205 Neoproterozoic Geobiology: Fossils, Clocks, Isotopes, and Rocks

Wednesday, 5 November 2003
8:00 AM - 12:00 PM

TRUE POLAR WANDER, METHANE, AND MOLECULAR CLOCK COMPRESSION OF THE CAMBRIAN EXPLOSION

Paper number: 205-10
Program: Technical Sessions
Time: 10:15 AM – 10:30 AM

Authors

Abstract

The most reliable paleomagnetic data for terminal Neoproterozoic time, taken at face value, calls for multiple episodes of rapid true polar wander (TPW) or else nonuniformitarian geodynamic processes to explain the magnitude and sense of apparent plate motions for all continents[1,2,4].

We have presented a testable hypothesis linking multiple true polar wander events, the Cambrian Carbon Cycles, and the Cambrian Explosion through global greenhouse cycling caused by iterative destabilization of extensive methane clathrate deposits during a legacy of TPW-driven thermohaline eddy and marine sedimentation regime instability[3].

Since generation time in any given phylum varies inversely with ambient temperature, our "True Polar Wander-Clathrate" hypothesis for the Cambrian Explosion predicts an increased intrinsic rate of speciation during the Cambrian Explosion, consistent with independent estimates from geochronologic recalibration of the Cambrian timescale.

We note here a specific but generalizable example in which molecular clock estimates for the divergence of clades are incremented non-linearly. Allopatric speciation and population bottleneck events cause biased divergence date estimates that may be in error by ~33%. Unexpectedly old molecular clock estimates for the last common ancestor of bilateria and metazoans may reflect artifacts induced by enhanced allopatric speciation during the Cambrian Explosion.

[1] D.A. Evans, R.L. Ripperdan and J.L. Kirschvink, Polar Wander and the Cambrian, Science, 279 (1998) 9a-9e. [2] D.A.D. Evans, True polar wander and supercontinents, Tectonophysics, 362 (2003) 303-320. [3] J.L. Kirschvink and T.D. Raub, A methane fuse for the Cambrian explosion: carbon cycles and true polar wander, C. R. Geosci., 335 (2003) 65-78. [4] J.L. Kirschvink, R.L. Ripperdan and D.A. Evans, Evidence for a large-scale Early Cambrian reorganization of continental masses by inertial interchange true polar wander., Science, 277 (1997) 541-545.