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Amino acid geochronology of the type Cromerian of West Runton, Norfolk, UK.

Penkman KE, Preece RC, Keen DH, Collins MJ - Quat Int (2010)

Bottom Line: Two genera of freshwater gastropods (Valvata and Bithynia) are used to explore the value of using multiple amino acids from the intra-crystalline fraction, which should be more protected from the effects of diagenesis than the inter-crystalline component.In order to put the amino acid data from the West Runton Freshwater Bed into perspective, statistical analyses are used to compare them with results from the Hoxnian (MIS 11) site at Clacton-on-Sea, Essex.The data are also compared with results from Waverley Wood, an important archaeological site in the English Midlands falling within the 'Cromerian Complex'.

View Article: PubMed Central - PubMed

Affiliation: BioArCh, Dept of Chemistry, University of York, York YO10 5DD, United Kingdom.

ABSTRACT
Aminostratigraphic studies of continental deposits in the UK have hitherto relied almost exclusively on data from the aragonitic shells of non-marine molluscs for dating Pleistocene sequences. This is usually based on the d/l value of a single amino acid, d-alloisoleucine/l-isoleucine (A/I), in the total shell proteins. Two genera of freshwater gastropods (Valvata and Bithynia) are used to explore the value of using multiple amino acids from the intra-crystalline fraction, which should be more protected from the effects of diagenesis than the inter-crystalline component. Results are compared from both the aragonitic shells and opercula composed of calcite, a more stable form of calcium carbonate. In order to put the amino acid data from the West Runton Freshwater Bed into perspective, statistical analyses are used to compare them with results from the Hoxnian (MIS 11) site at Clacton-on-Sea, Essex. Twelve protein decomposition indicators revealed that the results from the shells were not as clear-cut as those from the opercula. Five indicators from the Valvata shell suggest that West Runton is older than Clacton (at a 95% significance level), but two actually suggested a younger age. Seven indicators show that the Bithynia shells from West Runton are older than congeneric shells from Clacton. In marked contrast, all 12 indicators isolated from the opercula demonstrate that West Runton is significantly older than Clacton. The data are also compared with results from Waverley Wood, an important archaeological site in the English Midlands falling within the 'Cromerian Complex'. Contrary to earlier interpretations, the new amino acid data from Bithynia opercula indicate that West Runton is older than Waverley Wood, a relationship now consistent with the available biostratigraphy.

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Related in: MedlinePlus

Powder X-ray diffraction analysis of a Bithynia troschelii shell from Waverley Wood (in blue), with reference patterns for aragonite (green) and calcite (purple); the dominant peak of each reference spectra is scaled to the intensity of the shell spectrum. Bithynia shells are aragonitic, and therefore this shell’s spectra should only show peaks corresponding to that of aragonite. However, a large peak in the Bithynia spectrum can be observed at 2θ = 29.4°, corresponding to the dominant diffraction peak expected in a calcite spectra. This indicates mineral diagenesis of the original aragonite to calcite in this shell, which would have compromised the closed system intra-crystalline protein.
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fig5: Powder X-ray diffraction analysis of a Bithynia troschelii shell from Waverley Wood (in blue), with reference patterns for aragonite (green) and calcite (purple); the dominant peak of each reference spectra is scaled to the intensity of the shell spectrum. Bithynia shells are aragonitic, and therefore this shell’s spectra should only show peaks corresponding to that of aragonite. However, a large peak in the Bithynia spectrum can be observed at 2θ = 29.4°, corresponding to the dominant diffraction peak expected in a calcite spectra. This indicates mineral diagenesis of the original aragonite to calcite in this shell, which would have compromised the closed system intra-crystalline protein.

Mentions: These results from the opercula from Waverley Wood and West Runton conflict with the original A/I aminostratigraphy, which yielded ratios from West Runton younger than those at Waverley Wood (Bowen et al., 1989; Bowen, 1999). However, the data from the opercula reported here are in agreement with the prevailing molluscan and mammalian biostratigraphy (Preece and Parfitt, 2000, 2008; Preece, 2001). The factors which result in more consistent data from opercula relative to shell await further analysis. The two most obvious causes are the greater diagenetic stability of calcite and the higher level of intra-crystalline amino acids that this biomineral retains. Other studies have shown that the levels of mineral alteration of V. piscinalis shells within the West Runton site were undetectable by X-ray diffraction (e.g. Davies et al., 2000), but even a small degree of mineral diagenetic change, below that of the resolution of the X-ray diffraction (XRD) analysis, could affect the amino acid composition of the intra-crystalline fraction. A preliminary powder XRD study carried out here on one of the (theoretically purely aragonitic) B. troschelii shells from Waverley Wood shows a distinct peak at 2θ ∼ 29.4°, the dominant diffraction peak within a calcite spectra (Fig. 5). No calcite diffraction peak was present in the modern Bithynia shells analysed. Although the proportion of calcite present was not quantified, this shows clear evidence of diagenetic alteration of shell aragonite to calcite at this site. Mineral diagenesis would compromise the closed system protein within the intra-crystalline fraction; if this is a relatively common occurrence at this site/sites of this age, this would result in the greater variability and lower temporal resolution in the aragonitic shell amino acid data.


Amino acid geochronology of the type Cromerian of West Runton, Norfolk, UK.

Penkman KE, Preece RC, Keen DH, Collins MJ - Quat Int (2010)

Powder X-ray diffraction analysis of a Bithynia troschelii shell from Waverley Wood (in blue), with reference patterns for aragonite (green) and calcite (purple); the dominant peak of each reference spectra is scaled to the intensity of the shell spectrum. Bithynia shells are aragonitic, and therefore this shell’s spectra should only show peaks corresponding to that of aragonite. However, a large peak in the Bithynia spectrum can be observed at 2θ = 29.4°, corresponding to the dominant diffraction peak expected in a calcite spectra. This indicates mineral diagenesis of the original aragonite to calcite in this shell, which would have compromised the closed system intra-crystalline protein.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2991590&req=5

fig5: Powder X-ray diffraction analysis of a Bithynia troschelii shell from Waverley Wood (in blue), with reference patterns for aragonite (green) and calcite (purple); the dominant peak of each reference spectra is scaled to the intensity of the shell spectrum. Bithynia shells are aragonitic, and therefore this shell’s spectra should only show peaks corresponding to that of aragonite. However, a large peak in the Bithynia spectrum can be observed at 2θ = 29.4°, corresponding to the dominant diffraction peak expected in a calcite spectra. This indicates mineral diagenesis of the original aragonite to calcite in this shell, which would have compromised the closed system intra-crystalline protein.
Mentions: These results from the opercula from Waverley Wood and West Runton conflict with the original A/I aminostratigraphy, which yielded ratios from West Runton younger than those at Waverley Wood (Bowen et al., 1989; Bowen, 1999). However, the data from the opercula reported here are in agreement with the prevailing molluscan and mammalian biostratigraphy (Preece and Parfitt, 2000, 2008; Preece, 2001). The factors which result in more consistent data from opercula relative to shell await further analysis. The two most obvious causes are the greater diagenetic stability of calcite and the higher level of intra-crystalline amino acids that this biomineral retains. Other studies have shown that the levels of mineral alteration of V. piscinalis shells within the West Runton site were undetectable by X-ray diffraction (e.g. Davies et al., 2000), but even a small degree of mineral diagenetic change, below that of the resolution of the X-ray diffraction (XRD) analysis, could affect the amino acid composition of the intra-crystalline fraction. A preliminary powder XRD study carried out here on one of the (theoretically purely aragonitic) B. troschelii shells from Waverley Wood shows a distinct peak at 2θ ∼ 29.4°, the dominant diffraction peak within a calcite spectra (Fig. 5). No calcite diffraction peak was present in the modern Bithynia shells analysed. Although the proportion of calcite present was not quantified, this shows clear evidence of diagenetic alteration of shell aragonite to calcite at this site. Mineral diagenesis would compromise the closed system protein within the intra-crystalline fraction; if this is a relatively common occurrence at this site/sites of this age, this would result in the greater variability and lower temporal resolution in the aragonitic shell amino acid data.

Bottom Line: Two genera of freshwater gastropods (Valvata and Bithynia) are used to explore the value of using multiple amino acids from the intra-crystalline fraction, which should be more protected from the effects of diagenesis than the inter-crystalline component.In order to put the amino acid data from the West Runton Freshwater Bed into perspective, statistical analyses are used to compare them with results from the Hoxnian (MIS 11) site at Clacton-on-Sea, Essex.The data are also compared with results from Waverley Wood, an important archaeological site in the English Midlands falling within the 'Cromerian Complex'.

View Article: PubMed Central - PubMed

Affiliation: BioArCh, Dept of Chemistry, University of York, York YO10 5DD, United Kingdom.

ABSTRACT
Aminostratigraphic studies of continental deposits in the UK have hitherto relied almost exclusively on data from the aragonitic shells of non-marine molluscs for dating Pleistocene sequences. This is usually based on the d/l value of a single amino acid, d-alloisoleucine/l-isoleucine (A/I), in the total shell proteins. Two genera of freshwater gastropods (Valvata and Bithynia) are used to explore the value of using multiple amino acids from the intra-crystalline fraction, which should be more protected from the effects of diagenesis than the inter-crystalline component. Results are compared from both the aragonitic shells and opercula composed of calcite, a more stable form of calcium carbonate. In order to put the amino acid data from the West Runton Freshwater Bed into perspective, statistical analyses are used to compare them with results from the Hoxnian (MIS 11) site at Clacton-on-Sea, Essex. Twelve protein decomposition indicators revealed that the results from the shells were not as clear-cut as those from the opercula. Five indicators from the Valvata shell suggest that West Runton is older than Clacton (at a 95% significance level), but two actually suggested a younger age. Seven indicators show that the Bithynia shells from West Runton are older than congeneric shells from Clacton. In marked contrast, all 12 indicators isolated from the opercula demonstrate that West Runton is significantly older than Clacton. The data are also compared with results from Waverley Wood, an important archaeological site in the English Midlands falling within the 'Cromerian Complex'. Contrary to earlier interpretations, the new amino acid data from Bithynia opercula indicate that West Runton is older than Waverley Wood, a relationship now consistent with the available biostratigraphy.

No MeSH data available.


Related in: MedlinePlus