2005 Salt Lake City Annual Meeting (October 16–19, 2005)

Paper No. 3
Presentation Time: 8:00 AM-12:00 PM


DICKINSON, William R., Department of Geosciences, Univ of Arizona, Box 210077, Tucson, AZ 85721, wrdickin@geo.arizona.edu

Paleomagnetic remanence in redbeds of the Colorado Plateau, and in correlative strata on the High Plains as rotated into Colorado Plateau coordinates to compensate for plateau rotation, define a paleolatitude track implying that the sand seas of major Colorado Plateau Jurassic ergs were deposited at paleolatitudes of 10-17 degrees, wholly at variance with the current latitudes of modern low-altitude desert belts at 17-28 degrees. The discrepancy has been explained by the postulate of anomalous paleoclimatic patterns when Pangea lay astride the equator to disrupt the zonal circulation of global air masses. Recent E/I analysis of redbed paleomagetism in the Newark basin (Kent and Tauxe, 2005 Science 307:240-244) indicates, however, that redbed remanence incorporates significant compaction flattening (average f factor of 0.56), requiring adjustment of Newark paleopoles to compensate for the flattening. Unadjusted Newark paleopoles, when rotated into Colorado Plateau coordinates, imply the same Late Triassic paleolatitude for the Colorado Plateau as do unadjusted paleopoles derived from Upper Triassic Chinle redbeds on the Colorado Plateau and High Plains The flattening correction required to adjust Newark paleopoles suggests that all paleopoles (n~35) derived from Colorado Plateau redbeds also require adjustment to compensate for flattening of paleomagnetic vectors. Either the Newark E/I analysis is invalid or the unadjusted Colorado Plateau paleopoles are invalid. If the flattening factor derived from E/I analysis for Newark redbeds is applied to Colorado Plateau paleomagnetic data to derive adjusted paleopoles, the implied paleolatitude for major Colorado Plateau Jurassic ergs is raised to 17-28 degrees, removing the discrepancy with known latitudes for modern desert belts. If my treatment of Colorado Plateau data by analogy with Newark data is valid, all apparent polar wander paths based in whole or in part on redbed paleomagnetism require additional scrutiny to remove the effects of compaction flattening of paleomagnetic vectors.