NEW PALEOMAGNETIC RESULTS FROM THE LATEST TRIASSIC TO EARLIEST JURASSIC MOENAVE FORMATION, SOUTHWEST UTAH, AND NORTHWEST ARIZONA

The apparent polar wander (APW) path for North America across the Triassic-Jurassic boundary (TJB) is characterized by a major change in plate motion known as the J-1 cusp. The morphology of the TJB APW path (a sharp versus more diffuse loop) has been a subject of considerable debate, reflecting poorly-sampled sections, uncertainty in stratigraphic relationships, and amount of Colorado Plateau rotation. Both palynological and biostratigraphic arguments suggest the Dinousaur Canyon Member (DCM) (~ 55 m of hematitic fluvial sandstones and siltstones) and overlying Whitmore Point Member (WPM) (~ 25 m of mostly lacustrine deposites) of the Moenave Formation were deposited across the TJB. Paleomagnetic data from the Moenave Formation are useful in the stratigraphic placement of the TJB and better define the path of the J-1 cusp. We have examined four previously un-sampled and well-exposed sections of the DCM and WPM; three are located near St. George, Utah, in the western transition zone of the Colorado Plateau. The fourth is on the Colorado Plateau near Fredonia, Arizona, and is the type section of the WPM. Thermal demagnetization of characteristic remanent magnetization fully unblocks around 670^O, suggesting remanence is mainly held in hematite. Preliminary data from the DCM yields exclusively normal polarity magnetizations. WPM yields mostly normal polarity and one narrow interval of reverse polarity, consistent with previous magnetostratigraphic studies that report a short interval of reverse polarity directly above the TJB, suggesting the TJB may lie within the WPM. Continued field work and paleomagnetic data acquisition will provide further insight into the stratigraphic placement of the TJB and will also refining the morphology of the J-1 cusp.