HR: 0830h
AN: GP41C-0056    [PDF]
TI: Testing for compaction-shallowing, and tectonic implications of the paleomagnetism of the late Cretaceous sediments of the Gualala Block, northern California
AU: * Heim, K A
EM: kheim02@yahoo.com
AF: Western Washington University, 516 High Street MS 9080, Bellingham, WA 98225
AU: Housen, B A
EM: bernieh@cc.wwu.edu
AF: Western Washington University, 516 High Street MS 9080, Bellingham, WA 98225
AB: The Gualala Block is a discrete package of sediments of late Cretaceous to Eocene age contained in the Point Arena Terrane. The terrane is located on the continental margin outboard of the San Andreas Fault in northern California. Rudistid bivalves were discovered in the late Cretaceous Anchor Bay member, suggesting a sub-tropical paleolatitude (Kodama and Ward, 2001). A paleomagnetic study will be undertaken to determine paleolatitude to provide an estimate of post-Cretaceous displacement with implications for Cordilleran margin paleogeography. A total of 395 specimens from 26 sites were collected from the Anchor Bay and Stewarts Point members of the Gualala Block. At present, 130 specimens have been demagnetized via several methods with varying results. Among the demagnetization methods employed are low temperature treatment with liquid nitrogen, alternating field, thermal, and combinations of alternating field and thermal. Most specimens so far exhibit a well-behaved first-removed component of magnetization. After removal of this magnetization component, the vast majority of the specimens do not display a well-defined primary magnetization. At present 4 of the sites exhibit the potential to contain definable second-removed components. The anisotropy of magnetic susceptibility will be measured for each specimen indicating the amount of magnetic fabric. The magnetic fabric will be compared with the inclination to evaluate for possible compaction shallowing. The results of the compaction shallowing study will be used to determine the paleolatitude of the Anchor Bay Formation.
DE: 1525 Paleomagnetism applied to tectonics (regional, global)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2003 Fall Meeting