RECONSTRUCTING THE CAMBRIAN WORLD THROUGH PALEOMAGNETISM

Cambrian continental reconstructions create a biogeographic framework for the ?explosion? of animal life, and they may also provide clues toward the causes of biological radiation. The unusual rapidity of Cambrian continental motions is now well established; more contentious has been the recent proposal that these motions were synchronized in a true polar wander (TPW) event involving wholesale migration of the mantle as much as 90° relative to Earth?s spin axis (Kirschvink et al., Science, 1997). Rapid TPW should have been a dominant influence on relative sea-level variations and oceanic circulation patterns, affecting rates of allopatric speciation and biogeochemical fluxes. As an example, a significant portion of the Sauk transgression across Laurentia may result from delayed viscoelastic response of the upper mantle to realignment of the planet?s equatorial bulge, rather than merely eustatic sea-level rise. Similar large-magnitude changes to flooding of other continents could have promoted burial and release of methane hydrates to the atmosphere, affecting both global temperature and carbon cycling (represented by numerous seawater 13-C excursions) in the Early Cambrian. The TPW model also predicts an absolute paleogeography for the major continents, that is consistent with tectonostratigraphically based reconstructions. New paleomagnetic data from Gondwanaland and Siberia support an Early Cambrian TPW rotation of 60-70°, whereas data from Laurentia and Baltica are presently inadequate to test the hypothesis.