Figure F20. Latitudinal transect of Si mass accumulation rate (MARs) for three time slices: early Oligocene (25–34 Ma), middle Eocene (38–45 Ma), and early Eocene (50–55 Ma). Si accumulation in the early Eocene is low and probably has a major contribution from detrital aluminosilicates. Middle Eocene Si accumulation is high, about double modern opal accumulation at the equivalent longitude. Early Oligocene Si accumulation resembles that of modern sediments (Lyle, 1992).