Stratigraphy and Sedimentation Rates from Oxygen Isotope Composition, Organic Carbon Content, and Grain-Size Distribution at the Peru Upwelling Region: Holes 680B and 686B

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