NATURE OF THE CANADIAN POLAR MARGIN NORTHWEST OF AXEL-HEIBERG ISLAND

Theoretical responses, which have properties comparable to the complex field observations of the 1985 and 1986 offshore reflection experiments of the Frontier Geoscience Program, were derived from sonic log and borehole geological information from the Arctic continental margin. Tests of a specially developed reverberation suppression algorithm, both on the theoretical and field observations, proved quantitatively that this simple but robust technique effectively removes most of the coherent noise patterns from these records. Correlation of spatially generated velocity-traveltime information to the borehole data allowed establishment of the basic stratigraphic sequences offshore, west of Axel Heiberg Island. Five sedimentary units were recognized under the thin water cover, The first, nearest to the surface, represents the Tertiary Arctic Terrace Wedge with an average velocity characteristic of 2750 m/s. It appears to cover most of the Canadian segment of the continental shelf. The next, a relatively thin reflector, has a velocity of 3650 m/s and is comprised of a diversity of Mesozoic to Early Tertiary strata along the known parts of the shelf The third layer (5180 m/s) is representative of the Lower Mesozoic to Upper Paleozoic rock units. The high velocity, 5840 m/s, fourth layer is revealed by a significant thickness of Lower Paleozoic Franklinian rocks. Regional acoustic properties of these last two strata are rather uniform across the shelf. The surveys mapped a local depocentre with sedimentary rock accumulations slightly over 7000 m. The lowermost strata, having 6400 m/s velocity are interpreted as the crystalline basement. The total sedimentary section discovered by the reflection investigation is somewhat more than either the land to offshore geologic extrapolations or the results of the 1985 refraction survey.