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Amino acid racemization dating of marine shells: A mound of possibilities.

Demarchi B, Williams MG, Milner N, Russell N, Bailey G, Penkman K - Quat Int (2011)

Bottom Line: Only species which pass both tests can be considered suitable for further studies to obtain reliable age information.This amino acid geochronological technique is also applied to midden deposits at two latitudinal extremes: Northern Scotland and the Southern Red Sea.Results obtained in this study indicate that the application of this new method of AAR dating of shells has the potential to aid the geochronological investigation of shell mounds in different areas of the world.

View Article: PubMed Central - PubMed

Affiliation: BioArCh, Department of Chemistry, University of York, Heslington, York YO10 5DD, UK.

ABSTRACT
Shell middens are one of the most important and widespread indicators for human exploitation of marine resources and occupation of coastal environments. Establishing an accurate and reliable chronology for these deposits has fundamental implications for understanding the patterns of human evolution and dispersal. This paper explores the potential application of a new methodology of amino acid racemization (AAR) dating of shell middens and describes a simple protocol to test the suitability of different molluscan species. This protocol provides a preliminary test for the presence of an intracrystalline fraction of proteins (by bleaching experiments and subsequent heating at high temperature), checking the closed system behaviour of this fraction during diagenesis. Only species which pass both tests can be considered suitable for further studies to obtain reliable age information. This amino acid geochronological technique is also applied to midden deposits at two latitudinal extremes: Northern Scotland and the Southern Red Sea. Results obtained in this study indicate that the application of this new method of AAR dating of shells has the potential to aid the geochronological investigation of shell mounds in different areas of the world.

No MeSH data available.


(a) FAA vs THAA plot for Asx d/l measured in Scottish archaeological Patella; error bars represent one standard deviation around the mean for each site. Modern (collected in 2001 AD) Patellad/l values are also plotted for comparison. (b) Asx, Glx, Ser, Ala and Val THAA d/l values measured in Scottish archaeological Patella plotted against the age of each site. Error bars represent age uncertainty on the x-axis and one standard deviation around the mean of d/l values for each site on the y-axis. (c) “Spider diagram” illustrating the increase of THAA d/l values for Asx, Glx, Ser, Ala and Val with increasing age of the archaeological deposit. Note that different amino acids have different resolving powers over different timescales. Error bars represent one standard deviation around the mean.
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fig5: (a) FAA vs THAA plot for Asx d/l measured in Scottish archaeological Patella; error bars represent one standard deviation around the mean for each site. Modern (collected in 2001 AD) Patellad/l values are also plotted for comparison. (b) Asx, Glx, Ser, Ala and Val THAA d/l values measured in Scottish archaeological Patella plotted against the age of each site. Error bars represent age uncertainty on the x-axis and one standard deviation around the mean of d/l values for each site on the y-axis. (c) “Spider diagram” illustrating the increase of THAA d/l values for Asx, Glx, Ser, Ala and Val with increasing age of the archaeological deposit. Note that different amino acids have different resolving powers over different timescales. Error bars represent one standard deviation around the mean.

Mentions: Archaeological Patella samples from the Scottish sites detailed in section 4.1 were analysed and the dl ratios of multiple amino acids represented on FAA vs THAA plots, as described for the heating experiments on Strombus and Chicoreus (Fig. 3a). All values fell on a trendline for Asx (Fig. 5a) as well as Ser, Ala, Glx, and Val (data not shown), thus satisfying the first condition for closed system behaviour. All the amino acids considered displayed the expected increase in dl ratios with increasing age when THAA and FAA d/l values for each subsample were compared to independent geochronological information (Table 1, Fig. 5a–c). However, not all the amino acids allow the same resolution over different timescales. Different amino acids racemize at different rates as a function of their molecular structure, position in the protein chain, flanking residues and status (free or bound; e.g. Kriausakul and Mitterer, 1980). Ser and Asx are among the fastest racemizers and will therefore give better resolution over Holocene timescales (Fig. 5b and c). The fast racemization rates of Asx have been successfully used to date young samples in both warm (Goodfriend, 1992; Barbour Wood et al., 2006; Hearty and Kaufman, 2009) and cold (e.g. Goodfriend et al., 1996) climates. Data obtained in this study confirm the possibility of applying the technique to extremely young samples, even at the low burial temperatures experienced by the shells in Scotland.


Amino acid racemization dating of marine shells: A mound of possibilities.

Demarchi B, Williams MG, Milner N, Russell N, Bailey G, Penkman K - Quat Int (2011)

(a) FAA vs THAA plot for Asx d/l measured in Scottish archaeological Patella; error bars represent one standard deviation around the mean for each site. Modern (collected in 2001 AD) Patellad/l values are also plotted for comparison. (b) Asx, Glx, Ser, Ala and Val THAA d/l values measured in Scottish archaeological Patella plotted against the age of each site. Error bars represent age uncertainty on the x-axis and one standard deviation around the mean of d/l values for each site on the y-axis. (c) “Spider diagram” illustrating the increase of THAA d/l values for Asx, Glx, Ser, Ala and Val with increasing age of the archaeological deposit. Note that different amino acids have different resolving powers over different timescales. Error bars represent one standard deviation around the mean.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3117143&req=5

fig5: (a) FAA vs THAA plot for Asx d/l measured in Scottish archaeological Patella; error bars represent one standard deviation around the mean for each site. Modern (collected in 2001 AD) Patellad/l values are also plotted for comparison. (b) Asx, Glx, Ser, Ala and Val THAA d/l values measured in Scottish archaeological Patella plotted against the age of each site. Error bars represent age uncertainty on the x-axis and one standard deviation around the mean of d/l values for each site on the y-axis. (c) “Spider diagram” illustrating the increase of THAA d/l values for Asx, Glx, Ser, Ala and Val with increasing age of the archaeological deposit. Note that different amino acids have different resolving powers over different timescales. Error bars represent one standard deviation around the mean.
Mentions: Archaeological Patella samples from the Scottish sites detailed in section 4.1 were analysed and the dl ratios of multiple amino acids represented on FAA vs THAA plots, as described for the heating experiments on Strombus and Chicoreus (Fig. 3a). All values fell on a trendline for Asx (Fig. 5a) as well as Ser, Ala, Glx, and Val (data not shown), thus satisfying the first condition for closed system behaviour. All the amino acids considered displayed the expected increase in dl ratios with increasing age when THAA and FAA d/l values for each subsample were compared to independent geochronological information (Table 1, Fig. 5a–c). However, not all the amino acids allow the same resolution over different timescales. Different amino acids racemize at different rates as a function of their molecular structure, position in the protein chain, flanking residues and status (free or bound; e.g. Kriausakul and Mitterer, 1980). Ser and Asx are among the fastest racemizers and will therefore give better resolution over Holocene timescales (Fig. 5b and c). The fast racemization rates of Asx have been successfully used to date young samples in both warm (Goodfriend, 1992; Barbour Wood et al., 2006; Hearty and Kaufman, 2009) and cold (e.g. Goodfriend et al., 1996) climates. Data obtained in this study confirm the possibility of applying the technique to extremely young samples, even at the low burial temperatures experienced by the shells in Scotland.

Bottom Line: Only species which pass both tests can be considered suitable for further studies to obtain reliable age information.This amino acid geochronological technique is also applied to midden deposits at two latitudinal extremes: Northern Scotland and the Southern Red Sea.Results obtained in this study indicate that the application of this new method of AAR dating of shells has the potential to aid the geochronological investigation of shell mounds in different areas of the world.

View Article: PubMed Central - PubMed

Affiliation: BioArCh, Department of Chemistry, University of York, Heslington, York YO10 5DD, UK.

ABSTRACT
Shell middens are one of the most important and widespread indicators for human exploitation of marine resources and occupation of coastal environments. Establishing an accurate and reliable chronology for these deposits has fundamental implications for understanding the patterns of human evolution and dispersal. This paper explores the potential application of a new methodology of amino acid racemization (AAR) dating of shell middens and describes a simple protocol to test the suitability of different molluscan species. This protocol provides a preliminary test for the presence of an intracrystalline fraction of proteins (by bleaching experiments and subsequent heating at high temperature), checking the closed system behaviour of this fraction during diagenesis. Only species which pass both tests can be considered suitable for further studies to obtain reliable age information. This amino acid geochronological technique is also applied to midden deposits at two latitudinal extremes: Northern Scotland and the Southern Red Sea. Results obtained in this study indicate that the application of this new method of AAR dating of shells has the potential to aid the geochronological investigation of shell mounds in different areas of the world.

No MeSH data available.