A sustained +21 m sea-level highstand during MIS 11 (400 ka): direct fossil and sedimentary evidence from Bermuda |
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| Authors: | Storrs L Olson Paul J Hearty |
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| Institution: | 1. U.S. Geological Survey, MS 980, Box 25046, Federal Center, Denver, CO 80225, USA;2. Departamento de Biología, Universidad de Las Palmas de Gran Canaria, 35017 Las Palmas, Canary Islands, Spain;3. U.S. Geological Survey, MS 963, Box 25046, Federal Center, Denver, CO 80225, USA;1. Normandie Univ, France;2. UCBN, M2C, F-14000 Caen, France;3. CNRS, UMR 6143 M2C, F-14000 Caen, France;4. CNRS UMR 6112, LPG Nantes, France;5. CNRS UMR 5275, ISTerre, Grenoble, France;6. Geosciences Department, Williams College, MA 01267 USA;7. Institute of Earth and Environmental Science, University of Potsdam, 14476 Potsdam, Germany;8. CNRS UMR, 8217 Géosystèmes, Bâtiment SN5, Avenue Paul Langevin, 59655 Villeneuve D''Ascq Cedex, France;9. Institute of Volcanology and Seismology, FED RAS, Petropavlovsk-Kamchatsky 683006, Russia;10. Université de Brest (UBO) and CNRS, UMR 6538, Domaines Océaniques, Institut Universitaire Européen de la Mer, 29238 Plouzané, France;11. Université de Toulouse, UPS (OMP), LMTG, 14 Av Edouard Belin, F-31400 Toulouse, France;12. IRD, LMTG, F-31400 Toulouse, France;13. CNRS, LMTG, F-31400 Toulouse, France |
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| Abstract: | A small, protected karstic feature exposed in a limestone quarry in Bermuda preserved abundant sedimentary and biogenic materials documenting a transgressive phase, still-stand, and regressive phase of a sea-level in excess of 21.3 m above present during Marine Isotope Stage (MIS) 11 (400 ka) as determined by U/Th dating and amino acid racemization. Cobbles and marine sediments deposited during the high-energy transgressive phase exhibit rim cements indicating a subsequent phreatic environment. This was succeeded stratigraphically by a still-stand deposition of fine calcareous lagoonal sediments containing bioclasts of red algae and benthic and planktonic foraminifera that was intensely burrowed by marine invertebrates, probably upogebiid shrimp, that could not be produced under any condition other than sustained marine submergence. Overlying this were pure carbonate beach sands of a low-energy regressive phase containing abundant remains of terrestrial and marine vertebrates and invertebrates. The considerable diversity of this fauna along with taphonomic evidence from seabird remains indicates deposition by high run-up waves over a minimum duration of months, if not years. The maximum duration has yet to be determined but probably did not exceed one or two thousand years. The most abundant snails in this fauna are two species indicative of brackish water and high-tide line showing that a Ghyben-Herzberg lens must have existed at > + 20 m. The nature of these sediments and fossil accumulation is incompatible with tsunami deposition and, given the absence of evidence for tectonic uplift of the Bermuda pedestal or platform, provide proof that sea-level during MIS 11 exceeded +20 m, a fact that has widespread ramifications for geologists, biogeographers, and human demographics along the world's coastlines. |
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