HR: 0800h
AN: GP11D-0873    [Abstracts]
TI: A Late Cretaceous Reversal Recorded in Lavas of the High Canadian Arctic
AU: * Sinnett, D K
EM: ds002k@mail.rochester.edu
AF: Department of Earth & Environmental Sciences, University of Rochester 227 Hutchison Hall, Rochester, NY 14627 United States
AU: Tarduno, J A
EM: john@earth.rochester.edu
AF: Department of Earth & Environmental Sciences, University of Rochester 227 Hutchison Hall, Rochester, NY 14627 United States
AU: Cottrell, R D
EM: rory@earth.rochester.edu
AF: Department of Earth & Environmental Sciences, University of Rochester 227 Hutchison Hall, Rochester, NY 14627 United States
AB: We report new directional data from Late Cretaceous basaltic lavas of northern Ellesmere Island, Canada (present day latitude 81-82$^{o}$ N). Analyses of a preliminary field sampling suggested the presence of a reversed to normal polarity transition. We collected new sites (drilled as standard paleomagnetic cores oriented with a Sun compass) from the same stratigraphic section as the preliminary sampling to confirm the reversal. A portable magnetometer (a three axis fluxgate magnetometer in Mu-metal shields) was used to check sample polarity in the field and guide sampling. In addition to the lavas, we sampled dikes from an adjacent area; the two areas are separated by faults. Detailed thermal and alternating field demagnetizations of cores from 34 sampling sites yield characteristic remanent magnetization directions that can be grouped into the following: reversed polarity lava flows, normal polarity lava flows, transitional lava flows, and normal polarity dikes. Based on these results, the lavas are considered to be at least 15 million years younger (corresponding to chron 33r or younger) than the widespread $\sim$95 Ma volcanic rocks of the Strand Fiord Formation. Fisher averages of the preliminary normal and reversed polarity flows are nearly antipodal. Sites from the dikes, however, represent a distinct group of directions and therefore may differ in age from the lavas. The preliminary paleomagnetic data and reconstructions based on other data indicate that the lavas were erupted near the tangent cylinder, that imaginary cylinder parallel to the spin axis and tangent to the solid inner core. Hence, directional and paleointensity results from these and future sites may ultimately be useful for understanding the dynamo.
DE: 1525 Paleomagnetism applied to tectonics (regional, global)
DE: 1535 Reversals (process, timescale, magnetostratigraphy)
DE: 1594 Instruments and techniques
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting