New Paleomagnetic Results From the Nanaimo Group, British Columbia: Additional Localities for Testing the Baja-British Columbia Hypothesis
Raub, T D (1), Kirschvink, J L (1), Ward, P D (2)
(1) Division of Geological and Planetary Sciences, Caltech 170-25, Pasadena, CA 91125; (2) Department of Geological Sciences, University of Washington, Seattle, WA 98195
Abstract:
Prior paleomagnetic analysis of fossiliferous upper Campanian Nanaimo Group sedimentary rock on Hornby Island indicates low-latitude formation (25 degrees) and supports the Baja-British Columbia Hypothesis [Ward et al., 1997]. During July and August of 1998 we sampled an additional twenty sites (73 cores) from more than 500m of overlying strata. Preliminary analysis of these cores indicates that many show reversed polarity (C31R, 30R, or 29R?), possibly indicating recovery of some Maastrichtian and/or Paleocene data. Microfossil age control is underway but not yet finished. The presence of iridescent aragonitic mollusk fossils indicates that thermochemical alteration has been minimal. Stratigraphically-bound reversed as well as normal magnetozones also suggest that the characteristic remanent magnetism (ChRM) recovered from these samples is likely primary or early depositional. Although still in progress, progressive demagnetization experiments on these samples (AF in 2.5mT steps to 10mT followed by finely-spaced thermal steps) yield demagnetization behaviors similar to those reported by Ward et al. (1997). Paleolatitudes have not yet been determined for these cores. We also collected 35 cores from six sites on Gabriola Island (Upper Campanian/Maastrichtian?) and 27 cores from a 25m thick, previously unsampled outcrop in the Queen Charlotte Islands (late Campanian). Both areas contain aragonitic molluscan fossils.
No results are yet available for these sites, however the approximately fifteen million-year time range covered by this collection of samples ought to provide a test for the hypothesis of progressive northward movement of the Insular Superterrane once paleolatitudes have been determined.
