27. PALEOMAGNETIC AND ROCK MAGNETIC PROPERTIES OF SEDIMENT SAMPLES FROM OCEAN DRILLING PROGRAM LEG 116, CENTRAL INDIAN OCEAN1

A representative suite of samples from cores obtained at the three Leg 116 sites, 717, 718, and 719, were studied to determine their magnetic properties and measure paleomagnetic directions. These samples were treated to alternating field and thermal demagnetization. Additionally, selected samples were examined by thermomagneti c analysis, isothermal remanent magnetization acquisition analysis, and measurement of the anisotropy of magnetic susceptibility (AMS). Most samples were dominated by a vertical overprint that in many cases was impossible to fully remove. As a consequence, paleolatitudes determined from these samples are unreliable. The rock magnetic studies indicate that magnetite and hematite are probably the primary magnetic minerals, but that maghemite and goethite also contribute to the magnetism of these sediments. Attempts to correlate magnetic behavior with sediment lithology met with little success and demonstrated that the magnetic properties vary as much within each lithology as between different lithologies. AMS measurements showed a clear sedimentary fabric with a horizontal axis of maximum susceptibility. However, because of the lack of azimuthal orientation of the cores, it was not possible to determine whether the maximum susceptibility axes show a preferred direction or trend.