Holes 1209A and 1211A on Southern High, Shatsky Rise contain expanded, nearly continuous records of carbonate-rich sediment deposited in deep water of the equatorial Pacific Ocean during the Paleocene and Eocene. In this study, we document intervals of carbonate dissolution in these records by examining temporal changes in four parameters: carbonate content, coarse size fraction (>38 Ám), benthic foraminiferal abundance, and planktonic foraminiferal fragmentation ratio. Carbonate content is not a sensitive indicator of carbonate dissolution in the studied sections, although rare intervals of low carbonate may reflect times of relatively high dissolution. The proportion of coarse size fraction does not accurately record carbonate dissolution either because the relative abundance of nannofossils largely determines the grain-size distribution. Benthic abundance and fragmentation covary (r2 = 0.77) and are probably the best indicators for carbonate dissolution. For both holes, records of these parameters indicate two episodes of prominent dissolution. The first of these occurs in the upper Paleocene (~59–58 Ma) and the second in the middle to upper Eocene (~45–33.7 Ma). Other intervals of enhanced carbonate dissolution are located in the upper Paleocene (~56 Ma) and in the upper lower Eocene (~51 Ma). Enhanced preservation of planktonic foraminiferal assemblages marks the start of both the Paleocene and Eocene epochs.
1Hancock, H.J.L., and Dickens, G.R., 2005. Carbonate dissolution episodes in Paleocene and Eocene sediment, Shatsky Rise, west-central Pacific. In Bralower, T.J., Premoli Silva, I., and Malone, M.J. (Eds.), Proc. ODP, Sci. Results, 198 [Online]. Available from World Wide Web: <http://www-odp.tamu.edu/publications/198_SR/116/116.htm>. [Cited YYYY-MM-DD]
2School of Earth Sciences, James Cook University, Townsville QLD 4811, Australia. Haidi.Hancock@jcu.edu.au
3Department of Earth Science, Rice University, Houston TX 77005, USA
Initial receipt: 8 April 2004
Acceptance: 15 March 2005
Web publication: 24 August 2005