Limits...
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.


Related in: MedlinePlus

(a) THAA amino acid composition for unheated and “suspected heated” Sand samples. Error bars represent one standard deviation around the mean. (b) THAA Glx vs THAA Asx d/l plot for unheated and “suspected heated” Sand samples. The trendlines for heating experiments at 140 °C and 280 °C, performed on modern Patella (Demarchi, 2009), is also reported: note that the “suspected heated” samples from Sand fall on a different trajectory, possibly indicating different diagenetic pathways induced by exposure to very high temperatures due to fire.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3117143&req=5

fig6: (a) THAA amino acid composition for unheated and “suspected heated” Sand samples. Error bars represent one standard deviation around the mean. (b) THAA Glx vs THAA Asx d/l plot for unheated and “suspected heated” Sand samples. The trendlines for heating experiments at 140 °C and 280 °C, performed on modern Patella (Demarchi, 2009), is also reported: note that the “suspected heated” samples from Sand fall on a different trajectory, possibly indicating different diagenetic pathways induced by exposure to very high temperatures due to fire.

Mentions: Anomalous d/l values were found for two of the samples from Sand, which differ from other values from the same site. These did not appear macroscopically “burnt” or charred. However, when the compositional data are considered (Fig. 6a), a similar pattern to that described by Brooks and colleagues is shown, especially regarding the decrease in aspartic acid, serine and arginine. Currently, heating experiments at 280 °C on bleached Patella are in progress. Preliminary results appear to confirm the same trend as observed on ostrich eggshell. On the contrary, other Patella samples analysed in the NEaar laboratory, from a ∼250 ka raised beach deposit in Northern England, show a “normal” concentration profile, different from the “suspected heated” samples (Demarchi, 2009). This indirectly confirms that the d/l values of two of the Sand samples had been artificially raised by heating and do not represent real age differences. The chromatograms for “suspected heated” samples also show a striking difference when compared to “normal” samples, displaying not only the relative compositional differences described above, but also the presence of a number of other peaks that do not correspond to known standards. These peaks are postulated to be peptide/amino acid degradation products and could potentially be identified using mass spectrometry.


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) THAA amino acid composition for unheated and “suspected heated” Sand samples. Error bars represent one standard deviation around the mean. (b) THAA Glx vs THAA Asx d/l plot for unheated and “suspected heated” Sand samples. The trendlines for heating experiments at 140 °C and 280 °C, performed on modern Patella (Demarchi, 2009), is also reported: note that the “suspected heated” samples from Sand fall on a different trajectory, possibly indicating different diagenetic pathways induced by exposure to very high temperatures due to fire.
© Copyright Policy
Related In: Results  -  Collection

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

fig6: (a) THAA amino acid composition for unheated and “suspected heated” Sand samples. Error bars represent one standard deviation around the mean. (b) THAA Glx vs THAA Asx d/l plot for unheated and “suspected heated” Sand samples. The trendlines for heating experiments at 140 °C and 280 °C, performed on modern Patella (Demarchi, 2009), is also reported: note that the “suspected heated” samples from Sand fall on a different trajectory, possibly indicating different diagenetic pathways induced by exposure to very high temperatures due to fire.
Mentions: Anomalous d/l values were found for two of the samples from Sand, which differ from other values from the same site. These did not appear macroscopically “burnt” or charred. However, when the compositional data are considered (Fig. 6a), a similar pattern to that described by Brooks and colleagues is shown, especially regarding the decrease in aspartic acid, serine and arginine. Currently, heating experiments at 280 °C on bleached Patella are in progress. Preliminary results appear to confirm the same trend as observed on ostrich eggshell. On the contrary, other Patella samples analysed in the NEaar laboratory, from a ∼250 ka raised beach deposit in Northern England, show a “normal” concentration profile, different from the “suspected heated” samples (Demarchi, 2009). This indirectly confirms that the d/l values of two of the Sand samples had been artificially raised by heating and do not represent real age differences. The chromatograms for “suspected heated” samples also show a striking difference when compared to “normal” samples, displaying not only the relative compositional differences described above, but also the presence of a number of other peaks that do not correspond to known standards. These peaks are postulated to be peptide/amino acid degradation products and could potentially be identified using mass spectrometry.

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.


Related in: MedlinePlus