Mammalian biostratigraphy of the later Middle Pleistocene in Britain

This study explores and develops the potential of fossil mammals to differentiate between the various climatic episodes of the post-Anglian Middle Pleistocene in Britain. Mammalian fossils are particularly valuable as biostratigraphic indicators on account of their morphological evolution and rapid turnover, through origination and extinction of species. Furthermore, the large-scale climatic fluctuations that affected north-west Europe during the Quaternary produced major shifts in the geographical distributions of many species, resulting in discernible patterns of presence and absence in the fossil record of a particular region. The development of a globally-applicable climatostratigraphic framework, based on the oxygen isotope record from deep-ocean sediments, has provided a new and challenging scheme for the interpretation of the British Quaternary record. Long fluvial sequences in Britain have been related to this record with considerable success, thereby providing a detailed archive of climatic change through the Pleistocene. The Thames valley was selected as a framework for the relative dating of the various climatic fluctuations, since it has been claimed to have the most reliably-dated long terrestrial sequence in the later Middle Pleistocene. The Thames model was therefore adopted as a testable hypothesis against which the mammalian evidence could be compared. The findings of this study confirm the presence of four complete climatic cycles between the Anglian and the Holocene, each with its own distinctive mammalian suite. In addition, it has been possible to identify subdivisions within these temperate stages, probably representing smaller-scale climatic fluctuations within an interglacial, and perhaps corresponding to isotopic substages. It has been possible to resolve a longstanding controversy concerning the age of the British type Hoxnian Interglacial. Amino acid geochronology had suggested that sediments at Hoxne belonged to a later interglacial than deposits from the first post-Anglian temperate episode in the Thames valley, such as Swanscombe. The results of the present study reveal close similarity between the mammalian fauna from Hoxne and that from Swanscombe, suggesting that there was indeed a single Hoxnian Interglacial, and that it directly post-dated the Anglian (i.e. Stage 11). Sediments of this age can be distinguished from those attributable to two other late Middle Pleistocene interglacials, all of them distinct from and older than, the Ipswichian. It has been suggested that distinctive mammalian assemblages can be identified from interglacials equivalent to oxygen isotope stages 9 and 7; moreover, it is apparent that the assemblages from warm Substages 7c and 7a differed from one another in species composition. Certain useful characters have also been determined, which can permit useful separation of some of the late Middle Pleistocene cold episodes, although in comparison with the interglacials, the evidence from these is scanty. The present study has provided a new biostratigraphic framework that may be both tested and refined as new sites become available in Britain, and also compared with the evidence from continental north-west Europe

Fossils from Quaternary fluvial archives : sources of biostratigraphical, biogeographical and palaeoclimatic evidence.

Fluvial sedimentary archives have the potential to preserve a wide variety of palaeontological evidence, ranging from robust bones and teeth found in coarse gravel aggradations to delicate insect remains and plant macrofossils from fine-grained deposits. Over the last decade, advances in Quaternary biostratigraphy based on vertebrate and invertebrate fossils (primarily mammals and molluscs) have been made in many parts of the world, resulting in improved relative chronologies for fluviatile sequences. Complementary fossil groups, such as insects, ostracods and plant macrofossils, are also increasingly used in multi-proxy palaeoclimatic and palaeoenvironmental reconstructions, allowing direct comparison of the climates and environments that prevailed at different times across widely separated regions. This paper reviews these topics on a regional basis, with an emphasis on the latest published information, and represents an update to the 2007 review compiled by the FLAG-inspired IGCP 449 biostratigraphy subgroup. Disparities in the level of detail available for different regions can largely be attributed to varying potential for preservation of fossil material, which is especially poor in areas of non-calcareous bedrock, but to some extent also reflect research priorities in different parts of the world. Recognition of the value of biostratigraphical and palaeoclimatic frameworks, which have been refined over many decades in the 'core regions' for such research (particularly for the late Middle and Late Pleistocene of NW Europe), has focussed attention on the need to accumulate similar palaeontological datasets in areas lacking such long research histories. Although the emerging datasets from these understudied regions currently allow only tentative conclusions to be drawn, they represent an important stage in the development of independent biostratigraphical and palaeoenvironmental schemes, which can then be compared and contrasted

The River Orontes in Syria and Turkey: downstream variation of fluvial archives in different crustal blocks

The geomorphology and Quaternary history of the River Orontes in western Syria and south-central Turkey have been studied using a combination of methods: field survey, differential GPS, satellite imagery, analysis of sediments to determine provenance, flow direction and fluvial environment, incorporation of evidence from fossils for both palaeoenvironments and biostratigraphy, uranium-series dating of calcrete cement, reconciliation of Palaeolithic archaeological contents, and uplift modelling based on terrace height distribution. The results underline the contrasting nature of different reaches of the Orontes, in part reflecting different crustal blocks, with different histories of landscape evolution. Upstream from Homs the Orontes has a system of calcreted terraces that form a staircase extending to ~200 m above the river. New U-series dating provides an age constraint within the lower part of the sequence that suggests underestimation of terrace ages in previous reviews. This upper valley is separated from another terraced reach, in the Middle Orontes, by a gorge cut through the Late Miocene–Early Pliocene Homs Basalt. The Middle Orontes terraces have long been recognized as a source of mammalian fossils and Palaeolithic artefacts, particularly from Latamneh, near the downstream end of the reach. This terraced section of the valley ends at a fault scarp, marking the edge of the subsiding Ghab Basin (a segment of the Dead Sea Fault Zone), which has been filled to a depth of ~ 1 km by dominantly lacustrine sediments of Pliocene–Quaternary age. Review of the fauna from Latamneh suggests that its age is 1.2–0.9 Ma, significantly older than previously supposed, and commensurate with less uplift in this reach than both the Upper and Lower Orontes. Two localities near the downstream end of the Ghab have provided molluscan and ostracod assemblages that record somewhat saline environments, perhaps caused by desiccation within the former lacustrine basin, although they include fluvial elements. The Ghab is separated from another subsiding and formerly lacustrine depocentre, the Amik Basin of Hatay Province, Turkey, by a second gorge, implicit of uplift, this time cut through Palaeogene limestone. The NE–SW oriented lowermost reach of the Orontes is again terraced, with a third and most dramatic gorge through the northern edge of the Ziyaret Dağı mountains, which are known to have experienced rapid uplift, probably again enhanced by movement on an active fault. Indeed, a conclusion of the research, in which these various reaches are compared, is that the crust in the Hatay region is significantly more dynamic than that further upstream, where uplift has been less rapid and less continuous

Improving chronological control for environmental sequences from the last glacial period

Recognition of palaeoclimatic instability in the Greenland ice cores has spurred researchers to identify corresponding evidence in other terrestrial records from the last glacial stage. Such evidence is critical for establishing how much environmental stress precipitated Neanderthal and Late Pleistocene megafaunal extinctions, although a need for improved chronology has been consistently highlighted. In formerly glaciated and periglaciated areas of northern Europe, palaeoenvironmental sequences are frequently discontinuous. These often yield high-resolution proxy-based quantitative palaeotemperature estimates but can be hard to date, due to difficulties in removing contamination from biological samples at the limits of the radiocarbon technique (c.30-50kya). Here we demonstrate, for the first time using samples with independent age control, that different radiocarbon pretreatments can generate different age data and that gentler, less effective treatments applied to avoid sample loss may not yield reliable age-estimates. We advocate alternative harsher pretreatment using a strong acid-base-acid protocol. This provides an acceptable balance between contamination removal and excessive sample loss and generates more accurate ages, significantly enhancing our ability to detect and understand the impacts of palaeoclimatic instability in the terrestrial record of the last glacial

Middle to late Pleistocene palaeoecological reconstructions and palaeotemperature estimates for cold/cool stage deposits at Whittlesey, eastern England

Fossiliferous beds in a complex sequence of late Middle to Late Pleistocene deposits at Whittlesey, eastern England, provided a rare opportunity for a multidisciplinary study of the palaeoecology of cool/cold stage deposits from different glacial stages. The fossiliferous sediments investigated form part of the River Nene 1st Terrace. Three of the four fossil assemblages investigated pre-date the last interglacial stage (Ipswichian/Eemian/marine oxygen isotope stage (MIS) 5e), whereas the other dates to part of the MIS 3 interstadial complex (Middle Devensian/Weichselian). Pollen, plant macrofossil, molluscan, coleopteran, ostracod, foraminifera and vertebrate data are available to a greater or lesser extent for each cool/cold stage assemblage, and they broadly present the same ecological picture for each one: a continuum from low-energy permanent to non-permanent aquatic habitats through marshland with associated waterside taxa, together with flood influxes of fluvial, riparian and ruderal taxa. Although each fossil assemblage records cool/cold climatic conditions, to a greater or lesser extent, these conditions are more apparent in the insect and ostracod faunas. In comparison with results published for the Last Glacial Maximum (LGM) stadial in The Netherlands, palaeotemperature estimates based on ranges of mutual agreement between independent coleopteran and ostracod methods for the three pre-Ipswichian/Eemian assemblages indicate minimum mean July air temperatures that are from +1° to +3 °C warmer, but January values that embrace the −8 °C estimate for the LGM. There is, however, a disparity between the coleopteran and ostracod palaeotemperature estimates for the Middle Devensian/Weichselian fossil assemblage, which are based on two different sample stratigraphic levels; the lower, coleopteran assemblage is indicative of very cool, continental climates, whereas the stratigraphically slightly higher ostracod assemblage suggests a climatic amelioration. Lack of numerical age-estimates prevents a robust stratigraphical interpretation, but the youngest pre-Ipswichian/Eemian fossil assemblage could date to the MIS 7–6 transition, at a time when cooling possibly preceded glacially driven sea-level fall. It is apparent from the rich coleopteran data that some continental cold-indicator taxa also appeared in pre-Ipswichian/Eemian cold stages and therefore assignment of continental cold-indicator taxa to particular Devensian/Weichselian intervals should be undertaken with care

Implications of new Quaternary uplift models for correlation between the Middle and Upper Thames terrace sequences, UK.

Modelling of uplift histories in the Upper and Middle Thames valleys has revealed an important difference, in the form of additional early post-Anglian uplift in the Middle Thames, attributed to an Anglian (~440 ka) glacio-isostatic effect. Terraces in the Upper Thames around Oxford seem unaffected by glacio-isostasy and their heights show regional uplift of ~35–40 m since the Anglian. The result of the glacio-isostasy is that Anglian terraces are significantly higher above the valley floor in the Middle Thames (up to 55 m) than in the Upper Thames. Recognition of this displacement of Middle Thames terraces has solved long-standing problems of correlation between this area and the Upper Thames: the pre-Anglian (Cromerian Complex) age of the Sugworth Channel deposits, indicated by biostratigraphy, is no longer a difficulty, whereas the Hanborough Terrace is now thought to be of Anglian age, albeit incorporating pre-Anglian faunal remains and perhaps with a significant early post-Anglian component. These findings have implications for the understanding of the effects of Middle Pleistocene glacio-isostasy and of landscape evolution on the periphery of glaciated regions