HR: 0800h
AN: GP21A-0117    [Abstracts]
TI: Paleomagnetism and Magnetostratigraphy of the Upper Triassic Chinle Group in North- Central, Western and Eastern New Mexico
AU: * Zeigler, K E
EM: kaerowyn@unm.edu
AF: Dept. of Earth & Planetary Sci., Northrop Hall, MSC 03-2040 University of New Mexico, Albuquerque, NM 87131, United States
AU: Geissman, J W
EM: jgeiss@unm.edu
AF: Dept. of Earth & Planetary Sci., Northrop Hall, MSC 03-2040 University of New Mexico, Albuquerque, NM 87131, United States
AB: The Upper Triassic Chinle Group spans most of the Late Triassic and was deposited by a large scale fluvial system. Chinle Group strata are composed of predominantly red to purple mudstones with lesser orange siltstones and buff to red sandstones. In the Chama Basin, north-central New Mexico, both lower and upper Chinle strata are well-exposed and sections at several localities have been sampled to develop a more complete magnetic reversal chronology for the Late Triassic of the American Southwest. Localities in eastern and west- central New Mexico were also sampled for comparative purposes. Sampling at all sections concentrated on hematitic mudrocks and these materials typically carry a well-defined, well-grouped, dual polarity magnetization dominated by pigmentary hematite with laboratory unblocking temperatures about 660C we interpret as a primary, Late Triassic remanence (e.g., Painted Desert Mbr., corrected grand mean: D = 182.9°, I = 4.4°, α₉₅ = 2.9°, k = 61.7, N/No = 40/45 sites (14 levels of N polarity, 26 levels of R polarity). The Shinarump Formation (lowest unit of the Chinle Group) failed to yield interpretable magnetizations. The Salitral, Poleo, Petrified Forest and Rock Point formations all yielded magnetizations with either south or north-seeking declinations and shallow inclinations, comparable to those of the Painted Desert Member(e.g.: Poleo Formation grand mean: D = 183.1°, I = 0.3deg, α₉₅ = 5.7°, k = 33.9, N/No = 20/30). Although the Chinle Group of New Mexico was sampled at a relatively coarse sampling interval, the composite, yet incomplete,magnetic reversal chronology derived from these sections compares, at a gross scale, to similar age strata from Arizona, eastern North America and the Tethyan region of southern Europe. Chinle Group strata of Carnian age (based on palynostratigraphy) are of mixed polarity. Lower Norian strata are dominantly of reverse polarity and upper Norian strata are of mixed polarity. Paleopoles calculated from averaged VGPs show very little motion along the apparent polar wander path throughout the Carnian (Salitral Fm. Pole: 56.9°N, 62.0°E, A₉₅ = 4.8°) and early Norian (Petrified Forest Fm., Painted Desert Member: 55.3°N, 67.3°E, A₉₅ = 3.2°), followed by a shift in the pole position in the Late Norian (Rock Point Fm.: 58.5°N, 42.4°E, A₉₅ = 14.8deg).
DE: 1500 GEOMAGNETISM AND PALEOMAGNETISM
DE: 1520 Magnetostratigraphy
DE: 1535 Reversals: process, timescale, magnetostratigraphy
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Fall Meeting