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Characterization of magnetic mineral composition within the sedimentary interval containing the Mono Lake excursion from Summer Lake, Oregon, U.S.A.
A high-resolution paleomagnetic record of the 34-31 ka Mono Lake excursion was acquired from sediments of Summer Lake, Oregon. In order to fully understand and trust the magnetic-field behavior recorded in these cores, it is necessary to determine the nature and consistency of the magnetic mineral carrier; particularly with respect to the estimate of paleointensity. Although the magnetic properties are consistent throughout the excursion zone, saturation isothermal remnant magnetization (SIRM), X-Ray diffraction (XRD), and scanning election microscopic (SEM) studies of the excursion interval suggest that there are 3 to 5 different minerals carrying a measureable magnetization. In contrast, Day diagrams derived from hysteresis measurements suggest the mineralogy consists of a uniformly distributed very fine-grained detrital (titano)magnetite. Squareness plots support the notion of multiple magnetic mineral carriers and suggest that a more modern view of nonuniform micromagnetic structures, such as flower and vortex remanent states, is necessary to understand the magnetic properties for the Summer Lake samples.
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