LATEST TRIASSIC TO EARLIEST JURASSIC PALEOMAGNETIC POLE POSITION FROM STRATA ON AND OFF THE COLORADO PLATEAU, WESTERN USA, COMPARED TO ROCKS OF THE NEWARK AND HARTFORD BASINS, EASTERN USA

Paleomagnetic data were acquired from strata of the uppermost Triassic through lowermost Jurassic Moenave Formation, Colorado Plateau region, to obtain a well- defined paleomagnetic pole that could be adequately corrected for the error associated with sediment compaction (inclination shallowing). This new robust dataset is used to test whether the inclination error associated with Moenave Formation strata is consistent with the flattening factor reported for other sedimentary units, and to attempt to reconcile the paleomagnetic data of the southwest USA with those from the Newark and Hartford basins of the eastern USA. Characteristic remanent magnetization (ChRM) directions for 58 sites, from four localities both on and off the Colorado Plateau, were isolated by progressive thermal and chemical demagnetization. The four locality mean directions are statistically indistinguishable, and the normal and reverse polarity data sets share a common mean. The ChRM in the Moenave Formation is interpreted as having been acquired close to the time of sediment deposition across the Triassic-Jurassic transition. Elongation/inclination analysis on the Moenave Formation data set estimates a flattening factor of about 0.73, which is less than that obtained for strata of the Newark and Hartford basins. The paleomagnetic pole we obtained combined with data from previous studies (corrected for inclination error) is at 56.6° N, 62.6° E (A95 = 7.4°, N = 102 independent sites). The pole is corrected for an estimated 4° of clockwise Colorado Plateau rotation, which took place sometime between the mid-Cretaceous and the present and is a maximum estimate of plateau rotation. The combined Moenave Formation pole, corrected with a locally derived flattening factor, supports the existence of a long-proposed J1 cusp, as elucidated by Paleomagnetic Euler Pole (PEP) apparent polar wander path (APW) constructions and lies about 11° west of the composite ca. 200 Ma poles defined by sliding time window methods of the APW path construction for North America.