Terrestrial environments during MIS 11: evidence from the Palaeolithic site at West Stow,Suffolk, UK

Multidisciplinary investigations of the sequence at Beeches Pit, West Stow (Suffolk, UK), have a direct bearing the age of the Hoxnian Interglacial and its correlation with the continental Holsteinian and with the global marine record. At this site, glacial deposits (till and outwash gravels) referable to the Anglian Lowestoft Formation fill a subglacial channel cut in Chalk bedrock. Above these glacial deposits a series of interglacial sediments occurs, consisting of limnic, tufaceous and colluvial silts, lacking pollen but rich in shells, ostracods and vertebrates. Lower Palaeolithic flint artefacts of Acheulian character have also been recovered, including refitting examples. Charred material is abundant at certain horizons and many of the bones have been burned. Several discrete areas of burnt sediment are interpreted as hearths. The molluscan fauna comprises some 78 taxa and includes species of considerable zoogeographical and biostratigraphical importance. The land snail assemblage from the tufa consists of woodland taxa with no modern analogue, including species that are either extinct (e.g. Zonitoides sepultus) or which no longer live in Britain (e.g. Platyla polita, P. similis, Neniatlanta pauli). This is also the type locality of Retinella (Lyrodiscus) skertchlyi, which belongs to a subgenus of zonitid land snail now living only on the Canary Islands. There are indications from this fauna (‘the Lyrodiscus biome’) that the climate was wetter and perhaps warmer than the present day. The vertebrate fauna is also noteworthy with species of open habitats, such as rabbit (Oryctolagus cf. cuniculus), and of closed forest, such as squirrel (Sciurus sp.) and garden dormouse (Eliomys quercinus) present at different times. The occurrence of southern thermophiles, such as Aesculapian snake (Zamenis longissimus), indicates temperatures warmer than those of eastern England today. The upper levels include much material reworked from the interglacial sediments, although there is clear faunal evidence for climatic deterioration. Both the molluscan and vertebrate faunas suggest correlation of the interglacial sediments with the Hoxnian. Uranium series dates from the tufa (∼455 ka BP), TL dates from burnt flints (414±30 ka BP) and a range of amino acid racemization data all support correlation of this interglacial with MIS 11. However, four OSL dates from sand beneath the interglacial sequence yield a mean age of 261±31 ka BP, far younger than all other age determinations and far younger than implied by the biostratigraphy. Archaeologically the site is unusual in showing prolonged human occupation within closed deciduous forest and evidence for controlled use of fire in a Lower Palaeolithic context. Biostratigraphical correlations with other Lower Palaeolithic sites support the suggestion that Acheulian and Clactonian industries both occurred in southern Britain during the same substage of the Hoxnian, although not necessarily at precisely the same time. The characteristics of the MIS 11 interglacial in Britain are discussed in the light of evidence from Beeches Pit and elsewhere.     

The δ18O stratigraphy of the Hoxnian lacustrine sequence at Marks Tey,Essex, UK: implications for the climatic structure of MIS 11 in Britain

Marine Isotope Stage 11 (MIS 11) is considered one of the best analogues for the Holocene. In the UK the long lacustrine sequence at Marks Tey, Essex, spans the entirety of the Hoxnian interglacial, the British correlative of MIS 11c. We present multiproxy evidence from a new 18.5‐m core from this sequence. Lithostratigraphy, pollen stratigraphy and biomarker evidence indicate that these sediments span the pre‐, early and late temperate intervals of this interglacial as well as cold climate sediments that post‐date the Hoxnian. The δ¹⁸O signal of endogenic carbonate from this sequence produces several clear patterns that are interpreted as reflecting the climatic structure of the interglacial. As well as providing evidence for long‐term climate stability during the interglacial and a major post‐Hoxnian stadial/interstadial oscillation the δ¹⁸O signal provides strong evidence for abrupt cooling events during the interglacial itself. One of these isotopic events occurs in association with a short‐lived increase in non‐arboreal pollen (the NAP phase). The results presented here are discussed in the context of other MIS 11 records from Europe and the North Atlantic, particularly with respect to our understanding of the occurrence of abrupt climatic events in pre‐Holocene interglacials. Copyright © 2016 The Authors. Journal of Quaternary Science Published by John Wiley & Sons Ltd.     

U-series dating of Hoxnian interglacial deposits at Marks Tey,Essex, England

A U–Th dating study was carried out on the authigenic carbonate component of interglacial lake sediments at Marks Tey, Essex, England. Isochron methods were necessary because of the presence of non-carbonate detritus. Calculated dates around the limit of the U–Th method were obtained for two horizons. Error limits were determined by Monte Carlo sampling from the normal distributions of errors in the isotope ratios. Comparison of the resulting empirical distribution functions with the marine oxygen isotope time-scale indicates with 87% confidence that the Marks Tey sediments correlate with OIS 11 or some older stage. As the Marks Tey deposits rest without stratigraphical break on Anglian till, and can be firmly correlated with the Hoxnian interglacial type site at Hoxne, Suffolk, England, this result implies that the Anglian glaciation took place in OIS 12 and the Hoxnian Stage of the British chronostratigraphy commenced in OIS 11. Copyright © 1999 John Wiley & Sons, Ltd.     

Incised palaeo-channels of the late Middle Pleistocene Thames: age,origins and implications for fluvial palaeogeography and sea-level reconstruction in the southern North Sea basin

Multidisciplinary investigations of the infills of steeply-incised buried channels on the coast of Essex, England, provide important insights into late Middle Pleistocene climate and sea-level change and have a direct bearing on the differentiation of MIS 11 and MIS 9 in terrestrial records. New data are presented from Rochford and Burnham-on-Crouch where remnants of two substantial palaeo-channels filled with interglacial sediment can be directly related to the terrace stratigraphy of the Thames. The sediments in both channels accumulated in an estuarine environment early in an interglacial when mixed oak forest was becoming established. Lithological evidence suggests that the interglacial beds post-date the brackish-water infill of an older palaeo-channel ascribed to the Hoxnian and correlated with part of MIS 11, and pre-date terrace gravels (Barling Gravel) ascribed to MIS 8. An MIS 9 attribution is supported by molluscan biostratigraphy, palaeo-salinity and amino-acid racemization data. The relative sea-level record in this area thus includes evidence for two major marine transgressions during MIS 11 and MIS 9, with local maxima of >10 m O.D. Both are associated with sediments that show ‘Hoxnian’ palynological affinities. The wider significance of these findings, and of an intermediate phase of pronounced fluvial incision during MIS 10, is discussed.     

The Clacton-on-Sea (Essex,UK) GCR site and SSSI: New data and continuing importance

The complex Geological Conservation Review (GCR) site at Clacton-on-Sea, Essex, was notified in 1986 as a Site of Special Scientific Interest. It is an internationally important geosite and Britain's only Lower Palaeolithic type locality, giving its name to the Clactonian stone-tool industry. Fossil- and artefact-bearing channel-fill deposits laid down by the River Thames ~ 420,000 years ago, during the Hoxnian Interglacial (Marine Isotope Stage 11c), have been observed in foreshore and cliff exposures, and beneath developed and open ground in an inland arcuate footprint. These sediments provide a record of the lower reaches and estuary of the Thames during this lengthy and warm interglacial, an important partial analogue for the Holocene. Palaeoclimatic and palaeoecological evidence has been obtained from assemblages of fossil molluscs, ostracods and vertebrates, together with pollen and plant macrofossils; Clacton is also the type locality for several of the represented animal taxa, including the biostratigraphically significant ostracod Scottia browniana and a large subspecies of fallow deer, Dama dama clactoniana. This paper provides an overview of the continuing importance of the Clacton GCR site and Site of Special Scientific Interest (SSSI), summarizing recently acquired data that have enhanced understanding of the Hoxnian and the palaeoenvironments that prevailed at the time of deposition. The wider geosite has benefitted from sustained Palaeolithic archaeological interest, with the local planning authority mandating investigation of the sediments as a condition for development projects. SSSI status ensures that the significant collections of palaeontological and archaeological material amassed from the Clacton deposits over almost two centuries can be related to their context, and studies of both these archived collections and new material from the protected in situ sediments continue to provide new data and contribute to the development of cutting-edge techniques.     

Terrestrial and freshwater carbonates in Hoxnian interglacial deposits, UK: micromorphology, stable isotopic composition and palaeoenvironmental significance

MIS 11 is often considered to be the best climatic analogue for the Holocene. Many studies have suggested, however, that it is a period of extreme climate warmth comparable in temperatures to the Middle and Late Pliocene. In Britain deposits of the Hoxnian interglacial are correlated to MIS 11 and multi-proxy techniques can be used to reconstruct the climate of this interglacial. Soil, groundwater and freshwater carbonates are common in Hoxnian deposits and the stable isotopic composition of these precipitates can be used to increase our understanding of MIS 11 environments in Britain. Carbonates from Marks Tey, Clacton, Swanscombe, Elveden and West Stow are studied, the stratigraphic context of which indicates that their formation is broadly synchronous (in the mid-Hoxnian, pollen zones Ho II to Ho III). The carbon isotopic composition of groundwater and pedogenic carbonates is typically depleted with respect to δ¹³C (ca −9 to −8‰ VPDB) reflecting uptake of plant respired CO₂ during water migration/recharge. The carbon isotopic composition of lacustrine carbonate is more enriched with respect to δ¹³C (ca 0-1‰VPDB) reflecting the equilibration of lake waters with atmospheric CO₂. The δ¹⁸O of groundwater and pedogenic carbonates is slightly more enriched than modern soil carbonates but not as enriched as soil carbonates formed under interglacials that were warmer than the Holocene (i.e. the Cromerian). The stable isotopic composition of Hoxnian carbonates does not, therefore, indicate that this interglacial was characterised by uniquely warm climates in the context of other Middle Pleistocene interglacials and the Holocene. This is contrary to many marine and littoral records from around the world but consistent with environmental records from Britain and Europe.     

Evolution of the Thames estuary during MIS 9: insights from the Shoeburyness area, Essex

Multidisciplinary, litho-, bio- and amino-stratigraphical investigations of 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 Shoeburyness, where a deeply incised channel filled with interglacial sediment can be directly related to the terrace stratigraphy of the River Thames. Fossil assemblages confirm that the interglacial beds began accumulating in a freshwater environment, which became transformed into a dynamic estuary as relative sea-levels rose. Pollen data confirm that this occurred early in the interglacial when mixed oak forest was becoming established.The geological context of the sediments indicates that they post-date the Anglian glaciation, yet pre-date the Barling Gravel terrace aggradation, which has been ascribed to MIS 8. Amino acid racemisation data based on Bithynia opercula further constrain the age to the Hoxnian (=MIS 11) or to MIS 9. An MIS 9 attribution is favoured because (i) AAR data suggest that the sequence post-dates the interglacial channel-fill at Clacton, which is widely ascribed to the Hoxnian; (ii) the bivalve Corbicula occurred early within the interglacial (unlike its late appearance during the Hoxnian); and (iii) the sequence includes evidence for a marine transgression that occurred earlier in the interglacial cycle than it did at local Hoxnian sites.Plant macrofossil remains suggest that the early part of the Shoeburyness interglacial was associated with warmer-than-present summer temperatures. This is in keeping with inferences from sites at Barling, Cudmore Grove and Purfleet, which are also attributed to MIS 9. All three sites are similar in terms of their palaeo-vegetation and inferred relative sea-level histories and provide an emerging picture of this temperate episode in southern Britain.     

Pleistocene geochemical stratigraphy of the borehole 1317E (IODP Expedition 307) in Porcupine Seabight,SW of Ireland: applications to palaeoceanography and palaeoclimate of the coral mound development

Stable isotopes and element compositions of the fine‐grained matrix were measured for IODP Expedition 307 Hole U1317E drilled from the summit of Challenger Mound in Porcupine Seabight, northeast Atlantic, to explore the palaeoceanographic and palaeoclimatic background to development of the deep‐water coral mound. The 155 m long mound section was divided into two units by an unconformity at 23.6 mbsf: Unit M1 (2.6–1.7 Ma) and Unit M2 (1.0–0.5 Ma). Results from 519 specimens show a difference in δ¹³C value between Unit M1 (?0.6‰ to ?5.0‰) and Unit M2 (?1.0‰ to 1.0‰), but such a distinct difference was not seen in δ¹⁸O values (1.0‰–2.5‰), CaCO₃ content (40–60 wt%), Sr/Ca ratio (2.0–8.0 mmol mol^?1), and Mg/Ca ratio (10.0–20.0 mmol mol^?1) through the mound. Positive δ¹⁸O and negative δ¹³C shifts at the mound base are consistent with the oceanographic changes in the northeast Atlantic at the beginning of the Quaternary. The positive δ¹³C regression in Unit M2 suggests a linkage to the mid Pleistocene intensified glaciation in the Northern Hemisphere. Warm Mediterranean Upper Core Water of Mediterranean Outflow Water, Eastern North Atlantic Water and cold Labrador Sea Water of North Atlantic Deep Water are key oceanographic features that cause spikes and shifts in stable isotope and element composition. However, the stable isotope values of the sediment matrix could not primarily record the glacial–interglacial eustatic/temperature change, but indirectly indicate current regimes of the intermediate oceanic layer where the coral mound grew. Similarly, elemental ratios and CaCO₃ content may not represent the productivity and temperature of surface sea water, respectively, but superpose the fractions from both surface and bottom water. It is concluded that palaeoceanographic change coupled to the Pleistocene glacial/interglacial cycles is a key control on the geochemical stratigraphy of the matrix sediments of the carbonate mound developed in Porcupine Seabight. Copyright © 2011 John Wiley & Sons, Ltd.     

Middle pleistocene interglacial sediments at Tye green,Stansted Airport,Essex, England

Interglacial lake deposits at Tye Green, Stansted, resting on unweathered till and overlain by a weathered diamicton are correlated with the temperate Hoxnian Stage. The sediments represent the infilling of an isolated kettle-hole type of lake basin formed at the end of the cold Anglian Stage. Through the temperate period this basin was infilled by inorganic and organic sediments that record the development and decline of deciduous forest. Later periglacial conditions are indicated by the final infilling of the basin by reworked till. The sedimentary sequence and vegetational development recorded in the sediments at Tye Green are compared with 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. Copyright © 1999 John Wiley & Sons, Ltd.     

A new Middle Pleistocene interglacial record from Denmark: Chronostratigraphic correlation,palaeovegetation and fire dynamics

Previously only three terrestrial interglacial periods were known from southern Scandinavia, all of which could be relatively easily correlated within the central European stratigraphical framework. Here, we present a new interglacial–interstadial pollen, plant macrofossil and charcoal record from Trelde Klint, Denmark, and analyse its biostratigraphy, correlation with other European records, vegetation development, fire dynamics and absolute dating. Except for a slight truncation of the early part of the record, the pollen stratigraphy exhibits a full interglacial succession, including temperate trees (Quercus, Ulmus and Tilia) during its mesocratic stage. Macrofossil analysis allowed identification to species level for Quercus robur, Picea abies and two mosses. Conifers (Pinus and Picea) dominate the pollen record of the interglacial sequence, and the occurrence of Larix pollen in the top part of the interglacial record as well as in the interstadial sediments is especially indicative of this interglacial. The overall diversity of tree genera is rather low. These biostratigraphical features suggest that Trelde Klint is unique among Danish records, but it is similar to records from northern Germany. Numerical analyses (REVEALS and DCA) indicate that forests during the temperate stage were dense and that vegetation openness increased only towards the end of the interglacial, accompanied by increased fire occurrence. A short interstadial sequence with a dominance of Pinus and Betula and the presence of Larix is present above the interglacial deposit. We argue that lack of attention to differences in fire regimes may hamper understanding of between‐site correlations of interglacial pollen records. OSL dating, using a novel feldspar technique, yields an average age of 350±20 ka for the sandy sediments above the interglacial layers at Trelde Klint, suggesting that the whole interglacial–interstadial succession belongs to Marine Isotope Stage 11.     

Devils Hole, Nevada, δO record extended to the mid-Holocene

The mid-to-late Pleistocene Devils Hole δ¹⁸O record has been extended from 60,000 to 4500 yr ago. The new δ¹⁸O time series, in conjunction with the one previously published, is shown to be a proxy of Pacific Ocean sea surface temperature (SST) off the coast of California. During marine oxygen isotope stages (MIS) 2 and 6, the Devil Hole and SST time series exhibit a steady warming that began 5000 to > 10,000 yr prior to the last and penultimate deglaciations. Several possible proximate causes for this early warming are evaluated. The magnitude of the peak δ¹⁸O or SST during the last interglacial (LIG) is significantly greater (1 per mill and 2 to 3°C, respectively) than the peak value of these parameters for the Holocene; in contrast, benthic δ¹⁸O records of ice volume show only a few tenths per mill difference in the peak value for these interglacials. Statistical analysis provides an estimate of the large shared information (variation) between the Devils Hole and Eastern Pacific SST time series from ∼ 41 to ∼ 2°N and enforces the concept of a common forcing among all of these records. The extended Devils Hole record adds to evidence of the importance of uplands bordering the eastern Pacific as a source of archives for reconstructing Pacific climate variability.     

Environmental changes and growth history of a cold-water carbonate mound (Propeller Mound,Porcupine Seabight)

On- and off-mound sediment cores from Propeller Mound (Hovland Mound province, Porcupine Seabight) were analysed to understand better the evolution of a carbonate mound. The evaluation of benthic foraminiferal assemblages from the off-mound position helps to determine the changes of the environmental controls on Propeller Mound in glacial and interglacial times. Two different assemblages describe the Holocene and Marine Isotope Stage (MIS) 2 and late MIS 3 (∼31 kyr BP). The different assemblages are related to changes in oceanographic conditions, surface productivity and the waxing and waning of the British Irish Ice Sheet (BIIS) during the last glacial stages. The interglacial assemblage is related to a higher supply of organic material and stronger current intensities in water depth of recent coral growth. During the last glaciation the benthic faunas showed high abundances of cassidulinid species, implying cold bottom waters and a reduced availability of organic matter. High sedimentation rates and the domination of Elphidium excavatum point to shelf erosion related to sea-level lowering (∼50 m) and the progradation of the BIIS onto the shelf. A different assemblage described for the on-mound core is dominated by Discanomalina coronata, Gavelinopsis translucens, Planulina ariminensis, Cibicides lobatulus and to a lower degree by Hyrrokkin sarcophaga. These species are only found or show significantly higher relative abundances in on-mound samples and their maximum contribution in the lower part of the record indicates a higher coral growth density on Propeller Mound in an earlier period. They are less abundant during the Holocene, however. This dataset portrays the boundary conditions of the habitable range for the cold-water coral Lophelia pertusa, which dominates the deep-water reefal ecosystem on the upper flanks of Propeller Mound. The growth of this ecosystem occurs during interglacial and interstadial periods, whereas a retreat of corals is documented in the absence of glacial sediments on-mound. Glacial conditions with cold intermediate waters, a weak current regime and high sedimentation rates provide an unfavourable environmental setting for Lophelia corals to grow. A Late Pleistocene decrease is observed in the mound growth for Propeller Mound, which might face its complete burial in the future, as it already happened to the buried mounds of the Magellan Mound province further north.     

Middle Pleistocene biota of the early Anglian ‘Arctic Fresh-water Bed’ at Ostend, Norfolk, UK

At three sites along the North Norfolk coast, freshwater sediments containing arctic plants have been reported to occur immediately beneath the glacial deposits. The sections at Mundesley and Beeston are no longer visible but a small exposure of this ‘Arctic Fresh-water Bed’ has recently been rediscovered at Ostend near Bacton. The fossils from this deposit are distinctly high boreal/arctic in character, indicating a small, possibly ephemeral, pool in a generally open landscape supporting some dwarf shrubs and conifers. Noteworthy records include three beetle species (Pterostichus brevicornis, P. middendorffi and Helophorus obscurellus) that today have their closest occurrences on either the Kanin or Kola peninsulas in arctic Russia. A Mutual Climatic Range reconstruction on the limited beetle fauna suggests that the mean temperatures of the warmest and coldest months were between 9 °C and 11 °C and between −36 °C and −10 °C, respectively. Other noteworthy occurrences include the aquatic pulmonate gastropod Gyraulus rossmaessleri (second and earliest British record), the ostracod Amplocypris tonnensis (earliest British record), ground squirrel (Spermophilus sp.) and the first record of arctic lemming (Dicrostonyx sp.) from the Cromer Forest-bed Formation (CF-bF). The ‘Arctic Fresh-water Bed’ has been assigned to the Bacton Member of the CF-bF and formed during the early Anglian, correlated with Marine Isotope Stage (MIS) 12 of the deep sea record. The Ostend assemblage is therefore important in providing a glimpse of conditions that occurred during a major cold stage in the early Middle Pleistocene.     

Productivity cycles in Lake Hovsgol, NW Mongolia, during the last 1 Ma and the age model of the HDP-04 drill core record

Repetitive patterns in the records of total organic carbon (TOC), total nitrogen (TN) and δ¹³C_org observed in the Lake Hovsgol sediment section from HDP-04 drill core reflect past changes in productivity of Lake Hovsgol and in the isotopic composition of the lake's carbon pool. Lake Hovsgol productivity proxy signals are interpreted to represent the response of the Hovsgol lacustrine system to glacial–interglacial cycles of the Pleistocene. This interpretation is supported by the apparent orbitally-forced pattern in the TOC, TN and δ¹³C_org records of the past 250 ka in the BDP-96-2 drill core from neighboring Lake Baikal.The intervals with independent age control, such as the radiocarbon-dated last glacial–interglacial transition and the paleomagnetic reversals, make it evident that productivity proxy signals are reliable indicators of past cold-to-warm and warm-to-cold climate transitions, as seen from the agreement with the pattern of global climate change in marine δ¹⁸O records. The Brunhes/Matuyama reversal during the MIS 19 interglacial coincides with a distinct peak of TOC and TN in the Hovsgol record, similar to the signal during the Holocene interglacial. By contrast, the upper Jaramillo reversal in the Lake Hovsgol record occurs in a diatom-free calcareous interval characterized by minima in TOC, TN and by a ‘glacial’-type range of δ¹³C_org values. In both Lake Baikal and Lake Hovsgol records, peaks in TOC and TN contents help distinguishing past interglacials and interstadials, and isotopically-heaviest δ¹³C_org values help identify past glacial intervals.An age model for the HDP-04 drill core section is proposed based on recognizing the repetitive patterns in Lake Hovsgol productivity and lithologic records as regional paleoclimate cycles of middle to late Pleistocene. Absolute dates and diatom biostratigraphic correlation ties to the Lake Baikal record are used as key controls. In the proposed age model, the interval 81–24 m in the HDP-04 sediment section below the major unconformity is correlated to MIS 27 through late MIS 13, whereas the upper 24 m of the HDP-04 section is suggested to have recovered the sedimentary record of late MIS 7 to MIS 1.     

山西晋中盆地晚新生代地层划分、沉积环境及其先秦以来气候和湖泊演化

【研究目的】晋中盆地位于汾渭断陷盆地带的中部,新生代最大沉积厚度超过3800 m,建立晋中盆地精确地层年代框架和高分辨率沉积层序对于理解汾渭断陷盆地带的演化、华北地区气候变化具有重要意义。【研究方法】本文对晋中盆地东北部晚新生代标准孔ZK01（钻孔深度870.5 m）岩心开展了年代学和沉积学研究。【研究结果】将ZK01孔揭示的松散沉积物分为6个岩性组。首次通过磁性地层学研究,划分出13个正极性时段和12个负极性时段,建立了ZK01孔地层年代框架。晋中盆地新生代沉积物底部最老年龄约8.1 Ma,将晋中盆地活动的起始时间从前人一般认为的上新世初期,确定为中新世晚期,提前了约3 Ma。区内晚新生代地层划分为新近系中新统灞河阶（N₁⁴）和保德阶（N₁⁵）,上新统高庄阶（N₂¹）和麻则沟阶（N₂²2）,第四系下更新统泥河湾阶（Qp¹）,中、上更新统和全新统。【结论】构造活动与气候变化是盆地沉积环境的主要控制因素,共同导致了上新世早期和早更新世中晚期的两次湖泊大规模发育。全新世时期,早中期即先秦（约2.5 ka以前）,盆地中仍是河湖共存阶段;晚期（2.5 ka以来）,出现湖消河长的局面,直至明、清时期湖泊全部消失,气候变化和人类活动影响是盆地中湖泊最终消失的主要原因。创新点：首次通过磁性地层学将晋中盆地发育时间确定为中新世晚期约8.1 Ma;盆地的湖泊发育早期主要受构造和气候控制,全新世以来气候变化和人类活动造成湖泊最终消亡。     

Climatic deterioration and the end of the Gortian Interglacial in sediments from Derrynadivva and Burren Townland,near Castlebar,County Mayo,Ireland

Pollen and macrofossil analyses of two sequences of organic sediment in western Ireland have allowed the recognition of the latter parts of the Gortian Interglacial, a Middle Pleistocene temperate stage. The palaeobotanical information from the two sites identifies the preservation of partial sequences from the Gortian Interglacial (believed to be the equivalent of the Hoxnian Stage of Britain and the Holsteinian of Europe). The pollen and macrofossil data from one of the sites, Derrynadivva, span the middle and latter parts of the temperate stage. The results show that fire influenced the vegetation throughout the middle part of the temperate stage, and the termination of the organic depositional sequence appears to have been due to environmental deterioration. The former is identified through the abundant occurrence of charcoal in the sediments, whereas the latter is apparent in the sediment sequence and in the reworking of thermophilous pollen types into the upper part of the deposit. The second site, Burren Townland, records only part of the later zones of the interglacial, but the ericaceous assemblages of the latter part of the Gortian Interglacial are well developed and well preserved. Macrofossil analyses and scanning electron microscopy work on the pollen at the latter site has allowed the recognition of Rhododendron ponticum, adding to previous records of this species, which now has a very disjunct European distribution.     

Evidence from coleopteran assemblages for a short but intense cold interlude during the latter part of the MIS11 Interglacial from Quinton, West Midlands, UK

A sequence of fossiliferous organic sediments spanning the whole of an interglacial has been investigated from Quinton, near Birmingham, United Kingdom This interglacial can be correlated on palynological grounds with the Hoxnian Interglacial of England; equivalent to the Holsteinian Interglacial of central Europe and to Marine Isotope Stage 11. A pollen diagram and coleopteran spectrum were obtained from the same series of samples. By using the mutual climatic range method on the coleopteran assemblages, it has been possible to quantify the thermal climatic conditions at this time. They show clear evidence for a sudden and intense climatic oscillation during the late temperate stage of the interglacial—named the Quinton Cold Interlude. At this time mean temperatures of the warmest month (July) declined suddenly by at least 5 °C and mean temperatures of the coldest months (January and February) by more than 10 °C. Subsequently cool-temperate conditions returned. The pollen diagram through this interval shows little or no response to this climatic event. It is too early yet to generalise about the regional significance of the Quinton Cold Interlude but a similar climatic oscillation also occurs towards the closing stage of the MIS11 Interglacial at Hoxne, Norfolk, UK, suggesting that the cold interlude was at least regional in extent. A short climatic oscillation of similar intensity has also been interpreted from coleopteran evidence towards the end of the MIS13 Interglacial at Waverley Wood Farm Pit, Warwickshire, UK, indicating that such events may characterise the later stages of other interglacials. These severe climatic oscillations towards the end of interglacials may have relevance to our understanding of the closing phase of the present interglacial.     

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

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 mineralogical 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 further 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.     

An Early Pleistocene hippopotamus from Westbury Cave,Somerset, England: support for a previously unrecognized temperate interval in the British Quaternary record

Although fossil assemblages from the late Early Pleistocene are very rare in Britain, the site of Westbury Cave in Somerset, England, has the potential to address this gap. The mammal fossils recovered previously from the Siliceous Member in Westbury Cave, though few in number, have hinted at an age for the deposits that is as yet unparalleled in Britain. Here, we describe the first bona fide occurrence of Hippopotamus in the British Early Pleistocene, discovered during recent reinvestigation of the Siliceous Member. The hippo fossil indicates a refined biochronological age of ca. 1.5–1.07 Ma for the Siliceous Member and a palaeoclimate that was warm and humid, which accords well with previous palaeoenvironmental inferences. A synthesis of late Early Pleistocene hippo occurrences suggests that the Siliceous Member hippo may have been part of an early colonization of north-west Europe by these megaherbivores, possibly during MIS (Marine Oxygen Isotope Stage) 31. Alternatively, it evidences a currently cryptic northward migration during an even earlier temperate phase. In either case, the Siliceous Member is likely to represent a warm period that has not been recognized previously in the British Quaternary record.     

Late Quaternary multiple incised valley systems: An unusually well‐preserved stratigraphic record of two interglacial valley‐fill successions from the Arno Plain (northern Tuscany,Italy)

Un‐fragmented stratigraphic records of late Quaternary multiple incised valley systems are rarely preserved in the subsurface of alluvial‐delta plains due to older valley reoccupation. The identification of a well‐preserved incised valley fill succession beneath the southern interfluve of the Last Glacial Maximum Arno palaeovalley (northern Italy) represents an exceptional opportunity to examine in detail evolutionary trends of a Mediterranean system over multiple glacial–interglacial cycles. Through sedimentological and quantitative meiofauna (benthic foraminifera and ostracods) analyses of two reference cores (80 m and 100 m long) and stratigraphic correlations, a mid‐Pleistocene palaeovalley, 5 km wide and 50 m deep, was reconstructed. Whereas valley filling is chronologically constrained to the penultimate interglacial (Marine Isotope Stage 7) by four electron spin resonance ages on bivalve shells (Cerastoderma glaucum), its incision is tentatively correlated with the Marine Isotope Stage 8 sea‐level fall. Above basal fluvial‐channel gravels, the incised valley fill is formed by a mud‐prone succession, up to 44 m thick, formed by a lower floodplain unit and an upper unit with brackish meiofauna that reflects the development of a wave‐dominated estuary. Subtle meiofauna changes towards less confined conditions record two marine flooding episodes, chronologically linked to the internal Marine Isotope Stage 7 climate‐eustatic variability. After the maximum transgressive phase, recorded by coastal sands, the interfluves were flooded around 200 ka (latest Marine Isotope Stage 7). The subsequent shift in river incision patterns, possibly driven by neotectonic activity, prevented valley reoccupation guiding the northward formation of the Last Glacial Maximum palaeovalley. The applied multivariate approach allowed the sedimentological characterization of the Marine Isotope Stage 7 and Marine Isotope Stage 1 palaeovalley fills, including shape, size and facies architecture, which revealed a consistent river‐coastal system response over two non‐consecutive glacial–interglacial cycles (Marine Isotope Stages 8 to 7 and Marine Isotope Stages 2 to 1). The recurring stacking pattern of facies documents a predominant control exerted on stratigraphy by Milankovitch and sub‐Milankovitch glacio‐eustatic oscillations across the late Quaternary period.