HR: 0800h
AN: PP21C-1578    [Abstracts]
TI: New Dates and Revelations on the Last Interglacial Terrace, Barbados, West Indies
AU: * Freiburger, N C
EM: freib012@d.umn.edu
AF: Department of Geological Sciences, University of Minnesota Duluth, 229 Heller Hall 1114 Kirby Dr., Duluth, MN 55812 United States
AU: Gallup, C D
EM: cgallup@d.umn.edu
AF: Department of Geological Sciences, University of Minnesota Duluth, 229 Heller Hall 1114 Kirby Dr., Duluth, MN 55812 United States
AU: Taylor, F W
EM: fred@utig.ig.utexas.edu
AF: Institute for Geophysics, University of Texas at Austin, 4412 Spicewood Springs Road, Austin, TX 78759 United States
AU: Cheng, H
EM: cheng021@umn.edu
AF: Department of Geology and Geophysics, University of Minnesota, 310 Pillsbury Drive SE, Minneapolis, MN 55455 United States
AU: Edwards, R L
EM: edwar001@umn.edu
AF: Department of Geology and Geophysics, University of Minnesota, 310 Pillsbury Drive SE, Minneapolis, MN 55455 United States
AB: Fourteen new samples from the last interglacial terrace on Barbados reveal a well-preserved mid-last interglacial deposit. The fossil coral deposit lies ±20 m below the top of the last interglacial terrace, which underlies the University of West Indies on the southwest side of Barbados. Four of the fourteen samples measured with U-Th methods (Edwards et al., 1987) by ICP-MS (Finnigan ELEMENT; Shen et al., 2002) have initial δ²³⁴U values within error of the modern value (145.8 ñ 1.7‰ Cheng et al., 2000), suggesting that they provide accurate and reliable ages (Gallup et al., 1994; Thompson, et al., 2005). The base of the outcrop is a mix of Acropora palmata (Ap) and head corals such as Porites. Ap is usually a reef crest coral, but the presence of head corals may indicate growth in deeper waters. New dates from this unit are 126.3 ± 0.8 ka (Porites); 124.6 ± 0.8 ka (Ap); and 121.5 ± 0.7 ka (Ap). This unit is overlain by a lense of coral cobbles containing one head coral tilted on its side that computes an age of 125.7 ± 0.7 ka (Siderastrea). Overlying the cobble unit is a fore-reef unit of Acropora cervacornis; within this unit is a 1.5 m tall sea cave ~1-2 m above the cobble unit, indicating a sea level drop that carved a notch into the deposit of Acropora cervacornis and presumably created the cobbles from the mixed Ap/head coral deposit. The top of the last interglacial terrace at the University of the West Indies has been dated extensively (Gallup et al., 2002). Though none of the samples have initial δ²³⁴U values within error of the modern value, the last interglacial U-Th ages and the ~10 m thick deposit of Ap establish that the top of the terrace is the main crest of the last interglacial deposit at this location. Thus, given the mixed species assemblage of the new deposit and its location 20 m below the crest, we conclude that it grew in deeper water during the last interglacial period. The cobble deposit and the sea cave suggest that this deeper-water, mid-last interglacial deposit was eroded as sea level fell. The new dates within the lower units indicate that this sea level change and erosion occurred after 121 ka, the youngest age in the deposit.
DE: 1115 Radioisotope geochronology
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005