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.

在深海钻探计划（Deep Sea Drilling Project, DSDP）544B钻孔中，氧同位素地层学（oxygen-isotope stratigraphy）、碳酸盐占比、黏土矿物学以及陆源（terrigenous）粒度数据显示，自5.1百万年至今存在短期的米兰科维奇型（Milankovitch-type）沉积旋回，而在此之前的沉积环境相对均一。该类旋回之上叠加了两次大规模的沉积物组成与通量偏移，这两次偏移与底栖生物delta18O组成的显著变化（最大幅度达0.7‰）相吻合。这两次偏移分别对应1.05~1.65百万年以及2.4~4.5百万年期间的主要沉积间断，且可与全球气候演化的特定事件建立关联。约2.4百万年时，绿泥石（chlorite）占比与陆源物质粒度均出现显著升高，这可能反映了阿特拉斯山脉（Atlas Mountains）物理风化与剥蚀作用增强，以及海平面下降。上述沉积间断可能由增强的等深流（contour currents）作用形成，而该作用同样可能导致布容正极性世（Brunhes Magnetic Epoch）期间陆源物质与碳酸钙通量均出现下降。