HR: 11:35h
AN: GP41D-06    [PDF]
TI: Paleomagnetism of Devonian Red Beds in the Appalachian Plateau and Valley and Ridge Provinces
AU: * Cox, E
EM: mmkec@aol.com
AF: School of Geology and Geophysics, 100 E. Boyd St., University of Oklahoma, Norman, OK 73019 United States
AU: Elmore, R D
EM: delmore@ou.edu
AF: School of Geology and Geophysics, 100 E. Boyd St., University of Oklahoma, Norman, OK 73019 United States
AU: Evans, M
EM: mae6+@pitt.edu
AF: Department of Geosciences and Planetary Sciences, University of Pittsburgh, Pittsburgh, PA 15260 United States
AB: Samples of fluvial to marine sandstones of the Chemung and Hampshire formations were analyzed from regional-scale and roadcut-scale folds across the structural trend of the Valley and Ridge (VR) and Appalachian Plateau (AP) provinces of northeast Virginia, western Maryland, and northeast West Virginia. Alternating field demagnetization only removes a modern VRM. After removal of a modern VRM, thermal demagnetization of most specimens reveals a characteristic remanent magnetization (ChRM) with southerly declinations and shallow inclinations between 350-600oC. Rock magnetic studies indicate this component resides in hematite. An additional hematite component is removed at temperatures greater than 600oC in a few specimens but is obscured by erratic decay and/or creation of new magnetic phases. Specimens without the ChRM generally have weak NRMs, lack red pigment, only contain the modern VRM, and are dominated by magnetite based on rock magnetic studies. Incremental fold tests for the ChRM yield generally prefolding results from the AP and synfolding results from the VR. The pole positions at the 95% confidence level overlap the late Carboniferous to middle Permian part of the APWP. Low burial temperatures indicate that the ChRMs are chemical remanent magnetizations (CRMs). Thin section analysis shows the presence of detrital magnetite with oxidation rims, authigenic specularite (some within quartz overgrowths), and a submicron size red pigment. Geochemical/fluid inclusion studies indicate that mixed orogenic/meteoric fluids altered the VR red beds; the CRM in the VR could be related to such fluids. In the AP, there is no evidence that the red beds have been altered by orogenic fluids and another chemical mechanism is needed to explain the remagnetization.
DE: 1525 Paleomagnetism applied to tectonics (regional, global)
DE: 1527 Paleomagnetism applied to geologic processes
DE: 1533 Remagnetization
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2003 Fall Meeting