HR: 0830h
AN: GP41A-11    [Abstracts]
TI: Magnetic polarity stratigraphy of "Mexican Solnhofen" Tlayua Formation, Tepexi de Rodriguez, State of Puebla, Mexico
AU: Benammi, M
EM: mouloud@igeofcu.unam.mx
AF: Instituto de Geofisica Depto de Paleomagnetismo y Geofisica Nuclear UNAM, Ciudad Universitaria, MEXICO D.F., 04510 Mexico
AU: Alvarado-Ortega, J
EM:
AF: Instituto de Geologia UNAM, Ciudad Universitaria, MEXICO D.F., 04510 Mexico
AU: * Urrutia-Fucugauchi, J
EM: juf@igeofcu.unam.mx
AF: Instituto de Geofisica Depto de Paleomagnetismo y Geofisica Nuclear UNAM, Ciudad Universitaria, MEXICO D.F., 04510 Mexico
AB: The Tlayua Formation is the richest Cretaceous fossiliferous locality in Mexico. Research in the quarry has yielded thousands of fossil fish associated with other vertebrate remains. From a vertical section, a total of 95 paleomagnetic specimens from 31 horizons were measured to determine the paleomagnetic signal. Limestones are weakly magnetized and exhibit in general two component magnetizations. The magnetic properties and characteristic remanence are dominated by soft and hard coercivity magnetic minerals, most of which probably formed early in the depositional and diagenetic history. Rock-magnetic properties and a positive reversal test suggest that remanence is primary. The section displays both reverse and normal polarities with mean directions: D = 344.9°, I = 32.4°, k= 21, a95= 4.2°; and D = 149.4°, I = -36.6°, k= 17, a95= 8.7°. Comparison with the North America reference curve, indicates tectonic stability of the region since the Cretaceous. Correlation of these polarity zones with the geomagnetic polarity time scale provides a time framework for the discrepancy of the previous biochronological studies. Based on biostratigraphic age assignments using ammonites, the polarity magnetozone sequence correlates with C34n.1n-C34n.2n chrons, with an age of 100 to 105 Ma for the Tlayua Formation.
DE: 1535 Reversals (process, timescale, magnetostratigraphy)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2005 Joint Assembly