PALEOMAGNETISM OF THE JURA-CRETACEOUS KYUQUOT GROUP, VANCOUVER ISLAND, BRITISH COLUMBIA

The Kyuquot Group is a series of marine clastic deposits of Late Jurassic to Early Cretaceous age located on Vancouver Island. These sediments have been folded, but not metamorphosed, and so provide an attractive target for paleomagnetic study. Results from these rocks fill a significant (100 m.y.) time gap in our knowledge of the paleomagnetic paleolatitude record of Wrangellia. Paleomagnetic results from the underlying Bonanza Volcanics (Symons, 1984) show no significant relative latitudinal displacement of Wrangellia to North America. This, along with geological correlations between other similar-aged clastic sediment units, has led several workers (Brandon et al., 1988, McClelland et al., 1992) to propose that the Kyuquot Group represents a clastic overlap tying Wrangellia to the North American margin. Younger sedimentary rocks from Vancouver Island (the Late Cretaceous Nanaimo Group) have shallow inclinations, indicative of 2500 km of translation (Enkin et al., 2001). A total of 324 samples from the Jurassic Kapoose Formation and the Cretaceous One Tree Formation were collected. Thermal cleaning of 111 specimens from the Berriasian to Lower Valanginian One Tree Formation revealed two remanence components; one a low T_ub overprint, the other a high T_ub component displayed in 77 of the specimens. The high T_ub component passes both an inclination only test and a combined great circle and line-fit fold test after correction for a suspected small block rotation. The fold test results in a 100% bedding corrected direction of Dec. 214.4°, Inc. 85.6°, a₉₅ 3.3°, and k 25.2. Results from the Lower Callovian to Upper Tithonian, Kapoose Formation are more scattered. 132 specimens were measured, 66 specimens have a recognizable high T_ub component. The high T_ub component fails both an inclination only fold test and a combined great circle and line-fit fold test. The Lower Cretaceous One Tree Formation mean inclination corresponds to a paleolatitude of 81.3° ± 6.5°, which is 28° (3100km) north of the expected paleolatitude, assuming North American paleogeography. This high paleolatitude combined with the low latitude results for the Late Cretaceous is inconsistent with paleolatitudes predicted by models for Wrangellia (WV-1 and WV-2, Debiche et al., 1987). The results are consistent with the revised plate model of Engebretson et al. (1995).