Late Neogene and Quaternary coarse-fraction and carbonate stratigraphies for Site 586 on Ontong-Java Plateau and Site 591 on Lord Howe Rise.

Abstract

The late Miocene from 10.5 to 6.5 Ma ago was a time of relatively constant, quiet, pelagic sedimentation with typical southwest Pacific sedimentation rates of 20-25 m/Ma. These conditions were interrupted between 6.5 to 4.0 Ma ago when increased upwelling at the Subtropical Divergence and the Equatorial Divergence produced greater productivity of calcareous planktonic organisms. The maximum of productivity was about 4.0 Ma ago. This period of increased upwelling is coincident with the inferred development of the West Antarctic ice sheet. The high productivity was followed by an abrupt increase in winnowing. By 2.0 Ma ago, quiet, pelagic sedimentation conditions prevailed, similar to those of the late Miocene. The last 0.7 m.y. has been a period of relatively intense winnowing on Lord Howe Rise but not on Ontang-Java Plateau. The coarse-fraction data have both long- and short-period fluctuations. -from Authors