Paleomagnetism of the Moenkopi and Chinle Formations in central New Mexico: Implications for the North American Apparent Polar Wander Path and Triassic magnetostratigraphy

In central New Mexico, red sedimentary rocks unconformably overlying Permian carbonates of the San Andres Formation have been correlated with the Early-Middle Triassic Moenkopi and Late Triassic Chinle Formations of the Colorado Plateau. Paleomagnetic samples from Triassic sections exposed on basement cored uplifts along both the east and west side of the Rio Grande rift near Albuquerque yield, upon thermal and chemical demagnetization, well-defined, high unblocking temperature, dual-polarity magnetizations carried by hematite. The characteristic magnetization is interpreted as an early acquired chemical remanent magnetization based on a positive intraformational microconglomerate test and bedding-parallel magnetization polarity zonation. The Moenkopi and lowermost Chinle formations produced paleomagnetic poles respectively at 57.6°N-100.3 °E (N=36 sites, K=74.1, A95=2.8°) and 60.8°N-88.9°E (N=17 sites, K=130.3, A95= 3.1°). These data plus previously published and additional results from the underlying Permian strata suggest that portions of central New Mexico have experienced a small clockwise rotation (i.e., less than 10°) similar to that of the Colorado Plateau with respect to the North American craton. The paleomagnetic directions of the Chinle Formation and related strata in eastern New Mexico document about 12° (great circle distance) of rapid apparent polar wander during mid-Carnian to late Norian times along a track which contains other cratonic poles of similar age. We present a preliminary magnetic polarity time scale for the Triassic that incorporates the present New Mexico data and previously published data, mostly form continental red bed sequences. This magnetic polarity scale provides a basic framework which can be tested with future data from Triassic sections where additional biostratigraphic control exists.