Stable isotopes from ODP Hole 130-806B (Fig. 1)

The age of the Brunhes-Matuyama boundary, until recently taken as 730 k.y. in standard time scales for the Quaternary (e.g., Imbrie et al., 1984; Prell et al., 1986, doi:10.1029/PA001i002p00137) and in Ocean Drilling Program results (Kroenke et al., 1991, doi:10.2973/odp.proc.ir.130.1991; Shackleton et al., 1992 doi:10.2973/odp.proc.ir.138.1992) has been revised to between 780 k.y. and 790 k.y., based on both orbital tuning of oxygen isotope data (e.g., Shackleton et al., 1990) and on new 40Ar-39Ar dates on volcanic rocks (e.g., Baksi et al., 1992, doi:10.1126/science.256.5055.356). We apply the revised chronology to an oxygen isotope record for Ontong Java Plateau (ODP Leg 130, western equatorial Pacific). Using this time scale, we find excellent agreement between the record and a template based on orbital forcing. The equation for the template is DeltaICE = IGR - INS a * ICE b * MEM L c [1] where the change in ice-mass is given as the difference between constant ice growth (IGR) and variable amounts of melting. Melting depends on summer insolation at 65°N (INS), the current ice?mass present (ICE), and the average ice?mass (MEM) over a given time interval (L). The memory base L and the exponents are adjusted for best fit. The fit to the relevant portion of the record yields an age of 790±6 k.y. for the Brunhes?Matuyama boundary. The age assignment is robust relative to substantial changes in parameter settings.