Aminostratigraphy of UK Pleistocene deposits

An integrated approach to the taxonomic identification of prehistoric shell ornaments

Shell beads appear to have been one of the earliest examples of personal adornments. Marine shells identified far from the shore evidence long-distance transport and imply networks of exchange and negotiation. However, worked beads lose taxonomic clues to identification, and this may be compounded by taphonomic alteration. Consequently, the significance of this key early artefact may be underestimated. We report the use of bulk amino acid composition of the stable intra-crystalline proteins preserved in shell biominerals and the application of pattern recognition methods to a large dataset (777 samples) to demonstrate that taxonomic identification can be achieved at genus level. Amino acid analyses are fast (<2 hours per sample) and micro-destructive (sample size <2 mg). Their integration with non-destructive techniques provides a valuable and affordable tool, which can be used by archaeologists and museum curators to gain insight into early exploitation of natural resources by humans. Here we combine amino acid analyses, macro- and microstructural observations (by light microscopy and scanning electron microscopy) and Raman spectroscopy to try to identify the raw material used for beads discovered at the Early Bronze Age site of Great Cornard (UK). Our results show that at least two shell taxa were used and we hypothesise that these were sourced locally.

A Levallois Knapping Site at West Thurrock, Lower Thames, UK: its Quaternary Context, Environment and Age

Levallois knapping debris is present beneath the sides of a disused tramway cutting connected to Lion Pit, West Thurrock, Essex. This occurrence, first recorded during the early 20th century, is in the basal gravel of the Taplow/Mucking Formation, which dates from the end of Marine Oxygen Isotope Stage (MIS) 8. The relatively undisturbed nature of this knapping debris is confirmed by the incidence of refitting material, although finer debitage is absent, presumably winnowed out. The Levallois character of the assemblage is demonstrated by the occurrence of characteristic ‘tortoise’ cores and flakes with faceted striking platforms. The artefact-bearing gravel is overlain by >10 m of predominantly fine-grained sediments, including fossiliferous sands and massive clayey silt, as well as laminated silts, clays, and sands of possible estuarine origin. These are attributed to deposition under temperate conditions during MIS 7. To the south, a younger fluvial gravel, attributed to MIS 6, has been incised into the interglacial sequence. The top of the estuarine sequence has been affected by pedogenesis, both before and after its burial by an unbedded solifluction gravel.

An aminostratigraphy for the British Quaternary based on Bithynia opercula

Aminostratigraphies of Quaternary non-marine deposits in Europe have been previously based on the racemization of a single amino acid in aragonitic shells from land and freshwater molluscs. The value of analysing multiple amino acids from the opercula of the freshwater gastropod Bithynia, which are composed of calcite, has been demonstrated. The protocol used for the isolation of intra-crystalline proteins from shells has been applied to these calcitic opercula, which have been shown to more closely approximate a closed system for indigenous protein residues. Original amino acids are even preserved in bithyniid opercula from the Eocene, showing persistence of indigenous organics for over 30 million years. Geochronological data from opercula are superior to those from shells in two respects: first, in showing less natural variability, and second, in the far better preservation of the intra-crystalline proteins, possibly resulting from the greater stability of calcite. These features allow greater temporal resolution and an extension of the dating range beyond the early Middle Pleistocene. Here we provide full details of the analyses for 480 samples from 100 horizons (75 sites), ranging from Late Pliocene to modern. These show that the dating technique is applicable to the entire Quaternary. Data are provided from all the stratotypes from British stages to have yielded opercula, which are shown to be clearly separable using this revised method. Further checks on the data are provided by reference to other type-sites for different stages (including some not formally defined). Additional tests are provided by sites with independent geochronology, or which can be associated with a terrace stratigraphy or biostratigraphy. This new aminostratigraphy for the non-marine Quaternary deposits of southern Britain provides a framework for understanding the regional geological and archaeological record. Comparison with reference to sites yielding independent geochronology, in combination with other lines of evidence, allows tentative correlation with the marine oxygen isotope record.

A chronological framework for the British Quaternary based on Bithynia opercula

Marine and ice-core records show that the Earth has experienced a succession of glacials and interglacials during the Quaternary (last ∼2.6 million years), although it is often difficult to correlate fragmentary terrestrial records with specific cycles. Aminostratigraphy is a method potentially able to link terrestrial sequences to the marine isotope stages (MIS) of the deep-sea record. We have used new methods of extraction and analysis of amino acids, preserved within the calcitic opercula of the freshwater gastropod Bithynia, to provide the most comprehensive data set for the British Pleistocene based on a single dating technique. A total of 470 opercula from 74 sites spanning the entire Quaternary are ranked in order of relative age based on the extent of protein degradation, using aspartic acid/asparagine (Asx), glutamic acid/glutamine (Glx), serine (Ser), alanine (Ala) and valine (Val). This new aminostratigraphy is consistent with the stratigraphical relationships of stratotypes, sites with independent geochronology, biostratigraphy and terrace stratigraphy. The method corroborates the existence of four interglacial stages between the Anglian (MIS 12) and the Holocene in the terrestrial succession. It establishes human occupation of Britain in most interglacial stages after MIS 15, but supports the notion of human absence during the Last Interglacial (MIS 5e). Suspicions that the treeless 'optimum of the Upton Warren interstadial' at Isleworth pre-dates MIS 3 are confirmed. This new aminostratigraphy provides a robust framework against which climatic, biostratigraphical and archaeological models can be tested.

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

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.

Dating pleistocene archeological sites by protein diagenesis in ostrich eggshell

Eggshells of the African ostrich (Struthio camelus), ubiquitous in archeological sites in Africa, have been shown by laboratory simulation experiments to retain their indigenous organic matrix residues during diagenesis far better than any other calcified tissue yet studied. The rate of L-isoleucine epimerization to D-alloisoleucine follows reversible first-order kinetics and has been calibrated for local temperature effects and used to estimate the age range of stratified archeological sites. Age estimates are consistent with radiocarbon dates from several stratified archeological sites. With adequate calibration, this technique can provide accurate ages to within 10 to 15 percent for strata deposited within the last 200,000 years in the tropics and the last 1,000,000 years in colder regions such as China.

Differentiation of MIS 9 and MIS 11 in the continental record: vegetational, faunal, aminostratigraphic and sea-level evidence from coastal sites in Essex, UK

Multidisciplinary investigations of the vegetational, faunal and sea-level history inferred from the infills of buried channels on the coast of eastern Essex have a direct bearing on the differentiation of MIS 11 and MIS 9 in continental records. New data are presented from Cudmore Grove, an important site on Mersea Island that can be linked to the terrace sequence of the River Thames. The vegetational history has been reconstructed from a pollen sequence covering much of the interglacial represented. The temperate nature of the climate is apparent from a range of fossil groups, including plant remains, vertebrates (especially the rich herpetofauna), molluscs and beetles, which all have strong thermophilous components. The beetle data have been used to derive a Mutual Climatic Range reconstruction, suggesting that mean July temperatures were about 2 degrees C warmer than modern values for southeast England, whereas mean January temperatures may have been slightly colder. The sea-level history has been reconstructed from the molluscs, ostracods and especially the diatoms, which indicate that the marine transgression occurred considerably earlier in the interglacial cycle than at the neighbouring Hoxnian site at Clacton. There are a number of palynological similarities between the sequence at Cudmore Grove and Clacton, especially the presence of Abies and the occurrence of Azolla filiculoides megaspores. Moreover, both sites have yielded Palaeolithic archaeology, indeed the latter is the type site of the Clactonian (flake-and-core) industry. However, the sites can be differentiated on the basis of mammalian biostratigraphy, new aminostratigraphic data, as well as the differences in the sea-level history. The combined evidence suggests that the infill of the channel at Cudmore Grove accumulated during MIS 9, whereas the deposits at Clacton formed during MIS 11. The infill of a much later channel, yielding non-marine molluscs and vertebrates including Hippopotamus, appears to have formed during the Ipswichian (MIS 5e). This evidence is compared with other important sites of late Middle Pleistocene age in Britain and elsewhere on the continent and the importance of a multidisciplinary approach is stressed.

Closed-system behaviour of the intra-crystalline fraction of amino acids in mollusc shells

When mollusc shells are analysed conventionally for amino acid geochronology, the entire population of amino acids is included, both inter- and intra-crystalline. This study investigates the utility of removing the amino acids that are most susceptible to environmental effects by isolating the fraction of amino acids encapsulated within mineral crystals of mollusc shells (intra-crystalline fraction). Bleaching, heating and leaching (diffusive loss) experiments were undertaken on modern and fossil Corbicula fluminalis, Margaritifera falcata, Bithynia tentaculata and Valvata piscinalis shells. Exposure of powdered mollusc shells to concentrated NaOCl for 48 h effectively reduced the amino acid content of the four taxa to a residual level, assumed to represent the intra-crystalline fraction. When heated in water at 140 degrees C for 24 h, only 1% of amino acids were leached from the intra-crystalline fraction of modern shells compared with 40% from whole shell. Free amino acids were more effectively retained in the intra-crystalline fraction, comprising 55% (compared with 18%) of the whole shell after 24 h at 140 degrees C. For fossil gastropods, the inter-shell variability in D/L values for the intra-crystalline fraction of a single-age population was reduced by 50% compared with conventionally analysed shells. In contrast, analysis of the intra-crystalline fraction of C. fluminalis does not appear to improve the results for this taxon, possibly due to variability in shell ultrastructure. Nonetheless, the intra-crystalline fraction in gastropods approximates a closed system of amino acids and appears to provide a superior subset of amino acids for geochronological applications.

Testing the aminostratigraphy of fluvial archives: the evidence from intra-crystalline proteins within freshwater shells

Until recently few studies of amino acid racemization of fossil bivalves and gastropods collected from river terrace deposits in Europe were based on the analysis of the intra-crystalline fraction. Instead they were based on the epimerization (racemization) of a single amino acid, isoleucine, and its inter-conversion to alloisoleucine. This paper presents data from the analysis of the intra-crystalline fraction of the shells, using a preparation technique of sample bleaching to remove the leachable matrix, thus leaving a component that exhibits closed-system behaviour. Reverse-phase HPLC separation with fluorescence detection allows the interpretation of four amino acids in detail: aspartic acid, glutamic acid, alanine and valine. The intra-crystalline fraction offers greater potential for improved resolution, especially when combined with the analysis of multiple amino acid d/l values, which racemize at different rates. This is explored using three species of freshwater gastropods (Bithynia tentaculata and troschelii, Valvata piscinalis) and the bivalve Corbicula. Sites of different ages within the Lower Thames river terrace sequence are used as a stratigraphical framework, with samples from other southern UK sites providing supplementary evidence. The results indicate better resolution using the intra-crystalline fraction over that obtained using unbleached shells, with differentiation possible at sites of up to MIS 7 age. However, for older sites, although values are always higher, the separation is less successful. A species effect has been identified between the gastropod shells. Despite the analysis of intra-crystalline protein, amino acid data from Corbicula remain problematical. Preliminary data on the opercula from Bithynia indicate that better resolution is possible, particularly at older sites.

Fossil proteins in vertebrate calcified tissues

Selected fossil vertebrates and the enclosing sediments dating from 1300 years B.C. to approximately 400 million years ago were subjected to amino acid assay. The amino acid analyses revealed little evidence of intact collagen in fossils of Tertiary, Mesozoic or Palaeozoic age. There was, however, evidence of contemporary proteinaceous material which may have been derived from bacteria. In Palaeozoic material the analyses detected a general background of amino acids common to both fossils and sediments. The degree of racemization was routinely determined as a means of measuring modern contamination of geologically older samples. An electron microscope study of Quaternary (Pleistocene) collagen revealed a significant reduction of the 64 nm banding to about 50 nm. The same Pleistocene material gave amino acid compositional profiles typical of collagen. However, when this material was subjected to digestion by the proteolytic enzymes collagenase, pronase and subtilisin, the resulting peptide fingerprints showed small but significant differences from those obtained from modern collagen digests, indicating the possibility of changes having occurred during fossilization affecting susceptible cleavage sites in the molecule.

The Pleistocene sea-level and neotectonic history of the eastern Solent, southern England

In the eastern extremity of the Isle of Wight, near Bembridge, marine interglacial deposits occur at a variety of different elevations. The highest of these, the Steyne Wood Clay, is an estuarine deposit that lies between 38 and 40 m o.d . and rests on Bembridge Marls (Lower Oligocene). The Steyne Wood Clay, which had previously been assigned to the post-temperate substage of a Middle Pleistocene interglacial, has now yielded a diverse coccolith assemblage dominated by Gephyrocapsa oceanica and G. caribbeanica . The absence of both Pseudoemiliania lacunosa , with a last occurrence datum at ca. 0.475 M a B P. and Emiliania huxleyi , with a first occurrence datum at ca. 0.275 Ma B P, suggests deposition during this time interval. The dating of the Steyne Wood Clay is further constrained by palaeomagnetic data, indicating normal geomagnetic polarity, and by amino acid ratios consistent with an early M iddle Pleistocene age. An extended and revised list of Foraminifera and Ostracoda is given, including the description of Leptocythere steynewoodensis sp.nov. The low-level interglacial deposits make up the Bembridge Raised Beach, here formally defined as consisting of high-energy beach gravels, intertidal sands and organic muds, which represent a single fining-upwards sequence. Pollen analysis of the organic muds indicates that these accumulated during the early and late-temperate substages of the Ipswichian interglacial (Ip IIb - III) . Therm oluminescence dates of ca . 115 Ka BP have been obtained from sand lenses within the Raised Beach itself, which also support correlation with the Ipswichian. The Bembridge Raised Beach occupies an altitudinal range of 5-18 M O.D . and thickens rapidly in a westerly direction where it abuts a cliff cut into the Bembridge Marls. Details are given of the composition, morphology and sedimentology of the gravels constituting the Beach, and similarities to recent cuspate foreland and split accumulations are highlighted. A similar origin is proposed for this feature. The upper surface of the Beach has been soliflucted and deposits of matrixsupported gravel, rich in clay, thicken downslope in an easterly direction. This solifluction has been disturbed by cryoturbation. Both the in situ and soliflucted beach are mantled by brickearth, a reworked aeolian silt, which reaches a maximum thickness of 10 m. A Late Devensian age for this unit has been established by thermoluminescence dates in the range 16.0+1.5 to 21.5 + 2 K a BP. Near Lane End, a sedge-peat rich in plant macrofossils and insects occurs between two gravel units. These appear to post-date the Raised Beach and are interpreted as of fluvial origin. The gravel capping the cliffs at Priory Bay, the richest source of Palaeolithic artefacts on the Isle of Wight, occurs between 29 and 33 M O.D. and is also thought to be a fluvial aggradation unrelated to the Raised Beach. The relationship of these marine deposits to those occurring on the adjacent mainland are considered. The Steyne Wood Clay is correlated with the Slindon Sands at Boxgrove, part of the Goodwood-Slindon Raised Beach, which occur at an identical elevation and have produced a similarly diverse coccolith assemblage. Additional palaeontological evidence from Boxgrove suggests that the interglacial deposits should be assigned to a temperate stage falling in the latter part of the ‘Cromerian Complex’. Correlation of the Steyne Wood Clay and Slindon Sands with oxygen isotope stage 9, 11 or 13 seems very probable. Reasons for the occurrence of marine deposits of this age at ca. 40 M O.D.. are considered and it is thought that neotectonic activity is at least partly responsible. Mean rates of uplift of between 5.3 and 15.5 mm ka -1 have been calculated from age estimates for stages 9, 11 and 13 derived from the deep-sea record. However, it is unlikely that the uplift was uniform in either rate or direction. The diverse coccolith assemblages preserved in the Steyne Wood Clay and in the Slindon Sands indicate a full open connection with the marine waters of the central English Channel, and suggests that a thermocline was then present in the Channel at a time when the Straits of Dover were probably closed. The interglacial channel deposits on the modern foreshore of Bracklesham Bay near Earnley have produced a limited coccolith assemblage. Because the altitudinal and palynological differences between these deposits and the Steyne Wood Clay are so great, they are thought to belong to different interglacial stages. The Bembridge Raised Beach is thought to equate with similar deposits on the northern shore of the Solent at Selsey, Stone and West Wittering, which has also now yielded pollen, reported here.

Stratigraphy and palaeoenvironments of the Red Crag and Norwich Crag formations between Aldeburgh and Sizewell, Suffolk, England

This study uses a variety of criteria to examine short-range correlation within the Crag deposits in order to assess the validity of longer-range correlations within the British Pleistocene stage system. To this end, six rotary cored boreholes spaced at 0.5-1.0 km intervals were drilled along a north-south-aligned traverse between Aldeburgh and Sizewell, Suffolk. These show that the thick Red/Norwich Crag sequence is confined to a deep, sharply bounded basin, which is of probable erosional rather than tectonic origin. The undisturbed borehole core material enabled an assessment of the limits of stratigraphic resolution within these dominantly high-energy, shallow marine sediments to be made. Subdivision of the sequence was done on the basis of lithostratigraphical and biostratigraphical (foraminifera, pollen and spores, dinoflagellate cysts, and molluscs) criteria; chronostratigraphical methods (palaeomagnetism and amino acid chronology) were also applied. The various subdivisions indicated by each of these disciplines were in large part consistent, demonstrating that valid stratigraphic units had been identified. Only amino acid chronology did not indicate any obvious subdivision of the sequence. Three lithostratigraphical units were recognized within the thick Crag sequence. The lowest unit (AS-Lith 1) consists of coarse shelly sands interbedded with thinly laminated muds and fine sands. The middle unit (AS-Lith 2) consists of fine- to coarse-grained shelly sands arranged in two coarsening-upwards cycles. Units AS-Lith 1 and AS-Lith 2 are correlated on a lithostratigraphical basis with the Red Crag Formation of the adjacent Aldeburgh-Orford area to the south and are named the Sizewell Member and the Thorpeness Member respectively. The uppermost unit (AS-Lith 3) comprises fine- to medium-grained, well-sorted sands; it correlates with the Chillesford Sand Member of the Norwich Crag Formation of the adjacent Aldeburgh-Orford area. The Sizewell Member of the Red Crag Formation is normally magnetized and palaeontologically distinctive. The pollen, foraminifera and dinoflagellate assemblages firmly establish it as Pre-Ludhamian in age, and probably equivalent to an interval within the Reuverian C to Praetiglian Stages of the Netherlands. The Thorpeness Member of the Red Crag Formation is less easy to place within the British Pleistocene stage system. It is reverse magnetized, at least in part, and foraminifera assemblages suggest possible correlation with the Ludhamian Stage. No identifiable pollen or dinoflagellate assemblages were obtained. The Chillesford Sand Member of the Norwich Crag Formation is largely unfossiliferous but the borehole material has yielded a single pollen spectrum that suggests correlation with the Bramertonian Stage.