Robert C. Sim HBSc thesis abstract

The geology of the Thunder Bay area exhibits a sequence of flat-lying Proterozoic Aphebian sedimentary rocks essentially free from tectonic deformation.  These unconformably overly the Archean metamorphic rocks.

Within the Proterozoic sequence lies a pronounced, thin, stratiform lapilli tuff.  The tuff comprises crystal fragments, pumice fragments as well as accretionary lapilli and lapilli of other origins.

There has been a strong post-depositional compaction.  This was recognized from shape (strain) analysis of the accretionary lapilli and from the shape and orientation of the magnetic susceptibility ellipsoid.  A preliminary paleomagnetic investigation indicates a paleolatitude of the time of sedimentation (or diagenesis) of about 66°.