Protein diagenesis in Patella shells: implications for amino acid racemisation dating

Se analiza la racemización de aminoácidos en proteínas inter e intracristalinas en conchas de Patella y su utilización como herramienta geocronológica, fundamentalmente empleadas en yacimientos arqueológicos.The inter- and intra-crystalline fractions of Patella vulgata limpets recovered from archaeological sites in Northern Spain (covering Neolithic, Mesolithic, Magdalenian, Solutrean, and Aurignacian periods) were examined for amino acid composition and racemisation over time. The calcitic apex and rim areas of the shells were found to probably be composed of similar proteins, as the D/L values and amino acids were comparable and varied in the same way with increasing age; however, the mineral structures present in these areas differed. The aragonitic intermediate part of the shell showed a distinctly different amino acid composition and mineral structure. The main protein leaching from the inter-crystalline fraction occurred within the first 6000 yr after the death of the organism. In contrast, the intra-crystalline fraction — comprised of a different protein composition than the inter-crystalline fraction — appeared to behave as a closed system for at least 34 ka, as reflected by the lack of a significant decrease in the amino acid content; however, changes in the amino acid percentages occurred during this period. The concentration of aspartic acid remained almost constant with age both in inter- and intra-crystalline proteins, and its contribution to the total amino acid content increased with age at the expense of other amino acids such as glutamic acid, serine, glycine and alanine. Temperature is thought to play a key role in the amino acid racemisation of P. vulgata and could explain why in the localities belonging to the Gravettian and Solutrean period, which formed during relatively cold conditions, D/L values were similar to those detected in shells from sites formed during the Magdalenian.

Paleontological and sedimentological investigations of a sediment profile from northeast Greenland

The Kap Mackenzie area on the outer coast of northeast Greenland was glaciated during the last glacial stage, and pre-Holocene shell material was brought to the area. Dating of marine shells indicates that deglaciation occurred in the earliest Holocene, before 10 800 cal. a BP. The marine limit is around 53 m a.s.l. In the wake of the deglaciation, a glaciomarine fauna characterized the area, but after c. one millennium a more species-rich marine fauna took over. This fauna included Mytilus edulis and Mysella sovaliki, which do not live in the region at present; the latter is new to the Holocene fauna of northeast Greenland. The oldest M. edulis sample is dated to c. 9500 cal. a BP, which is the earliest date for the species from the region and indicates that the Holocene thermal maximum began earlier in the region than previously documented. This is supported by driftwood dated to c. 9650 cal. a BP, which is the earliest driftwood date so far from northeastern Greenland and implies that the coastal area was at least partly free of sea ice in summer. As indicated by former studies, the Storegga tsunami hit the Kap Mackenzie area at c. 8100 cal. a BP. Loon Lake, at 18 m a.s.l., was isolated from the sea at c. 6200 cal. a BP, which is distinctly later than expected from existing relative sea-level curves for the region.

Pollen profile from sediment core KB1, Holzminden, Northern Germany

The Nachtigall clay pit near Holzminden, northern Germany, is located in a subrosional basin filled with 43 m of interglacial, interstadial and stadial deposits adjacent to the Weser River. The succession separates the Older Middle Terrace from the Younger Middle Terrace of the Weser River. Nachtigall core KB1 (1998) mainly contains silt and clay with intercalated peat layers. The layers of fen peat and intercalated humic silt are between 36 and 22.5 m depth. According to palynological studies, the peat layers and some humic silts were deposited during interglacial and interstadial periods marked by forest vegetation, termed Nachtigall 1 and Nachtigall 2. They are subdivided by a stadial, termed Albaxen. The peat of Nachtigall 1 is interrupted twice by silt and clay strata (Allochthonous Unit I, II) which are reworked sediments of older glacial periods, possibly of late Elsterian or early Holsteinian age. The palynological sequences of Nachtigall and Göttingen/Ottostrasse show the same pattern. Moreover, the contemporaneous pollen profiles of Nachtigall and Göttingen/Ottostrasse can be compared with the Velay pollen sequence (France). The Nachtigall core section 36-26.02 m corresponds to Bouchet 2 - Bonnefond - Bouchet 3 in Velay. The profiles of Velay and Nachtigall are independently correlated to the MIS-timescale and correspond to MIS 7c, 7b, and 7a. TIMS 230Th/U-dating shows ages ranging from 227 + 9/-8 to 201 + 15/-13 ka, which are in good agreement with the inferred MIS 7 age.