Paleomagnetism

The paleomagnetic data suggest that the Insular super-terrain and related coastal mountains’ origin was 3000 km to the south during the middle to late Cretaceous. About 85 to 55 MA the super-terrain was transported northward along the North American coast to its current location on the British Columbia coast, see Figure 1. This is the main idea behind the Baja BC hypothesis (Cowan et al. 1997).

Figure 1. (Cowen et al. 1997)

Because this is a case of latitude transport, the paleolatitudes must be defined, there are two ways of doing this. The first is by paleomagnetism. The second way is to identify the ancient climate (tropical or polar) recorded in the rocks. Faunal data from Baja BC do not provide paleolatitude information beyond Jurassic ammonites having Tethyan and South American affinities, which is not useful in the Baja BC debate (Keppie and Dostal 2001).

To disprove the Baja BC hypothesis the paleomagnetic data must not include poleward transport. Tilting of Cretaceous plutonic rocks, compaction of sedimentary rocks, or synfolding remagnetization of volcanic rocks would all cause errors in the paloemagnetic interpretations. (Housen and Beck 1999). However, since the original data was published in 1972, several more paleomagnetic studies by different authors have been conducted, all showing similar results. No evidence of the above causes of error have been identified.

Ague and Brandon (1996) investigated the possibility of tilting of Mount Stuart and concluded it had only been tilted 8 degrees and posed no significant change in paleomagnetic inclination. In order for compaction to cause a problem, sediments would have to compact enough to shallow the inclination by 30 degrees, Kodama and Ward (2001) found shallowing was no more than 16 degrees. No significant rotation evidence has been found either (Housen and Beck 1999). Fold tests established a 100 percent pre-folding age for the remnants of the rocks studied (Housen et al. 2003).