Paleomagnetism of the Zn-rich Pennsylvanian Stark black shale, Kansas City area, U.S.A

HR: 0800h
AN: GP41B-01 [Abstracts]
TI: Paleomagnetism of the Zn-rich Pennsylvanian Stark black shale, Kansas City area, U.S.A.
AU: * Kawasaki, K
EM: kawasak@uwindsor.ca
AF: Department of Earth Sciences, University of Windsor, 401 Sunset Ave., Windsor, ON N9B3P4, Canada
AU: Symons, D T
AF: Department of Earth Sciences, University of Windsor, 401 Sunset Ave., Windsor, ON N9B3P4, Canada
AU: Coveney, R M
AF: Department of Geosciences, University of Missouri, 5100 Rockhill Road, Kansas City, MO 64110, United States
AB: Paleomagnetic results are reported from the metalliferous Stark black shale (Heebner-type) in the Upper Pennsylvanian Kansas City Group. Paleomagnetic analysis of 400 specimens from 28 sites gives a characteristic remanent magnetization (ChRM) in 17 sites that yields a Late Mississippian to Middle Pennsylvanian paleopole at 32.2 ° N 128.5 ° E (dp = 4.7° and dm = 8.8°). The fact that the observed age is slightly older than the host rock age indicates that the shale’s mineralization has a syngenetic origin. The main remanence carrier in the Stark Shale is single or psudosingle domain magnetite or titanomagnetite. Trace hematite, which was generated during modern weathering, likely causes the slightly older age by steepening the primary ChRM by ~2°. The large oval of 95 % confidence is interpreted to be caused by the formation of clay-magnetite aggregates during sediment transport that are easily biased by the gentle paleocurrent at each site acting on their large flat surface. Therefore, the scattered distribution of the site mean remanence declinations found for the Stark Shale is evidence of a detrital remanent magnetization that is formed by primary sedimentary processes and not of remagnetization by secondary hydrothermal processes. The finding that the primary ChRM directions of Heebner-type black shales are so easily scattered by sedimentary processes implies that a highly clustered ChRM direction in a mineralized black shale, such as in Zn-Pb rich SEDEX deposits, is evidence of coeval or post-depositional hydrothermal fluids.
DE: 1527 Paleomagnetism applied to geologic processes
DE: 1540 Rock and mineral magnetism
DE: 3022 Marine sediments: processes and transport
DE: 5109 Magnetic and electrical properties (0925)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Joint Assembly