Abstract
Deep fractures ("fissures") and avens ("skylights") in limestone cave roofs create natural traps for sediments and biota. Fissures fill quickly with surface sediment and organisms soon after opening. Debris cones are formed as materials fall, wash, or drift on air through openings in cave skylights. Such deposits in Admiral's and Grand Canyon Cave, Bermuda contain distinct beds and are composed of mixtures of sediment and charcoal, together with fossils of land snails, crabs, birds, reptiles, and bats. The "pitfall" accumulations were periodically sealed over by calcite flowstone. A stratigraphic record of surface activity and fauna through both glacial and interglacial periods has been preserved. The succession also provides an ideal setting in which to compare several geochronological methods. Calibrated 14C ages on charcoal and shells provide dated horizons at 1600, 12,800, and about 35,000 14C yr BP. Thermal ionization mass spectrometric (TIMS) ages on several flowstone layers constrain the entire sequence in the Admiral's Cave sequence between 126,300±900yr (Termination II) and historical times. A continuous relative-age record generated by amino acid epimerization (AAE) geochronology (D-alloisoleucine/L- isoleucine or aIle/Ile) on the pulmonate land gastropod Poecilozonites verifies the biostratigraphy, reveals a minimal degree of mixing between stratigraphic units, and establishes an independent temporal link between the subterranean and subaerial deposits of Bermuda. This convergence between stratigraphy and geochronology yields a precisely dated succession from the oceanic island of Bermuda, and thus presents a unique opportunity to assess the rates and processes of evolutionary and climate change during that interval.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 1151-1171 |
| Number of pages | 21 |
| Journal | Quaternary Science Reviews |
| Volume | 23 |
| Issue number | 9-10 |
| DOIs | |
| State | Published - May 2004 |
Bibliographical note
Funding Information:Initial funding for cave excavation was provided by the Bermuda Aquarium, Museum, and Zoo (BAMZ, Museum Curator, Dr. Wolfgang Sterrer). The project was made possible by the overall cooperation and support of the Bermuda Government including Conservation Officers D. Wingate and J. Madeiros. The Bermuda Ministry of the Environment and the Smithsonian Institution generously provided funding for the bulk of AAE and 14 C analyses. We are grateful to Grotto Beach Hotel for logistical support and running electricity into the cave. Fred Collier facilitated our study of Gould's specimens, while K. Burns measured museum specimens during our visit to the Museum of Comparative Zoology at Harvard University. Two AMS 14 C ages were funded by the Australian Institute of Nuclear Science and Engineering (AINSE grant to PJH, Australia). TIMS uranium-series dating was supported by NSF 9809459 to RLE. Support for field and laboratory logistics, as well as collaborative visits to the Smithsonian Institution was provided by a Queensland-Smithsonian Fellowship in 2001 to PJH. For support of field work and dating of specimens we thank the Alexander Wetmore Endowment, the Radiocarbon Fund, and the Office of the Associate Director for Research and Collections (Ross Simons), all of the National Museum of Natural History, Smithsonian Institution. This is contribution number #64 of the Bermuda Biodiversity Project.