A negative fold test on the Lorrain Formation of the Huronian Supergroup: Uncertainty on the paleolatitude of the Paleoproterozoic Gowganda glaciation and implications for the great oxygenation event

Previous paleomagnetic studies of the glaciogenic Gowganda and Lorrain formations have identified several low-inclination magnetic components of high thermal stability, which suggest low-latitude glaciation during deposition of the Huronian Supergroup, Canada. While extraordinary claims demand extraordinary proof, prior authors have been unable to support their interpretations of these components conclusively with any of the classic field stability tests (e.g., conglomerate, fold, and baked contact) capable of demonstrating that the magnetization was acquired at or soon enough after the time of deposition to be used to constrain the paleolatitude of the Gowganda or Lorrain formations. We report here the results of a fold test from the bpurple siltstoneQ member of the Lorrain Formation near the town of Desbarats, Ontario, which indicate that none of the reported components dates to the time of deposition. Hence, the paleolatitude of the Gowganda glaciation is uncertain. Comparison of the lithostratigraphic, paleomagnetic, and radiometric constraints on the Huronian sequence and the Transvaal Supergroup of Southern Africa implies that the one verified low-latitude Paleoproterozoic glacial event (the Makganyene glaciation, Transvaal Supergroup, South Africa) is younger than the three glacial units of Canada. With this correlation, the physical rock record indicates that the dgreat oxygenation eventT began in the time interval between the Gowganda and Makganyene glaciations. These data are consistent with the sudden evolution of oxygenic photosynthesis destroying a methane greenhouse and thereby triggering the first Snowball Earth event in Earth history. D 2005 Elsevier B.V. All rights reserved.