HR: 09:30h
AN: GP41A-07    [PDF]
TI: Environmental Magnetism of Corals from Moorea, French Polynesia
AU: * Verosub, K L
EM: verosub@geology.ucdavis.edu
AF: Dept. of Geology, University of Californa, Davis, Davis, CA 95616 United States
AU: Delusina, I
EM: delusina@geology.ucdavis.edu
AF: Dept. of Geology, University of Californa, Davis, Davis, CA 95616 United States
AB: We have examined the environmental magnetic record of cores from corals on the island of Moorea in French Polynesia. The cores were collected by diamond core drilling in a nearshore environment, and each core represents about twenty years of coral accretion. The cores were sub-sampled to produce continuous strips of material that were placed in u-channels and measured with an automated long-core cryogenic magnetometer. Not surprisingly, the overall concentration of magnetic material in the cores is at or below the detection limits of the magnetometer. However, several cores contain thin layers with considerably higher levels of magnetic material. We have studied the behavior of these layers during the acquisition of a saturation isothermal remanent magnetization as well as the alternating field demagnetization of that magnetization and an anhysteretic remanent magnetization. This behavior can be compared with that of soils collected from the island itself. We find a good match between the magnetic properties of the layers in the corals and the soils developed on strongly weathered volcanic rock. We suggest that the layers in the corals were created when large amounts of soil were washed from the island into nearby lagoons. If that hypothesis is correct, then the environmental magnetic record of corals can provide new information about the occurrence of very large storm events on tropical volcanic islands.
DE: 0315 Biosphere/atmosphere interactions
DE: 0400 Biogeosciences
DE: 1512 Environmental magnetism
DE: 1540 Rock and mineral magnetism
DE: 4808 Chemical tracers
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2003 Fall Meeting