GEOLOGY: Tales of Wander

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Science  15 Sep 2006:
Vol. 313, Issue 5793, pp. 1542c
DOI: 10.1126/science.313.5793.1542c

True polar wander describes relative motion between Earth's spin vector and the solid Earth. One class of this phenomenon, inertial interchange true polar wander, occurs when normal advection of mantle density heterogeneities produces changes in the relative magnitudes of the principal inertia axes, causing Earth to rotate quickly by as much as 90°, until the new major rotational axis is aligned with the spin vector. In addition to the paleomagnetic variations that would accompany such a rapid change of Earth's orientation, another observable consequence could be transient sea-level variations resulting from the differential response of the slowly re-equilibrating mantle/lithosphere and the rapidly re-equilibrating world ocean. A third potential but indirect effect, arising from sea-level change, is perturbation of the carbon cycle, as marine biological productivity is affected by water depth variations.

In an investigation of possible true polar wander, Maloof et al. present paleomagnetic data from three Middle Neoproterozoic carbonate units in Svalbard, Norway, which show large shifts in paleomagnetic orientation coincident with abrupt changes in δ13C and relative sea level. They conclude that the best explanation for the data is that this area experienced rapid shifts of paleogeography during a pair of true polar wander events. Their hypothesis can be further tested by analyzing sediments of the same age from other basins for predictable related changes. — HJS

Geol. Soc. Am. Bull. 118, 1099 2006).

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