Geology of Offshore Areas of The Canadian Arctic Islands Based On Geophysical Data

Surface geologic exposures in the Arctic Islands are excellent, as is the case in most of the world's deserts. The sparse subsurface information from bore holes is limited to only a few islands. The geology of the inter-island areas is much more speculative. Preliminary interpretations based on erosion and isostatic readjustments after the melting of the continental ice sheet may have to be revised after a review of the geophysical data which are now becoming available. Hypotheses concerning block faulting with horst and graben development represent a conservative approach, whereas the consideration of rift and drift hypotheses gains popularity. Recently obtained reconnaissance data indicate the possibility that a distinct geologic section exists offshore compared to the onshore boundaries. This conclusion is based on regional geophysical data obtained by government and industry. Magnetic and gravity surveys coyer much of the Arctic Archipelago Seismic profiles in marine areas of sourthern Arctic Islands indicate a wide range of large structures, and refraction probes are useful in defining the velocity, and thus the possible geologic age of these sediments. Introduction THE CANADIAN ARCTIC ISLANDS have attracted the venturous for more than 300 years and even in our own time we have seen men in quest of a northwest passage. Continental borderlands have become major oil search areas throughout the world since the development of a concept that the offshore is more than just an extension of onshore geology. Continental shelves often present a whole new and very thick sedimentary section. Integration of the large volume of data compiled by the Canadian Government with newly acquired data from industry stimulates renewed interest in the offshore and inter-island areas of the Arctic Archipelago. The Canadian Arctic Islands are on the north flank of the North American craton. Major extensions of the Precambrian basement are noted, such as the Minto Arch in the southwest and the Boothia Uplift on the south, as seen in Figure 1. Hachured areas indicate Paleozoic sediments comprising the stable shelf and geosynclinal trough of the Franklinian geosyncline. The thickest portion of this earlr depositional area along the north edge of the Paleozoic outcrop has been compressed and faulted by late Paleozoic deformation. Most of the exposed area of the Franklinian geosyncline (Kerr, 1967a) is of miogeosynclinal suite. Eugeosynclinal sediments are exposed in Northern Ellesmere Island (Trettin, 1967). The central portion of the Arctic Islands has been called the Sverdrup Basin. This depositional basin is about 700 miles long and 250 miles wide, and is composed of Mesozoic and Cenozoic sedimentary sequences. The Paleozoic Franklinian geosyncline accumulated about 40,000 feet of carbonates, shales and some sands. An additional 40,000 feet of shales and sands are present in the Mesozoic Sverdrup Basin. Excellent geologic exposures facilitated aerial photographic mapping of the islands, and aerial field mapping was carried on during the short summer seasons. Aeromagnetic gravity and seismic work followed on shore and, although logistics are difficult good results were generally obtained.