Tectonostratigraphy and allochthonous salt tectonics of Axel Heiberg Island, central Sverdrup Basin, Arctic Canada
Authors: Harrison J C , Jackson M P A 
Published: October 2014

Axel Heiberg Island (northern Nunavut) contains the thickest Mesozoic section in Sverdrup Basin. The approximately 370 km long island is second only to Iran in its concentration of exposed diapirs. Forty-six diapirs of Carboniferous evaporites and associated
minibasins are impressively exposed on the island. Regional anticlines, which formed during the Paleogene Eurekan Orogeny, trend roughly north on a regular approximately 20 km wavelength and probably detach on the autochthonous Carboniferous Otto Fiord Formation evaporites. These evaporites comprise
halite overlain by thick anhydrite containing thin limestone beds. Unlike the rest of the island, a 60 km wide area, known as the wall-and-basin region, has bimodal fold trends and irregular (&amp;lt;10 km) fold wavelengths. Here, crooked, narrow walls of superficially gypsified anhydrite crop
out in tight anticline cores, which are separated by wider synclinal minibasins. We interpret the wall-andbasin region to detach on a shallow, partly exposed canopy of coalesced allochthonous evaporite sheets. This inference is based on four lines of evidence: 1) a halving of fold wavelength
relative to folds outside the wall-and-basin region, 2) the exposure of anomalously young strata of Paleogene and Late Cretaceous age, 3) the occurrence of clustered equant minibasins having similarities to those in the northern Gulf of Mexico, and 4) a strikingly uniform level of piercement
pointing to a stratiform allochthonous source layer. A canopy would require an evaporite depocentre, which may have ponded in a sinistral pull-apart basin of Carboniferous age. Strata record a salt-tectonic history spanning the Late Triassic (Norian) epoch to the Paleogene period. Stratigraphic
thinning against diapirs and angular unconformities up to 90° indicate mild regional shortening in which diapiric roof strata were bulged up and flanking strata steepened. This bulging culminated during Hauterivian times, when diapiric evaporites broke out and coalesced at the surface to form a
canopy. As the canopy was buried, it yielded second-generation diapirs, which rose between minibasins subsiding into the canopy. A consistent high emplacement level indicates that all exposed diapirs inside the wall-and-basin region rose from the canopy. In contrast, diapirs along the wall-and-basin
margins were sourced in autochthonous salt as first-generation diapirs. Apart from the large diapir-centred unconformities, Jurassic-Cretaceous depositional evidence of salt tectonics also includes submarine debris flows and boulder conglomerates shed from at least three emergent diapirs. The report
area's geological history includes six main tectonostratigraphic phases in the wider Arctic area, beginning with Carboniferous rifting and ending with the Paleogene Eurekan Orogeny. Extreme local relief, tectonic slide blocks, steep talus fans, and subaerial debris flows suggest that many
wall-and-basin diapirs continue to rise today. Freeboard calculations suggest that the rise of diapirs having surface relief of even 400 m could be driven purely by gravitational loading, but additional mild tectonic shortening cannot be ruled out. The Axel Heiberg canopy is one of only three known
exposed evaporite canopies, each revealed at a different structural level: above the canopy (Axel Heiberg), through the canopy (Great Kavir, Iran), and possibly beneath a canopy (Sivas Basin, Turkey).