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、碳酸盐占比、黏土矿物学以及（陆源）粒度数据显示，5.1百万年至今的沉积记录存在短期（米兰科维奇型）沉积旋回，而该时间节点之前的沉积环境相对均一。这些沉积旋回之上叠加了两次大规模的沉积物组成与通量变化，其变化趋势与底栖生物δ¹⁸O平均组成的显著变化（最大幅度达0.7‰）相吻合。这两次大规模变化对应了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。在约2.4百万年前后，绿泥石占比与陆源物质粒度显著升高，这或许反映了阿特拉斯山脉物理风化与剥蚀作用增强，以及海平面下降。这些沉积间断可能由增强的等深流作用形成，而该作用同样可能导致布容磁性期（Brunhes Magnetic Epoch）期间陆源物质与碳酸钙沉积通量均出现下降。