Cornwallis Island and adjacent smaller islands, Canadian Arctic Archipelago

This report describes the bedrock geology of Cornwallis Island and adjacent smaller islands that lie near the geographic centre of the Canadian Arctic Archipelago. Five concordant rock successions separated by regional unconformities crop out within the report area. From oldest to youngest the successions include: (1) Lower Ordovician to Lower Devonian marine carbonates, elastics, and evaporates, that total some 21, 000 feet in thickness and constitute the preponderance of bedrock within the area; (2) Lower Devonian red beds, and equivalent marine carbonates; (3) Middle Devonian marine carbonates and elastics; (4) Upper Devonian marine elastics; and (5) Upper Cretaceous and Lower Tertiary non-marine elastics. The oldest succession was deposited within the Franklinian miogeosyncline. Subsequent successions were deposited as generally thin, stable-platform sediments that are preserved in grabens, synclinal troughs, and along the downfaulted sides of normal faults. The regional unconformities that separate the various sedimentary successions mark successive tectonic movements of the Cornwallis fold belt. The two oldest unconformities, one of Early Devonian age, the other of late Early or early Middle Devonian age, date the principal movements that established the northwesterly regional strike of the folds belt. The relative effects of later tectonic movements on the fold belt are not definitely known. Nevertheless, these movements mark episodes of faulting, and some folding post-dates the two earliest movements.