1960s when a single 32 m high stratigraphic section was reported to contain 3-5 glacials and associated inter-glacial deposits. Subsequent magnetostratigraphic investigations indicated that a fluvial gravel unit underlying this section was reversed, as were 3 overlying tills, and that the section was capped by two magnetically normal tills. Correlations were then made with complex Quaternary glacial histories on Banks Island and elsewhere, and with Neogene fluvial Beaufort Fm deposits along the western Canadian Arctic Archipelago.

Recent field investigations conducted in 2018 have fundamentally revised the interpretation of this site, and with it, understanding of the regional Plio-Pleistocence glacial history. Preliminary cosmogenic ¹⁰Be-²⁶Al burial age dating of the basal (?glaciofluvial) gravel and the immediately overlying till suggest a pre-Pleistocene age. The former complex glacial and inter-glacial stratigraphy is rejected, owing in large measure to the previous lack of recognition and misidentification of extensive rafts of local poorly- to un-lithified Cretaceous bedrock, in some cases upwards of 6 m thick. The composite 52 m high section displays interlayered glaciotectonized till, diamict and bedrock deposits with eastward clast azimuths, save one with a westward azimuth. It is possible that rather than separate glacials, much of the lower 34 m of the section records a glaciotectonized accretion of diamicts and bedrock through a single, pre-Pleistocene glaciation. Whether a large (6+ m thick) bedrock raft at the 10-16 m depth marks the end of the previous glacial or the truncation of underlying stratigraphy consequent with the advance of a subsequent glaciation is uncertain. However, overlying this prominent upper bedrock raft is an 8 m thick massive to laminated diamict interpreted to be a Late Wisconsinan Laurentide till. No convincing evidence of fluvial Beaufort Fm deposits are found within the area, and those deposits previously identified as such are rejected instead as local fluvial and Late Wisconsinan glaciofluvial outwash and kame terraces.