Proterozoic and paleozoic geology of Banks island, Franklin
Authors: Miall A D 
Published: March 2017

Banks Island is the southwesternmost island of the Canadian Arctic Archipelago, comprising an area of 60.100 square kilometres (23,200 sq miles). Proterozoic rocks crop out along the south coast and Upper Devonian strata are exposed in the northeast portion of
the island. The remainder of Banks Island is covered by Mesozoic and Cenozoic sediments. This report is concerned primarily with the subsurface stratigraphy, based on data obtained from the first four wells to be drilled in the area. A limited amount of surface data is also included as a result of
the writer's field work in 1973 and 1974. The oldest rocks exposed in the area are Late Proterozoic cherty dolomites and quartzose sandstones of Glenelg Formation comprising part of a craton sequence of mainly shallow marine origin. A sequence of Cambrian to Middle Devonian strata 1200 metres (4,000
ft) thick overlies the Precambrian in Victoria Island. Cambrian to Silurian rocks are not exposed at the surface on Banks Island and have not been penetrated by any wells drilled to date; the succession in Banks Island is assumed to be similar to that of Victoria Island except that a westward
transition from cratonic to geosynclinal facies may occur in the western part of Banks Island, similar to that which is now known to characterize the overlying Devonian rocks. The latter range in age from Lower to Upper Devonian and total an estimated 2400 metres (8,000 ft) in thickness. Early and
Middle Devonian strata display abrupt lateral facies changes. Blue Fiord Formation represents sedimentation on a shelf area which was confined mainly to the southern and eastern part of the island. The rocks are mainly carbonates. They pass laterally westwards and northwards into a basin slope
facies, the calcareous shales of Orksut Formation, and these in turn pass laterally into siliceous shales comprising a deep basin facies, Nanuk Formation. The deep basin represents a southward extension of Hazen Trough and it probably linked to a similar basin in the northern
Yukon area, Richardson Trough. The facies belts underwent a southward migration during the Early and Middle Devonian. Commencing in the late Middle Devonian a elastic wedge (Melville Island Group) spread southward into the Banks Island area. The source of the detritus was probably a tectonic
landmass to the west and north of the report area. Rocks of Late Paleozoic age are not known in Banks Island. However, several lines of evidence suggest that strata of this age may have been deposited, but that they were removed in pre- Jurassic time. For example, the level of hydrocarbon maturation
in the Devonian sediments is everywhere considerably greater than that of the Mesozoic deposits, suggesting deep burial before Mesozoic sedimentation commenced. There is no evidence of any significant structural deformation of the Proterozoic and Paleozoic rocks other than normal faulting. Dips are
generally less than 10°. Hydrocarbon potential in the Paleozoic strata is considered to be fair. Stratigraphic traps may be present at the carbonate-shale facies change. In view of the high degree of maturity exhibited by these rocks, any hydrocarbons present are likely to be dry gas. The
carbonate-shale facies change also has potential as a locus for sulphide ore enrichment.