Paleomagnetic and mineral magnetic analyses were carried out on Miocene clays from upper unit II at Sites M0027 and M0028 recovered during Integrated Ocean Drilling Program Expedition 313 on the New Jersey shallow shelf. A zone of mixed polarity in the lower section of Hole M0028A and dual overlapping magnetization components in upper Hole M0027A indicate that the sediments may have been chemically remagnetized during one or several events. Mineral magnetic investigations reveal that the magnetization is carried by the ferromagnetic iron-sulfide greigite (Fe3S4), possibly with traces of titanomagnetite. Study authors Andreas Nilsson and colleagues find that several changes in polarity coincide with variations in magnetic mineral grain size and/or concentration. They interpret these variations to be different stages of greigite growth, which were triggered by changes in pore-water chemistry and/or upward migration of methane.
Geometry and Quaternary slip behavior of the San Juan de los Planes and Saltito fault zones, Baja California Sur, Mexico: Characterization of rift-margin normal faults
Melanie M. Coyan et al., School of Earth and Space Exploration, Arizona State University, PO Box 871404, Tempe, Arizona 85287, USA. Published online 4 Apr. 2013; http://dx.doi.org/10.1130/GES00806.1. Themed issue: Origin and Evolution of the Sierra Nevada and Walker Lane.
An array of north-striking, left-stepping, active normal fault
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Geological Society of America