The most widely used methods of high-resolution marine stratigraphy rely on the record of changes in delta-018, paleontology or paleomagnetics. Unfortunately, these techniques are limited to sediments either rich in carbonate- or silica- bearing fossils, or from magnetically oriented cores. Dr. Herbert will develop techniques for using GRAPE (Gamma Ray Attenuation Porosity Evaluator) bulk density measurements to identify orbital frequencies in 5 DSDP and ODP cores from the equatorial eastern Pacific. These "Milankovitch" signals are known within 2% precision back through the Neogene, and the author intends to "tune" the sedimentation rates to fit these frequencies. Preliminary work has shaon that a "moving window" scheme will result in 5% precision and 100 Kyr resolution of sedimentation rates back to 17 MY. As this is a developmental experiment, he proposes several validation checks against existing biostratigraphy and paleomagnetic calibrations, as well as inter-site consistency checks. If found to be valid, this technique will not only provide much improved chronologies at these and other cores, but will also: 1) make possible equally improved mass accumulation rate estimates for CaCO3, Corg, SiO2, and aeolian dust; 2) provide the first chance of finding paleoceanographic periodicities longer than 500 Kyrs; and 3) lead to better understanding of the mean and variance of orbital forcings back to 17 MY.
