Major reversals of the earth's magnetic field have left a good record in sediment cores taken from ice-island T-3 in the Arctic Ocean. Times of major magnetic reversals, such as the Brunhes-Matuyama boundary, can be correlated with radiometric age determinations, and from this figure sedimentation rates can be calculated. These sedimentation rates may be used to calculate and identify times of other magnetic events in contrast to magnetic noise in the cores. The reliability of this can be checked by comparison with the magnetic standard that is based on radiometric determinations.
Minor magnetic events (including the Blake, Jaramillo and others in the Matuyama and Gauss Epochs) can be identified in the cores. Color is a good stratigraphic indicator, as well, and certain sediment types have widespread distribution in the 100 cores studied.