| Title: | Cretaceous Marine d18O Cooling Excursions: An Ice Sheet for Every Event? |
| Author: | Brian T Huber |
| Date Submitted: | 05/03/2002 |
| Address: | Department of Paleobiology, MRC: NHB-121
Washington
DC
USA
20013-7012
|
| Phone: | 202-786-2658 |
| Email: | huber.brian@nmnh.si.edu |
| Co-Authors: | MacLeod, Kenneth G., University of Missouri, macleodk@missouri.edu; Norris, Richard D., norris@whoi.edu |
| Affiliation: | Smithsonian Museum of Natural History |
| | |
| Abstract URL: | http://cis.whoi.edu/science/GG/ccod/viewAbstracts.cfm?RefNumber=19725634 |
| Keywords: | oxygen isotopes, foraminifera, sea level, glacio-eustasy |
| Abstract: | The concept of long-term stability and equitability of the Cretaceous greenhouse climate is giving way to recognition of much greater variability in global temperatures on both short and long time scales as a result of increasingly detailed oxygen isotope paleotemperature studies. Recognition of short-term positive  shifts combined with apparent 3rd order sea level fluctuations in several intervals has revitalized the debate about whether or not continental ice sheets existed at polar latitudes during the Cretaceous. Correlation between 0.5 to 1.5 per mil positive shifts in their bulk carbonate curve with lowstands in the EXXON sea level curve during the middle Cenomanian, late Turonian and early Santonian (~84-85 Ma) was used by Stoll and Schrag (2000) to support glacial forcing. Similarly, Miller et al. (1999) argued for glacio-eustasy during the lower Maastrichtian (~ 69-71 Ma) to explain correlation between an unconformity in the New Jersey margin, positive shifts at several deep-sea sites, and cool high latitude SSTs during the early Maastrichtian.
Without direct geological evidence of Cretaceous continental glaciation, confirmation of the existence of Cretaceous ice-sheets requires demonstration that the oxygen isotopic shifts and lowstand events are globally synchronous and consistently correlated and that ice buildup is reasonable. The oxygen isotope record from ODP Site 1050 on Blake Nose (subtropical North Atlantic) can be used to test for glacial forcing within the late Aptian-early Albian, late Albian-early Coniacian, and mid-Campanian-late Maastrichtian. The middle bathyal benthic foraminifer record at Site 1050 contains six short-term, positive shifts that range from 0.3 to 1.0 per mil, but none are likely to be related to polar ice sheets because (1) the benthic shifts are not accompanied by positive shifts in co-occurring planktonic foraminifera; (2) the shifts do not correlate with recognized sea-level lowstands; (3) synchronous positive shifts do not occur at other deep sea sites; and (4) bottom water temperatures and high latitude SSTs at the time of the excursions were generally too warm to allow for a positive snow balance at polar latitudes. Until reasons are found for why only selected Cretaceous positive excursions were glacially forced, we argue that non-glacial explanations for short-term variations are favored. |
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