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Steve Boreham: Publication abstracts/summaries

Forensic Science

Horton, B. P., Boreham, S. and Hillier, C. (2006) The Development and Application of a Diatom-Based Quantitative Reconstruction Technique in Forensic Science. Journal of Forensic Science, Vol. 51, No. 3 643-650.

Diatoms are a group of unicellular algae that have been recorded and classified for over 200 years and have been used in a range of applications in forensic science. We have developed a quantitative diatom-based reconstruction technique to confirm drowning as a cause of death and localize the site of drowning in two recent, high-profile, case studies. In both case studies we collected diatom samples from the local and/or regional area to act as a control in the examination of diatom assemblages associated with lungs and clothing.

In Case Study 1 the modern analog technique suggested that all lung and clothing samples have statistically significant similarities to control samples from shallow water habitats. In Case Study 2, the analog matching suggested that the majority of lung samples show a statistically significant relationship to samples from a pond, indicating that this was the drowning medium.

Quaternary geology of Britain

Pleistocene geology of the Palaeolithic sequence at Redhill, Thetford, Norfolk, England

P. L. Gibbard, R. G. West, A. Pasanen, J. J. Wymer, S. Boreham, K. M. Cohen & C. Rolfe (2008)

The Pleistocene river terrace deposits in the Little Ouse valley at Redhill are described and related to earlier records. Lowestoft Formation (Anglian-age) glacial deposits underlie the interfluve area into which the valley was excavated, whilst the present valley is underlain by Holocene alluvial sediments beneath the modern river floodplain. The sediments beneath the Redhill terrace represent deposition in a gravel-bed braided-type stream. Ground Penetrating Radar (GPR) survey clarifies the internal structure, areal distribution and relation of the sediments to bedrock in the he local area. The sediments are overlain by aeolian 'cover sand'. The valley sides provided a source of chalk and flint, the latter exploited locally by Palaeolithic humans, as indicated by the prolific finds of palaeoliths from the sediments. Contemporaneous periglacial conditions are indicated by putty chalk, silty sand and associated sharp flint pebbles and diamicton-like coarse gravel with highly angular clasts, which was interbedded with the fluvial sediment. These materials, together with the artefacts, were soliflucted onto the river braidplain. The Redhill artefact assemblage includes Late Middle Acheulian pointed and sub-cordate hand-axes. Comparison of the artefact and vertebrate assemblages with those from the River Thames' sequence shows a striking similarity to those recovered from the Lynch Hill/Corbets Hill/Tey Member (late Middle Pleistocene Wolstonian Stage; Marine Isotope Stages 10–8). This appears to represent a significant period of human occupation of lowland Britain.

Fluvial response to rapid climate change during the Devensian (Weichselian) Lateglacial in the River Great Ouse, southern England, UK.

Gao, C., Boreham, S., Preece, R.C., Gibbard P.L., Briant R.M. (2007) Fluvial response to rapid climate change during the Devensian (Weichselian) Lateglacial in the River Great Ouse, southern England, UK. Sedimentary Geology 202 (2007) 193-210

Few Lateglacial (15,200-11,500 Cal BP) fluvial deposits are known from southern England, UK. This paper outlines a sedimentological investigation of a Lateglacial site near the village of Roxton in the middle reach of the River Great Ouse. Below the Holocene argillaceous alluvium, several large gravelly lithofacies units representing long-term fluvial processes are recognised based on their lower bounding surfaces and sedimentary features. In line with palaeontological evidence and radiocarbon dating, detailed facies analysis indicates that the river changed from a braided to a wandering/meandering regime in response to the warming-induced reduction in nival peak discharge and increase in vegetation cover consisting of birch woodland and grassland during the Lateglacial Interstadial (15,200-12,700 Cal BP). This was followed by a change back to a braided river in response to climatic deterioration during the Younger Dryas Chronozone (12,700-11,500 Cal BP). The interstadial floodplain consisted of both overbank fines and channel lateral or point-bar sands and gravels. The two suites of contemporaneous sediments in the geological succession may be easily mis-interpreted as independent climato-stratigraphical units due to their cross-cutting relationship and marked difference in facies assemblage. Lateral channel movement in such a system also implied that the floodplain underwent constant erosion, resulting in underdeveloped overbank sequences, insufficient to withstand post-depositional removal by erosion. This probably accounts for the rare preservation of fine-textured overbank deposits of the Lateglacial Interstadial in southern England.

Age-estimate evidence for Middle–Late Pleistocene aggradation of River Nene 1st Terrace deposits at Whittlesey, eastern England

Langford, H. E. , Bateman, M. D. , Penkman, K. E. H. , Boreham, S., Briant, R. M. , Coope G. R. & Keen D. H. 2007 Age-estimate evidence for Middle–Late Pleistocene aggradation of River Nene 1st Terrace deposits at Whittlesey, eastern England. Proceedings of the Geologists' Association, 118, 283–300.

At Whittlesey, eastern England, Pleistocene interglacial sediments (unit G3) deposited in marine oxygen isotope stage (MIS) 7 appear to be truncated by a sequence comprising: (i) a limestone-rich gravel containing organic mud beds (unit F1); (ii) vertically aggrading gravel beds with sand–clay-lined bases (unit F2); and (iii) interbedded sands and gravels (units F4–F6) with associated overbank deposits (unit G4). Preliminary investigations of the floral and faunal assemblages of the organic muds were consistent in providing evidence for deposition under cool conditions. This apparent single cool/cold-phase sequence therefore could have been deposited in either MIS 6 or MIS 5d–2. The presence of sand beds in units F5, F6 and G4 and of molluscs in the organic mud beds of unit F1 provided the opportunity for obtaining age estimates using optically stimulated luminescence (OSL) and amino acid racemization (AAR). Rather than a single cool/cold-phase sequence the age-estimate data revealed multiphase aggradation, with the AAR data indicating the possibility that the organic muds in unit F1 were deposited earlier in MIS 7 than the interglacial deposits of unit G3. Therefore, the succession could be: unit F1 was truncated initially by unit G3, with unit F2 subsequently incising both unit F1 and unit G3. The OSL age estimates indicate that units F5, F6 and G4 are Early to Middle Devensian in age (MIS 5d–2), and therefore unit F2 was deposited sometime between late MIS 7 and MIS 5d. This paper has demonstrated the utility of using dual age-estimate techniques in dating complex fluvial sequences. Furthermore, the organic mud beds of unit F1 could provide important new information on the complex character of the MIS 7 interglacial. In addition, the OSL data and the fluvial style recorded by units F4–F6 and G4 allow comparisons to be made with recent investigations of nearby Devensian deposits.

The Milton Formation and Late Cenozoic drainage development of the English Midlands: A comment on Belshaw, Hackney & Smith (2005)

Boreham, S. & Langford H. The Milton Formation and Late Cenozoic drainage development of the English Midlands: A comment on Belshaw, Hackney & Smith (2005). Quaternary Newsletter, 108, 14-23. Quaternary Research Association.

The article by Belshaw et al. (2005) is a very welcome contribution to our understanding of Early Pleistocene drainage patterns in the English Midlands. The authors would like to further this discussion by considering previous palaeodrainage models, thus encouraging a more open-minded approach to the study of these issues (Langford 2002), together with aspects of their work on the southern and western margins of the Fen Basin.

A simplified model for drainage development across southern England since the Pliocene might start with a broadly flat surface gently dipping towards the southeast, with little influence of bedrock lithology on relief. This would give rise to a sub-parallel dip-slope drainage network flowing towards the southeast. As time progressed, differential relief due to variations in bedrock lithology would have become more pronounced, leading to an increase in the incidence of strike controlled streams. Subsidence of the North Sea basin and compensatory tilting and uplift of southern England would have accentuated the development of strike drainage, thus causing the Thames to migrate southwards and engendering Fenland drainage through the Wash.

In Late Pliocene times, rivers such as the Thames, Milton, Letchworth, Bytham (Trent) and Ancaster were all dip-slope streams. The proto-Soar, confluent with the Bytham River (Rose et al., 2002), and the Lower Thames (Bridgland 2003) both apparently adopted a strike orientation, flowing towards the northeast in the Early Pleistocene. This would suggest that the emergence of relief as a dominating influence on drainage patterns had occurred by this time. In the case of the Lower Thames this is likely to have been influenced by dip-slope streams following the regional dip away from the northern edge of the Wealden anticline.

Evidence For A New Hoxnian Interglacial Site at School Field, Tednambury, Hertfordshire

Betts, R. T. & Boreham, S. (2004) 'Evidence For A New Hoxnian Interglacial Site At School Field, Tednambury, Hertfordshire'. Quaternary Newsletter, 104, 2-11. Quaternary Research Association.

This study was carried out in the summer of 2002 to investigate the temporal and spatial nature of organic deposits reported by the British Geological Survey (Millward et al., 1987) at School Field, Tednambury, Hertfordshire. The BGS concluded that these deposits were temperate and post-Anglian, but were unable to determine which particular temperate episode the sediments represented. The presence in the area of fossiliferous silts overlying a basal grey till had been known for some time (West & Donner, 1956) but it was not until the BGS evaluation (Millward et al., 1987) that the sediments at Tednambury were fully described.

Seventeen boreholes were made at School Field, Tednambury using a hand auger on a grid system across an area 150m x 100m to determine the extent and thickness of sub-surface organic deposits reported by Millward et al. (1987). A geological cross-section through the deposits has been constructed using some of this data. Sediments from four boreholes (BH6, BH9, BH11 & BH17) were sampled for pollen analysis (RTB). This material also yielded plant macrofossils (identified by C. Turner, Open University), molluscs, and vertebrate remains (identified by R. C. Preece, University of Cambridge). Although comparable pollen data were recovered from all four boreholes investigated, the most complete pollen data came from BH6, from which a pollen diagram with 10 levels has been produced.

The Structure and Formation of the Wandlebury Area

Boreham, S. (2004) 'The Structure and Formation of the Wandlebury Area' Proceedings of the Cambridge Antiquarian Society XCIII: 5-8.

Wandlebury on the southern edge of the Gog Magog Hills, is generally underlain by thin soils overlying Middle Chalk bedrock, but also includes a patch of deeper loam developed on gravelly 'superficial' deposits, mapped as 'Glacial Gravel'. Two distinct types of gravel have been identified capping the Gog Magog Hills; one rich in exotic far-travelled material, the other dominated by chalk and flint. The former is interpreted as glacial outwash of the Anglian ice sheet, whilst the later appear to have been deposited by small local chalk streams. The position of these ancient river deposits high up on the Gog Magog Hills is explained by the inversion of relief through intense periglacial activity, which has occurred over the past 420 thousand years. An appreciation of how this landscape has developed over time assists our understanding of the complex 'canvas' on which archaeological features are imposed.

Fluvial system response to Late Devensian (Weichselian) aridity, Baston, Lincolnshire, England

Briant R. M., Coope G. R., Preece R. C., Keen D. H., Boreham S., Griffiths, H. I., Seddon M. B. & Gibbard P. L. (2004) 'Fluvial system response to Late Devensian (Weichselian) aridity, Baston, Lincolnshire, England.' Journal of Quaternary Science, 19(5): 479-495.

Little is known about the impact of Late Devensian (Weichselian) aridity on lowland British landscapes, largely because they lack the widespread coversand deposits of the adjacent continent. The concentration of large interformational ice-wedge casts in the upper part of many Devensian fluvial sequences suggests that fluvial activity may have decreased considerably during this time. The development of optically stimulated luminescence (OSL) dating enables this period of ice-wedge cast formation to be constrained for the first time in eastern England, where a marked horizon of ice-wedge casts is found between two distinctive dateable facies associations. Contrasts between this horizon and adjacent sediments show clear changes in environment and fluvial system behaviour in response to changing water supply, in line with palaeontological evidence. In addition to providing chronological control on the period of ice-wedge formation, the study shows good agreement of the radiocarbon and OSL dating techniques during the Middle and Late Devensian, with direct comparison of these techniques beyond 15 000 yr for the first time in Britain. It is suggested that aridity during the Late Devensian forced a significant decrease in fluvial activity compared with preceding and following periods, initiating a system with low peak flows and widespread permafrost development.

Holocene (Flandrian) organic deposits preserved in a lowland alder carr fen at Millpond Wood, Sevenoaks, Kent.

S. Boreham

In 1989 Bernard Worsnam contacted Dr P. L. Gibbard, concerning an organic deposit that had been encountered during preliminary investigations for a housing development at Millpond Wood, Sevenoaks, Kent. The author was asked to investigate the site to determine the extent and nature of the deposit. As part of this investigation, eight boreholes (BH1-8) were sunk to form a transect across the site to determine the stratigraphic relationship of the deposits. A hand auger was initially used for the boreholes, and a core of the longest sequence (BH3) was then taken using a Livingstone corer. The borehole data have been used to a construct section through the deposit. The sequence from BH3 was sampled for pollen analysis and yielded a skeletal pollen diagram of 14 levels. A bulk radiocarbon date was also obtained from near the base of the sequence at BH3.

Geology of the Biggleswade district

Moorlock, B. S. P., Sumbler, M. G., Woods, M. A. & Boreham, S. (2003)

This Sheet Explanation describes the geological 1:50 000 Series Sheet 204 Biggleswade that lies on the Mesozoic strata to the southwest of Cambridge. In the western part of the district is the northerly flowing River Great Ouse and its tributary the River Ivel, and the east is drained by the easterly flowing River Cam (or Rhee) with Bourn Brook farther to the north. A low discontinuous ridge of Woburn Sands Formation (Lower Greensand), locally wooded, extends from Shefford to Gamlingay and divides the Jurassic mudstone to the northwest from the Cretaceous mudstone to the south-east. Near Royston, the chalk-land rises to over 130 m above sea level. The region is predominantly agricultural, with Biggleswade the focus of an important market gardening area.

The district lies on the northern margin of a concealed massif of Palaeozoic rocks known as the London Platform, which was deformed during the Variscan orogeny. During the Mesozoic, the platform remained as a high surrounded by areas in which subsidence and thus sediment accumulation was greater. Mesozoic strata gradually onlapped onto the platform, but parts of the interior probably remained as dry land (the London Landmass) throughout the Jurassic.

Geology of the Biggelswade district

Moorlock, B. S. P., Boreham, S., Woods, M. A. & Sumbler, M. G. (2003)

This Sheet Explanation describes the geological map Sheet 205 Saffron Walden, which includes the outskirts of southern Cambridge, Haverhill and the northern part of Saffron Walden. The map has been revised from earlier editions (p.21), and the stratigraphy of the Chalk has been revised to bring it in line with modern nomenclature. Resistivity logs are available for many of the boreholes within the district and these have greatly aided correlation of the buried Chalk formations. The district lies on the northern margin of the London Platform, a massif of Palaeozoic rocks, which was deformed during the Variscan orogeny, and, during the Mesozoic, formed a stable structural high surrounded by areas of gradual subsidence. Mesozoic strata lapped progressively onto this platform (see cross-section on map), but parts of its interior probably remained as dry land (the so-called London Landmass) until the Cretaceous.

Last Interglacial and Devensian deposits of the River Great Ouse at Woolpack Farm, Fenstanton, Cambridgeshire, UK

Gao, C. Keen, D. H., Boreham, S., Coope, G. R., Pettit, M. E., Stuart, A. J., Gibbard, P. L. (2000) Last Interglacial and Devensian deposits of the River Great Ouse at Woolpack Farm, Fenstanton, Cambridgeshire, UK. Quaternary Science Reviews 19, 787-810

This paper describes Pleistocene fluvial deposits of the River Great Ouse at Woolpack Farm, Fenstanton, Cambridgeshire, UK. These sediments consist of a basal gravel, fossiliferous fluviatile muds, sands and gravels later disturbed and formed into a diamicton, and overlying gravels. The regional climate inferred from palaeobotany, Mollusca, Coleoptera and vertebrates from the diamicton indicates temperate conditions. Coleopteran evidence suggests a mean July temperature of ca. 21°C, 4°C warmer than today in eastern England, and winter temperatures a little colder than at present. Molluscan assemblages indicate a slight brackish influence during deposition of the muds which form the diamicton. The gravel succession is represented by three members which have a broad distribution in the Great Ouse Valley, and which were laid down in a braided river under periglacial conditions. The occurrence of permafrost is indicated by the presence of ice wedge casts in the gravels. The pollen and macrofossil evidence from the diamicton suggests correlation with Ipswichian substage IpII (Pinus-Quercetum mixtum -Corylus phase). The basal gravel is of pre-Ipswichian age. A Devensian age is proposed for the overlying gravels and their attendant periglacial phenomena.

Middle Pleistocene interglacial sediments at Tye Green, Stansted Airport, Essex, England

S. Boreham, M. H. Field & P. L. Gibbard

Interglacial lake deposits at Tye Green, Stansted, resting on unweathered till and overlain by a weathered diamicton are correlated with the Hoxnian temperate Stage. The sediments represent the infilling of an isolated kettle-hole type lake basin formed at the end of the cold Anglian Stage. Through the temperate period this basin was infilled by inorganic and organic sediments through the temperate period which record the development and decline of deciduous forest. Later periglacial conditions are indicated by the final infilling of the basin recycled till. The sedimentary sequence and vegetational development recorded in the sediments at Tye Green are compared to other Hoxnian sites in eastern England. Changes in deposition rates are interpreted as representing water-table fluctuations resulting from changes in precipitation. The deposits at Tye Green provide a useful stratigraphical marker in the glacial sequence of the district.

Middle Pleistocene interglacial Thames-medway deposits at Clacton-on-Sea, England: Reconsideration of the biostratigraphical and environmental context of the type Clactonian industry

Bridgland, D. R., Field, M. H., Holmes, J. A., McNabb, J., Preece, R. C., Selby, I, Wymer, J. J., Boreham, S., Irving, B. G., Parfitt, S. A., Stuart, A. J.

In 1987 an archaeological investigation was undertaken during redevelopment of the erstwhile Butlin's holiday camp at Clacton-on-Sea, on the grounds that the Middle Pleistocene Clacton Channel Deposits, containing the type-Clactonian Palaeolithic industry, were known to extend beneath the site. Excavations for a storm-drain allowed sampling at points along a longitudinal traverse of the main Clacton Channel. Analysis of these samples has provided new palaeontological information, including data pertaining to the rise in relative sea level during the interglacial represented. Systematic studies of molluscs and ostracods, the latter undertaken at Clacton for the first time, have been particularly valuable. Information from the Butlin's site supplements evidence previously gathered from the West Cliff section and from other localities at Clacton. The calcareous clay ('marl') that underlies the Clacton golf course extends beneath Butlin's, where it was found to be part of the Freshwater Beds, not the Estuarine Beds, as hitherto supposed. The Clacton Estuarine Beds, restricted to the eastern end of the site, have their base just below 2 m O.D., implying that their superposition upon the Clacton Freshwater Beds occurred when relative sea level in this area was close to present ordnance datum. Correlation of the Clacton Channel Deposits with the interglacial immediately following the Anglian/Elsterian Stage appears secure; equivalence with Oxygen Isotope Stage 11 of the oceanic sequence is most probable. A borehole survey and subsequent excavation revealed a Holocene sequence of unlithified tufa and organic sediments beneath part of the site.

Buried channel deposits at March, Cambridgeshire, Eastern England

Buried channels are not uncommon features associated with Anglian glacial deposits, and some examples for the area are shown in Figure 1. In fact, Gallois (1988) notes an anomalous thickness (27 m) of 'chalky Jurassic till' at Wimblingdon Road, Town End, March (TL 4179 9482), about 4 km to the south of the site described here. He suggests that this could mark the course of a preglacial tributary of the River Great Ouse.

Although borehole data exist that provide sedimentological and lithological information on buried channels within the area (e.g. Horton, 1970; Gallois, 1979), little information is available from sections exposed within them. The sections exposed in what is believed to be a buried channel at March therefore offered a rare opportunity to examine the facies architecture of sediments infilling such a feature. As such opportunities are so rare, a brief report is presented here of observations made during a preliminary site visit.

The term buried channel is used here to describe linear depressions that have no relationship to the present topography and which have been infilled by relict depositional systems that have no relationship with systems operating to form the present landscape. No genetic interpretation of these features is intended by this description.

Holocene (Flandrian) organic deposits preserved in an icing hollow at Bardfield Bridge, Borley, Essex

In June 1992 Essex County Council Highways Department contacted Dr P. L. Gibbard, concerning an organic deposit, which had been encountered during borehole investigations for engineering work at Bardfield Bridge, Borley (near Sudbury), Essex (Figure 1). Four boreholes (BH1-4)had been sunk around the bridge, and organic material had been encountered in three of these, reaching more than 3 m thickness in BH1. The author was asked to investigate the site to determine the extent and nature of the deposit. As part of this investigation, ten boreholes (BH5-14) were sunk around the bridge to determine the stratigraphic relationship of the deposits. A hand auger was used for BH5, and a 'Minuteman' mobile drill was used for the remaining boreholes. In addition, a single borehole record (BH15) was made available by the National Rivers Authority. The borehole data have been used to construct sections through the deposit (Figure 2), and to produce contour plots of the basin morphology and thickness of the organic deposit (Figure 3). The sequence from BH5 was sampled for pollen analysis and yielded a skeletal pollen diagram of 10 levels (Figure 4). Some problems were encountered in recovering samples from the base of the sequence due to the extremely unconsolidated nature of the sediment.

Middle Pleistocene lacustrine deposits in eastern Essex, England and their palaeogeographic implications

P. L. Gibbard, S. Boreham & H. M. Roe

Investigations in quarry exposures in the Asheldham Gravel and related deposits of southeast Essex are described. Section logging, mapping and borehole investigations are supported by clast lithological, heavy and clay mineral determinations. The sediments are derived from reworking of local Thames basin materials, fine sediment being predominantly from the London Clay. The sequence is shown to represent an aggradation that began as the fluvial infilling of the River Medway valley. The River Thames, diverted into this valley by glaciation futher west, overwhelmed the Medway, reworking the deposits. The valley was subsequently drowned and fine laminated lake sediment was initially deposited. This was during a period when the valley was drowned by the glacial lake ponded in the southern North Sea basin by the Anglian/Elsterian ice sheet. Progradation by a braid-delta complex advanced along the valley and subsequently fluvial deposition returned. Valley widening and straightening accompanied the delta progradation. The deposits were dissected by deep fluvial valleys infilled by Hoxnian interglacial sediments. The Asheldham Gravel is therefore placed in the Anglian/Elsterian Stage.

Middle Pleistocene Hoxnian Stage interglacial deposits at Hitchin, Hertfordshire, England

S. Boreham & P. L. Gibbard

Interglacial lake deposits resting on till and glaciofluvial gravels, and overlain by 'brickearth' 1km south of Hitchin town centre are correlated with the Hoxnian Stage. These deposits are shown to be equivalent to those previously described by Clement Reid at the turn of the century. The sediments fill a basin-like depression or depressions that may have originated as a kettle-hole. The inorganic character of the sediments suggests that the basin may have been fed by a stream. The basal part of the deposit represents the development of thermophilous woodland. Vertebrate remains and Palaeolithic artefacts associated with the sediments are discussed. Later infill of the basin by 'brickearth' probably took place under a periglacial climate. In common with many other Hoxnian sites in Hertfordshire, the sequence records only part of the interglacial. Such incomplete sequences have been attributed to climatic variation in water supply through the period.

Late Quaternary sediments with Chara encrustations in southern Fenland

Boreham S. & West, R. G. (1993) Late Quaternary sediments with Chara encrustations in southern Fenland. Geological Magazine, 130(4), 543-544.

Lacustrine sediments formed in highly calcareous water may contain calcium carbonate encrustations formed around the axes of Chara plants. Where such encrustations are abundant a characteristic sediment is formed, described as Chara-kalk by Lundquist (1927) and von Bulow (1931), and as algal micrite by Murphy & Wilkinson (1980). The sediment is usually formed in shallow water, still or slowly moving, a few metres in depth at the most. Lundquist (1927) points out that such sediments may accumulate rapidly, and result from the death and silting-up of dense Chara meadows. Wave action in shallow water may break up and concentrate the encrustations. Species of Chara known to develop strong encrustations (e.g. C. vulgaris, C. contraria, C. hispida; Wood, 1952) occur in Europe in the vegetative state throughout most of the year (Corillion, 1957), while Chara hispida shows 'self pruning', with apical growth balanced by death of the basal parts of the plant (Andrews et al. 1984). Such growth and decay is likely to favour the rapid sedimentation of encrustations.

Thermokarst activity and periglacial landscape change

The role of thermokarst and solution in the formation of Quidenham Mere, Norfolk, compared with some other Breckland meres

S. Boreham and D.C. Horne

Quidenham Mere is a small, shallow lake situated in a flat-bottomed embayment, c.11 km northwest of Diss and 5 km east of the River Thet, on the eastern edge of Breckland in south Norfolk (TM 040875). The palaeolimnology of Quidenham Mere is currently being studied by DCH as part of a NERC PhD studentship. It has been suggested that Quidenham Mere and other Breckland meres probably owe their origin to solution of Chalk beneath an overlying till mantle, which collapsed into the hollow formed (Bennett et al., 1990; Peglar, 1993c). Whilst this is a superficially plausible explanation, the dense jointing patterns and low physical strength of the Chalk bedrock limit the scale of solution collapse features (Sparks, 1971). Hollows (dolines) formed primarily by solution of the Chalk are often relatively small features, which are not necessarily associated with contemporary drainage, and usually occur where thin deposits overlie the bedrock (Jones, 1981). Indeed, Breckland is pock-marked by numerous shallow Chalk solution features, such as Ringmere, Langmere and Fowlmere (Jones and Lewis, 1941; Prince, 1962).

The scale, geological setting and geomorphology of the flat-bottomed embayment which contains Quidenham Mere, makes formation by solution and collapse alone seem unlikely. An alternative interpretation might be that this feature was at least partly formed by physical weathering, erosion and transport processes under periglacial conditions within a thermokarst embayment, similar to those described by West (1991) from southern Fenland. This article describes contemporary periglacial backwearing processes and a complex of similar landforms in the vicinity of Quidenham Mere. It considers the genesis of some other Breckland meres, including Diss Mere which is attributed to solution collapse, and ascribes the formation of the Quidenham embayment to thermokarst activity during the Devensian (last cold stage), and other cold stages since the Anglian.

Thermokarst landforms in the Cambridge area

Thermokarst landforms have been recognised in Cambridgeshire by Burton (1976, 1987) from the western margin of the fenland and by West (1991) at Grunty Fen and elsewhere in southern Fenland. They are represented by near circular depressions and larger flat-bottomed embayments cut into Jurassic or Cretaceous clay- or silt-rich bedrock and surrounded by low, rounded hills. It appears that these features were formed during the Devensian (the last cold stage), or in some cases in earlier cold stages, by the same processes that operate in arctic thaw lakes today. Their formation has been independent of past fluvial processes, which have formed separate terrace aggradations. This study includes a brief description of thermokarst processes, details the geological setting of the thermokarst embayment at Grunty Fen described by West (1991), and identifies similar features south-east of Cambridge, near Swavesey, and at several other localities in southern Cambridgeshire.

Possible thermokarst landforms near Theydon Bois, Essex

Boreham, S. (1996) Possible thermokarst landforms near Theydon Bois, Essex. The London Naturalist 75, 21-26

The morphology and geology of flat-bottomed embayments near Theydon Bois, Essex, are described. Similar features in Siberia and Canada formed by contemporary periglacial backwearing processes (thermokarst) are outlined. In addition, flat-bottomed embayments from the southern Fenland of East Anglia, attributed to thermokarst activity, are also noted. The embayments around Theydon Bois are interpreted as the product of thermokarst activity which operated under periglacial conditions during the Devensian (last cold stage), and possibly other cold stages since the Anglian.

Three-dimensional landscape modelling and data manipulation

Three-dimensional stratigraphic data representation using a personal computer

Computer generated three-dimensional stratigraphic data representation is not new; indeed Everett and Shennan (1987) developed such techniques using the hardware and software available to them more than a decade ago. The danger of attempting to describe any data processing or presentation technique based on a personal computer is that it will inevitably, and probably rapidly, become out-dated. This article is not intended to be an exhaustive account of programs capable of three-dimensional representation of data. However, I hope it will give an insight into a number of techniques, which promise to provide new ways of processing and representing stratigraphic data. The challenge is to convince workers that rather than being merely a curiosity, this is a valuable way of looking at Quaternary geology. I would encourage others to experiment and use these methods to bring Quaternary Research into the 21st Century.

The figures in this article use selected borehole data from the vicinity of Magdelene Bridge, Cambridge, which are from a database that I have been compiling as part of an Open University PhD project. Some of this data was previously published as a section by Sparks and West (1965).

Woodland ecology, methodology and urban wildlife

A simple and effective methodology for sampling modern pollen rain in tropical environments

William D. Gosling, Francis E. Mayle, Timothy J. Killeen, Marcelo Siles, Lupita Sanchez and Steve Boreham

Gosling, W. D., Mayle, F. E., Killeen, T. J., Siles, M., Sanchez L. and Boreham S. (2003) 'A simple and effective methodology for sampling modern pollen rain in tropical environments' The Holocene 13,4, 613-618.

To gain a better insight into the nature of palaeovegetation change in tropical ecosystems, more information needs to be gleaned from the limited number of fossil pollen records that exist. To achieve this, a detailed understanding of modern tropical ecosystems and the pollen they produce is required. To facilitate this, a practicable and effective mechanism for sampling modern pollen rain from the tropics is required. This paper presents a modified field methodology based upon three years of trapping experience in Noel Kempff Mercado National Park, Bolivia, and improved laboratory preparation methodologies. We demonstrate here a simple and very effective way to sample modern pollen rain in tropical environments using a funnel trap mounted on a stake containing cotton fibre as the trapping medium.

Lower Wood, Weston Colville

Boreham S. and F. Applin (1995) Lower Wood. Nature in Cambridgeshire. 37, 24-34.

Lower Wood is situated approximately 0.5 km north of Weston Green in the parish of Weston Colville in south-east Cambridgeshire, centred on TL 625528. The wood slopes gently towards the south-east, from a maximum elevation of about 111 m O.D. It is underlain by chalky boulder clay, and consequently the soils are rather poorly drained. Precipitation is c. 600 mm each year, with a slight summer maximum. This area of ancient woodland has a piecemeal history stretching back some 400 years and is possibly a remnant of the primeval 'wildwood' dating from early post-glacial times. It comprises about nine hectares of mixed wet Ash-Field Maple woodland with an understorey of Hazel and a ground flora including Oxlips Primula elatior, Bluebells Hyacirlthoides non-scripta and Dog's Mercury Mercurialis perennis.

The characteristically diverse ground flora of ancient woodland results from complex relationships between factors such as soil type and topography and from established management practices. Ancient woods usually have a continuous history of coppicing from about 1,000 years ago until the Second World War, when many were cleared or became derelict. Coppicing has the effect of opening up tracts of the woodland floor to light and generally leads to a succession of woodland plants as the coppice matures. In Lower Wood, past management has created a mixture of standard and coppiced trees and several well-defined rides. This paper presents work on the soils and vegetation carried out in 1990 and 1991. Nomenclature of vascular plants follows Stace (1991).

Observations on the wildlife potential of cities with particular reference to Cambridge

Boreham, S., and Albrecht, J. S. (1992) 'Observations on the wildlife potential of cities with particular reference to Cambridge' Nature in Cambridgeshire 34, 52-57.

There is a growing realisation of the importance of wildlife conservation in urban areas, not only for animals and plants, but for people who would otherwise be deprived of any contact with 'nature'. This attitude is not universal amongst planners and politicians, who often see open urban land as space for in-fill development. Cambridge is widely recognised for its pleasant tree-lined green open spaces. Although such resources are relatively easy to identify, the wildlife value of smaller, less obvious plots and urban gardens may be much greater. The challenge is to accommodate development without destroying these attractive and valuable attributes. This study attempts to refute the assertion that, in general, urban areas have little wildlife value and demonstrates the use of simple indices to identify those areas in Cambridge with few wildlife resources.

Lichens as air pollution indicators

Changes in the lichen flora on birch Betula pendula in northern Epping Forest

The lichen flora of Epping Forest has long been affected by air pollution from London. However, over the last 20 years Epping Forest has experienced a reduction in airborne sulphur dioxide, so that by 1985 mean winter levels were between 30 and 40 µgm-3. The epiphytic flora at the base of 170 mature silver birch trees in northern Epping Forest has been monitored over the five-year period 1987-91. The crustose lichen Lecanora conizueoides became less abundant, and Cladonia coniocraea and Hypogymnia physodes

showed some expansion. However, recolonization was very weak when compared to that recorded in other woodlands around London. Results suggest that it is now acid rain, rather than sulphur dioxide, which limits recolonization of lichens on silver birch trees in Epping Forest.

A Study of Corticolous Lichens on London Plane Platanus x hybrida Trees in West Ham Park, London

Falling sulphur dioxide levels in London during the last 25 years have produced more favourable conditions for lichen growth. Other workers have surveyed the recovery of corticolous lichens in north and west London in response to this change. In this study lichens epiphytic on London plane trees in West Ham Park have been investigated and related to declining aerial sulphur dioxide pollution. This has provided a baseline study of the corticolous flora of the London Plane and a record of lichen recolonization in east London. The Xanthorion was found to be colonizing tree bases and the Physodion, bark higher up the trees.

Freshwater macro-invertebrates as pollution indicators and freshwater ecology

A study of fresh water invertebrate distribution and abundance from fieldwork by secondary school students in an Epping Forest pond

Records of freshwater invertebrates from fieldwork undertaken by 14-18-year-old secondary school students over a two-year period have been collated to give an account of their varying distribution and abundance, and an Insight into the community dynamics In Lower Wake Valley Pond, Epping Forest. Student data have been processed to provide information on invertebrate habitat preferences and the abundance and biomass present in different trophic levels over time, using the concept of Eltonian pyramids. Throughout the study period, herbivores and detritivores were usually the dominant trophic groups. However, during the summer months there were episodes when abundance and biomass became severely depressed, and large carnivores became dominant. These inversions of number and biomass pyramids reflected extreme variations in waterflea populations, which in turn resulted principally from seasonal variations in primary production by planktonic algae, affected by seasonal changes in temperature, insolation and nutrient status. It appears that waterfleas and a few other invertebrate taxa are responsible for transferring the majority of energy in this pond ecosystem, but that many other diverse taxa, each with different niches, subsist by transferring relatively small amounts of energy.

Brookhouse Brook Revisited: Notes on the Recovery of Macro-invertebrates Following Livestock Slurry Pollution in a Clay Stream

The macro-invertebrate benthos of eight sites on an Essex clay stream were investigated in October 1989 and October 1990 to monitor its recovery following chronic livestock slurry pollution outlined in previous work (Boreham et al 1989). Although a rapid recovery occurred, this has been limited by dry summers which have seriously affected previously species-rich sites in the headwater catchment.

Freshwater pollution studies in an urban catchment

The importance of fieldwork in the teaching of biology has been emphasized by the freshwater studies specified in many GCSE and A level syllabuses. In particular freshwater pollution studies are often problematic, since suitable rivers or streams are often hard to find, access can be difficult and the sites themselves may pose potential health risks. The runoff from urban areas is widely cited as being of poor quantity due to a combination of factors.

These factors include; heavy metals, hydrocarbons, detergents, de-icing salt in winter, domestic chemicals, pesticides, leaks from the sewerage system, high temperatures in summer, low dissolved oxygen, and a rapid 'flashy' rise in discharge after rain. They present problems for urban freshwater pollution studies, since they rarely act continuously and are often 'non-point' sources, such as incipient leakages. In addition pollutants tend to accumulate in the catchment during dry weather, only to be concentrated by runoff.

In an urban stream where environmental conditions may vary greatly with discharge, physico-chemical parameters are often poor indicators of water quality.

In this study these problems have been largely overcome by using benthic macro-invertebrates as indicators of water quality, and by treating an entire urban catchment and stream as a point source of pollution, at its confluence with a non-urbanized stream. Such studies are particularly appropriate on the urban fringes of towns and cities where such a situation may commonly occur.

The Effects of Livestock Slurry Pollution on the Benthic Macro-invertebrate Fauna of a Clay Stream

Boreham, S., Hough A. R. & Birch P.

The benthic macro-invertebrate fauna of a clay stream polluted by livestock slurry was investigated at eight Essex sites in October 1985, April 1987 and October 1988. In addition some chemical data were also collected. A succession relative to the pollution tolerance of the taxa occurred downstream of the slurry outfall. Although the pollution had persisted for a number of years, there was evidence that it had become less severe and that this trend would continue in the future.

A study of freshwater succession from fieldwork by secondary school students in an Epping forest pond

Detailed vegetation maps from fieldwork undertaken by 14-18 year old secondary school students have been collated to provide an account of freshwater succession at Golding's Hill Pond, Epping Forest. Historical data show that in 1920 vegetation cover was sparse, but by 1973 plants covered over half the pond's surface. Between 1973 and 1985 vegetation dominated by emergent plants increased rapidly. There were also periods of accelerated growth by freefloating and marsh plants. It appears that an initial phase of colonization by pioneer species was followed by a period of expansion with little inter-specific competition. Finally, competitive species invaded areas occupied by other plants. Clearance of the pond in 1986 only slightly reduced subsequent vegetation cover which became dominated by rooted floating plants.