The project will link the record of Plio-Pleistocene magnetic reversals to lithologic variations in sediment cores from the North Atlantic, Equatorial Atlantic and western tropical Pacific, using continuous records of sediment porosity, magnetic susceptibility, and optical density. Results will address three problems: (1) the nature of short-term magnetic events reported elsewhere; (2) the depth at which magnetic grain orientation becomes established; (3) the relative accuracy and precision of the previously-established age scale for magnetic reversals based on K-Ar dating versus more recent approaches based on "tuning" lithologic variations to orbital forcing.