Geological Society of America

229 Recent Advances in Paleoclimatology/Paleoceanography

Wednesday, 3 November 2010
8:00 AM - 12:00 PM
Room 607

TRACKING SEALEVEL WITH CORALS AND MOLLUSCS: ESR DATING on SAN SALVADOR ISLAND, BAHAMAS

Paper number: 229-15
Program: Technical Sessions
Time: 11:30 AM – 11:45 AM

Authors

Aislinn E. Deely Presenting Author
Glenwood Landing, NY
Bonnie Blackwell
Williams College, Williamstown, MA
John E. Mylroie
Mississippi State University, Mississippi State, MS
James L. Carew
College of Charleston, Charleston, SC
Joel Blickstein
RFK Science Research Institute, Glenwood Landing, N/A
R. Laurence Davis
University of New Haven, West Haven, CT
Anne R. Skinner
Williams College, Williamstown, MA

Abstract

Sealevel curves are best developed on tectonically stable coastlines, but require accurate dates for the units which define the sealevel heights. On San Salvador, eolianites with associated ooids and terrestrial molluscs preserve transgressive and regressive phases associated with Quaternary high seastands. Fringing, lagoonal patch, and small bank margin barrier reefs grew during the highstands, while the lowstands saw no deposition. At 11 locations around San Salvador, terrestrial molluscs (Cerion) from the transgressive or regressive dunes, and lagoonal bivalves (Codakia) and corals from the highstand deposits in the Quaternary Grotto Beach and the Rice Bay Formations were dated by ESR (electron spin resonance). Sediment dose rates were calculated from NAA analyses of U, Th, and K in associated sediment. These range from as low as 296 ± 36 μGy/y in the reefs to as high as 745 ± 58 μGy/y in the dunes. Cosmic dose rates were calculated by assuming geologically rapid changes in water depths or sedimentary covers as determined from each sample's current geologic context.

All the loose coral heads dated from the Holocene Rice Bay Formation, ranged from 3.9 ± 0.3 to 7.1 ± 0.4 ka (OIS 1). These were probably moved by storms into the modern lagoons. In situ corals from the Cockburn Town Reef, part of the Cockburn Town Member reef facies in the Grotto Beach Formation, range in age from 125 ka to 115 ka, correlating with OIS 5e. To check for temporally mixed molluscs samples, multiple random grab samples were analyzed from each locality where sufficient shells were available. Minimum ages for the Cockburn Town Member (Grotto Beach Formation) regressive phase ranged from 58.5 ± 4.6 to 74.9 ± 7.6 ka, when corrected for their cosmic doses (OIS 3-4).