Summer temperatures of late Eocene to early Oligocene freshwaters
- 1Department of Geology, Royal Holloway University of London, Egham, Surrey TW20 0EX, UK
- 2Department of Palaeontology, Natural History Museum, Cromwell Road, London SW7 5BD, UK
- 3Department of Geology, Royal Holloway University of London, Egham, Surrey TW20 0EX, UK
Abstract
The marine foraminiferal isotope record displays a positive δ18O shift early in the Oligocene, which has been identified as the onset of the Antarctic Oi-1 glaciation. Reported here are the first oxygen isotope–derived summer paleotemperatures for continental freshwater in the Northern Hemisphere (Hampshire Basin, Isle of Wight, UK) leading up to and across this event. These paleotemperatures are derived from multiple paleoproxies (rodent tooth enamel, gastropod shells, charophyte gyrogonites, and fish otoliths) and are independent of freshwater evaporation effects and changes in ice volume. We conclude that a fluctuating mesothermal climate existed, but that there was no significant decrease in summer temperatures across the Oi-1 glaciation. This result is concordant with several other studies in suggesting that the majority of the isotopic shift in the marine realm across the Oi-1 glaciation is linked to changes in Antarctic ice volume and not to global temperature change. Our new approach has allowed us to derive numerical values for summer temperatures as well as to reconstruct relative temperature change across this key interval of the Eocene-Oligocene transition.
Footnotes
-
↵*Present address: School of Earth, Ocean and Environmental Sciences, University of Plymouth, Drake Circus, Plymouth, Devon PL4 8AA, UK. stephen.grimesplymouth.ac.uk
-
↵GSA Data Repository item 2005035, Appendix DR1, sample preparation techniques, methodology, and additional evidence linking paleoproxies with a water body, Table DR1, mean δ18O values, Table DR2, mean summer paleotemperatures for six fossil assemblages, and Tables DR3–DR15, phosphate and carbonate oxygen isotope and X-ray diffraction results, is available online at www.geosociety.org/pubs/ft2005.htm, or on request from editinggeosociety.org or Documents Secretary, GSA, P.O. Box 9140, Boulder, CO 80301-9140, USA.
-
- Accepted 18 November 2004.
- Received 29 July 2004.
- Revision received 17 November 2004.
- Geological Society of America
