Color reflectance (red/blue ratio) and total reflectance show characteristic cycles in olive-gray sediments from the Congo Fan region (Ocean Drilling Program Site 1075). To test the hypothesis that these are productivity cycles with a precessional periodicity, we constructed a detailed age model based on matching the magnetic susceptibility record to an oxygen-isotope standard from the Ontong Java Plateau (OJsox96). The fit is excellent for sedimentation rates near 100 m/m.y., especially if the susceptibility data are processed by partial forward integration (assuming that peaks in susceptibility are associated with sea-level rise). The age model thus derived allows a study of spectra and phase of the color cycles. The red/blue ratio has indeed strong precessional power (as expected for productivity cycles in this region), which is especially pronounced in the last 500 k.y. Total reflectance displays the characteristic beat pattern from eccentricity modulation. Obliquity cycles are present in the last 350 k.y., but they are subdued. This indicates that monsoonal forcing is much more important here than high-latitude forcing in producing lithologic changes expressed as sediment color.
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