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Calculating Sediment Compaction for Radiocarbon Dating of Intertidal Sediments

Published online by Cambridge University Press:  18 July 2016

M I Bird*
Affiliation:
National Institute of Education, Nanyang Technological University, 1 Nanyang Walk, Singapore, 637616.
L K Fifield
Affiliation:
Department of Nuclear Physics, Research School of Physical Sciences and Engineering, Australian National University, Canberra, A.C.T. 0200, Australia.
S Chua
Affiliation:
National Institute of Education, Nanyang Technological University, 1 Nanyang Walk, Singapore, 637616.
B Goh
Affiliation:
National Institute of Education, Nanyang Technological University, 1 Nanyang Walk, Singapore, 637616.
*
Present address: School of Geography and Geosciences, University of St. Andrews, St. Andrews, Fife, KY16 9AL, Scotland, United Kingdom. Corresponding author. Email: [email protected].
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Abstract

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This study estimates the maximum and minimum degrees of autocompaction for radiocarbon-dated Holocene mangrove sediments in Singapore, in order to correct apparent sediment accretion rates for the effects of sediment compression due to autocompaction. Relationships developed for a suite of modern (surface) sediment samples between bulk density, particle-size distribution, and organic matter content were used to estimate the initial (uncompacted) bulk density of buried and variably compressed Holocene sediments, based on the grain-size distribution and organic matter content of the sediment. The difference between measured (compacted) and initial (uncompacted) bulk density of each buried sediment interval can be interpreted as the amount of length shortening experienced by each interval since burial. This allows the elevation of samples selected for 14C dating to be corrected for the effects of autocompaction of the underlying sediment sequence, so that accurate estimates of vertical sediment accretion rates can be calculated.

The 3 Holocene mangrove sequences analyzed and dated for this study ranged in age from 2000 to 8500 cal BP. The effects of autocompaction are significant, even in comparatively thin sequences, with subsidence of up to 56 cm calculated for carbon-dated samples presently 2 m above incompressible basement. The vertical sediment accretion rates for these mangrove sequences ranged from 0.99 to 6.84 mm/yr and carbon sequestration rates ranged from 0.9 to 1.7 t/ha/yr, all within the range observed for comparable Holocene and modern mangrove sediments elsewhere.

Type
Articles
Copyright
Copyright © 2004 by the Arizona Board of Regents on behalf of the University of Arizona 

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