Magnetostratigraphic importance of secondary chemical remanent magnetizations carried by greigite (Fe3S4) in Miocene sediments, New Jersey shelf (IODP Expedition 313)

摘要

Paleomagnetic and mineral magneticnanalyses were carried out on Miocene claysnfrom upper unit II at Sites M0027 and M0028nrecovered during Integrated Ocean DrillingnProgram Expedition 313 on the New Jerseynshallow shelf. A zone of mixed polarity in thenlower section of Hole M0028A and dual overlappingnmagnetization components in uppernHole M0027A indicate that the sedimentsnmay have been chemically remagnetized duringnone or several events. Mineral magneticninvestigations reveal that the magnetizationnis carried by the ferrimagnetic iron-sulfi dengreigite (Fe3S4), possibly with traces of titanomagnetite.nWe fi nd that several changes innpolarity coincide with variations in magneticnmineral grain size and/or concentration. Weninterpret these variations as different stagesnof greigite growth, which were triggerednby changes in pore-water chemistry and/ornupward migration of methane.