Oxygen isotope composition, organic carbon content, and grain size distribution at the Peru upwelling region@en

A high-resolution chronostratigraphy was established for Holes 680B and 686B, drilled during Ocean Drilling Program (ODP) Leg 112 off Peru. The stratigraphy is largely based on oxygen isotopes of benthic foraminifers and supplemented by data for organic-carbon content and sediment texture. At both drill sites, during isotope Stage 1, the sedimentation rate was more than twice that of the older stages, which partly reflects lack of compaction in the youngest sediments. In Hole 680B, located at the center of a modern coastal upwelling cell in a water depth of 252.5 m, the mean sedimentation rate is 6.6 cm/k.y. in isotope Stages 1 through 15. Hole 686B lies at the fringe of another active upwelling cell off Capo Nazca in a water depth of 447 m. A prominent hiatus is evident between 105 and 120 m below seafloor (bsf). The mean sedimentation rate is 17.1 cm/k.y. above the hiatus (isotope Stages 1 through 15) and about 100 cm/k.y. below.针对秘鲁外海大洋钻探计划（Ocean Drilling Program, ODP）第112航次所钻取的680B与686B钻孔，研究建立了高分辨率年代地层格架。该地层格架主要基于底栖有孔虫的氧同位素数据，并辅以有机碳含量与沉积物结构数据。在两个钻孔位点，同位素阶段1的沉积速率均为较老阶段的两倍以上，这在一定程度上反映了最新沉积物未发生明显压实作用。位于现代沿岸上升流区中心、水深252.5米处的680B钻孔，其同位素阶段1至15的平均沉积速率为6.6厘米/千年。686B钻孔位于纳斯卡角外海另一活跃上升流区的边缘，水深447米，在海底以下105至120米（bsf）处存在显著沉积间断。该钻孔在沉积间断之上（对应同位素阶段1至15）的平均沉积速率为17.1厘米/千年，间断之下的平均沉积速率约为100厘米/千年。