Amino Acid Racemization Dating Research Articles

More Reliable Dating of Japanese Silk Mounting Textiles for Conservation Decisions: Effects of Silk Processing on Silk Surface Morphology and Aspartic Acid Racemization

ABSTRACT Dating silk mounting textiles is important for understanding their condition and susceptibility to degradation. Amino acid racemization is a technique currently used for this purpose. The research presented here aimed to clarify when this technique is reliable and when it is not. Silk fibers taken from a cocoon and from Japanese mounting textiles were studied using optical microscopy to document surface roughness. Chiral capillary electrophoresis mass spectrometry for amino acid racemization dating (AAR), liquid chromatography mass spectrometry for dye analysis, and FTIR for analysis of sericin and other materials adhering to the silk were also used. A change from rough fiber surfaces (greater than a hundred years old) to smooth fiber surfaces (less than a hundred years) was found. This correlated with the time of the introduction of Western degumming methods in Japan. Synthetic dyes were not found on the earlier silk fibers with rough surfaces. AAR dating measurements on rough surfaced fibers with remaining sericin correlated better with the estimated age of the silk fabrics than fibers with smooth surfaces, suggesting the technique should only be used for silk fibers with rough surfaces. A screening method for fibers for AAR analysis was outlined.

Chronology of Early to Mid-Pleistocene sediments in the northern North Sea: New evidence from amino acid and strontium isotope analyses

Sediments deposited during glacial-interglacial cycles through the Early to Mid-Pleistocene in the North Sea are chronologically poorly constrained. To contribute to the chronology of these units, amino acid racemization (AAR) and strontium (Sr) isotope analyses have been performed on samples from four shallow borings and one oil well along a transect in the northern North Sea. D/L Asp (aspartic acid) values obtained through reverse-phase liquid chromatography in the benthic foraminiferal species Elphidium excavatum is focused on because of consistent results and a good stratigraphic distribution of this benthic species. For the Early Pleistocene, an age model for the well 16/1–8, from the central part of the northern North Sea based on Sr ages allows for dating of the prograding wedges filling the pre-Quaternary central basin. A regional calibration curve for the racemization of Asp in Elphidium excavatum is developed using published ages of radiocarbon-dated samples and samples associated with the previously identified Bruhnes/Matuyama (B/M) paleomagnetic boundary and a Sr age from this study. Based on all the available geochronological evidence, samples were assigned to marine oxygen isotope stages (MIS) with uncertainties on the order of 10–70 ka. Sr ages suggest a hiatus of <2 million years (Ma) possibly due to non-deposition or low sedimentation between the Utsira Formation (Pliocene) and the Early Pleistocene. An increase in sedimentation rates around 1.5 ± 0.07 Ma (∼MIS 51) may partly be due to sediment supply from rivers from the south-east and partly due to the extension of ice sheet around 1.36 ± 0.07 Ma from the Norwegian coast to the central North Sea. A possible basin-wide glaciation occurred around 1.1 Ma (∼ MIS 32) (upper regional unconformity/top of unit Q4 in this study), resulting in erosion and regional unconformity. Two interglacials in the Norwegian Channel have been dated: the Radøy Interglacial to 1.07 ± 0.01 Ma (possibly MIS 31, the ‘super interglacial’), and the Norwegian Trench Interglacial to 0.50 ± 0.02 Ma (possibly MIS 13). A massive till unit identified at the same stratigraphic level in all shallow borings may partly represent an extensive MIS 12 glaciation. This study shows that the combined use of amino acid racemization data and Sr isotope chronology can refine the chronological ambiguities of Quaternary North Sea sediments related partly to the impact of glacial processes.

The Whale Point Formation: A stratigraphic record of high-frequency climate and sea-level fluctuations in the Bahamas during Marine Isotope Stage 5a (ca. 80 ka BP)

In this paper, we formally define a series of bioclastic eolianites and protosols exposed on high-energy bank margins throughout the Bahamas archipelago as the Whale Point Formation (WPF). The position of this new lithostratigraphic unit above and seaward of deposits dated to Marine Isotope Stage (MIS) 5e and below Holocene sediments constrains its age to the latest Pleistocene, more precisely to MIS 5a (ca. 88–74 ka BP). This age is further corroborated by amino-acid racemization data calibrated with UTh ages. Based on their sedimentological characteristics, the WPF eolianites are interpreted as landward-advancing dunes decoupled from their source beaches. Relying on the faunal content, the maximum elevation of relative sea level during MIS 5a can be roughly estimated at ca. 9 ± 2 m below the present stand. The WPF includes two phases of eolian deposition separated by an interval of negative sediment budget and pedogenesis. These different facies possibly reflect millennial-scale sea-level and climate instability during MIS 5a, the latter being likely related to shifts in the mean annual position of the intertropical convergence zone and associated rainfall belt.

Lipid biomarkers and metal pollution in the Holocene record of Cartagena Bay (SE Spain): Coupled natural and human induced environmental history in Punic and Roman times

We reconstructed the palaeoenvironmental conditions of Cartagena Bay during the Holocene after a multidisciplinary study to identify natural variations and the anthropic processes of this coastal area. A total of 119 samples were recovered for amino acid racemization dating, 3 for radiocarbon dating (14C), and four sets of 80 samples for sedimentological and palaeontological determination, mineralogical content, biomarker and trace elements quantification. Two natural scenarios were identified from the variations of n-alkane indices and palaeobiological content. The first period (6650–5750 yr cal BP) was marked by the development of euhaline marine conditions with strong inputs from aquatic macrophytes and high biodiversity. After a hiatus, the area underwent a profound change, becoming a paucispecific brackish marsh environment with increasing inputs from land plants, with possible episodes of emersion with a greater presence from terrestrial gastropods (3600–300 cal yr BP). By combining trace element abundance and stanol distributions, our study also provides a novel approach to identify the predominant influence of anthropogenic factors in the last three millennia in the coastal record of Cartagena Bay. Findings confirmed that Pb mining and metallurgy began during the Bronze Age, with considerable inputs of this heavy metal into the atmosphere during Phoenician, Punic and particularly Roman times compared to the Middle Ages. Pollution by Cu and Zn was also observed during Punic and Roman times, and was first documented in the Middle Ages. In addition, faecal stanols, such as coprostanol, derived mainly from humans, and 24-ethylcoprostanol from herbivores were present, thereby indicating for the first time a continuous presence of human populations and significant pollution input since 3600 yr cal BP, this being greater in the late Bronze Age and Phoenician, Punic and Roman times than during Late Antiquity and the Middle Ages, when the city was in decline.

Molluscan aminostratigraphy of the US Mid-Atlantic Quaternary coastal system: Implications for onshore-offshore correlation, paleochannel and barrier island evolution, and local late Quaternary sea-level history

The Quaternary record of the US Mid-Atlantic coastal system includes onshore emergent late Pleistocene shoreline deposits, offshore inner shelf and barrier island units, and paleovalleys formed during multiple glacial stage sea-level lowstands. The geochronology of this coastal system is based on uranium series, radiocarbon, amino acid racemization (AAR), and optically stimulated luminescence (OSL) methods. We report over 600 mollusk AAR results from 93 sites between northeastern North Carolina and the central New Jersey shelf, representing samples from both onshore cores or outcrops, sub-barrier and offshore cores, and transported shells from barrier island beaches. AAR age estimates are constrained by paired 14C analyses on specific shells and associated U-series coral ages from onshore sites. AAR data from offshore cores are interpreted in the context of detailed seismic stratigraphy. The distribution of Pleistocene-age shells on the island beaches is linked to the distribution of inner shelf or sub-barrier source units. Age mixing over a range of time-scales (~1 ka to ~100 ka) is identified by AAR results from onshore, beach, and shelf collections, often contributing insights into the processes forming individual barrier islands. The regional aminostratigraphic framework identifies a widespread late Pleistocene (Marine Isotope Stage 5) aminozone, with isolated records of middle and early Pleistocene deposition. AAR results provide age estimates for the timing of formation of the three major paleochannels that underlie the Delmarva Peninsula: Persimmon Point paleochannel ≥800 ka; Exmore paleochannel ~400–500 ka (MIS 12); and Eastville paleochannel > 125 ka (MIS 6). The results demonstrate the value of synthesizing abundant AAR chronologic data across various coastal environments, integrating multiple distinct geologic studies. The ages and elevations of the Quaternary units are important for current hypotheses about relative sea-level history and crustal dynamics in the region, which was likely influenced by the Laurentide ice sheet, the margin just ~400 km to the north.

Late Pleistocene interstadial sea-levels (MIS 5a) in Gulf St Vincent, southern Australia, constrained by amino acid racemization dating of the benthic foraminifer Elphidium macelliforme

In contrast to the detection and resolution of Late Pleistocene interstadials (Marine Isotope Stages; MIS 5c, 5a and 3) in marine and ice core-based oxygen isotope records, accurately defining palaeosea-levels for these events from sea level indicators remains a challenge. Commonly, such investigations have been undertaken in tectonically active, subduction-related settings, on emergent marginal marine-coastal successions above present sea level, given that the higher ice volumes during these Marine Isotope Stages resulted in ice-equivalent sea levels significantly below present, particularly in far-field settings. Delineation of palaeosea-levels for this period, has accordingly involved an assumption about the long-term rate of coastal uplift. Core SV#23 collected from the tectonically highly stable, remote far-field setting of southern Gulf St Vincent, southern Australia, in a present water depth of 40 m obtained a 3.89 m undisturbed sedimentary record of Late Pleistocene to Holocene age. The basal 2.39 m of the sediment record is of Late Pleistocene interstadial age, as it overlies the Last Interglacial Glanville Formation (128–118 ka; MIS 5e) and occurs beneath the Holocene St Kilda Formation. The extent of aspartic acid and glutamic acid racemization in the benthic foraminifer Elphidium macelliforme sampled at 2 cm intervals continuously from the interstadial succession in Core SV#23, confirms the relative age interpreted from lithostratigraphy. A mean amino acid racemization (AAR) age of 75 ± 13 ka indicates a correlation with MIS 5a, and highlights the utility of E. macelliforme as a species for AAR geochronology. As the foraminifers more closely define the timing of sedimentation, the interstadial succession is regarded as beyond the range of radiocarbon dating (>50 kyr), as revealed in a comparison of radiocarbon ages of fossil molluscs with AAR ages for E. macelliforme from the same depth intervals within the interstadial succession. All of the radiocarbon ages for fossil marine molluscs from the interstadial succession represent minimum ages, resulting from contamination by trace levels of modern radiocarbon. The foraminiferal faunal assemblages within the interstadial succession reveal changes of water depth at the time of deposition, pointing to millennial-scale sea level variability. In particular, the ratio of Elphidium crispum to E. macelliforme indicates several oscillations in relative sea level within a bandwidth of 26 to 24 ± 4.6 m below present sea level (BPSL). Notwithstanding the large uncertainty associated with palaeosea-level estimation based on the Elphidium ratio, the inferred relative sea level record is in accord with the sea level records of Barbados and the Red Sea, and points to Sub-Milankovitch interstadial sea level variability as noted in Greenland and Antarctic ice cores.

Peesey Swamp—a Last Interglacial (MIS 5e) marine corridor across southern Yorke Peninsula, southern Australia

Peesey Swamp on southern Yorke Peninsula, southern Australia, is a north-northwesterly—south-southeasterly trending lowland depression, approximately 24 km long and 4 to 10 km wide. The richly fossiliferous mollusc and foraminiferal faunal assemblages of the last interglacial Glanville Formation in Peesey Swamp indicate that the paleoenvironment was a low- to medium-energy, sheltered sandflat to shallow-water seaway during the Last Interglacial Maximum (Marine Isotope Substage [MIS] 5e; 128–116 ka). The presence of the fossil bivalve molluscs Katelysia rhytiphora, Chlamys (Equichlamys) bifrons and Fulvia tenuicostata, in life position, indicate that the paleowater depth was ≤4 m in Peesey Swamp. The seaway cut across southern Yorke Peninsula, establishing a marine connection between southern Spencer Gulf and Investigator Strait during deposition of these taxa. Amino acid racemisation dating of the fossil marine molluscs Katelysia sp. and Fulvia tenuicostata confirms that the shelly assemblages at Peesey Swamp are correlative with the last interglacial Glanville Formation, a succession of richly fossiliferous, mixed quartz–skeletal carbonate sands documented from many sites along the southern Australian coastline. This study illustrates the significant changes in the geographical configuration of coastlines that may accompany relatively modest (<5 m) sea-level changes on low-gradient coastal landscapes. KEY POINTS Peesey Swamp on southern Yorke Peninsula was flooded by seawater forming a 4 to 10 km-wide seaway during the Last Interglacial Maximum (MIS 5e). Fossil mollusc and foraminiferal assemblages reveal deposition within shallow subtidal to intertidal sandflat environments indicating that the paleowater depth and height of sea-level in Peesey Swamp was ≤4 m. Amino acid racemisation dating of fossil marine molluscs confirms that the shelly assemblages at Peesey Swamp are of last interglacial (MIS 5e) age. The distribution of the foraminifer Marginopora vertebralis indicates that the eastward flow of the warm-water Leeuwin Current, during the Last Interglacial Maximum, was retarded by the biogeographical barriers of Kangaroo Island and Fleurieu Peninsula.

Mimicking the effects of anthropogenic heating on amino acid racemisation dating of gastropod shells

Abstract Pre- or post-depositional heating of fossil biominerals will impact resulting amino acid dates, but the study on the effects on their amino acids of dry artificial heating of molluscs has not yet been fully tested. Here we report a study on three mollusc species to show how amino acid content can potentially be used to identify archaeological samples that have been subjected to artificial heating. The identification of markers of exposure to high temperature could be useful to reject compromised samples for amino acid racemisation dating. In order to identify markers of heat exposure, we artificially heated modern shell samples belonging to three marine molluscs found in abundance at archaeological sites, namely Patella vulgata, Phorcus lineatus and Littorina littorea. The markers found were compared with data from an archaeological dataset for these three species. Our results indicate that there is unlikely to be a single marker indicating artificial heating of a sample, especially for archaeological samples, which have been exposed to a wide variety of complex conditions that cannot be simulated in an isothermal experiment. However in general, we observed changes in shell composition which were indicative of heating: higher %Glx and %Ala and lower %Asx and %Ser for a given Asx D/L value. Moreover, samples heated at high temperatures showed higher than expected Glx and Ala D/L values for a given Asx D/L value. Likewise, the amino acid content of the shells decreased with heating time and temperature. Furthermore, shells artificially heated at > 300 °C had additional compounds evident in the chromatogram, and a poor baseline, thus causing a loss of resolution of late eluting amino acids. Of note, samples heated at 500 °C (5 min) and 400 °C (10–20 min) preserved negligible amino acid content. Archaeological samples that deviated from the expected unheated trend were therefore identified as having been heated.

The Pleistocene and Holocene records of the Mazarrón Basin (SE Spain)

Here we reconstructed the evolution of the Mazarrón Basin during the Pleistocene and Holocene. In this regard, we studied 9 cores with the aim to: 1) define a chronological framework; 2) obtain data on the palaeoenvironment; and 3) establish the relationship with recent tectonics. A total of 158 samples were recovered for amino acid racemization (AAR) dating, 4 for radiocarbon dating (14C), and 332 for sedimentological and palaeontological determination, and 110 for determination of the mineralogical content. These approaches allowed us to elucidate the evolutionary phases of the palaeo-landscape of the Mazarrón Basin, a fault-controlled graben affected by diverse faults, mainly those of Las Moreras and Rella. The ages of the records and the facies correlation indicate that Las Moreras Fault controlled sedimentation during Marine Isotope Stage (MIS) 7, whereas the Rella Fault was strongly active during the Middle Holocene. During MIS7, a brackish lagoon developed in the western area, overlying alluvial fan deposits. Later, the area was uplifted, thereby becoming exposed to erosion. The activity of the Rella Fault allowed sedimentation in the western part of the Mazarrón Basin during the Middle Holocene, while in the Upper Holocene sedimentation occurred in the eastern part. The Holocene transgression was reflected in a temporarily floodable marsh in the hinterland, with changing salinity conditions, from brackish to euhaline waters. Along the sea front, the marine influence was evident but not dominant. Thus, the Mazarrón Basin during the Holocene was brackish to highly euhaline, with variable biological diversity linked to a narrow and probably discontinuous communication with the sea, with restricted circulation and long flushing times, which was reflected by the significant presence of halite. The record ended with recent alluvial/anthropic sediments.

Development of Quaternary travertines in the carbonate mountains of the western Costa del Sol, Málaga, southern Spain

AbstractThe predominantly carbonate nature of the mountains near the coast of Málaga and Marbella (Costa del Sol, southern Spain) and the presence of springs have favored the formation of travertine buildups during the Quaternary. The geomorphic characteristics of the slopes and the location of the springs have determined the development of three types of travertine growths: (1) spring travertines, located preferentially on the south mountainside, where the slope is steepest; (2) pool-dam-cascade travertines, which form along the north and east edges, far from the carbonate relief and with a gentler slope; and (3) river-valley travertines, formed in the courses of the springs of any sector. Field observations combined with new amino acid racemization (AAR) dating of Helicidae gastropods show that most of the travertine formations are polyphasic and that their development was interrupted by stages of erosion and incision. Five stages of travertine development are evident, most of which are related to warm, moist episodes corresponding to marine oxygen isotope stages (MIS) 7, 5, 3, and 1, although local travertine growth also occurred during MIS 6 and during the transition from MIS 3 to 2.

A new method for enamel amino acid racemization dating: A closed system approach

Abstract Analysis of the predictable breakdown of proteins and amino acids in ancient biominerals enables age estimation over the Quaternary. We postulate that enamel is a suitable biomineral for the long-term survival of endogenous amino acids. Analysis of multiple amino acids for geochronological studies is typically achieved using a RP-HPLC method. However, the low concentrations of amino acids coupled with high concentrations of inorganic species make accurate determination of amino concentrations challenging. We have developed a method for the routine preparation of multiple enamel samples using biphasic separation. Furthermore, we have shown that amino acids that exhibit effectively closed system behaviour can be isolated from enamel through an exposure time of 72 h to bleach. Elevated temperature experiments investigating the processes of intra-crystalline protein degradation (IcPD) do not appear to match the patterns from fossil samples, reinforcing the need for a comprehensive understanding of the underlying mechanisms of protein degradation. This novel preparative method isolates intra-crystalline amino acids suitable for the development of mammalian geochronologies based on enamel protein degradation. The lower rates of racemization in enamel (cf. Bithynia opercula) suggest that the enamel AAR may be able to be used as a relative dating technique over time scales >2.8 Ma. Enamel AAR has the potential to directly date mammalian remains past the limit of all other current direct dating methods, providing an invaluable tool for geochronological studies.

New interglacial deposits from Copenhagen, Denmark: marine Isotope Stage 7

During a pre‐site survey and construction of a new metro route and station in Copenhagen, fossiliferous organic‐rich sediments were encountered. This paper reports on multidisciplinary investigations of these organic sediments, which occurred beneath a sediment succession with a lower till, glacifluvial sand and gravel, an upper till and glacifluvial sand. The organic sediments were underlain by glacifluvial sand and gravel. The organic‐rich sediments, which were up to 0.5 m thick, accumulated in a low‐energy environment, possibly an oxbow lake. They were rich in plant fossils, which included warmth‐demanding trees and other species, such as Najas minor, indicating slightly higher summer temperatures than at present. Freshwater shells were also frequent. Bithynia opercula allowed the sediments to be put into an aminostratigraphical framework. The amino acid racemization (AAR) ratios indicate that the organic sediments formed during Marine Isotope Stage 7 (MIS 7), which is consistent with optically stimulated luminescence dating that gave ages of 206 and 248 ka from the underlying minerogenic deposit. The assemblages from Trianglen are similar to interglacial deposits from the former Free Port (1.4 km away) in Copenhagen, except that Corbicula and Pisidium clessini were not found at Trianglen. The presence of these bivalves at the Free Port and the ostracod Scottia tumida at Trianglen indicates a pre‐Eemian age. AAR data from archived Bithynia opercula from the Free Port were almost identical to those from Trianglen, indicating that the two sites are contemporary. We suggest the Trianglen interglacial be used as a local name for the MIS 7 interglacial deposits in Copenhagen. MIS 7 deposits have rarely been documented from the region, but MIS 7 deposits may have been mistaken for other ages. The use of AAR ratios in Bithynia opercula has a great potential for correlation of interglacial non‐marine deposits in mainland northern Europe.

Protein diagenesis in archaeological gastropod shells and the suitability of this material for amino acid racemisation dating: Phorcus lineatus (da Costa, 1778)

The inter-and intra-crystalline fractions of the topshell Phorcus lineatus recovered from modern specimens and shells from archaeological sites in Northern Spain covering Neolithic, Mesolithic, and Upper Magdalenian periods were examined for amino acid composition and racemisation over time. The main loss of proteins from the inter-crystalline fraction occurred within the first 6000 years after the death of the organism. In contrast, the intra-crystalline fraction isolated by bleaching—with a different protein composition to that of the inter-crystalline fraction—appeared to behave like a closed system for at least 12.6 ka, as reflected by the lack of a significant decrease in amino acid content. However, changes in the relative composition of the amino acids present in these shells occurred during this period. The concentration of aspartic acid remained almost constant with age within the intra-crystalline fraction and its contribution to the total amino acid content also remained the same. Good correspondence was obtained between Asx D/L values in unbleached and bleached samples and age, thereby allowing the dating of archaeological sites and the determination of chronometric age.

The Moyjil site, south-west Victoria, Australia: chronology

An unusual shell deposit at Moyjil (Point Ritchie), Warrnambool, in western Victoria, has previously been dated at 67±10 ka and has features suggesting a human origin. If human, the site would be one of Australia’s oldest, justifying a redetermination of age using amino acid racemisation (AAR) dating of Lunella undulata (syn. Turbo undulatus) opercula (the dominant shellfish present) and optically stimulated luminescence (OSL) of the host calcarenite. AAR dating of the shell bed and four Last Interglacial (LIG) beach deposits at Moyjil and Goose Lagoon, 30 km to the west, confirmed a LIG age. OSL analysis of the host sand revealed a complex mixing history, with a significant fraction (47%) of grains giving an early LIG age (120–125 ka) using a three-component mixing model. Shell deposition following the LIG sea-level maximum at 120–125 ka is consistent with stratigraphic evidence. A sand layer immediately below the shell deposit gave an age of ~240 ka (i.e. MIS 7) and appears to have been a source of older sand incorporated into the shell deposit. Younger ages (~60–80 ka) are due to bioturbation before calcrete finally sealed the deposit. Uranium/thorium methods were not applicable to L. undulata opercula or an otolith of the fish Argyrosomus hololepidotus because they failed to act as closed systems. A U–Th age of 103 ka for a calcrete sheet within the 240 ka sand indicates a later period of carbonate deposition. Calcium carbonate dripstone from a LIG wave-cut notch gave a U–Th age of 11–14 ka suggesting sediment cover created a cave-like environment at the notch at this time. The three dating techniques have collectively built a chronology spanning the periods before and after deposition of the shell bed, which occurred just after the LIG sea-level maximum (120–125 ka).

ESR dating of Middle Pleistocene archaeo-paleontological sites from the Manzanares and Jarama river valleys (Madrid basin, Spain)

In this work, three important Pleistocene sites of the Madrid basin located close to the junction of the Manzanares (PRERESA site) and the Jarama (Valdocarros site and Maresa quarry) rivers have been studied in order to improve the existing chronological framework of the basin and to clarify the geological evolution of these fluvial systems and their relationship with human occupations. To do so, Electron Spin Resonance (ESR) dating was applied to four fossil teeth and nine optically bleached quartz grain samples. Most of the obtained dates are consistent with the existing preliminary age estimates by biostratigraphy, luminescence (OSL and TL) or Amino Acid Racemization (AAR) dating. This ESR dating study suggests an age of Late Middle Pleistocene (early MIS6) for PRERESA site. At the Jarama valley (Valdocarros site and Maresa quarry), the Arganda I unit could be correlated to the MIS 9 and MIS10, the Arganda II unit seems to belong to MIS8 and MIS7 and the Arganda III to the MIS6.

Relative sea-level variability during the late Middle Pleistocene: New evidence from eastern England

Unravelling patterns of relative sea-level change during previous interglacials enhances our understanding of ice sheet response to changing climate. Temperate-latitude estuarine environments have the potential to preserve continuous records of relative sea level from previous interglacial (warm) periods. This is important because, currently, we typically only have snapshots of sea-level highstands from low-latitude corals and raised palaeoshoreline indicators while the (continuous) deep-sea oxygen isotope record only provides indirect evidence of sea-level changes. Here, we focus on the Nar Valley in eastern England, in which is preserved evidence of a late middle-Pleistocene marine transgression more than 20 vertical metres in extent. By applying a model of coastal succession and sea-level tendencies, as used in Holocene sea-level studies, we assess the mode (abrupt versus gradual) of sea-level change recorded by the interglacial Nar Valley sequences. Compiled palaeo-stratigraphic evidence comprising foraminifera, pollen and amino acid racemization dating, suggests that the mode of sea-level change in the Nar Valley interglacial sequence was gradual, with potentially two phases of regional transgression and relative sea-level rise occurring at two separate times. The first phase occurred during the latter part of marine Oxygen Isotope Stage (MIS) 11 from ∼8 to 18 m OD; and, the second phase potentially occurred during early MIS 9 from ∼-3 to 3 m OD (with long-term tectonic uplift included in these estimates). We cannot conclusively preclude an alternative MIS 11 age for these lower sediments. The lack of indicators for rapid sea-level oscillations in the Nar Valley adds weight to an argument for steady melt of the ice sheets during both MIS 11 and 9.

Well-dated fluvial sequences as templates for patterns of handaxe distribution: Understanding the record of Acheulean activity in the Thames and its correlatives

The use of Acheulean (handaxe) typology as a cultural and temporal marker has been a topic of controversy in recent decades, with many archaeologists continuing to reject such an approach out of hand. Much of the controversy stems, however, from difficulties in reconciling the archaeological record from Quaternary sediments with a flawed and overly simplified chronostratigraphical template. With the adoption of the ‘expanded chronology’ based on the marine oxygen isotope record, underpinned by biostratigraphical and geochronological dating, has come the recognition of a meaningful progression of artefact types, such as the first appearance of Levallois technique, attributed to MIS 9–8 over widespread parts of the Old World. More recently it has been established that assemblages in Britain with twisted ovate handaxes in significant numbers represent MIS 11 occupation, while those with significant proportions of cleavers and ‘ficron’ handaxes appear to be correlated with deposits formed at around the time of the MIS 9 interglacial. The recognition of such patterns stems largely from the well-dated Thames sequence; it should not be confused with the previous use, in the mid-20th century, of archaeological typology as a crude dating indicator based on a relative refinement of tool making. Key means of age constraint for the Thames sequence have been mammalian assemblage zones representing the last four interglacial cycles, molluscan biostragraphy and amino acid racemization dating of molluscan material, especially the calcitic opercula of the gastropod Bithynia tentaculata, thus providing a framework within which the archaeological patterns can be identified.

Isoaspartic acid is present at specific sites in myelin basic protein from multiple sclerosis patients: could this represent a trigger for disease onset?

Multiple sclerosis (MS) is associated with breakdown of the myelin sheath that coats neurons in the central nervous system. The cause of MS is not known, although the pathogenesis involves destruction of myelin by the immune system. It was the aim of this study to examine the abundant myelin protein, myelin basic protein (MBP), to determine if there are sites of modification that may be characteristic for MS. MBP from the cerebellum was examined from controls and MS patients across the age range using mass spectrometry and amino acid analysis. Amino acid racemization data indicated that myelin basic protein is long-lived and proteomic analysis of MBP showed it to be highly modified. A common modification of MBP was racemization of Asp and this was significantly greater in MS patients. In long-lived proteins, L-Asp and L-Asn can racemize to three other isomers, D-isoAsp, L-isoAsp and D-Asp and this is significant because isoAsp formation in peptides renders them immunogenic.Proteomic analysis revealed widespread modifications of MBP with two surface regions that are altered in MS. In particular, isoAsp was significantly elevated at these sites in MS patients. The generation of isoAsp could be responsible for eliciting an immune response to modified MBP and therefore be implicated in the etiology of MS.Electronic supplementary materialThe online version of this article (doi:10.1186/s40478-016-0348-x) contains supplementary material, which is available to authorized users.

Oil platforms in the Persian (Arabian) Gulf: Living and death assemblages reveal no effects

Environmental impact assessments require pre-impact data to discriminate between natural and anthropogenic sources of community shifts. True pre-impact data, however, are rarely available because the onset of ocean biomonitoring in the 20th century frequently postdates the timing of such shifts. Death assemblages (DAs) sampled on a sea-floor capture previous community states and represent archives of past pre-impact conditions. This is because they change more slowly (10–10,000 years) than the corresponding living assemblage (LA) (yearly scales of turnover). Strong and rapid directional changes such as those due to human activities are therefore not immediately captured by DAs, leading to a greater live-dead (LD) mismatch than under natural processes alone. We used this approach to infer disturbance of benthic habitats around platforms in two major oilfields in the Persian (Arabian) Gulf: Umm Al Dalkh (UA) and Zakum (ZK). We found that, first, LD metrics showed no correlation with contamination levels or distance from the platform. Second, although LAs and DAs significantly differed in species composition and did not overlap in multivariate space, the difference was generated by a single species, the semelid deposit-feeding bivalve Ervilia purpurea. This bivalve was not found alive, but constituted 30–50% of the DAs at the field scale and up to 92% at some stations. Radiocarbon-calibrated amino acid racemization dating of valves of this species showed considerable spatial and temporal heterogeneity in production over the last decades and centuries, implying a boom-and-bust population dynamics; its absence in LAs is thus likely unrelated to the onset of oil platform production in the 20th century. The remaining LD differences probably reflect within- and multiple-habitat temporal or spatial averaging, and taxonomic similarity and rank-order agreement in species abundance at the field scale are comparable with values recorded in pristine areas. Therefore, we found no evidence of major community shifts in this oilfield area.

Pecten as a new substrate for IcPD dating: The quaternary raised beaches in the Gulf of Corinth, Greece

Intra-crystalline protein diagenesis (IcPD), a recent development of amino acid racemization dating (AAR), is now established as a reliable geochronological tool for the Quaternary. However, extending the method to new biominerals requires extensive testing in order to provide evidence for the closed-system behaviour of the intra-crystalline proteins and to assess the temporal span that can be covered.Here we present results from high-temperature experiments on the IcPD of the bivalve Pecten, demonstrating that a fraction of proteins can be isolated from a bleach-resistant mineral matrix, which effectively operates as a closed system under conditions of accelerated diagenesis in the laboratory. Analyses of Pecten from the well-dated terrace system of the Gulf of Corinth (Greece) provided a pilot test for the integrity of the intra-crystalline fraction in subfossil shells. The small sample sizes in this preliminary study preclude a full assessment of the aminostratigraphic power of Pecten IcPD, but a concordance is observed between the extent of IcPD and sites dating from between MIS 5 and MIS 11.We conclude that Pecten is a potentially good substrate for IcPD dating in the Mediterranean, and that the temporal limit of the technique in this area lies beyond MIS 11.