Demersal habitat of Late Cretaceous ammonoids: Evidence from oxygen isotopes for the Campanian (Late Cretaceous) northwestern Pacific thermal structure
- 1Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
- 2Department of Earth Science, Graduate School of Social and Cultural Studies, Kyushu University, 4-2-1 Ropponmatsu, Chuo-ku, Fukuoka 810-8560, Japan
- 3National Institute of Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8567, Japan, and Department of Geoenvironmental Science, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
- 4Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
- 5Department of Geoenvironmental Science, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
Abstract
Comparison of oxygen isotope data for exceptionally well preserved cooccurring plankton and benthos from the Campanian of Hokkaido, Japan, with nine species of ammonoids clearly indicates the demersal (nektobenthic) habitat of ammonoids; unlike Nautilus, the ammonoids studied did not engage in significant short-term vertical migrations in the water column. The new foraminiferal isotopic data suggest that sea-surface and sea-bottom temperatures were ∼26 and 18 °C, respectively, at 40°N in the Campanian northwestern Pacific. The temperatures were significantly warmer than those in the modern northwest Pacific. This finding provides the first reliable evidence for the warm Late Cretaceous mid-latitude North Pacific. Isotopic analyses of ammonoids show that the average calcification temperature of all ammonoid shells analyzed was ∼19 °C, comparable to those of cooccurring benthos. None of these ammonoids display calcification temperatures equivalent to those of planktonic foraminifers.
Footnotes
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↵GSA Data Repository item 2003015, Table DR1, Taxonomic positions, oxygen isotope compositions, and calculated (paleo)temperatures, Table DR2, Summary of data used in Figure 3, Figure DR1, Calibration curve for estimation of aragonite content showing weight percent aragonite, and Figure DR2, FeO and MnO contents of the foraminiferal shell wall and fibrous calcite filling in the chambers, is available from Documents Secretary, GSA, P.O. Box 9140, Boulder, CO 80301-9140, editinggeosociety.org, or at http://www.geosociety.org/pubs/ft2003.htm.
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- Accepted October 21, 2002.
- Received July 19, 2002.
- Revision received October 17, 2002.
- Geological Society of America
