A comparison of U/Th and rapid-screen 14C dates from Line Island fossil corals

Pamela R. Grothe, Kim M. Cobb, Shari L. Bush, Hai Cheng, Guaciara M. Santos, John R. Southon, R. Lawrence Edwards, Daniel M. Deocampo, Hussein R. Sayani

Research output: Contribution to journalArticlepeer-review

7 Scopus citations

Abstract

Time-consuming and expensive radiometric dating techniques limit the number of dates available to construct absolute chronologies for high-resolution paleoclimate reconstructions. A recently developed rapid-screen 14C dating technique reduces sample preparation time and per sample costs by 90%, but its accuracy has not yet been tested on shallow-water corals. In this study, we test the rapid-screen 14C dating technique on shallow-water corals by comparing 44 rapid-screen 14C dates to both high-precision 14C dates and U/Th dates from mid- to late-Holocene fossil corals collected from the central tropical Pacific (2-4°N, 157-160°W). Our results show that 42 rapid-screen 14C and U/Th dates agree within uncertainties, confirming closed-system behavior and ensuring chronological accuracy. However, two samples that grew ∼6500 years ago have calibrated 14C ages ∼1000 years younger than the corresponding U/Th ages, consistent with diagenetic alteration as indicated by the presence of 15-23% calcite. Mass balance calculations confirm that the observed dating discrepancies are consistent with 14C addition and U removal, both of which occur during diagenetic calcite recrystallization. Under the assumption that aragonite-to-calcite replacement is linear through time, we estimate the samples' true ages using the measured 14C and U/Th dates and percent calcite values. Results illustrate that the rapid-screen 14C dates of Holocene-aged fossil corals are accurate for samples with less than 2% calcite. Application of this rapid-screen 14C method to the fossil coral rubble fields from Kiritimati Island reveal significant chronological clustering of fossil coral across the landscape, with older ages farther from the water's edge.

Original languageEnglish (US)
Pages (from-to)833-845
Number of pages13
JournalGeochemistry, Geophysics, Geosystems
Volume17
Issue number3
DOIs
StatePublished - Mar 2016

Bibliographical note

Funding Information:
This work was support by NSF grant 0752091 and NOAA grant NA11OAR4310166 to KMC as well NSF 1103403 to RLE and HC and NSF 1029020 to DMD.

Publisher Copyright:
© 2016. American Geophysical Union. All Rights Reserved.

Keywords

  • coral
  • dating
  • diagenesis
  • radiocarbon
  • thorium
  • uranium

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