FOURIER STRATIGRAPHY - SPECTRAL GAIN ADJUSTMENT OF ORBITAL ICE MASS MODELS AS AN AID IN DATING LATE NEOGENE DEEP-SEA SEDIMENTS

Orbital tuning has become an important means of dating deep-sea sediments of Pliocene-Pleistocene age. One approach is to generate a template simulating ice mass history based on Milankovitch forcing for comparison with a given delta(18)O record. To obtain a template that closely mimics a given delta(18)O record, we propose the following steps: (1) generate a preliminary template based on a simple ice mass model, (2) find the Fourier matrix for this model, (3) find the Fourier matrix for the delta(18)O record to be tuned (if necessary, adjust preliminary sedimentation rate so that maxima appear at the correct spectral lines), (4) import the spectral power distribution from the matrix of the record into the matrix of the template (while preserving phase of template), and (5) generate the new template from the gain-adjusted template matrix. The record should now show optimum coherency with the template over the appropriate interval. The efficiency of this method (''Fourier matrix conjugation'') in producing hybrid templates is illustrated using four examples: (1) testing the stacked record of Prell et al. (1986) for constant sedimentation rate, (2) testing the date of 790 ka of the Brunhes/Matuyama boundary in Ontong Java Plateau Ocean Drilling Program Hole 805C (Berger et al., 1993a), (3) testing the age scale for a core from the Norwegian Sea containing meltwater events (Jansen, 1989), and (4) checking the age model of Ocean Drilling Program Site 677 (Shackleton et al., 1990) for internal consistency. The template shows just where the given age models have optimum coherency with the selected orbital model and where in the record discrepancies arise.