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PALEOCEANOGRAPHY, VOL. 20, PA1012, doi:10.1029/2004PA001064, 2005

Paleogene calcite compensation depth in the eastern subtropical Pacific: Answers and questions

David K. Rea

Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan, USA


Mitchell W. Lyle

Center for the Geophysical Investigation of the Shallow Subsurface, Boise State University, Boise, Idaho, USA


Abstract

Ocean Drilling Program Leg 199 drilled a north-south transect across the Eocene paleoequator in the eastern Pacific, permitting reconstruction the calcite compensation depth (CCD) since earliest Eocene time. The CCD was relatively shallow near the early Eocene Pacific equator, 3200 m, and unlike modern latitudinal CCD gradients deepened to the north (to ∼3600 m; paleolatitude ∼10°N). At 41 Ma the CCD underwent a brief, sharp, transient deepening of 700 m, then remained shallow until the Eocene/Oligocene boundary. At the E/O boundary, the CCD deepened by 1200 m in less than 300 kyr. This rapid deepening served to more than double the area of seafloor subject to CaCO3 deposition. Sea level fall associated with ice volume buildup, and ensuing shelf-basin fractionation, is unlikely to be the sole cause of the increased deep-ocean CaCO3 burial; rather, a sudden, rapid increase in the amount of Ca entering the ocean appears necessary to explain the observations.

Received 23 June 2004; accepted 30 November 2004; published 19 February 2005.

Keywords: ODP Leg 199; calcite compensation depth; Pacific Ocean; Paleogene.

Index Terms: 4863 Oceanography: Biological and Chemical: Sedimentation (1861); 9606 Information Related to Geologic Time: Paleogene; 9355 Geographic Location: Pacific Ocean; 3036 Marine Geology and Geophysics: Ocean drilling; 9604 Information Related to Geologic Time: Cenozoic.

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Citation: Rea, D. K., and M. W. Lyle (2005), Paleogene calcite compensation depth in the eastern subtropical Pacific: Answers and questions, Paleoceanography, 20, PA1012, doi:10.1029/2004PA001064.