An allochthonous salt canopy on Axel Heiberg Island, Sverdrup Basin, Arctic Canada

Abstract

Axel Heiberg Island (northern Nunavut) contains the thickest Mesozoic section in the Sverdrup Basin. The ∼370-km-long island is second only to Iran in its concentration of exposed evaporite diapirs. However, the tectonics of this remote region is not well known. A polar desert on the island provides excellent exposure of 46 diapirs of Carboniferous evaporites and associated minibasins. Paleogene (Eurekan) anticlines trend roughly north on a regular ∼20 km wavelength and probably detach on autochthonous Carboniferous Otto Fiord evaporites. In contrast, a 60-km-wide area, known as the wall-and-basin structure (WABS) province, has bimodal fold trends and irregular wavelengths of <10 km. Here, crooked walls of diapiric anhydrite crop out in the cores of tight anticlines. Wider synclinal minibasins separate the diapiric walls. We interpret the WABS province to detach on a shallow evaporite canopy. This comprises an allochthonous coalescence of evaporite diapirs that spread extrusively during the Hauterivian (Early Cretaceous, ca. 130 Ma), close to the onset of seafloor spreading in the Arctic Ocean and of flood basalt volcanism associated with Alpha Ridge. Since then, the evaporite canopy has yielded second-generation diapirs, now exhumed and exposed by modest Eurekan shortening. Strata record minibasin evolution and diapirism since at least the Late Triassic. Stratigraphic thinning against diapirs and spectacular angular unconformities at four levels are present between the Jurassic and Paleocene. The most widespread is the Early Cretaceous event marking the time of canopy emplacement. Outcrops record the later fate of the canopy, including exposure, onlap of diapirs, and off-diapir debris flows.