amino acid dating

shelly till

glaciation SE Caithness







Data from Gerard Sykes (personal communication 1993)

Amino acid ratios for shells from the shelly till of Caithness

Significance: amino acids that form proteins within shells change in structure through time after death and so provide the potential to date when molluscs were alive.

Shells from the shelly till of Caithness have been analysed in an attempt to tie down the maximum age of the shelly till (Bowen and Sykes, 1988). The cold-water molluscs Arctica islandica and Macoma balthica grow large, thick shells which resist weathering and erosion and these occur in the shelly till at sites from Dunbeath northwards along the Moray Firth coast. Although the full data set has never been published, it is clear from the known ratios that the shells cover a range of ages. Comparison to amino acid ratios from marine deposits elsewhere in western Europe indicates that the shells lived in the period spanned by Marine Isotope Stages 9-3.

Site GR Lab-No Species D/L Ratio n
Dunbeath Bridge ND 159298 LOND-572 Arctica 0.176 0.030 5
LOND-573 Macoma? 0.221 1
Lybster ND 245351 LOND-576 Arctica 0.203 1
LOND-577 Arctica 0.213 1
LOND-578 Macoma 0.263 1
Forse Bay Upper ND 221338 LOND-579 Arctica 0.168 0.031 3
Forse Bay Lower ND 221338 LOND-581 Arctica 0.252 0.041 3
LOND-582 Arctica 0.250 0.021 5
Dunbeath Cemetery ND 128323 LOND-585 Arctica 0.146 0.006 2
LOND-586 Macoma? 0.085 1
LOND-591 ? 0.062 0.012 5

The low ratios at Dunbeath Cemetery match others from Latheronwheel (Bowen and Sykes, 1988) and indicate that the molluscs now found at these  sites lived around 30-50 thousand years ago. The marine sediments which buried them on the floor of the Moray Firth were later incorporated by glacial erosion into the shelly till of the last ice sheet.