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Rocky Mountain (63rd Annual) and Cordilleran (107th Annual) Joint Meeting (18–20 May 2011)

Paper No. 2
Presentation Time: 8:25 AM

PRELIMINARY MAGNETIC POLARITY CHRONOLOGY DATA FOR THE LOWER CHINLE FORMATION (LATE TRIASSIC) FROM THE SOUTHERN PORTION OF PETRIFIED FOREST NATIONAL PARK, ARIZONA


ZEIGLER, Kate E., Natural Resources, New Mexico Highlands University, Box 9000, Las Vegas, NM 87701, PARKER, William G., Jackson School of Geosciences, University of Texas, Austin, TX 78712-0254, MARTZ, Jeffrey W., Division of Resource Management, Petrified Forest National Park, P.O. Box 2217, 1 Park Road, Petrified Forest, AZ 86028, HUFFMAN, Amanda H., Dept. of Earth and Planetary Sciences, Univ of New Mexico, Northrop Hall, Albuquerque, NM 87131 and GEISSMAN, J.W., Department of Geosciences, University of Texas at Dallas, 800 West Campbell Road, Richardson, TX 75080, katezeigler@nmhu.edu

Recent work in the Upper Triassic Chinle Formation at Petrified Forest National Park (PEFO) in eastern Arizona seeks to refine a composite magnetic polarity chronology previously reported by Steiner and Lucas (2000). Localities with either detailed measured stratigraphy and/or well-characterized vertebrate fossil assemblages, which provide the best biostratigraphic and lithostratigraphic constraints, were examined for magnetic polarity. New detrital zircon geochronologic data from the Sonsela Member greatly refine age constraints for magnetostratigraphic correlations. We concentrated on the lowest strata exposed in the park, the Mesa Redondo, Blue Mesa and Sonsela Members, as well as the base of the Petrified Forest Member (stratigraphy of Martz and Parker, 2010). Sampling involved either drilling cores or collecting oriented blocks of mudstone and up to eight individual oriented samples were taken every meter at two localities and every three meters at two others. Preliminary site mean data for the Blue Mesa and Sonsela Members indicate that most Chinle strata from southern PEFO yield magnetizations with south or north-seeking declinations and shallow inclinations (e.g., Jim Camp Wash beds Site 1: D = 006.6º, I = -2.8º, α95 = 4.9º, k = 191.1, N/No = 6/7 samples), which are interpreted as primary, Late Triassic magnetizations. We utilize a more robust lithostratigraphic framework than previous work and incorporate all relevant biostratigraphic and chronostratigraphic information to develop a more accurate composite magnetic polarity for the Chinle Formation in northern Arizona. Recent work in New Mexico shows that Chinle strata include numerous subtle disconformities. Comparisons of magnetostratigraphic data for different localities of Upper Triassic strata will shed additional light on the timing and duration of sedimentation in different parts of the Chinle depositional basin.

Session No. 1

Sedimentology and Stratigraphy
Wednesday, 18 May 2011: 8:00 AM-12:00 PM
Cottonwood (Riverwoods Conference Center)
Geological Society of America Abstracts with Programs. Vol. 43, No. 4, p.1
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