HR: 0800h
AN: GP11D-0859    [Abstracts]
TI: Refinement of the Magnetostratigraphy of the Chinle Group (Late Triassic) of North-Central and Central New Mexico
AU: * Zeigler, K E
EM: kaerowyn@unm.edu
AF: Dept. of Earth & Planetary Sciences, University of New Mexico, Albuquerque, NM 87131 United States
AU: Geissman, J W
EM: jgeiss@unm.edu
AF: Dept. of Earth & Planetary Sciences, University of New Mexico, Albuquerque, NM 87131 United States
AU: Lucas, S G
EM: SLucas@nmmnh.state.nm.us
AF: New Mexico Museum of Natural History, 1801 Mountain Road NW, Albuquerque, NM 87104 United States
AB: The Upper Triassic Chinle Group spans most of the Late Triassic, as indicated by vertebrate biostratigraphy and palynostratigraphy. The Chinle Group was deposited by a fluvial system and consists predominantly of red to purple mudstones with some red to orange siltstones and red to buff sandstones. The Chama basin, north-central New Mexico, and the Zuni Mountains, central New Mexico, contain excellent exposures of both lower and upper Chinle Group strata that can be used to develop a magnetic reversal chronology for the Late Triassic from these vertebrate-bearing, continental, fluvial-dominated sequences to compare to the Newark as well as to marine magnetostratigraphic records. Our sampling concentrated on mudrocks, using an intricate block sampling approach. These typically carry a well-defined, well grouped magnetization dominated by pigment hematite that is unblocked below about 660\deg C (e.g., for a single horizon, with six independent samples, Decl. = 185.5\deg, Incl. = 0.3\deg, a95= 6.6\deg, and k = 102.6). Sandstones and siltstones contain pigment hematite and, based on preliminary experiments, contain both detrital hematite and some magnetite. An initial reversal chronology has been developed for Poleo and Petrified Forest strata (middle and upper Chinle Group) in the Chama basin and the Bluewater Creek Formation and Blue Mesa Member, Petrified Forest Formation (lower Chinle Group) in the Zuni Mountains. The Petrified Forest Formation in the Chama basin is characterized by fairly regular reversals, and the Poleo Formation is dominated by reverse polarity. In the Zuni Mountains, a reverse polarity chron is defined by strata at the boundary between the Bluewater Creek Formation and the Blue Mesa Member.
DE: 1520 Magnetostratigraphy
DE: 1535 Reversals (process, timescale, magnetostratigraphy)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting