A strong 41-k.y. periodicity characterizes wet-bulk density and optical density variation at both sites throughout most of the past 3.4 m.y. Cyclicity at the 41-k.y. periodicity is characterized by a lack of coherence between wet-bulk density and optical density suggesting that the bulk density and color cycles reflect the mixed influence of varying abundance of terrigenous sediments and organic matter. The 23-k.y. periodicity in wet-bulk density and sediment color cycles is generally characterized by significant coherence between wet-bulk density and optical density, which reflects an inverse relationship between these parameters.