A late Pleistocene long pollen record from Lake Urmia, NW Iran

A palynological study based on two 100-m long cores from Lake Urmia in northwestern Iran provides a vegetation record spanning 200 ka, the longest pollen record for the continental interior of the Near East. During both penultimate and last glaciations, a steppe of Artemisia and Poaceae dominated the upland vegetation with a high proportion of Chenopodiaceae in both upland and lowland saline ecosystems. While Juniperus and deciduous Quercus trees were extremely rare and restricted to some refugia, Hippophaë rhamnoides constituted an important phanerophyte, particularly during the late last glacial period. A pronounced expansion in Ephedra shrub-steppe occurred at the end of the penultimate late-glacial period but was followed by extreme aridity that favoured an Artemisia steppe. Very high lake levels, registered by both pollen and sedimentary markers, occurred during the middle of the last glaciation and late part of the penultimate glaciation. The late-glacial to early Holocene transition is represented by a succession of Hippophaë, Ephedra, Betula, Pistacia and finally Juniperus and Quercus. The last interglacial period (Eemian), slightly warmer and moister than the Holocene, was followed by two interstadial phases similar in pattern to those recorded in the marine isotope record and southern European pollen sequences.     

Climate-driven changes in lake conditions during late MIS 3 and MIS 2: a high-resolution geochemical record from Les Echets, France

A new set of geochemical data obtained from a long sediment sequence from the Les Echets basin provides a new record of palaeoenvironmental change for western Europe. The sequence covers the late part of Marine Isotope Stage (MIS) 3 and MIS 2 ( c . 46.1–15.0 cal. kyr BP) and extends over 30 m of sediment, allowing for high sampling resolution. Distinct cyclic fluctuations in aquatic productivity proxies suggest a tempo of environmental change at Les Echets that resembles the one established for Dansgaard-Oeschger cycles and Heinrich events. Increases in organic carbon are paralleled by high hydrogenous contents and enriched δ¹³C_org and C_org/N_tot ratios, implying a mixture of aquatic and land-derived constituents. The stable isotope values are directly linked to primary aquatic productivity and the input of terrestrial organic matter, enriched during warm, productive, periods, and drastically depleted during cold periods, particularly Heinrich events. Phases of relatively high productivity correlate with Dansgaard-Oeschger interstadials 8–2, while Heinrich events 3 and 2 are also clearly delineated by distinct lithological horizons with very low organic contents, high dry densities and enhanced organic matter oxidation. A large hiatus occurring about the time of Heinrich event 4 suggests that the cold and dry climate reconstructed for this event in the North Atlantic region also greatly affected Les Echets and its catchment.     

The lithostratigraphy of the Les Echets basin, France: tentative correlation between cores

Two new long sediment cores (EC1 and EC3), recovered from different locations within the infilled basin at Les Echets, France, provide a new high-resolution record of terrestrial and lacustrine responses to climatic changes during Marine Isotope Stages (MIS) 3 and 2. The lithologies of the cores are described in detail and correlated with each other by stratigraphic marker horizons, fluctuations in organic matter and AMS radiocarbon ages. The tentative correlation of the new cores to those described and analysed by de Beaulieu et al. (1980) and de Beaulieu & Reille (1984a) provides a preliminary chronostratigraphic framework. Sedimentation during MIS3 started with accumulation of sands and silts and was followed by alternating gyttja and clayey gyttja silts. Exceptionally high sedimentation rates during MIS2 led to the infilling of the basin. Alternating organic-rich and minerogenic-rich sediments appear to coincide with changes in pollen assemblages (de Beaulieu & Reille 1984a) and suggest that millennial-scale climatic changes controlled lake productivity and catchment stability during most of MIS3.     

A late Early Pleistocene pollen record from Fontana Ranuccio (central Italy)

A pollen record from a sediment core drilled underneath the Acheulian site of Fontana Ranuccio provides new data on the vegetation characters in central Italy during the late Early Pleistocene, in a forest phase possibly corresponding to a substage of Marine Isotope Stage 21. A number of tree taxa nowadays extinct in Europe (Cathaya, Tsuga, Taxodium type, Carya and Pterocarya) are present at Fontana Ranuccio in a temperate phase characterised by dense forest conditions, dominated by Alnus and Pterocarya. The comparison of the Fontana Ranuccio record with other dated sites distributed along the Italian peninsula indicates that the floristic and vegetational characters of the Mid Pleistocene revolution present a rather distinct succession of biostratigraphic events. Compared to other Early Pleistocene pollen records from southern Europe, the Italian Peninsula shows greater floristic similarities with the Eastern Mediterranean regions than with the Iberian Peninsula. Copyright © 2011 John Wiley & Sons, Ltd.     

Age, origin and significance of a new middle MIS 3 tephra horizon identified within a long-core sequence from Les Echets, France

A new tephra has been identified within a long core (EC 3) sequence recovered from Les Echets, near Lyon, France. This visible tephra was discovered as part of a high resolution multiproxy re-investigation of the Les Echets sequence. Independent chronological information suggests that the tephra is c . 2 000–45 000 years old, and geochemical analysis indicates that it is of basanitic composition. The latter suggests a possible origin in the Eifel; however, as yet, no other volcanic events or deposits can be correlated to the Les Echets tephra. New sedimentological and chronological data are presented indicating that the tephra falls within an interval that most likely correlates with Dansgaard–Oeschger events 12-9. Thus, this tephra could potentially be an important middle MIS 3 marker horizon in central Europe if it can be traced in other palaeorecords.     

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. © 1998 John Wiley & Sons, Ltd.     

A middle Wisconsin pollen record from Hay Lake,Arizona

The lower part of a 5-m core from Hay Lake (34°N, 109° 25′W) at 2780 m in east-central Arizona provides a pollen record for the middle Wisconsin. Identification of fossil pines is based on a key modified from Hansen and Cushing (1973, Geological Society of America Bulletin84, 1181–1200). Pinus edulis and P. monophylla are similar in size and morphology but are significantly different from P. flexilis. Haploxylon pines dominate the pollen record. The abundance of pinyon pines during the middle Wisconsin is interpreted as indicating that this group was widespread at lower elevations. The local vegetation was mixed conifer forest consisting of Picea, P. aristata, P. flexilis and/or P. strobiformis, and with P. ponderosa and/or P. contorta after about 26,000 yr B.P. Tree line was above the elevation of Hay Lake. The middle Wisconsin climate is inferred to have been cooler than today and is marked by more available moisture that permitted pinyon pines to grow at low elevations.     

A late quaternary pollen record from the Transvaal bushveld, South Africa

Pollen spectra from cores of organic spring deposits from the Transvaal provide evidence for the climatic evolution of the province during the last 35,000 yr B.P. or more. The past climatic phases are derived from palynological reconstructions of past vegetation types by comparison of fossil pollen data with modern surface pollen spectra from various localities. Evidence is provided for an early moist, cool phase with relatively mesic bushveld and expanded montane forest in the central Transvaal, followed by a drier period with drier bushveld which probably lasted until approximately 25,000 yr B.P. During the next phase, which at the latest ended about 11,000 yr B.P., the temperatures were probably 5°–6°C cooler than at present. At that time bushveld vegetation in the central Transvaal was replaced by open grassland with macchia elements. Climatic amelioration came and semiarid savanna returned to the plains, at first gradually and then developing into a warm Kalahari thornveld-type vegetation. After 6000 yr B.P. it apparently became slightly wetter and a more broad-leafed bushveld developed. About 4000 yr B.P. it again became cooler and slightly wetter and the bushveld vegetation on the central and northern plains was comparable to present open upland types. After 2000 yr B.P. conditions gradually became warner until about 1000 yr B.P., when the modern climate of the central Transvaal bushveld originated.     

A Holocene pollen record of persistent droughts from Pyramid Lake, Nevada, USA

Pollen and algae microfossils preserved in sediments from Pyramid Lake, Nevada, provide evidence for periods of persistent drought during the Holocene age. We analyzed one hundred nineteen 1-cm-thick samples for pollen and algae from a set of cores that span the past 7630 years. The early middle Holocene, 7600 to 6300 cal yr B.P., was found to be the driest period, although it included one short but intense wet phase. We suggest that Lake Tahoe was below its rim for most of this period, greatly reducing the volume and depth of Pyramid Lake. Middle Holocene aridity eased between 5000 and 3500 cal yr B.P. and climate became variable with distinct wet and dry phases. Lake Tahoe probably spilled intermittently during this time. No core was recovered that represented the period between 3500 and 2600 cal yr B.P. The past 2500 years appear to have had recurrent persistent droughts. The timing and magnitude of droughts identified in the pollen record compares favorably with previously published δ¹⁸O data from Pyramid Lake. The timing of these droughts also agrees with the ages of submerged rooted stumps in the Eastern Sierra Nevada and woodrat midden data from central Nevada. Prolonged drought episodes appear to correspond with the timing of ice drift minima (solar maxima) identified from North Atlantic marine sediments, suggesting that changes in solar irradiance may be a possible mechanism influencing century-scale drought in the western Great Basin.     

A pollen record from the Agassiz Ice Cap, northern Ellesmere Island, Canada

A continuous pollen record from the last glacial period to 100 B.P. was obtained from an ice core drilled in 1977 near the top of the Agassiz Ice Cap. Pollen concentrations are low ( c . 15–173 grains/100 I) through-out the core and exotic pollen grains (from distant sources) dominate over regional pollen grains (from Ellesmere Island). The very low concentrations during the Wisconsinan glacial period and the early Holocene are attributed to the increased distance of potential sources as most of northern North America was ice-covered or supported tundra vegetation. An increase of exotic grains (mainly birch and alder) at c . 7,600 B.P. corresponds to the period of alder migration into the Low Arctic regions. The subsequent fluctuations of exotic pollen, especially the increase at c . 3,100 B.P., are unexplained at present. Regional pollen concentrations start to increase at c . 6,100 B.P. and a maximum concentration is reached at c . 3,100 B.P. The pollen record suggests that plant migration into northern Ellesmere was limited until 6,100 B.P., then increased gradually and continued to do so for about 1,000 years after the climate had started to deteriorate at about 4,000 B.P.     

A long pollen record from Lac du Bouchet, Massif Central, France: for the period ca. 325 to 100 ka BP (OIS 9c to OIS 5e)

Pollen analysis was carried out on sediments older than the Würm pleniglacial (OIS 4), in two new sequences (H and I) derived from the centre of Lac du Bouchet, Massif Central. The inferred vegetation history enables, for the first time in France, five temperate episodes to be defined which pre-date the last interglacial. These temperate episodes alternate with episodes during which the changes in vegetation are indicative of glacial climates. Comparison of these climatic episodes with the oceanic isotope record shows that the pollen record of sequences H and I from Lac du Bouchet spans the time interval from OIS 9c (Ussel interstadial) to OIS 5e (Ribains/Eemian interglacial). In the organic sediments from the Amargiers interstadial (OIS 9a), a trachytic layer, Ar/Ar dated to ca 275 ka, enables a correlation to be established with the upper part of a sequence derived from the nearby Praclaux crater, the lower part of this sequence being of Holsteinian age (OIS 11c). The cross-dating of the pollen sequences from Lac du Bouchet (cores H, I and D) and from Praclaux provides a complete record from the Massif Central, southern France, of successive glacial and interglacial episodes that span the last ca. 400 ka, that is the interval from the Holsteinian to the Holocene.     

A chronology for the long pollen record from Lake Wangoom,western Victoria (Australia) as derived from uranium/thorium disequilibrium dating

The chronology of a long pollen record from Lake Wangoom, one of the few long palaeoenvironmental records from southeastern Australia, is discussed in light of the acquisition of new uranium/thorium disequilibrium (UTD) dates. Of crucial importance has been the estimation of ages for two major pre‐Holocene phases of forest expansion recorded in the sequence, with implications for the timing of periods of high effective precipitation in the region. The new UTD ages indicate that the oldest forest phase falls within the Penultimate Interglacial whereas the later phase corresponds with the Last Interglacial. This is older than indicated by previously reported UTD and radiocarbon dates, but confirms a chronology based on direct correlation with the pollen record from marine core E55‐6. The new chronology of the Lake Wangoom sequence provides evidence that phases of sustained forest development in southeast Australia relate to interglacial periods. In comparison, interstadial periods appear to be characterised by only minor arboreal development. Marked differences in the pattern of vegetation development evident in each of the interglacials are thought to reflect varying climatic and anthropogenic influences. Copyright © 2002 John Wiley & Sons, Ltd.     

Re‐interpretation of the Meikirch pollen record,Swiss Alpine Foreland,and implications for Middle Pleistocene chronostratigraphy

The Meikirch drilling site in the Swiss Midlands north of Bern is re‐interpreted using a combination of sedimentological logging, pollen analyses and luminescence dating. The sedimentary sequence comprises about 70 m of lacustrine deposits, overlain by about 39 m of coarse glacial outwash interpreted to represent at least two independent ice advances. Pollen analyses of the apparently complete limnic sequence reveal a basal late glacial period followed by three warm phases that are interrupted by two stadial periods (Meikirch complex). The warm periods were previously correlated with the Holsteinian and Eemian Interglacials. According to luminescence dating, and with consideration of evidence for Middle Pleistocene climate patterns at other central European sites, a correlation of the Meikirch complex with marine isotope stage (MIS) 7 is now proposed. If this correlation is correct, it implies the presence of three intervals with interglacial character during MIS 7. However, the late Middle Pleistocene vegetational features of the Meikirch complex show significant differences when compared with the pollen record from the Velay region, central France. Possible explanations for this discrepancy are distinct Middle Pleistocene patterns of atmospheric circulation over central Europe and a different distribution of vegetation refugia compared to the Eemian Interglacial and the Holocene. Copyright © 2005 John Wiley & Sons, Ltd.     

Luminescence chronology of the Upper Pleistocene loess record at Kurtak in M iddle Siberia

The loess/palaeosol sequence of Kurtak, situated at the western bank of the upper Yenisei in Middle Siberia, represents one of the best developed Middle and Upper Pleistocene sediment records in Yenisei Siberia. More than 40 m thick loess and loess-like sediments intercalated by at least four pedocomplexes are exposed at a steep erosional slope at the bank of the Krasnoyarsk Water Reservoir. Infrared optically stimulated luminescence (IRSL) and thermoluminescence (TL) dating techniques have been applied on 38 fine grain samples from the upper 23 m of the profile, representing the penultimate and last interglacial–glacial cycle. The IRSL and TL age estimates are in good agreement with the geological estimates up to the last interglacial soil horizon (oxygen isotope substage (OIS) 5e). The luminescence ages show that the lowermost truncated palaeosol of kastanosjem-type is likely to have formed during the penultimate interglacial upon subaerial deposits. Three weak reddish brown palaeosols intercalated by reworked loess-like sediments correlate with early Upper Pleistocene interstadials (OIS5dion of -a), and a succession of humic horizons alternated by cryoturbation processes (Kurtak pedocomplex) is linked with OIS 3. Thick loess deposits between the pedocomplexes show now significant age increase with depth, indicating high accumulation rates at around 23 ka (OIS 2) and 60 ka (OIS 4).     

A 350,000-year climatic record from the loess sequence of Achenheim, Alsace, France

Up to now the best Quaternary climatic sequences come from oceanic isotope studies, but terrestrial sequences are also well known, usually for pollen or ice core data. A new sequence providing climatic information for the last 500,000 years has been studied in the loess series of Achenheim (Alsace), using the mollusc record in relation to other stratigraphical data. Mollusc assemblages are analysed using a multivariate method. The correspondence analysis used here allows us to explain, in ecological terms, the general variability of the Achenheim set. Most Pleistocene mollusc species have the advantage that modem individuals live in the same assemhlages. So, the known ecology and distribution of the modern molluscs allow us to conclude that the first two factors explain variations in temperature and moisture. Each loading, on a factor, of each association in its stratigraphical level contributes to characterizing the evolution of each climatic parameter through time. For the last five climatic cycles, these evolutions are expressed as a function of the depth within the series. As they are well preserved, the last three glacial cycles are studied in detail. They correspond to the last 350,000 years, are compared with SPECMAP data and particularly show correlations between continental and marine climatic indicators. The mollusc assemblages of the loess sequence also provide information on temperature and moisture conditions. The evolutions of each parameter are not identical during the last three cycles, indicating that the climatic history of one cycle cannot be transferred to the others. The mollusc assemblages also record the occurrence of an oscillatory system, especially during the Weichselian Upper Pleniglacial (isotopic stage 2) when it announces the Late Glacial variations. Similar oscillating excursions seem to have occurred during the older glacial stages.     

A 23,000-yr pollen record from Lake Euramoo, Wet Tropics of NE Queensland, Australia

A new extended pollen and charcoal record is presented from Lake Euramoo, Wet Tropics World Heritage rainforest of northeast Queensland, Australia. The 8.4-m sediment core taken from the center of Lake Euramoo incorporates a complete record of vegetation change and fire history spanning the period from 23,000 cal yr B.P. to present. The pollen record is divided into five significant zones; 23,000–16,800 cal yr B.P., dry sclerophyll woodland; 16,800–8600 cal yr B.P., wet sclerophyll woodland with marginal rainforest in protected pockets; 8600–5000 cal yr B.P., warm temperate rainforest; 5000–70 cal yr B.P., dry subtropical rainforest; 70 cal yr B.P.–AD 1999, degraded dry subtropical rainforest with increasing influence of invasive species and fire.The process of rainforest development appears to be at least partly controlled by orbital forcing (precession), though more local environmental variables and human activity are also significant factors. This new record provides the opportunity to explore the relationship between fire, drought and rainforest dynamics in a significant World Heritage rainforest region.     

Middle Pleistocene temperate deposits at Dingé, Ille-et-Vilaine,northwest France: pollen,plant and insect macrofossil analysis

Nine cores were taken from a damp depression at Dingé, Ille-et-Vilaine, northwest France. Analyses of the pollen, plant macrofossil and Coleoptera remains preserved in the same organic samples of two profiles suggest a temperate vegetation characterised by a mixed deciduous forest with mesophilous taxa (Carpinus, Fagus, Quercus) followed by a coniferous forest with Pinus and Picea. The determination of plant taxa to species was made either directly through the identification of plant macrofossil remains and pollen or indirectly through the identification of phytophagous Coleoptera specifically related to certain plants. Stratigraphical information derived from pollen, plant macrofossil and insect data indicates that this sequence may be correlated with a temperate episode older than the Eemian and younger than the Holsteinian, possibly the Bouchet 2 (Oxygen Isotope Stage 7c) or Bouchet 3 (Oxygen Isotope Stage 7a) temperate periods or the Landos Interglacial (Oxygen Isotope Stage 9 pro parte). © 1997 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.