Origin of the sedimentary magnetic record at Ocean Drilling Program Sites on the Owen Ridge, western Arabian Sea

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The 3.2-m.y. whole core magnetic susceptibility record obtained during ODP leg 117 from the Owen Ridge represents one of the most convincing demonstrations of the ability of rock magnetic measurements to yield paleoceanographically significant information. The salient features of this record are that 1) it correlates strongly with variations in the concentration and flux of eolian dust; 2) it is driven strongly at Earth orbital periodicities; and 3) there is a significant change in the spectral character at 2.4 m.y., which may reflect the effect of the initiation of major northern hemisphere glaciation on aridity cycles within the eolian source areas. In view of its potential paleoclimatic significance, the origin of the rock magnetic signal was examined in more detail. Despite the strong relationship throughout the record between magnetic susceptibility and percent terrigenous content, there has been significant postdepositional alteration of the magnetic minerals via the process of reductive diagenesis. It is found that titanomagnetite grains with higher Ti contents may be more resistant to this process. -from Authors

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Journal of Geophysical Research