Figure 1.

Spectra of early Pliocene (3.5–4.5 Ma) carbonate variations at Deep Sea Drilling Site 573, equatorial Pacific, and at Ocean Drilling Program Site 661, tropical Atlantic. Frequency is plotted as a function of stratigraphic position; no “tuning” has been performed to achieve a match to an orbital model. Spectral peaks interpreted to correspond to the short cycle of eccentricity (109 kyr), the obliquity cycle (41 kyr), and the two components of precession (≈23 and 19 kyr) are indicated by vertical lines.