D. H. Keen

Sedimentology, palaeontology and archaeology of late Middle Pleistocene River Thames terrace deposits at Purfleet, Essex, UK

Middle Pleistocene fluvial deposits of the Corbets Tey Formation at Purfleet, Essex, provide evidence of an un-named and previously poorly recognized interglacial, thought to corrrelate with Oxygen Isotope Stage (OIS) 9. Previous attributions of the sediments to the Ipswichian (Last Interglacial) Stage are refuted. New investigations have yielded rich molluscan, mammalian and ostracod assemblages that indicate fully temperate conditions and the distal influence of marine transgression. Pollen analyses suggest a previously unrecorded phase of interglacial vegetational development. Clast composition, geomorphological evidence and the occurrence of molluscs that favour large rivers all point to deposition by the Thames, rather than in a minor tributary, as suggested previously. Three separate Palaeolithic industries in stratigraphical superposition are recognized at Purfleet, these being Clactonian, Acheulean and Levallois. Purfleet is therefore a key locality in the understanding of the early human occupation and exploitation of southern Britain, as well as for the interpretation and correlation of the terrace sequence in the Thames Valley.

Towards a late Middle Pleistocene non-marine molluscan biostratigraphy for the British Isles

Abstract The fossils of non-marine Mollusca are among the most prominent in Pleistocene deposits. They were one of the first fossil groups to be noted in the literature, as early as the beginning of the 18th century. With the stabilisation of taxonomies in the 19th century numerous publications appeared with faunal lists of interglacial taxa, but few attempts were made to use the data for interpretation. Work from 1950 onwards, especially by Sparks and Kerney in Britain, Puissegur in France, and by Ložek in Central Europe, used a quantitative approach to sorting, counting and interpreting assemblages. Despite the adoption of this rigorous methodology to molluscan studies, interglacial faunas were used primarily to reconstruct past environments, and although faunal changes through the Pleistocene were recognised, it was thought that non-marine Mollusca were inherently badly fitted for use as tools for dating in the classic geological sense. Recent work, coupled with the re-evaluation of sites described in the literature, has allowed non-marine molluscan faunas to be used as biostratigraphic indicators. Biostratigraphic schemes evolved from this work are comparable with parallel investigations using Mammalia, Coleoptera and lithostratigraphy calibrated by a number of geochronometric methods, but may be at variance with pollen biostratigraphies.

The Upper Pleistocene deposits at Cassington, near Oxford, England

For much of the Middle and all of the Upper Pleistocene the Upper Thames valley has remained outside the limit of ice advance. The main agents of landform evolution have been the River Thames and its tributaries, which have cut down episodically and in so doing have abandoned a series of river terraces. This study reports the findings of an investigation into exposures in the deposits underlying the Floodplain Terrace at Cassington, near Oxford, England. The sequence exposed reveals a stratigraphy of basal, predominantly fine-grained, lithofacies overlain by coarser gravel lithofacies. The fluvial architecture of these deposits indicates a major change in fluvial style from a low-energy (meandering) to a high energy (braided) channel system. The flora and fauna from the lower fine-grained lithofacies display a marked change from temperate at the base, to colder conditions towards the top, indicating a close association between deteriorating climate and changing fluvial depositional style. Amino acid and luminescence geochronology from the basal fine-grained lithofacies suggest correlation with Oxygen isotope Stage 5 and hence it is argued that the major environmental change recorded at the site relates to the Oxygen-Isotope Stage 5-4 transition. Deposition of much of the overlying gravel sequence probably occurred during Oxygen isotope Stage 4, suggesting that the latter half of the Devensian may be less significant, in terms of fluvial landscape evolution in the Upper Thames valley, than was believed previously

Pleistocene deposits at Stoke Goldington, in the valley of the Great Ouse, UK

At Stoke Goldington in the valley of the Great Ouse in Buckinghamshire a river terrace at a height of about 7 m above the floodplain is underlain by fluvial sediments representing climatic fluctuations in the late Middle Pleistocene. Near the base of the succession, at a level only 1 m above the modern floodplain, a fossil assemblage, including pollen, plant macrofossils, molluscs, insects and ostracods, provides evidence for the local development of herb-rich grassland under temperate climatic conditions. The fossil record, amino-acid racemisation ratios and uranium disequilibrium dating all suggest deposition of this material during Oxygen Isotope Stage 7. The deposits containing the temperate assemblage are immediately overlain by typical cold-climate gravels of the Great Ouse. These have been subjected to a later cut-and-fill episode, with the fill accumulating in cool climatic conditions. The cut-and-fill episode was succeeded by aggradation, forming the overlying terrace surface. Amino-acid racemisation ratios indicate that the fill was emplaced, and the terrace surface created, during or after Oxygen Isotope Stage 5.

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

Abstract 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.

Sedimentology, palaeoecology and geochronology of Last Interglacial deposits from Deeping St James, Lincolnshire, England

Pollen, plant macrofossil, molluscan and coleopteran data from organic muds below the low terrace of the River Welland at Deeping St James, Lincolnshire indicate deposition in the mixed oak forest phase of a Late Pleistocene interglacial. Coleopteran and molluscan data suggest summer temperatures up to 4°C warmer than at present in eastern England, and plant macrofossil material suggests a climate more continental than that of Britain in the Holocene. No direct analogue of this biota, however, exists currently in Europe. Biostratigraphical indications from the pollen coleoptera and Mollusca suggest an age in the Ipswichian Interglacial. Thermoluminescence dates between 120 ka and 75 ka and amino-acid ratios with a mean of 0.11 show that deposition of the sediments took place during Oxygen Isotope Stage 5. This accurate dating of a partial Ipswichian succession allows discussion of the ages of a number of other interglacial sites in eastern England of assumed Ipswichian age. Copyright

Middle Pleistocene deposits at Frog Hall Pit, Stretton‐on‐Dunsmore, Warwickshire, English Midlands, and their implications for the age of the type Wolstonian

Organic sediment from Frog Hall Pit, near Coventry, has produced pollen, plant macrofossil, insect, ostracod and molluscan data indicative of the early part of a temperate episode in the Middle Pleistocene. The regional stratigraphy and clast lithological characteristics of the gravels underlying the temperate deposits show that the whole sequence at the site post-dates the major glaciation (the Wolstonian sensu Mitchell et al., 1973) of the Midlands. Amino-acid D/L ratios from molluscan shells give mean values of 0.24, which is consistent with an age in Oxygen Isotope Stage 9 and comparable with those from the Hoxnian Interglacial of East Anglia. This age-estimate for the Frog Hall organic deposit places a minimum age on the Wolstonian Glaciation of the Midlands in Oxygen Isotope Stage 10, and therefore close in time to the Anglian (Oxygen Isotope Stage 12) Cold Stage.

Mid‐Holocene environmental changes in the Bay of Skaill, Mainland Orkney, Scotland: an integrated geomorphological, sedimentological and stratigraphical study

A detailed multidisciplinary investigation of intertidal freshwater sediments exposed in the north of the Bay of Skaill, Mainland Orkney, Scotland, have revealed a complex sedimentary sequence. This provided evidence for dynamic coastal environmental changes in the area since the mid-Holocene. Freshwater ponds developed on glacial sediments ca. 6550 ± 80 yr BP (cal. bc 5590–5305). From ca. 6120 ± 70 yr BP (cal. bc 5040–4855), these were infilled by blown sand from the distal edge of a dune ridge located to the west. Thereafter, a series of sand-blow events alternating with periods of quiescence occurred until ca. 4410 ± 60 yr BP (cal. bc 3325–2900). Between ca. 5240 ± 160 and 4660 ± 80 yr BP (cal. bc 4370–3115), pollen and charcoal records show evidence of anthropogenic activities, associated with the nearby Neolithic settlement of Skara Brae. Agriculture was probably affected by recurrent sand movement and widespread deposition of calcium carbonate in the hinterland of the bay. Machair development between ca. 6100 and 5000 yr BP (cal. bc 5235–3540) corresponds to a mid-Holocene phase of dune formation recorded elsewhere in northwest Europe. The more recent and progressive formation of the bay has probably been related to increasing external forcing via storminess, long-term relative sea-level change and sediment starvation within this exposed environment. Copyright

Middle Devensian deposits of the Ivel Valley at Sandy, Bedfordshire, England

Fluvial gravels exposed beneath the surface of the low terrace of the River Ivel have been investigated in a quarry south of Sandy, Bedfordshire. Sedimentological investigations suggest that deposition occurred as bars and sheets in a braided river regime. Fossiliferous silt lenses occur within the gravel and their contents indicate deposition under slow moving or still water conditions in abandoned small channels. The palaeontological data from plant macrofossil remains, Mollusca and Coleoptera present a consistent picture of a harsh climate similar to that of the tundra areas of arctic Russia at the present day. Mutual Climatic Range (MCR) estimates based on Coleoptera indicate a mean temperature of the warmest month between +8°C and +11°C, and a mean temperature of the coldest month between -10°C and -28°C. Radiocarbon ages of 34 055+330-310 (Q-2936) and 29 250+460-420 (Q-2935) yrs BP suggest dates for the lower part of the gravelly sequence, in the Middle Devensian, at the end of the Upton Warren Interstadial Complex.

Molluscan assemblages from the loess of North Central China

Abstract Although molluscan faunas are the most widespread fossil remains in the Chinese loess. there have been very few attempts to use their potential for climatic reconstruction, or to develop cIimato-stratigraphic schemes. This paper reports assemblages of Mollusca from three sites in the North and South Central parts of the Loess Plateau, and evaluates the uses of molluscan faunas as climatic proxies in the S 1 palaeosol, the Malan Loess and S o palaeosol. The molluscan sequence is compared with the record obtained from pedological and magnetic techniques. The current study shows that major peaks in magnetic susceptibility, thought to be due to pedogenesis under warm, humid conditions, can be matched by levels of high molluscan abundance. The occurrence of a sharp molluscan peak within the Malan Loess, otherwise only indicated by a slight increase in magnetic susceptibility, is held to be due to the existence of a short-lived humid episode and demonstrates the sensitivity of Mollusca as indicators of relatively low magnitude climatic shifts not well indicated by other lines of evidence.