Earth Planets Space, Vol. 58 (No. 10), pp. 1295-1302, 2006
Mouloud Benammi1, Jesus Alvarado-Ortega2, and Jaime Urrutia-Fucugauchi1
1Laboratorio de Paleomagnetismo y Geofisica Nuclear, Instituto de Geofísica, UNAM, 04510 México, D.F., Mexico
2Departamento de Paleontologia, Instituto de Geologia, UNAM, 04510 México, D.F., Mexico
(Received November 23, 2005; Revised March 7, 2006; Accepted May 11, 2006; Online published November 8, 2006)
A stratigraphic sequence of magnetic polarity reversals consisting of nine magnetozones is recognized in Early Cretaceous sedimentary strata in the Tlayúa Quarry of Tepexi de Rodriguez, state of Puebla. Combined with biostratigraphic age assignments using ammonites that apparently belonging to the Albian, the geomagnetic polarity sequence can be correlated with the middle part of chron C34n (C34n.1n-C34n.2n chrons, with an age of 100-105 Myr), the Cretaceous long normal interval. The magnetic properties and characteristic remanence of magnetization are dominated by soft and hard coercivity magnetic minerals. 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°, respectively. Comparison with the North American apparent polar wander path indicates tectonic stability of the region since the Cretaceous.
Key words: Magnetostratigraphy, cretaceous, ammonite biostratigraphy, Tlayúa, Mexico, North America.