2006 Philadelphia Annual Meeting (2225 October 2006)
Paper No. 90-10
Presentation Time: 4:00 PM-4:15 PM

ASSESSING SEALEVEL CHANGE WITH COUPLED 230TH/234U-ESR ANALYSES IN HERMATYPIC CORALS

BLACKWELL, Bonnie A.B.1, TENG, Steve J.T.2, LUNDBERG, Joyce A.3, BLICKSTEIN, Joel I.B.4, and SKINNER, Anne R.4, (1) Department of Chemistry, Williams College, Williams College, Williamstown, MA 01267, (2) RFK Science Research Institute, Flushing, NY 11366, mteng1584@gmail.com, (3) Dept. of Geography, Carleton University, Ottawa, ON K1S 5B6, Canada, (4) Dept. of Chemistry, Williams College, Williamstown, MA 01267

Although coupled 230Th/234U-ESR dating has become routine for dating teeth, it has never been used to date corals. Both ESR and 230Th/234U can date coralline aragonite ranging in age from 1 to 400 ka. The ESR age depends on the time-averaged cosmic dose rate, Dcos(t), assumed, but the 230Th/234U dates do not depend on Dcos(t). Because Dcos(t) experienced by corals depends on the amount of water and sedimentary cover overlying the coral, Dcos(t) response reflects changing water depths due to subsidence, uplift, and sealevel change. An accurate ESR age, therefore, requires assumptions about Dcos(t). By coupling the two methods, one can determine the age and a unique Dcos(t) simultaneously.

For reefs on stable platforms, Dcos(t) recorded by the coral depends only on the water depth and sedimentary cover thickness overlying the dated coral sample. From a coral's water depth and sedimentary history predicted with a given sealevel curve, one can estimate a Dcos, sealevel(t). If Dcos, coupled(t) from the coupled analysis (i.e., Dcos(t) actually experienced by the coral) agrees well with Dcos, sealevel(t), this provides independent validation for the sealevel curve used to build Dcos, sealevel(t). For six corals ranging in age from 75 to 135 ka collected from reef crests on the Florida platform, their Dcos, coupled(t) values and ages agreed well with Dcos, sealevel(t)predicted from the sealevel curve by Waelbroeck et al. (2002). For three, however, their coupled Dcos, coupled(t) values and ages did not agree well with the Dcos, sealevel(t) estimated from the SPECMAP sealevel curve.

This study demonstrated that couple ESR-230Th/234U dating can independently test the validity of sealevel curves. More precise measurements for water depth and coral cover thickness would improve the precision. Where a large coral can be sampled at several points, or a reef can be sampled over a transect, a precise test for sealevel curves could be developed.

WAELBROECK, C., L. LABEYRIE, E. MICHEL, J.C. DUPLESSY, J.F. MCMANUS, K. LAMBECK, E. BALBON, M. LABRACHERIE, 2002. Sea-level and deep water temperature changes derived from benthonic foraminifera isotopic records. Quaternary Science Reviews 21: 295305.

2006 Philadelphia Annual Meeting (2225 October 2006)
General Information for this Meeting
Session No. 90
Archaeological Geology
Pennsylvania Convention Center: 109 AB
1:30 PM-5:30 PM, Monday, 23 October 2006

Geological Society of America Abstracts with Programs, Vol. 38, No. 7, p. 235

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