bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dissolution and depletion of ferromagnesian minerals from Holocene tephra layers in an acid bog, New Zealand, and implications for tephra correlation
Authors: Hodder A. P. W. , De Lange P. J. , Lowe D. J. 
Published: February 2007

AbstractThis study examines the depletion of ferromagnesian silicate minerals from a sequence of thin, distal, mainly rhyolitic tephra layers of Holocene age preserved in an acid peat bog (Kopouatai), North Island, New Zealand. The rate of such depletion has been fast, as indicated by the complete loss of biotite from one tephra layer (Kaharoa Tephra), in which it is normally dominant, in only ca. 770 yr. Chemical dissolution is advocated as the likely cause for the depletion, with amphiboles and other mineral grains commonly showing etch pits, microcaves, and other characteristic surface solution features. Theoretical thermodynamic and kinetic models show a marked increase in the rate of dissolution of all ferromagnesian minerals under conditions of low pH (< 4), but that where silica concentrations in solution are high the relative proportions of minerals remaining are unaffected. However, where concentrations of dissolved silica are low, as in most bog environments, the relative proportions of ferromagnesian minerals are affected as well as absolute amounts being decreased. Amphiboles are depleted relative to pyroxenes, consistent with kinetic studies.The results show that the identification and correlation of tephras on the basis of relative abundances of ferromagnesian minerals alone may be unreliable, and emphasise the need to use multiple criteria in such studies.
An 11 000‐year record of vegetation and environment from Lago di Martignano, Latium, Italy
Authors: Kelly Martyn G. , Huntley Brian 
Published: February 2007

AbstractA pollen diagram from Lago di Martignano, a maar lake in central Italy, provides an 11000‐year record of vegetation and environment change. The earliest pollen spectra are dominated by Artemisia and Gramineae, representing late glacial steppe vegetation typical of the Mediterranean region. Broad‐leaved forests were established by ca. 11 000 yr BP. Although Quercus initially dominated their canopy, a wide range of other mesophyllous trees were also present. Pollen values for sclerophyllous tree and shrub taxa characteristic of Mediterranean woodlands and scrub are initially low (<10%). After ca. 7000 yr BP, however, they begin to increase and rise to a peak of >40% of total land pollen at ca. 6700 yr BP, with Olea europaea the single most abundant taxon. Human influence upon the vegetation only becomes significant somewhat after this peak, with progressive clearance of woodland and expansion of herbaceous communities. Castanea sativa and luglans regia pollen is recorded consistently from the beginning of the rise in pollen values for taxa characteristic of Mediterranean scrub communities. Pollen values for arable crops increase progressively after ca. 5500 yr BP, following the peak pollen values for taxa characteristic of Mediterranean scrub vegetation. Late glacial and Holocene climate changes have been complex in this region, with the present character of the climate developing only during the last millennium. Rates of change of pollen spectra peak during this period.
A dated cave sediment record of Pleistocene transgressions on Berry Head, Southwest England
Authors: Proctor Christopher J. , Smart Peter L. 
Published: February 2007

AbstractBerry Head, a limestone headland in Torbay, southwest England, exhibits a series of subaerial marine erosion platforms and raised beaches spanning an altitude range of 97 m. Solution caves on the headland show preferred horizontal development at elevations that are correlated with the marine erosion platforms, and developed in a marine/freshwater mixing zone whose position was controlled by high sea‐level still‐stands. Corbridge Cave in Berry Head Quarry lies below the raised beaches in Torbay, and contains evidence of three marine transgressions in the form of fine‐grained marine ponding deposits with a marine microfauna. Uranium‐series dating of intercalated speleothems indicates that a transgression during oxygen isotope stage 5e reached an elevation of 5.8 m OD, while an earlier transgression (probably during stage 7) reached at least 7.2 m OD. These findings are used to constrain possible interpretations of the aminostratigraphy of raised beaches in Southwest Britain, and a correlation of the Unnamed Stage of Bowen, Sykes, Reeves, Miller, Andrews, Brew and Hare with oxygen isotope stage 5e is proposed.
Stratigraphy and geochemistry of a sequence of Quaternary palaeosols in the Lower Teleki Valley, Mount Kenya, East Africa — Implications for interregional correlations
Authors: Mahaney W. C. , Slowpoke R. G. V. Hancock , Rutter N. , Sanmugadas K. 
Published: February 2007

AbstractThe relative weathering of a sequence of five palaesols formed in different parent materials, including bedrock of phonolitic composition, is described and assessed. The three lower palaeosols (units 3–5) are considered to be of interglacial origin. The saprolite (unit 5), in phonolite, formed prior to deposition of the lower Brunhes‐age till, is considered to be as old as the Brunhes Matuyama boundary (0.73 myr). The other two palaeosols in this group (units 3 and 4), derived from loess and till, respectively, formed over middle to late Brunhes time under palaeoclimates that were wetter (and presumably warmer), and of sufficient leaching power to move clay, as well as organically complexed extractable Fe and Al. The palaeosols in unit 3 are more complex than the lower ones. Their upper and lower horizons have about the same chemical composition as the lowest two palaeosols, while the middle horizons are similar to the upper two palaeosols (units 1 and 2). Radiocarbon dates for unit 3 are considered to be too young to account for the strong weathering in the upper and lower horizons. This interpretation is supported by high D/L ratios of aspartic acid. Overlying sediments, emplaced by episodic colluvial (unit 2) and slope wash (unit 1) processes, are less weathered; the lower colluvial unit in this group was emplaced during the late stade of the last glaciation. The surface sediments were emplaced more recently during the same interval and weathered mainly during the post‐glacial period. Tentative correlations with core 82PCS18 from the Canary Basin show that upper unit 3 is probably equivalent to Isotope Stage 5e, lower unit 3 to Isotope Stage 7, unit 4 to Isotope Stage 8, and unit 5 to Isotope Stage 9. Units 1 and 2 are firmly correlated with Isotope Stage 2.
Late Quaternary climatic history of the Chilean Channels based on fossil pollen and beetle analyses, with an analysis of the modern vegetation and pollen rain
Authors: Ashworth Allan C. , Markgraf Vera , Villagran Carolina 
Published: February 2007

AbstractFossil beetles and pollen were examined from an intermorainal bog at Puerto Edén, Isla Wellington, Chile (latitude 49°08'S, longitude 74°25'W). Wood from near the base of the section has an age of 12 960 ± 150 yr BP. Occurrence of flightless beetle species in the basal peat sample is evidence that some members of the biota survived the last glacial maximum in refugia. The assumption that the Chilean Channels were entirely ice‐covered is incorrect. Plants and insects that invaded the deglaciated terrain were those of an Empetrum heathland in which patches of Nothofagus forest were restricted to sheltered locations. The climate supporting the heathland is inferred to have been windier and probably drier than that of the present day. From 13 000 yr BP to 9500 yr BP Nothofagus forest expanded, possibly in response to less windiness and more available moisture. Neither the fossil beetle nor pollen data support a return to significantly colder conditions between 11 000 and 10 000 yr BP at the time of the Younger Dryas Stade. From 9500 to 5500 yr BP the climate was as wet as that of the present day, based on an increased representation of the pollen of moorland plants and of aquatic beetle species. From 5500 to 3000 yr BP the climate was drier, as indicated by the expansion of Empetrum heath and the reduction in mesic habitats. From 3000 yr BP to the present‐day mesic habitats dominated as the climate returned to a wetter mode. The alternatively wetter and drier episodes are attributed to latitudinal shifts in the position of storm tracks in the belt of Southern Westerlies.
Late glacial and holocene lake level fluctuations in Lake Biel, western Switzerland
Authors: Wohlfarth Barbara , Schneider Anne Marie 
Published: February 2007

AbstractCores and outcrops from the southern shore of Lake Biel were studied to reconstruct the nearshore environment of the lake between ca. 12000 and 5000 yr BP. Core correlations were established by lithostratigraphical and pollen analytical correlations. From the Allerød to the Preboreal time quiet hydrodynamic conditions favoured the deposition of lake marl in the littoral zone and peat on the shore. Between the Preboreal(?) and the Atlantic the littoral zone shows a higher hydrodynamic environment with allochthonous material, whereas peat and clay layers are recorded from the shore. During the Older Atlantic severe erosional episodes caused the erosion of Boreal, Preboreal and Younger Atlantic layers. The previously described long hiatus between the Allerød and the Boreal time can now be connected with these erosional episodes. From Younger Atlantic to Subboreal time the littoral zone displays quiet conditions again with sedimentation of lake marl. On the basis of these results a lake level curve for Lake Biel is proposed: high lake level stands can be traced during the Allerød, Boreal, Older Atlantic and Younger Atlantic biozones; low lake level stands are found during the Allerød, Younger Dryas, Preboreal and Older Atlantic biozones.
Holocene palaeo‐oceanography of the northern Iceland Sea, indicated by Radiolaria and sponge spicules
Authors: Molina‐Cruz Adolfo , Geomar  
Published: February 2007

AbstractThe micropalaeontological analysis of 49 samples, from three box cores collected from the northern Iceland Plateau, indicates that radiolarian and sponge remains are rare in glacial sediments but are common after deglaciation; mostly during the first half of the Holocene. The record trend of the abundance of Oxycalthrop sponge spicules is regional in character. Fluctuations in radiolarian abundance, and the first occurrence of each of the species inhabiting the Iceland Sea at present, coincide with changes in oceanographic conditions that occurred during the Holocene. At the Younger Dryas chronozone, the downcore record of Cycladophora davisiana (Ehrenberg) depicts a maximum peak, because the sea surface was colder than it has been recently; though still seasonally free of ice‐cover. During the Preboreal, Boreal and Atlantic chronozones, Amphimelissa setosa (Cleve) was highly abundant, as a consequence of the increase in mixing between the Arctic Water and the North Atlantic Water. During the Subboreal chronozone, the East Icelandic Current became better developed, and initiated the onset of the ‘Arctic Front’ in the Iceland Sea; as is suggested by the Lithomitra lineata (Ehrenberg) record. This ‘cooled’ environment also allowed an increase in the occurrence of Artobotrys borealis (Cleve). The reappearance of Stylodictya validispina (Jörgensen) in the Iceland Sea, during the Sub Atlantic chronozone, indicates a larger input of Atlantic Water, via the Norwegian Current.
Late quaternary of the middle Caquetá River area (Colombian Amazonia)
Authors: Hammen Thomas Van Der , Duivenvoorden Joost F. , Lips Johanna M. , Urrego Ligia E. , Espejo Nohora 
Published: February 2007

AbstractThe late Quaternary history of the middle Caquetá River area in Colombia, northwestern Amazonia is described, based on observations of river bank sections, radiocarbon dates and palynological analyses of organic layers in floodplain and low terrace sediments of the Caquetá River. It is shown that the Late Pleistocene and Holocene climatic changes that took place in the Andean Cordilleras, were related to the depositional and erosional history of the Caquetá River in the Colombian Amazonian lowlands.The low terrace sediments consist of sandy and gravelly deposits covered by clays that sometimes contain lenses of peaty material. From these organic low terrace sediments, seven finite radiocarbon dates were obtained of Middle Pleniglacial age, between 56 000 and 30 000 yr BP. The coarse textured basal deposits of the low terrace apparently stem from the early part of the Middle Pleniglaciai period, during which the effective rainfall in the Andes was relatively high and the Andean glaciers had a considerable extension. Palynological data from silty sediments with organic remains at one site, show an interval when drier and more open types of vegetation on poor soils must have covered a larger area than today, but Amazonian forest was still the dominating type of vegetation. This interval might correspond to one of the Middle Pleniglacial savanna intervals from eastern Amazonia (Carajas).No organic sediments from the Upper Pleniglacial period were found and hence radiocarbon dates were not obtained. In the Andes this period had a very cold climate with low effective rainfall and in the east Amazonian Carajas area it is characterised by the relative extension of open savanna vegetation. The river run‐off and sediment transport must have been much lower than in the Middle Pleniglacial and the Caquetá River cut itself down in its own sediments.Two Late‐glacial radiocarbon datings obtained at one site (ca. 12 500 yr BP) indicate the existence of a Late‐glacial sedimentation phase, separated from the Holocene sequence by a minor erosional phase.Organic layers in the Holocene floodplain sediments yielded 28 radiocarbon dates between 10 000 and 355 yr BP. Holocene sedimentation started with the rapid deposition of (sandy) clay possibly in a partly permanently inundated Caquetá valley. During the major part of the Holocene (silty) clays were deposited, with a dominant seasonal inundation cycle.
Late‐glacial and Holocene sedimentation and fluctuations of river water level in the Caquetá River area (Colombian Amazonia)
Authors: Hammen Thomas Van Der , Urrego Ligia E. , Espejo Nohora , Duivenvoorden Joost F. , Lips Johanna M. 
Published: February 2007

AbstractThe sequence of Late‐glacial and Holocene alluvial sedimentation in the middle Caquetá River Basin of Colombian Amazonia is described, based on the study of the sediments and palynology of several river bank sections and on 30 radiocarbon dates.An early Late‐glacial sedimentation cycle is recognised, followed by a minor late Late‐glacial erosion phase.The Holocene valley fill consists of grey clays (often present in the lower part of the sections) deposited in open water and silty clays often with faint yellow mottling, deposited under a regime of seasonal flooding. The base of the Holocene sections is formed by sands, where exposed. In two places the transition of sand to open‐water grey clay was dated around 10 000 yr BP and there is a suggestion that open water may have been more common at the beginning of the Holocene than later, when sedimentation by seasonal flooding became important. In many places much of the earlier Holocene sediments may have been removed by erosion and replaced by younger sediments, by a process of lateral aggradation. A considerable part of the present valley fill is younger than ca. 3500 yr. However, in several places older Holocene sediments are found, apparently only little affected by later erosion, lying below younger varzea silty clays.During the Holocene more organic sediments were formed in periods with reduced river discharge, related to drier climates in the Andes and possibly in Amazonia. These dry periods, deduced from data in the Caquetá River area, correspond well with dry phases in other parts of northwestern South America (e.g. between approximately 2700‐1900 yr BP and approximately 3200‐3800 yr BP). Rates of average net sedimentation, calculated from dated sections that apparently lack major hiatuses caused by erosion, were high in the lower Holocene, low during the middle Holocene and increase again in the upper Holocene. Levee deposits became coarser and the high river level of the Caquetá increased during the late Holocene. These phenomena may be explained by the increasing influence of man on the vegetation cover in the Andean headwater areas and possibly also in the Amazonian catchment area of the Caquetá River.
Late Quaternary glaciation of the Cordillera Real, Bolivia
Authors: Seltzer Geoffrey O. 
Published: February 2007

AbstractGlacial geological studies in tropical mountain areas of the Southern Hemisphere can be used to address two issues of late Pleistocene climate change: the global synchroneity of deglaciation and the magnitude of temperature reduction in the tropics. Radiocarbon dates from the Cordillera Real and from other areas in Perú and Bolivia suggest that late Pleistocene glaciation culminated between 14 000 and 12 000 yr BP, followed by rapid deglaciation. Because deglaciation was apparently synchronous with that in Northern Hemisphere regions, insolation change at high latitudes may not have been the only factor that produced global deglaciation at this time. Late Pleistocene glaciation in the Cordillera Real culminated when precipitation was 200 mm yr−1 higher and temperatures were 3.5° ±1.6°C lower than today; this produced an equilibrium‐line altitude depression of about 300 ± 100 m on the western side of the cordillera. Prior to this, conditions were drier and probably at least as cold. However, the lack of moraines in the Cordillera Real dated to the Last Glacial Maximum (ca. 18000 yr BP) precludes using the equilibrium‐line altitude method to quantitatively evaluate the discrepancy between warm sea‐surface temperatures and cold terrestrial conditions reconstructed with other proxies for this time period.
Thermoluminescence dating and geochemistry of loessic deposits in southeast England
Authors: Parks David A. , Rendell Helen M. 
Published: February 2007

AbstractThe results of a thermoluminescence (TL) dating and geochemical survey of loessic deposits in southeast England, involving sampling at 26 localities, demonstrate that the loessic deposits appear to be the product of at least three depositional phases of aeolian silt during the Late Pleistocene, namely 10‐25 ka BP, 50–125 ka BP and > 170 ka BP. The majority of localities sampled date to the Late Devensian, but isolated pockets of older material were found throughout the area. The majority of the samples analysed were of decalcified material. The results of geochemical analyses of major oxide and trace element concentrations indicate the uniformity of material and suggest a common provenance.
Influence of glacier hydrology on the dynamics of a large Quaternary ice sheet
Authors: Arnold Neil , Sharp Martin 
Published: February 2007

AbstractThe influence of glacier hydrology on the time‐dependent morphology and flow behaviour of the late Weichselian Scandinavian ice sheet is explored using a simple one‐dimensional ice sheet model. The model is driven by orbitally induced radiation variations, ice‐albedo feedback and eustatic sea‐level change. The influence of hydrology is most marked during deglaciation and on the southern side of the ice sheet, where a marginal zone of rapid sliding, thin ice and low surface slopes develops. Such a zone is absent when hydrology is omitted from the model, and its formation results in earlier and more rapid deglaciation than occurs in the no‐hydrology model. The final advance to the glacial maximum position results from an increase in the rate of basal sliding as climate warms after 23000 yr BP. Channelised subglacial drainage develops only episodically, and is associated with relatively low meltwater discharges and high hydraulic gradients. The predominance of iceberg calving as an ablation mechanism on the northern side of the ice sheet restricts the occurrence of surface melting. Lack of meltwater penetration to the glacier bed in this area means that ice flow is predominantly by internal deformation and the ice sheet adopts a classical parabolic surface profile.
Danish pollen records radiocarbon‐dated to between 50000 and 57000 yr BP
Authors: Kolstrup Else 
Published: February 2007

AbstractRadiocarbon‐dated pollen diagrams from four Danish sequences are presented in their sedimentological context. The pollen diagrams indicate the former presence of stands of Betula and Pinus and of Ericales, Poaceae, Cyperaceae and other herbs. From a straightforward comparison with other diagrams, one of the present series is tentatively correlated with part of the Early Weichselian Brørup Interstadial and two with parts of the Odderade Interstadial, which has not been demonstrated previously in Denmark. One diagram and part of another do not seem to match previously published records in northwest Europe. Yet, the possibility that the sediments date to hitherto unrecorded periods with environmental conditions similar to those reflected in known Weichselian deposits is not excluded. In two of the sequences high percentages of charcoal particles suggest the former occurrence of fires, which influenced the palaeovegetation and soil surface stability. It is suggested that counting of charcoal particles is included in future investigations in order to establish whether periods with fires can be identified in the sedimentary sequences.
Geochemical stability of fine‐grained silicic Holocene tephra in Iceland and Scotland
Authors: Dugmore Andrew J. , Newton Anthony J. , Sugden David E. , Larsen Gudrun 
Published: February 2007

AbstractThis paper tests two assumptions fundamental to the use of fine‐grained silicic tephras from Iceland for creating chronological frameworks in northwest Europe. It is shown firstly, that glass shards can retain their overall chemical integrity on at least a four millennial time‐scale in contrasting depositional environments in Iceland and Scotland, and secondly, that an acid digestion process, the most practical method for extracting tephra from peat, does not significantly bias the results of major element analysis by electron microprobe. The implication is that there is great potential and an appropriate method for developing both the resolution and the spatial coverage of chronologies based on silicic Icelandic tephras in northwest Europe.