Abstract

Using an absolute time scale for the stratigraphic sections penetrated in 20 drill sites of the Deep Sea Drilling Project in the eastern equatorial Pacific, we have determined paleodepths, paleopositions, and average CaCO3 content for each 1-m.y. interval for the past 50 m.y. The calcite compensation level (CCD) at the equator was very shallow (3,000 m) during Eocene time, dropped precipitously to a low at 5,000 m in Oligocene time, then rose to its present position. The CCD outside the equatorial zone was also shallow during Eocene time, but while the equatorial CCD remained depressed during the Oligocene, the extra-equatorial CCD gradually shoaled. This suggests an increase in carbonate dissolution in the Pacific, matched by an increase in carbonate supply at the equator. During Miocene time, both the equatorial CCD and the Pacific CCD rose together. Finally, near the Miocene-Pliocene boundary, the extra-equatorial CCD dropped from its Miocene high of at least 3,900 m to its present level.

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