PALEOMAGNETIC ANALYSIS OF THE APACHE CANYON FORMATION, ARIZONA: IMPLICATIONS FOR TECTONICS OF THE BISBEE BASIN

The objectives of this project are to (1) constrain an age for lacustrine/fluvial sediments within the Chihuahua Trough, in particular the Bisbee Basin, and (2) determine the timing of this lacustrine sedimentation relative to the main episode of tectonism. The Bisbee Basin is an extensional basin of late Jurassic to early Cretaceous in age. Most previous studies suggest the lacustrine sediments were deposited in the Aptian-Albian after the main phase of extensional tectonics and during the long Cretaceous Normal Superchron. Preliminary paleomagnetic research indicates that deposition of the Bisbee Group may have occurred earlier than the Aptian-Albian. Paleomagnetic results indicate the presence of two magnetizations. One component removed by alternating field treatment, has generally northerly and down directions. The second component, removed by subsequent thermal demagnetization, has southerly and moderate up directions. The two components are arranged in apparent stratigraphic magnetozones. Additional work is underway to determine if the components are detrital in origin and record a magnetostratigraphy or if the rocks have been remagnetized and record a false magnetostratigraphy. If the magnetostratigraphy is real, then the results challenge the established depositional history of the Bisbee Basin and provides further insight into both tectonic and paleoclimatic regimes from the period. The tectonic history of the Bisbee Basin is changed if the lacustrine strata of the Bisbee Group are in fact late Jurassic in age since that implies they are coeval with the main rifting phase of the Bisbee Basin.