Magnetostratigraphy of the Late Cretaceous to Eocene Sverdrup Basin: Implications for heterochroneity, deformation, and rotations in the Canadian Arctic archipelago

The temporal and spatial patterns of sedimentation in the Sverdrup Basin provide clues to how deformation in the Canadian Arctic accommodated Late Cretaceous-Eocene relative motion between Greenland and North America. Although the sediments contain a rich assemblage of mammal and megafloral fossils, dating of the sequence has been controversial. Some work suggests a dramatic faunal and floral heterochroneity with species appearing in the Arctic 2-18 m.y. prior to their appearance at lower latitudes. To obtain a chronostratigraphic framework for these sediments, a 2.6-km section of the Eureka Sound Group and Kanguk Formation on western Axel Heiberg Island was sampled for magnetostratigraphy. After removal of a pervasive modern field overprint with thermal and alternating field demagnetization, a characteristic remanent magnetization (ChRM) is isolated. Despite high directional dispersion, the ChRMs form 11 distinct polarity intervals which can be correlated to chrons 34 to 24r. This correlation indicates that some of these sediments are similar to 10 m.y. younger than thought previously, reducing the need for large-scale heterochroneity. Sedimentation rates derived from the magnetostratigraphy suggest that an increase in basin subsidence is recorded near the middle of the section sampled. A similar pattern has been reported from the Eureka Sound Group exposed on Ellesmere island. We interpret this increased sedimentation as a response to crustal flexure caused by lithospheric loading during the middle Paleocene (C26r). The loading may be related to a blind thrust system to the west of Axel Heiberg Island that marks compression between North America and Greenland driven by rapid seafloor spreading in the Labrador Sea. The new data, together with prior results, indicate that most of the Cretaceous Canadian Arctic archipelago has undergone a counterclockwise vertical axis rotation. The new data are more consistent with this rotation being related to events during chron 26r, rather than marking block rotations associated with the terminal Eocene phases of Eurekan deformation.