Basal Peat Research Articles

A basin-based approach to the long-term history of forest fires as determined from peat strata

Valid reconstruction of long-term forest fire histories from individual peat cores usually fails, for a number of reasons, even though visible charcoal horizons in peat are indisputable evidence of local or in-situ fires. Both the dating and reliability of fire records from peat can be improved by the means of a ‘basin-based approach’, in which the gradual lateral growth of the peat is studied carefully by means of numerous dated basal peat samples. Applying this principle, the frequency of forest fires in an esker landscape in southern Finland was elucidated over the past 7000 years. The results indicate that a period of active land use, but undeveloped fire control in the area, reduced the mean fire interval from the natural background from c. 130 years to c. 40 years.

Vegetation and climate during the Weichselian Early Glacial and Pleniglacial in the Niederlausitz, eastern Germany — macrofossil and pollen evidence

AbstractCryoturbated organic beds and channel fills, intercalated with sandy and gravelly fluvial units, have been studied in an opencast brown‐coal mine near Nochten (Niederlausitz), eastern Germany. The fluvial–aeolian sequence covers parts of the Early, Pleni‐ and Late‐glacial. The detailed chronology is based on 11 radiocarbon and 12 OSL dates, covering the period between ca. 100 kyr and 11 kyr BP. Basal peat deposits are correlated with an Early Weichselian interstadial. During this period boreal forests were present and minimum mean summer temperatures were > 13°C. Early Pleniglacial deposits are absent. The Middle and Late Pleniglacial environments were treeless and different types of tundra vegetation can be recognised. Minimum mean summer temperatures varied between 10 and 15°C. Vegetation and climate is reconstructed in detail for the periods around 34–38 kyr BP and 24–25 kyr BP. Around 34–38 ka, a mixture between a low shrub tundra and a cottongrass tussock–subshrub tundra was present. The botanical and sedimentological data suggest that from the Middle to the Late Pleniglacial, the climate became more continental, aridity and wind strength increased, and the role of a protecting winter snow cover decreased. A sedge–grass–moss tundra dominated around 24 and 25 kyr BP. Copyright © 2001 John Wiley & Sons, Ltd.

Sulphur and iron geochemistry of Holocene coastal peats (NW Germany): a tool for palaeoenvironmental reconstruction

A drill core from the marshlands of NW Germany covering the entire Holocene was analysed at high-resolution by geochemical (XRF, Cirm-MS) and microfacies methods (diatoms, thin sections, SEM) in order to provide information about the palaeoenvironmental development. In addition, microbial experiments were carried out with sulphate-reducing bacteria (SRB) and cellulose fermenting fungi in seawater using peat as substrate. The core contains an intercalated reed peat layer (2.73–3.02 m) and a basal peat (5.78–6.42 m). The basal peat consists in the lowest part of fen woodland and raised bog peat, while the upper part is formed by a reed peat bed. The peat layers are characterised by a distinct enrichment of pyrite with negative bulk sediment δ 34S values (av. −11.5‰, range −2.6 to −26.7‰) reflecting microbial sulphate reduction in some peat intervals under almost open system conditions with respect to the input of seawater sulphate. Pyrite occurs exclusively with framboidal texture in close vicinity to the organic matter which indicates localised pyrite formation at the decay site in microenvironments with high concentrations of dissolved Fe. Microbial experiments reveal that peat does not represent an appropriate substrate for SRB and that SRB have to rely on the preceding decomposition of peat by other microorganisms in microenvironments. The total sulphur content of the peat layers averages to 7.8 wt% with a maximum value of 28.2 wt% unusually found within the basal peat at the transition of fen woodland and raised bog peat. The pyrite enrichments can be explained by two different scenarios which are related to the intensity of the sea-level rise. The first scenario applies to a moderate sea-level rise and is decisive for the reed peats where pyrite formation coincides with peat growth. A brackish zone is assumed for the peat-forming environment which is influenced by iron-rich freshwater and sulphate-rich seawater. As the freshwater forms the major Fe source the amounts of pyrite increase to a certain degree with decreasing salinity in this environment. The palaeosalinity is estimated by the investigation of littoral and pelagic diatoms. The second scenario applies to the extensive pyrite formation within the basal peat at the transition of fen and bog peat. This pyrite was likely formed after peat growth favoured by a steep sea-level rise. Thin sections of this peat interval reveal clastic layers (1–3 mm) with completely pyritised interfaces. As these clastic layers contain marine pelagic diatoms (e.g. Paralia sulcata) we propose that they are caused by tidal channel activities during a phase of a steep sea-level rise. The marine incursion led to a partial buoyancy of the basal peat at weak transition zones, i.e. the transition from fen to bog peat. As a result of the bouyancy, marine suspended particulate matter can be introduced laterally in-between the peat sections. When the peat settles down a clastic layer remains whose interface with the peat may have favoured the inflow of waters of higher salinity. Therefore, an enhanced formation of pyrite was possible due to the combination of sulphate-rich ground water and iron-rich peatland waters.

Late Quaternary sea level change in Southern Beringia: postglacial emergence of the Western Alaska Peninsula

Postglacial sea level trends have varied dramatically across the Bering Platform because of differences in coastal and shelf geologic settings. Emergent shorelines and basal peats along the western Alaska Peninsula indicate that relative sea level has fallen since regional deglaciation occurred ca. 13,000 cal. yr BP. Age/elevation determinations on four shorelines (25 m :>10 ka, 16 m : 9.6–6 ka, 6 m : 2.1 ka, and 2–3 m : 1.8–0.6 ka) in the vicinity of Cold and Morzhovoi bays provide an estimate of the pace and timing of of sea level change since the last glacial maximum (LGM, 22–17 ka). Isostatic recovery and shoreline regression following the disintegration of continental and alpine ice has been interrupted by transgressive conditions at least twice since deglaciation. Changes in the balance between eustatic sea level rise and isostatic uplift resulted in the reactivation of marine scarps during the early to middle Holocene, but terrace cutting and a gap in the archaeological record about 2.1 ka suggest that sudden tectonic displacements also influence the record. Reconstructions of coastal paleogeography constrain the timing and distribution of regional archaeological settlement. Periods of shoreline erosion during stillstands or transgressions, and the episodic reorganization of intertidal environments that accompanies tectonic displacements, have conditioned site preservation potential and long-term adaptive strategies.

An updated Holocene sea-level curve for the Delaware coast

Abstract We present an updated Holocene sea-level curve for the Delaware coast based on new calibrations of 16 previously published radiocarbon dates ( Kraft, 1976; Belknap and Kraft, 1977 ) and 22 new radiocarbon dates of basal peat deposits. A review of published and unpublished 137 Cs and 210 Pb analyses, and tide gauge data provide the basis for evaluating shorter-term (10 2 yr) sea-level trends. Paleosea-level elevations for the new basal peat samples were determined from the present vertical zonation of marsh plants relative to mean high water along the Delaware coast and the composition of plant fossils and foraminifera. Current trends in tidal range along the Delaware coast were used to reduce elevations from different locations to a common vertical datum of mean high water at Breakwater Harbor, Delaware. The updated curve is similar to Belknap and Kraft's [J. Sediment. Petrol., 47 (1977) 610–629] original sea-level curve from 12,000 to about 2000 yr BP. The updated curve documents a rate of sea-level rise of 0.9 mm/yr from 1250 yr BP to present (based on 11 dates), in good agreement with other recent sea-level curves from the northern and central U.S. Atlantic coast, while the previous curve documents rates of about 1.3 mm/yr (based on 4 dates). The precision of both estimates, however, is very low, so the significance of these differences is uncertain. A review of 210 Pb and 137 Cs analyses from salt marshes of Delaware indicates average marsh accretion rates of 3 mm/yr for the last 100 yr, in good agreement with shorter-term estimates of sea-level rise from tide gauge records.

A diatom and radiocarbon perspective of the palaeoenvironmental history and stratigraphy of Holocene deposits between Oostende and Nieuwpoort (Western Coastal Plain, Belgium)

Diatom and radiocarbon data of two cores from the north-eastern part of the western Belgian coastal plain are discussed. The palaeoenvironmental reconstruction of these sites and additional stratigraphic and geochronological information, allow an assessment of the general development of this region throughout the Holocene. Prior to c. 7500 yrs cal. BP a rapidly transgressing coast exists. Basal peat development may have been fairly widespread. Extensive erosion channels form towards the interior once the volume of the developing tidal basin has increased sufficiently. In spite of very high rates of sediment accumulation, high-intertidal environments remain poorly developed due to the high rate of RSL rise and the relatively steep slope of the transgressed terrain. Diatom taphocoenoses of this period consist primarily of coastal tychoplankton (mainly Cymatosira belgica), deposited in association with flood transported sediment, and some epipsammon. Hereafter, the incidence of negative tendencies in marine influence increases, culminating between c. 6300 to 5600 yrs cal. BP. Diatom assemblages are now more varied with an improved representation of tidal flat and salt marsh communities. The marine species Paralia sulcata and Pseudopodosira westii become abundant in high intertidal deposits, which may involve selective transport, sedimentation and preservation mechanisms. In general, the environmental changes reflect the development of a broad intertidal sedimentation zone in which sediment supply remained high, combined with a gradual slowing down of the RSL rise. Coastal progradation finally leads to sufficiently sheltered conditions for long-lasting peat growth in the intracoastal area up to perhaps c. 2100 yrs cal. BP. Presumably a coastal barrier, which remains intersected by some inlets, also develops during this period. At places, peat growth is interrupted at about 4200 yrs cal. BP by a marked but short-lived period of marine sedimentation. Within the general framework of a return to a transgressive setting and a destabilisation of the barrier system due to a decreasing sediment supply, climatic conditions and human interference may have played a role in the final termination of peat growth and the resumption of tidal activity. So far, the exact chronology of the return of tidal sedimentation in the study area remains unclear. No general sedimentation cycles, or so-called Dunkerque transgressions, are identified during the deposition of the upper tidal deposits, which are again characterized by a high representation of Cymatosira, reflecting a more open coastal setting. A tentative chronology of regional tendencies in the marine influence is derived from both bio- and lithostratigraphical indications and compared with the assumed chronology of transgressive and regressive phases in the northern Netherlands. Points of agreement are discussed in terms of possible supra-regional processes.

Holocene isostasy and relative sea-level changes on the east coast of England

Abstract Analysis of sea-level data from the east coast of England identifies local-scale and regional scale factors to explain spatial and temporal variations in the altitude of Holocene sea-level index points. The isostatic effect of the glacial rebound process, including both the ice (glacio-isostatic) and water (hydro-isostatic) load contributions, explains regionalscale differences between eight areas: c. 20 m range at 8 cal. ka bp and by 4 cal. ka bp relative sea-level in Northumberland was above present, whereas in areas to the south relative sea level has been below present throughout the Holocene. Estimates for pre-industrial relative sea-level change range from 1.04 ± 0.12 mm a −1 in the Fenland to −1.30 ± 0.68 mm a −1 (i.e. sea-level fall) in north Northumberland, although this may overestimate the current rate of sea-level fall. Isostatic effects will produce similar relative differences in rates of sea-level change through the twenty-first century. The data agree closely with the patterns predicted by glacio- and hydro-isostatic models, but small systematic differences along the east coast await testing against new ice models. Local scale processes identified include differential isostatic effects within the Humber Estuary and the Fenland, tide range changes during the Holocene, and the effects of sediment consolidation. These processes help explain the variation in altitude between sea-level reconstructions derived from index points taken from basal peats and those from peats intercalated within thick sequences of Holocene sediments.

Stratigraphic architecture, relative sea-level, and models of estuary development in southern England: new data from Southampton Water

Abstract This paper presents the results of an investigation into the Holocene depositional history of Southampton Water, southern England. A three phase history of estuary development is proposed. Between c. 7500 and 5000 bp (8200 to 5700 cal. a bp ), mean sea-level rose rapidly from c. −9m to −4 m od . During this interval thin basal peats which developed in present outer estuary locations were inundated and the area of intertidal and subtidal environments within the estuary expanded. Relative sea-level (RSL) rise began to slow between 5000 and 3000 bp (5700 and 3200 cal. a bp ) and a phase of saltmarsh and freshwater peat accumulation occurred. In this interval freshwater peat-forming communities extended outwards and seawards across former saltmarsh and mudflat environments and caused a reduction in the extent of the intertidal area within the estuary. During the late Holocene there was a switch to renewed minerogenic sedimentation as most of the freshwater coastal wetlands of Southampton Water were inundated. This tripartite model is broadly applicable to the Thames and the Severn estuaries, suggesting that regional processes have controlled their macroscale evolution. RSL change and variations in sediment supply emerge as key controls during the first two phases of estuary development. The late Holocene demise of the estuary wetlands probably reflects a propensity for increased sediment reworking and unfavourable conditions for the accumulation and preservation of organogenic deposits due to reduced rates of long-term RSL and watertable rise.

Deltas, radiocarbon dating, and measurements of sediment storage and subsidence

In Holocene marine deltaic sequences there is no simple relationship between radiocarbon age and depth of sampling. The Nile and Ganges-Brahmaputra deltas show remarkably similar radiocarbon age-depth relationships: (1) most radiocarbon dates, by conventional and accelerator mass spectrometric (AMS) analyses, are older (some by 4000 yr) than reasonably expected; (2) dates are commonly inverted (i.e., older upcore); and (3) sample dates at delta surfaces commonly exceed 2000 yr B.P. These anomalous age-depth phenomena are in part a response to reservoir effects, introduction of old carbon, and, emphasized herein, influence of sediment storage and remobilization that prevail in fluvial and delta plains. In fluvial systems, sediment generally is not transported in a single episode from its original source area to the sea. Rather, material transported from upland reaches and river valley to coast is subject to a repeated series of depositional, burial, and erosional events induced by episodic flooding, overbank sedimentation, and channel migration. Because sediment is likely to be temporarily stored in the delta plain, it is difficult to determine the time of a sediment9s final deposition and burial at a delta site. A successful strategy requires use of several independent dating methods, including AMS analyses of in situ basal peats and fossils and, where possible, archaeological evaluation of associated artifacts that are in place. Accurate dates are needed for reliable measurement of rates of delta plain aggradation and land subsidence, information to help implement effective coastal protection measures.

Middle and Late Holocene Sea-Level Changes in Eastern Maine Reconstructed from Foraminiferal Saltmarsh Stratigraphy and AMS 14C Dates on Basal Peat

A relative sea-level history is reconstructed for Machiasport, Maine, spanning the past 6000 calendar years and combining two different methods. The first method establishes the long-term (103 yr) trend of sea-level rise by dating the base of the Holocene saltmarsh peat overlying a Pleistocene substrate. The second method uses detailed analyses of the foraminiferal stratigraphy of two saltmarsh peat cores to quantify fluctuations superimposed on the long-term trend. The indicative meaning of the peat (the height at which the peat was deposited relative to mean tide level) is calculated by a transfer function based on vertical distributions of modern foraminiferal assemblages. The chronology is determined from AMS 14C dates on saltmarsh plant fragments embedded in the peat. The combination of the two different approaches produces a high-resolution, replicable sea-level record, which takes into account the autocompaction of the peat sequence. Long-term mean rates of sea-level rise, corrected for changes in tidal range, are 0.75 mm/yr between 6000 and 1500 cal yr B.P. and 0.43 mm/yr during the past 1500 years. The foraminiferal stratigraphy reveals several low-amplitude fluctuations during a relatively stable period between 1100 and 400 cal yr B.P., and a sea-level rise of 0.5 m during the past 300 years.

Foraminiferal isoleucine epimerization determinations from the Nar Valley Clay, Norfolk, UK: implications for Quaternary correlations in the southern North Sea basin

Fully temperate freshwater, brackish and marine sediments overlying Anglian till and glacilacustrine sediments in the Nar Valley area of northwest Norfolk, UK, have been attributed to the Middle Pleistocene Hoxnian temperate stage on palynological grounds, and basal peats associated with this sequence have been recently correlated with oxygen isotope stage 9 on the basis of a series of 230Th/238U dates (mean 317±14 ka). At Tottenhill these sediments (Nar Valley Freshwater Beds, Nar Valley Clay) underlie a deltaic complex attributed to the Wolstonian ice margin. The lithostratigraphical relations between the major formations in the Nar Valley, and the pollen stratigraphy of the fully temperate sequence, are very similar to the Pleistocene sequence in the Inner Silver Pit area of the southern North Sea, and correlation has been proposed between the successions described from these two localities. However, the Inner Silver Pit sequence has yielded aminostratigraphic data consistent with isotopic stage 11.Benthic foraminiferal assemblages and foraminiferal amino-acid determinations have been investigated from the Nar Valley Clay in order to test further the palaeoenvironmental setting of the sequence and to help resolve the age of the sequence and correlation with the Inner Silver Pit interglacial. The foraminiferal assemblages support previous sedimentological and palaeontological evidence for a transgressive tendency within this sequence. Multiple isoleucine epimerization determinations on Ammonia beccarii and Aubignyna perlucida from five levels within the Nar Valley Clay give mean aIle/Ile ratios of 0.135 and 0.111, respectively. The A. beccarii ratios are much lower than mean aIle/Ile ratios on equivalent species from the interglacial sequence in the Inner Silver Pit (upper Sand Hole Formation), which are close to 0.2, and the two datasets fail to overlap at the 1σ level. The new aminostratigraphic ratios indicate correlation of the Nar Valley Clay with oxygen isotope stage 9, and therefore support the pre-existing 230Th/238U data.These results suggest that two temperate stages of Hoxnian palynological affinity are present in the Quaternary record of East Anglia and the southern North Sea basin, a conclusion consistent with independent new U-series data from other Hoxnian sites in East Anglia. An alternative model in which the amino-acid ratios are explained as a function of different post-depositional thermal histories, related to length of cover by ice and water, is discussed but considered unlikely. The conclusions have important implications for the timing and number of glacial events in and around the southern North Sea basin, and help to resolve discrepancies in relative sea-level histories and biogeography in temperate sequences hitherto accommodated within a single stage.

The role of fire in the carbon dynamics of a mire, eastern Finland

The fire history and the effect of fires on the long-term (apparent) rate of carbon accumulation (LORCA) in the Patvinsuo mire complex, eastern Finland, were determined through stratigraphic and pollen analyses of 98 peat cores. The peat cores were characterized by a large number of charcoal layers and the age of the basal peat varied between 57 and 10 500 years. Mire fires slowed down the progress of vertical peat accumulation and resulted in great carbon losses. The average LORCA in the Patvinsuo cores was clearly lower, 9.2 ± 1.0 (SE) g m-2 yr-1, compared to the average value for all mire sites in the southern half of Finland, 17.7 ± 0.6 (SE) g m-2 yr-1. The average rate of carbon loss in Patvinsuo mire complex was 9.5 ± 1.0 (SE) g m-2 yr-1 and the mean carbon loss in an individual fire was estimated to be 2.5 kg m-2.

Peatland Initiation During the Holocene in Continental Western Canada

Today, the southern limit of peatlands in continental western Canada is largely limited by thermal seasonal aridity, although physiographic parameters of substrate texture, topography, and salinity also exsert important controls on the presence and absence of peatlands. Factors that control peatland distribution today also operated in the past, thus the initiation of peatlands during the Holocene was mainly limited by aridity and physiography. Calibrated radiocarbon dates of basal peat deposits from 90 locations across continental western Canada indicate that peat formation began approximately 8,000 to 9,000 years BP in nucleation zones along the upper elevations of the Montane region of Alberta and in northern Alberta uplands after an initial deglacial lag. Predictions of maximum early Holocene summer insolation by climate simulations provide a mechanism for limiting peatland establishment during the early Holocene. From 6,000 to 8,000 years ago, peat formation in continental western Canada expanded eastwards into Manitoba responding to decreases in summer insolation. Peatland expansion during the early Holocene was more extensive in Alberta than in Manitoba in response to a southwesterly shift in the Arctic front. The displacement of the Arctic front allowed for more frequent incursions of moist Pacific air into Alberta while limiting it in Manitoba. After 6,000 years BP, the trend of southeasterly peatland expansion continued. Peatlands are youngest in the southern Boreal Forest and Aspen Parkland Region as well as in the lower elevations of the Peace-Wapiti River drainage basin, forming over the last 3,000 to 4,000 years. Peatlands are also young in the lower elevations of the Hudson Bay Lowlands where peat initiation has been limited by timing of emergence from glacial rebound. The spatial and temporal distribution of peatland initiation during the Holocene is verified by existing pollen records and corroborates some simulated climate models.

Improving Methodology for High-Resolution Reconstruction of Sea-Level Rise and Neotectonics by Paleoecological Analysis and AMS14C Dating of Basal Peats

Sea-level research in several submerging coastal regions has traditionally been based on14C dating of basal peats that overlie a compaction-free substratum and can be related to paleo-(ground)water levels. Provided that an unequivocal relationship between (ground)water level and sea level can be assumed, this approach contains two sources of uncertainty: (1) the paleoenvironmental interpretation of samples is usually based on inherently inaccurate macroscopic descriptions in the field, and (2)14C ages of bulk peat samples may be erroneous as a result of contamination. Due to the uncertainties in both the altitude and the age—the two crucial sources of evidence necessary to arrive at accurate sea-level curves—sea-level index points are therefore represented by considerable, but typically not quantified, error boxes. Accelerator mass spectrometry (AMS) opens new perspectives for this type of sea-level research, as illustrated by a paleoecological and AMS14C study of basal peats from a small study area in the Rhine–Meuse Delta (The Netherlands), where previous (conventional) work revealed highly problematic results. A detailed macrofossil analysis has two purposes: (1) an inferred paleoecological succession indicates a relatively accurate level of paludification of the site, and hence rise of the (ground)water level; (2) suitable macrofossils from that specific level are then selected for AMS14C dating. In spite of very small sample sizes, our results are consistent and indicate that this approach can constitute a step forward in high-resolution reconstruction of sea-level rise. The new results further enable a revision of Holocene (ground)water gradient lines for the Rhine–Meuse Delta. A knickpoint in these gradient lines can be related to the effect of faulting. This approach therefore also has considerable potential to unravel and quantify neotectonic activity in submerging coastal settings.

Late pleistocene, Late-glacial and Holocene glacier advances on the Tibetan Plateau

Abstract Many end-moraine sequences in various mountain areas of the Tibetan Plateau have already been investigated in detail, but a homogeneous chronostratigraphy is still lacking. The ice-marginal limits are commonly given local names and often the classification does not seem to be secure. This is one reason for controversial discussions on the ice extent at the LGM. Because most organic material in Tibet developed at the beginning of the Holocene, only a few older radiocarbon dates are available. Up to now, Late-glacial terminal moraines have been found in the western Kunlun Shan and in the Tian Shan. Their radiocarbon ages (ca. 15 ka BP) correspond to a glacier advance south of the Qaidam basin, which can be correlated with Late-glacial lacustrine sediments. In Eastern Tibet different ages of peat development in different tongue-like basins have been obtained. Even the bases of peat bogs in basins at Nianbaoyeze mountains enclosed by (apparent) LGM end moraines gave Holocene ages. Three main Holocene intervals have been radiocarbon dated from palaeosols and basal peat layers in the area. Except for a younger glacier re-advance at about 3000 BP, and those of the Little Ice Age, the age of many last glaciation glacier advances on the Tibetan Plateau are constrained only on the basis of organic matter lying on top of the moraines and therefore might be of Late-glacial or Pleistocene age.

An air-pollution history of metallurgical innovation in iron- and steel-making: A geochemical archive of Sheffield

This paper explores the degree to which palaeoecological analyses can determine the history of metallurgical innovation and complex technological developments that took place in the iron- and steel industries ofthe City of Sheffield, Yorkshire, England. A knowledge of the key scientific breakthroughs as well as documentary evidence of industrial growth and decline in Sheffield are used as base-line historical data with which to interpret the palaeoecological and geochemical evidence presented here as a result of investigations of peats and days collected from the Tinsley Park Bog in the Lower Don Valley of Sheffield. These deposits were analysed for charcoal, pollen, mineral magnetic properties and some trace elements (Ti, V, Fe, Co, Ni, Zn, and Pb). Metal concentrations (measured using AAS) were as high as 320 ppm Ni, 472 ppm Cu, 613 ppm Zn, and 827 ppm Pb. Compared to the typical concentrations found in crustal rocks, Ni is enriched in the peats and sediments by as much as a factor of 5 times, Cu and Zn by a factor of 10, and Pb by more than 60 times. The lowest concentrations of Cu, Ni, Zn and V were found in the basal peats of Tinsley Park Bog, arguing against a natural geochemical source as the cause of the enrichments. The greatest Cu and Zn enrichments are found in the peats in the top 0.1 m ofthe bog, possibly an indication of a large Special Steels Plant which began production nearby in 1963. Below these levels in the peat, in contrast, Ni and V are relatively abundant. They are believed to reflect the manufacture of complex steels during the earlier part of the twentieth century. Lead is most abundant in samples from depths in the peat which are though to post-date the onset of coal utilisation at the nearby Rothervale Mine. Interpretation is hampered because at present there is no independent evidence of the antiquity of the peat deposits studied. Neither is there any clear understanding of the significance of the taphonomic processes which have influenced the geochemical and paleoecological records obtained from the deposits. Nevertheless, our present interpretation of the data presented here indicates that to a surprising extent, it is possible to detect in the peat monolith (i) evidence of the expansion and relative decline of the adjacent steel industry; (ii) the impact of this manufacturing economy and associated coal-mining upon the adjacent vegetation; and (iii) the introduction of trace elements in pure forms or as alloys, as steel-making processes developed through the 19th and 20th centuries.

The Long‐Term Stability of the Boreal Forest Limit in Subarctic Quebec

Using black spruce (Picea mariana) macrofossil remains at the forest—tundra to tundra transition in norther Quebec, Canada, we address the question: did the boreal forest limit shift in unison with climate change during the Holocene? Logs buried in peatlands, charcoal in the organic soil layers on well—drained sites, and dry peat underlying stunted clonal spruce were sampled across a 60—km transect south and north of the modern forest limit. Of 146 spruce logs sampled south of the modern forest limit, 34 were 14C dated between 4580 and 1540 yr BP, and 34 additional logs were cross—dated with 14C—dated spruces (3010—1540 yr BP) using diagnostic tree rings. South of the forest limit, charcoal with abundant spruce fragments was widespread in dry—mesic sites and dated between 1920 and 1140 yr BP. No spruce logs or charcoal were found in all the surveyed sites north of the forest limit. The residence time of humified peat confined to the area occupied by tundra clonal spruces ranged between 3040 and 630 yr BP. The absence of spruce macrofossils in the tundra zone, together with the geographic coincidence of the charcoal limit and forest limit, strongly suggest that the forest limit remained stable during the last 2000—3000 yr BP. Old—aged peat produced by tundra spruces is additional evidence for the stability of the forest limit. Because only spruce is able to accumulate such a thick organic layer, the 14C dates of basal peat indicate that spruce clones developed continuously in the absence of external disturbance at least over the last 3000 yr BP. The stability of the forest limit during war (≈ 2000 yr BP, medieval times, and this century) and cold (≈ 3000 and 1300 yr BP, and the Little Ice Age) periods of the late Holocene demonstrates that mechanisms allowing forest limit advance or retreat are not easily triggered by climatic change.

Fossil Beetle Evidence for a Short Warm Interval near 40,000 yr B.P. at Titusville, Pennsylvania

A brief cold–warm–cold climate change during the middle Wisconsinan is described for the first time in North America, based on fossil beetle assemblages at Titusville, Pennsylvania. AMS dating of insect chitin and wood suggests the change occurred between 39,000 and 43,500 yr B.P. Basal peats in river terrace deposits contain arctic–subarctic beetle species representing a climate similar to that found at treeline in Canada, where mean July temperatures range from 10° to 13°C. These cold-adapted beetles were replaced by species representing a climate similar to the mixed coniferous–deciduous forests of southern Canada, where mean July temperatures range from 18° to 20°C. In turn, these warmer-adapted beetles were replaced by arctic–subarctic species in the upper part of the section, representing a climate with mean July temperatures in the range 10°–13°C. The brief warm interval is informally designated the Titusville interstade. The difference in temperature between the colder and warmer intervals is about 5°–7°C. The Titusville interstade is correlated with the Upton Warren Interstade of the British Isles which is of similar age and intensity. It is also correlated with the high sea-surface temperature interval between Heinrich events 4 and 5 represented in North Atlantic sediment cores.

Characteristics, impacts and causes of the Carntogher bog‐flow, Sperrin Mountains, Northern Ireland

Abstract A large bog‐flow was triggered on the slopes of Carntogher, in the Sperrin Mountains of Northern Ireland, on the 10th September 1993, following a period of above average monthly rainfall and a high magnitude rainfall event on the preceding day. It is believed that high pore‐water pressures were established in the peat mass as a consequence of this antecedent rainfall and the transfer of additional water to the site by drainage ditches and seepage. The humified basal peat liquefied and breached the surface mat of fibrous peat. Disturbed peat extended 1 km downslope and a further 1.5 km along the floodplain of the stream into which the flow became confined. A significant amount of water was released by the flow, as demonstrated by hydrographs for a gauging station 23 km downstream. Rough grazing ground and fencing were destroyed by the bog‐flow and a number of sheep were killed. Hydro‐electric power to a linen mill, and fish stocks were also affected, with a total fish kill for a distance of 8 km downstream. Since the event, fish have partially recolonised this reach of the river by spawning.

Initiation of a sloping mire complex in southwestern Finland: Autogenicversusallogenic controls

:Sediment-stratigraphical techniques, together with radiocarbon dating, are applied in this paper to basal peat sequences of Lammansmossen, a sloping mire-complex in southwestern Finland, to reconstruct patterns of peat initiation within the peatland, and by inference, changes in environmental conditions. Peat accumulation commenced simultaneously over the whole lower-lying area of the drainage path about 4500 cal BP, and progressed rapidly by paludification in an upslope direction. By ca 3000 cal BP, about 70% of the present mire area was buried by peat, and the mire received its current configuration 2000 years ago. It is concluded that the rapid replacement of the forest by peatland vegetation occurred mainly in response to a climate change towards humid conditions at 4500 cal BP, although other complex driving mechanisms were operating as well. This interpretation is consistent with findings from other peatlands in southern Finland, as well as a growing body of evidence from other sources.