Stable isotope ratios of benthic foraminifera from DSDP Hole 79-544B (Table 1)

At DSDP Hole 544B, oxygen-isotope stratigraphy, carbonate proportion, clay mineralogy, and (terrigenous) grain sizes show short-term (Milankovitch-type) sediment cycles from 5.1 m.y. to the present and fairly uniform conditions of deposition before this date. The cycles are superimposed by two large-scale shifts of sediment composition and flux parallel to distinct changes of the average benthos delta18O composition (up to 0.7‰). The shifts coincide with major hiatuses from 1.05 to 1.65 and from 2.4 to 4.5 m.y. and can be correlated with specific events of the global climatic evolution. The marked increase in the proportion of chlorite and in the grain-sizes of terrigenous matter near 2.4 m.y. may reflect increased physical weathering and denudation of the Atlas Mountains and the lowering of sea level. These hiatuses were probably formed by strengthened contour currents that also may have caused the reduction of both terrigenous and calcium-carbonate flux rates during the Brunhes Magnetic Epoch.