I found this topic and the claim that 'pole shifts' happened recently and are about to happen again intriguing. When I was an undergraduate taking a philosophy of science course, we were required to write a paper on pseudoscience. I chose a book called "Pole Shift" by John White who claims, like Duane, that we are about to experience one of these events soon. At any rate, it is useful to examine whether or not such an event could occur. Geologists have assembled reasonable evidence for the following:
(a) Motion of the continents (lithosphere)
(b) Motion of the mantle+lithosphere as a single unit called True polar wander. The magnitude of this 'whole outer earth' motion is 1-2 degrees/million years max.
(c) Physically, it is also possible for the entire outer part of the earth to move through 90 degrees in a process called intertial interchange true polar wander (IITPW). What happens is that the moment of the intermediate axis of inertia becomes slightly greater than the maximum inertial axis (they are quite close anyway) such that the two interchange (i.e. intermediate becomes maximum and maximum becomes intermediate). While this is physically possible, the only postulated IITPW event (Kirschvink et al., 1997) did not hold up under scrutiny (see Torsvik et al., 1998 and Meert, 1999). I should also point out that this event takes ~15 million years to occur (66 cm/year). It does not happen as fast as postulated in this discussion. Basically, the viscosity of the mantle limits the speed at which the mass redistribution can take place.
(d) Magnetic reversals: Here (as others have mentioned), the north magnetic pole becomes oppositely directed, but there is no geographic change. For example, today the inclination at the north magnetic pole is straight down, in a reversal, the inclination would be straight up.
The bible speaks figuratively about earth changes in the days of Peleg, you are free to interpret the bible in this manner, but the evidence you cite (ice cores) has no bearing whatsoever on the issue of whether or not inertial axes have tumbled through 180 degrees (a double interchange event). Basically a short interchange event such as Duane wishes would require a near instantaneous response to mass imbalance and a near water-like viscosity for the mantle. That would have devastating effects on the continents which would sink rapidly to the core boundary and extinguish all life. So, it's up to Duane to posit a physical process that could result in such an event without causing other problems.
Ref:
Kirschvink et al. 1997, Science v. 277, pp. 541-545.
Torsvik et al., 1998, Science v. 279, p 9a (can be viewed online at
http://www.sciencemag.org/cgi/content/full/279/5347/9a)
Meert, 1999. Earth Planetary Science Letters, v. 168, 131-144 (can be downloaded at
http://www.clas.ufl.edu/users/jmeert/meert.pdf