Effect of surficial geology on remotely sensed data of bedrock in Northern Canada

The largely unvegetated northern Melville Peninsula, located north of the Arctic Circle in northeastern Canada, consists mainly of a well exposed granitoid Archean basement complex variably overlain by Pleistocene till deposits. A comparison of a map of surficial geology with an image of Landsat TM channel 7 shows that carbonate rich tills match the white (high reflectance) part of the image. These carbonate tills were carried by glaciers from lowlands to the east of the peninsula. The tills vary in thickness from less than one meter to more than 10 meters and effectively screen out radiation form the underlaying granitoid bedrock. A potassium map, derived from airborne gamma ray spectrometry, can be adequately explained only if the blanketing of the till, which overlies granitic bedrock, is taken into account. Bedrock geology, especially in glaciated regions, cannot be adequately mapped by Landsat and airborne spectrometry unless the nature of the surficial geology is well understood