HR: 1340h
AN: GP33A-0108    [Abstracts]
TI: Preliminary Magnetostratigraphy of the Pennsylvanian-Permian Horquilla Formation at New Well Peak, Big Hatchet Mountains, Southwestern New Mexico
AU: * Zeigler, K E
EM: kaerowyn@unm.edu
AF: Department of Earth & Planetary Sciences, Northrop Hall, University of New Mexico, Albuquerque, NM 87131
AU: Molina-Garza, R S
EM: rmolina@geociencias.unam.mx
AF: Centro de Geosciencias, Campus Juriquilla UNAM, Queretaro, 76230 Mexico
AU: Geissman, J W
EM: jgeiss@unm.edu
AF: Department of Earth & Planetary Sciences, Northrop Hall, University of New Mexico, Albuquerque, NM 87131
AU: Lucas, S G
EM: spencer.lucas@state.nm.us
AF: New Mexico Museum of Natural History and Science, 1801 Mountain Rd. NE, Albuquerque, NM 87104
AB: The Big Hatchet Mountains in southwestern New Mexico contain excellent outcrop exposures of the Pennsylvanian to Permian (Morrowan to Wolfcampian) Horquilla Formation. At New Well Peak in the Big Hatchets, the Horquilla section is about 1000 m thick and consists of intercalated limestones and marine shales, all of which generally dip ~25° to the southeast. This section is one of the few in the western USA where sedimentation was apparently continuous across the Pennsylvanian-Permian boundary. We sampled each limestone bed in the ~180-m-thick Horquilla section that spans the Pennsylvanian-Permian boundary, resulting in 42 sites (4-6 samples/site). To date, a small subset of the samples (30 specimens) shows well-defined magnetizations in both progressive thermal and alternating field demagnetization. 90% of NRM is unblocked by about 420°C and in AF demagnetization, median destructive fields are about 40-60 mT. This subset of the collection yields a preliminary in situ grand mean direction of D=2.5°, I=37.4°, α₉₅=4.9° and k=28 and a corrected grand mean direction of D=16.7°, I=59.4°. These initial data indicate that the upper Paleozoic carbonate rocks have been remagnetized (probably during the Tertiary); the direction of the secondary magnetization implies that the Big Hatchet Mountains have experienced a modest clockwise rotation post-Pennsylvanian-Permian deposition.
DE: 1520 Magnetostratigraphy
DE: 1525 Paleomagnetism applied to tectonics: regional, global
DE: 1533 Remagnetization
DE: 1535 Reversals: process, timescale, magnetostratigraphy
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005