**Figure F19.** Cyclic variation in gamma ray attenuation (GRA) density at Site 1237. **A.** Fluctuations in GRA density between 60 and 80 mcd (red curve) and the Gaussian weighted smooth (blue curve). The detrended record (green) represents the difference between blue and red records and was used in spectral analysis. Ages and depths of magnetic reversal boundaries are indicated as well as intervals of major changes in sedimentation rates. **B.** Results from spectral analyses. Cycle lengths are given in meters. Considering the sedimentation rates shown in A, cycles of 0.35-0.43 m reflect precession cycles (22 k.y.) and cycles of 0.74-0.98 m are related to obliquity cycles (41
k.y.).