HR: 12:05h
AN: GP12A-08    [Abstracts]
TI: Magnetic Hysteresis Parameters and Day-Plot Analysis to Delineate Diagenetic Alteration in Gas Hydrate-Bearing Sediments
AU: * Enkin, R J
EM: renkin@nrcan.gc.ca
AF: Geological Survey of Canada - Pacific, P.O. Box 6000, Sidney, BC V8S 1A9 Canada
AU: Baker, J
EM: jubaker@nrcan.gc.ca
AF: Geological Survey of Canada - Pacific, P.O. Box 6000, Sidney, BC V8S 1A9 Canada
AU: Nourgaliev, D
EM: danis.nourgaliev@ksu.ru
AF: Geology - Kazan State University, Kremlyevskaya str., 18, Kazan, 420008 Russian Federation
AU: Iassonov, P
EM: Paul.Iassonov@ksu.ru
AF: Geology - Kazan State University, Kremlyevskaya str., 18, Kazan, 420008 Russian Federation
AB: Gas hydrates are naturally occurring cage structures of ice found in continental slope and permafrost sediments. They contain vast quantities of methane which is important both as a climate driver and an energy resource. Hydrate formation alters the redox potential of interstitial fluids which can in turn alter magnetic minerals. Thus magnetic methods can help delineate diagenetic pathways, provide a proxy method to map out past hydrate occurrences, and eventually lead to new remote sensing methods in prospecting for gas hydrates. We present data acquired using a J-Meter Coercivity Spectrometer. Induced and remanent magnetism are simultaneously measured on 1.5 cc samples as they spin on a 50 cm diameter disk, 20 times per second. The applied field ramps between ± 500 mT to produce a hysteresis loop in 7 minutes. Sub-second viscous decay is measured to provide a proxy for the amount of superparamagnetism present. The rapid and simple measurements made possible by this robust machine are ideal for core logging. Measurements made on frozen core from the Mallik permafrost gas hydrate field in Canada's Northwest Territories demonstrates that the magnetic properties are dependent on the concentration of gas hydrate present. Day-plots of magnetic hysteresis parameter ratios distinguish the magnetic carriers in gas hydrate rich sediments. The original magnetite is often reduced to sulphide when gas hydrate concentration exceeds 40%. In other high-concentration gas hydrate horizons, fine single-domain (SD) grains of magnetite apparently dissolve leaving nothing but large multi-domain (MD) magnetite grains. Independently measured superparamagnetism is shown to push hysteresis ratios off the hyperbola expected for SD-MD mixtures, as predicted by Dunlop [JGR, 10.10291/2001JB000486, 2002]. Magnetic study of host sediments in gas hydrate systems provides a powerful core-logging tool, offers a window into the processes of gas hydrate formation, and forms the basis for quantitative analysis of magnetic surveys over gas hydrate fields.
DE: 1540 Rock and mineral magnetism
DE: 3004 Gas and hydrate systems
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005