characterizing changes in the sedimentary environment of a varved lake sediment record in southern central finland around 8000 cal yr bp the varved lake sediment record of lake nautajarvi in southern central finland indicates fluctuations in the annual sedimentation pattern and lake environment around 8000 cal yr bp annual accumulation of catchment derived mineral matter peaks a number of times and there are changes in the deposition rate of organic matter based on evidence from the lake nautajarvi sediment record the climate was characterised by a millennial scale colder period that terminated at one or several cooling events around 8000 cal yr bp during one of these events diatom composition undergoes a change from planktonic species dominance to more littoral species dominance at 8160 cal yr bp and a recovery around 8010 cal yr bp the timing of this 150 year long diatom anomaly is convergent with increased catchment erosion and decreased organic matter accumulation we interpret that during such a period the environment was characterised by colder winter temperatures prolonged duration of ice cover higher than normal spring discharge and rapid development of thermal stratification in the spring coupled with reduced water circulation and shorter growing seasons copyright 2008 john wiley sons ltd

nature and composition of shore zone sediments between jeddah and yanbu eastern red sea abstract the shore zone sediments between jeddah and yanbu west coast of saudi arabia are composed mostly of skeletal carbonate sands the nearshore sediments containing benthic foraminifera algal fragments and molluscs are multimodal the mean grain size varying between 0 76 and 2 35 o the beach sediments except samples dominated by cerithid gastropods in some localities are relatively finer than the nearshore sediments although the beaches to a great extent comprise sand sized material fine lime muds and coarse clastic gravels occur in certain areas the dune sediments comprising mostly algal grains and ooids are very fine with 50 percent of the material in the 0 25 0 18 mm size grade except a general northward decrease in mean grain size regional trends in the textural parameters of the sediments between jeddah and yanbu are not quite apparent lateral variations in the textural characteristics suggest a landward migration of the sediments in the shore zone under the influence of northerly and northwesterly winds the carbon and oxygen 13 c 4 80 to 4 84 pdb 13 o 0 04 to 0 53 pdb isotopic ratios of the lime muds occurring in certain shallow margins in the shore zone which are much higher than those of the green algae indicate that the fine carbonates are at least in part inorganic in origin like the shallow water carbonates in tropical seas aragonite and high mg calcite are the dominant carbonate minerals in the shore zone sediments there is a landward increase in aragonite contents caused by the landward migration of fine material from the nearshore the dominant clay mineral in the nearshore sediments is kaolinite with subordinate swelling chlorite and little illite kaolinite is contributed by the coastal regions under the sub tropical humid climate swelling chlorite is considered to have been formed in the nearshore by mechanical mixture of chlorite and montmorillonite derived from the metamorphic and igneous terrains of the tertiary mountains bordering the coastal plain

the continental and oceanic crust and lithosphere in the archaean isostatic thermal and tectonic models simple isostatic models of the development of selected archaean basins and greenstone belts can be used to constrain models of the archaean lithosphere geophysical geochemical and thermal data imply that in southern africa the late archaean crust was probably comparable in thickness to the modern continental crust and the whole lithosphere was perhaps over 80 100 km thick two archaean belts studied may have developed by stretching of the order of 1 3 1 6 1 isostatic and thermal data and petrological assumptions allow the construction of simple models of the archaean oceanic lithosphere oceans were probably deep mid ocean ridges were probably subaqueous and fed by komatiitic liquids calc alkaline volcanism in the archaean may have been produced as a consequence of the subduction of hydrated komatiitic oceanic crust into a hot low viscosity asthensophere

late holocene temperature and precipitation changes in vindelfjallen mid western swedish lapland inferred from chironomid and geochemical data in this article we present results from a palaeolimnological study from lake vuoksjavratje in the mountain tundra region in the vindelfjallen mountains northwest sweden we suggest that the influence of precipitation may be one of the factors causing discrepancies between chironomid based late holocene july temperature julyt reconstructions from fennoscandia we combine quantitative temperature reconstruction using chironomids for the last 5100 years with qualitative analysis of chironomid composition and geochemical analyses such as x ray fluorescence xrf total organic carbon toc and c n analysis the studied sequence is dated by 210pb 137cs and 11 14c datings from terrestrial macrofossils the aim of the study was to use chironomids to reconstruct late holocene summer temperature variation on a multi centennial to centennial timescale and to use geochemical data to identify periods during which the changes in chironomid composition might have been forced by environmental variables other than

ti rich komatiites from northern norway komatiites of the karasjok greenstone belt northern norway show two unusual features they have certain compositional differences compared with other komatiites and they are largely volcaniclastic in origin their geological setting suggests that the komatiites were crupted into shallow water thus permitting phreatomagmatic eruption in a small ocean basin that opened in the baltic shield the major oxides except for tio2 the trace elements y sc v heavy rare earth elements hree cr co ni and the platinum group elements pge cover similar ranges to those observed in other komatiites but tio2 sm zr and hf ti associated elements tae are enriched compared with abundances commonly reported for komatiites thus the karasjok komatiites have interelement ratios 2 to 3 times greater than chondritic between the tae and the hree pge sc v y al hre associated elements hae the light rare earth elements lree ta and th are enriched in some samples relative to ti sm zr and hf but are depleted in others one group of rocks that is similar to the karasjok komatiites both in terms of geological setting and geochemistry is the baffin bay picrites the reason for the high concentrations of tae in the karasjok komatiites could be that they formed at lower degrees of partial melting than most komatiites the greater than chondritic tae hae ratios indicate that garnet was a residual phase during their formation requiring that the melt formed at a pressure greater than 40 kb a model involving decompression melting of a mantle plume rising in a rifting environment can explain the main features of the karasjok komatiites

holocene tree line dynamics and inferred climatic changes in the abisko area northern sweden based on macrofossil and pollen records lake sediment records of pollen and macroscopic plant remains of terrestrial origin provide evidence of long term changes in forest composition close to the altitudinal tree line in the abisko area northernmost sweden a dominance of mountain birch betula pubescens ehrh ssp tortuosa ledeb nyman with a field layer of ferns grasses and sedges suggests that an oceanic climate with relatively high precipitation existed during the early holocene macrofossils of mountain birch were found 300 400 m above the present tree line which corresponds to a 1 5 2 c higher summer temperature than at present scots pine pinus sylvestris was present to some extent at altitudes above its present limit during the early holocene a pronounced expansion of pine took place above its present limit around 6300 cal bp 5500 bp this is interpreted as a result of successively drier and more continental climatic conditions a decreased abundance of pine from c 5200 cal bp 4700 bp followed by a gradual retraction of

stable isotope stratigraphy of holocene speleothems examples from a cave system in rana northern norway high precision tims u series dates and continuous stable oxygen and carbon isotope profiles of a 4000 year stalagmite record from rana northern norway are presented and compared with data from two other speleothems from the same cave the dating results yield ages from 3875 34 to 296 3 years before ad2000 with 2s errors from 0 5 to 1 the overall growth rate is 35 mm ka corresponding to a temporal resolution of 29 years mm the stalagmite is tested for isotopic equilibrium conditions where all hendy tests except one indicate isotopic equilibrium or quasi equilibrium deposition both the stable oxygen and carbon isotope records reveal a strong and abrupt enrichment in the near top measurements this corresponds in time to the opening of a second cave entrance in the late 1960s which caused changes in the cave air circulation the stable oxygen isotope signal is enriched compared to the modern value over the last 300 years indicating a negative response to temperature changes likewise the stable carbon isotope record is enriched in this period however both of the stable isotope records are shown to be significantly enriched compared to the isotope ranges displayed by other stalagmites in the same cave and this questions the reliability of the proxy records derived from the presented stalagmite still a general good correspondence of large scale fluctuations is found between the three stable oxygen isotope records from this cave the stable carbon isotope records show large variations within the cave and are believed to be governed by soil zone conditions percolation pathways and possibly driprates q 2001 elsevier science b v all rights reserved

two komatiitic pyroclastic units superior province northwestern ontario their geology petrography and correlation two archean komatiitic pyroclastic rock units occur on opposite sides of the quetico fault in northwestern ontario the eastern unit the dismal ashrock is located 3 km north of atikokan ontario on the north side of the quetico fault within the wabigoon subprovince of the superior province it is part of a suprascrustal sequence the steep rock group the grassy portage bay ultramafic pyroclastic rock unit gup is located 100 km to the west on the south side of the quetico fault and is part of an overturned succession comprising mafic metavolcanic rocks gup and metasedimentary rocks the dismal ashrock dips steeply is little deformed has undergone greenschist metamorphism and is divided into komatiitic lapilli tuff komatiitic volcanic breccia komatiitic volcaniclastic rocks and a mafic pillowed flow gup outcrops form an arcuate fold interference pattern are strongly deformed and have undergone amphibolite metamorphism gup is divided into komatiitic lapilli tuff and komatiitic volcanic br

a quantitative holocene climatic record from diatoms in northern fennoscandia abstract a diatom based calibration model for predicting summer temperatures was developed using climatically sensitive subarctic lakes in northern fennoscandia the model was applied to a sediment core from a treeline lake to infer trends in holocene climate the record exhibits long term variations as well as a series of shorter term fluctuations on a time scale of centuries summers were warmest in the area about 6200 cal yr b p and featured distinct cooling episodes around 8300 7200 4200 3000 and 400 cal yr b p most of these coinciding with some known climate events e g the 8200 cal yr b p event and the little ice age the similarity of the observed shifts with the pacings of climate events from marine and ice core records represents evidence for coupled ocean atmosphere forcing of the regional climate

a multiple cave deposit assessment of suitability of speleothem isotopes for reconstructing palaeo vegetation and palaeo temperature the suitability of speleothems for interpreting palaeoclimate is typically determined by using either the hendy test overlapping analysis or long term cave environment monitoring however in many cases these methods are not applicable because a speleothem lacks clearly traceable layers for the hendy test it is difficult to obtain an overlapping speleothem nearby or long term cave monitoring is impractical the authors propose a multiple cave deposit approach to assess the suitability of speleothems for palaeoclimate study speleothems collected from two sites within raccoon mountain cave tennessee usa exhibit remarkable spatial variation 13c 10 3 to 2 2 over a relatively short distance ca 260 m drip water 18o values exhibit a seasonal precipitation signal at site 1 and an annual signal at site 2 combining field observations water isotope analysis and trace element data the authors propose that the speleothem formation at site 1 and site 2 tapped distinct sources of co2 i co2 derived from overlying soils for site 1 and ii limestone dissolved inorganic carbon induced by ground water dissolution for site 2 using fresh cave deposits modern speleothem 13c 100 c3 vegetation as an analogue a simple model was developed to estimate land surface vegetation for speleothems the speleothem formation temperature estimated using fresh cave deposit 18o values generally reflects the mean annual temperature in this region this study indicates that spatial variations in carbon isotopes could be caused by different carbon sources dominating in different parts of the cave which should be taken into consideration by researchers when using speleothem 13c values to reconstruct temporal palaeo vegetation changes this study demonstrates a practical sampling strategy for verifying suitability of speleothems for palaeo vegetation and palaeo temperature reconstructions by analysing multiple cave deposits especially for cases in which the hendy test parallel sampling and long term monitoring of cave environment are not feasible

speleothems and climate a special issue of the holocene speleothems cave dripstones are formed as a part of the meteoric water cycle and therefore vari ations in their growth rate and composition reflect environmental changes on the land surface above the cave since they are continental deposits and possess a remarkably accurate dating potential using tims u series techniques speleothems are important palaeoclimatic archives for the terrestrial environment complementing the marine and ice core records the climatic proxies that can be deciphered from speleothems are growth rate stable isotope composition d18o d13c organic humic matter and trace element composition as well as luminescent laminae which may display annual rhythms the nine papers in this special issue oftheholocene present the latest results in palaeoclimatic analysis from speleothems

an extensional fault model for the early development of greenstone belts with reference to a portion of the abitibi belt ontario canada abstract detailed geological mapping of a small part of the archaean abitibi greenstone belt northwestern ontario suggests that the mafic and ultra mafic lavas were extruded in a submarine environment in which the volcanism was intimately associated with deformation of the growing volcanic pile the deformation led to the subsidence and progressive tilting of the lavas and to the development of discontinuities a review of selected areas of quaternary volcanism suggests that subsidence of the lava pile during volcanism is not unusual and that activity is frequently also associated with normal faulting in both volcanic and non volcanic extensional regimes deformation is dominated by the development of listric faults we argue that greenstone belts such as the abitibi were formed in extensional regimes and we show that a simple geometric model involving fissure volcanism and synvolcanic rotation of the lavas on listric faults accounts for the major primary features of greenstone belts and for some associated geophysical properties

archean layered mafic ultramafic intrusions in the west pilbara craton western australia a synthesis of some of the oldest orthomagmatic mineralizing systems in the world considerable exploration interest has been generated by the platinum group element pge and ni cu potential of the archean layered mafic ultramafic intrusions in the west pilbara craton western australia the munni munni intrusion contains the largest resource of pge associated with a layered intrusion in australia and the radio hill and mount sholl intrusions host significant resources of ni cu co sulfides titaniferous magnetite layers remobilized sulfides and structurally controlled hydrothermal polymetallic deposits have also been a focus for exploration in recent years the ca 2 9 ga munni munni andover radio hill mount sholl and sherlock layered intrusions are a cogenetic suite of high level 5 kbars bodies that represent some of the oldest mineralizing systems of their type in the world although they display similar field relationships and mineralogical geochemical and isotopic features their contrasting chalcophile metal distribution patterns show that the timing and mechanism of the s saturation event were critical for the development of pge enriched sulfide bearing layers and basal segregations of base metal sulfides the intrusions form thick 5 5 km dikelike bodies or relatively thin 0 5 2 km sheets and sills emplaced at different levels along major lithological discontinuities in the upper crust rhythmically layered ultramafic components are generally thinner than and occur along the northern sides of more massive overlying mafic components the ultramafic zones consist of dunite lherzolite wehrlite olivine websterite clinopyroxenite and websterite inverted pigeonite gabbronorite magnetite gabbro olivine gabbro anorthositic gabbro and anorthosite comprise the mafic sequences olivine and clinopyroxene were generally the first minerals to crystallize except in the andover intrusion where orthopyroxene preceded clinopyroxene and possibly reflects greater contamination of the parent magma by felsic crustal material the crystallization of chromite was inhibited in the ultramafic zones by the partitioning of cr into early crystallizing clinopyroxene thus downgrading the potential for pge chromite associations the pge mineralization in the munni munni intrusion occurs in the upper levels of a porphyritic plagioclase websterite orthocumulate layer directly below the ultramafic gabbroic zone contact mineral compositional trends and nd isotope data indicate that a pd pt au enriched s undersaturated magnesian basaltic magma was frequently injected into a small magma chamber during formation of the ultramafic zone a major influx of more fractionated s saturated tholeiitic gabbroic magma related to the resident magnesian magma rapidly inflated the chamber and induced turbulent magma mixing that resulted in the formation of the pge bearing porphyritic websterite layer in contrast the parent magmas that formed the mount sholl radio hill andover and maitland intrusions were saturated in s before they were emplaced into the magma chambers in these intrusions gravitational and structural controls were important for the concentration of pge poor 5 400 ppb pt pd au massive ni cu co sulfides in depressions and structural embayments along the basal contacts beneath the thickest sequences of mafic ultramafic cumulates the parent magmas to the west pilbara intrusions were siliceous high magnesian basalts of al depleted komatiitic affinity barberton type with 9 to 12 percent mgo 15 to 25 ppm sc 12 to 18 ppm y low al2o3 tio2 ca 11 or half chondrite ratios and light rare earth enrichment chondrite normalized la sm 2 7 la lu 9 0 they were generated with garnet in the residual asthenospheric mantle with probable involvement of a pre 3 0 ga subduction modified lithospheric mantle isotopic and geochemical modeling suggests that the magmas were contaminated by ca 3 0 to 3 3 ga archean tonalitic to granodioritic crust before being emplaced into high level magma chambers

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

a comparison of settling and sieve techniques for the analysis of bioclastic sediments this paper examines differences in the use of sieve and settling techniques for the determination of textural parameters of grain size distributions for 30 bulk bioclastic reefal deposits and examines the interpretive use of the results a comparison of results of the key textural parameters shows that sieve size estimates deviate from settled size determinations of mean grain size and dispersion values by up to 2 and up to 1 5 phi units respectively these differences are explained by the different grain properties measured by the two techniques exacerbated by the heterogeneous character of bioclastic deposits changes in sample components which control grain shape and grain bulk sample density also influence the magnitude of size and dispersion differences observed differences are discussed in relation to interpretation of the depositional environment and hydraulic regime leading to the conclusion that sieve results can grossly distort depositional and energy processes operating within bioclastic environments in contrast settled size estimates an index of deposit hydraulic behaviour show that bioclastic sediment transport systems operate within a much narrower energy regime than sieve sizes suggest hydraulic size estimates are considered to provide a better tool with which to interpret sedimentary processes in bioclastic environments

pb isotopic compositions of archean komatiites and sulfides abstract pb isotopic compositions were measured in komatiites and other volcanic rocks from several archean greenstone belts and in magmatic and exhalative sulfides associated with these volcanics thin komatiite flows generally yielded pb pb isochron ages consistent with other geochronological or geological information but thicker basaltic flows gave ages that are too young these results suggest that the thin komatiite flows were hydrothermally altered during eruption and that this event is recorded by the pb pb age thicker basaltic flows resisted alteration during eruption but were affected by later events their pb pb ages probably correspond to the time of metamorphism and not to the time of emplacement magmatic and exhalative sulfides from the abitibi belt in canada fall on the same trend in the 207 pb 204 pb 206 pb 204 pb diagram as komatiites basalts sedimentary rocks and k feldspars from granites the calculated 1 value is 7 8 0 1 a similar suite of rocks and minerals from the kambalda area in australia has distinctly higher 207 pb 204 pb and a higher 1 of 8 3 nd isotopic data demonstrate that some kambalda rocks are highly contaminated with older continental crust the differences in initial pb isotopic compositions are attributed to the presence or absence and the age of underlying granitoid basement kambalda greenstones are underlain and contaminated by old 3 0 ga granitoid crust but significantly older granitoid basement appears absent from the abitibi belt the pb isotopic compositions of kambalda greenstones are dominated by the crustal component and do not represent the composition of the mantle source of these rocks the abitibi greenstones are not highly influenced by crustal contamination and their pb isotopic compositions may reflect those of archean mantle

palaeolimnological and sedimentary responses to holocene forest retreat in the scandes mountains west central sweden a suite of analyses was performed on sediments accumulated duringthe last 10 700 years in lake spaime a small hydrologically open water body in the modern alpine tundra zone of the scandes moun tains west central sweden the study aimed to evaluate 1 the nature of climate changes that forced the late holocene loweringof altitudinal tree limit in the region the timingof which is known from prior stu dies based on radiocarbon dating of subfossil wood and 2 the impact of these vegetational changes on an aquatic ecosystem arboreal pollen and plant macrofossil data confirm the persistence of trees in the lake catchment at least from c 9700 cal bp until c 3700 cal bp although growing season temperature is com monly believed to be the dominant factor drivingboreal forest tree limit variations in the reg ion a chir onomid based reconstruction of mean july air temperature suggests that local deforestation during the late holocene was not accompanied by a significant cooling the tree limit retreat was more likely caused by increasing effective moisture and declining length of the growing season the ecohydrological response of lake spaime to this combination of climate and vegetational changes included a decline in primary pro ductivity as indicated by an abrupt decrease in sediment organic matter content while associated increases in organic d 13 c d 15 n and c n point to diminished fluxes and altered balance of catchment derived nutrients followingdeforestation the decline in aquatic productivity is also marked by a distinct change in the mineral magnetic properties from a high magnetic concentration assemblage dominated by fine grained magnetite of biogenic origin to one dominated by background levels of coarse grained detrital magnetite

stable isotope variations in stalagmites from northwestern sweden document changes in temperature and vegetation during the early holocene a reply to hammarlund and edwards in a comment on the paper by sundqvist et al 2007a hammarlund and edwards suggest that the oxygen isotope signal of the speleothem records k1 and l4 from northwestern sweden as well as for the earlier published stalagmite sg93 from northern norway should mainly reflect variation in the 18o of mean annual precipitation the main argument used by the authors is that the sg93 18o record should show remarkable similarities with the lacustrine carbonate 18o record from lake tibetanus the similarities between sg93 and lake tibetanus are mainly seen for the period between 10 and 9 ka bp which is a period where both records have higher 18o values compared with later in the holocene if true this would indicate that temperatures in northern scandinavia would have reached their holocene maximum between 10 and 9 ka bp which is contrary to what has been reported from other archives in the region which place the holocene climatic optimum somewhere between 8 and 5 ka bp several factors affect the 18o of

the gisp2 δ18o climate record of the past 16 500 years and the role of the sun ocean and volcanoes measured 18o 16o ratios from the greenland ice sheet project 2 gisp2 ice core extending back to 16 500 cal yr b p provide a continuous record of climate change since the last glaciation high resolution annual 18o 16o results were obtained for most of the current millennium a d 818 1985 and record the medieval warm period the little ice age and a distinct 11 yr 18o 16o cycle volcanic aerosols depress central greenland annual temperature 1 5 c maximally and annual 18o 16o for about 4 yr after each major eruptive event on a bidecadal to millennial time scale the contribution of solar variability to holocene greenlandic temperature change is 0 4 c the role of thermohaline circulation change on climate problematic during the holocene is more distinct for the 16 500 10 000 cal yr b p interval analogous to 14c age calibration terminology we express time in calibrated cal yr b p a d 1950 0 cal yr b p the oldest dryas bolling older dryas allerod younger dryas sequence appears in great detail bidecadal variance in 18o 16o but not necessarily in temperature is enhanced during the last phase of lateglacial time and the younger dryas interval suggesting switches of air mass transport between jet stream branches the branched system is nearly instantaneously replaced at the beginning of the bolling and holocene at 14 670 and 11 650 cal yr b p respectively by an atmospheric circulation system in which 18o 16o and annual accumulation initially track each other closely thermodynamic considerations of the accumulation rate temperature relationship can be used to evaluate the 18 o 16o temperature relationship the gisp2 ice layer count years of major gisp2 climate transitions also support the use of coral 14c ages for age calibration

marine transgressions in the west coast of saudi arabia red sea between mid pleistocene and present abstract marine abrasion terraces cut in coralline limestone formations are to be noticed at various elevations in the coastal plain of the west coast of saudi arabia in between jeddah and yanbu three prominent terraces occur at altitudes of 1 3 and 10 m above the present level coral limestone samples from the terraces were dated by the carbon 14 method the radiometric ages reveal four marine transgressions in the west coast of saudi arabia eastern red sea from the mid pleistocene to present sea level maxima were recorded at about 31 000 16 600 18 100 9980 yrs b p and mid holocene the absolute altitude of the sea levels during the transgressions could not be evaluated because of the tectonic instability of the region however it is evident that relative to the first marine transgression mid wurm interglacial upto 31 000 yrs b p the successive transgressions in the west coast of saudi arabia occurred at progressively lower levels

late pleistocene stalagmite growth in wolkberg cave south africa little is known about the sequence of climate and environmental change in southern africa during the last glacial period in spite of the intimations from records such as antarctic ice cores and archaeological sites that very marked changes took place which would have had profound effects on vegetation and animal distributions across the sub continent high resolution semi continuous climate and environmental records can be extracted from suitable cave speleothems speleothems are reasonably abundant in southern africa but their occurrence is patchy in time and space and the records can be difficult to interpret here we report our assessment of the stalagmite w5 from wolkberg cave in the northeastern part of south africa as an archive for glacial period climatic and environmental shifts the cave is located at 1450 m asl in the dolomitic limestones of the transvaal system in an area currently dominated by c4 grass vegetation nine u th dates show growth from 58 to 46 ka and a second brief phase ca 40 ka indicating that the available moisture was sufficient to allow speleothems to form the 18o and 13c values along the growth axis show variability in the order of 2 for the former while variability in the latter is characterized by a shift from values near 2 in the older section to 2 or more in the younger part these high 13c values are probably the combined result of co2 degassing of the percolating soil water prior to the carbonate precipitation in the cave chamber the increasing dominance of c4 over c3 vegetation and the high percentage of aragonite towards the stalagmite s top the retrieved data point towards increasingly drier and colder conditions during the growth period of the stalagmite furthermore the high frequency variations of 18o values indicate the presence of short term climate oscillations that are probably linked to shifts of the intertropical convergence zone

calibration of the speleothem delta function an absolute temperature record for the holocene in northern norway the speleothem delta function sdf provides a new transfer function between the d18o signal of speleothem calcite and surface ground temperature the function is based on physical principles relating d18o of the calcite to thermodynamic fractionation and to the dripwater function which in turn relates d18o of dripwaters to that of the local precipitation and thus to the modification of source water in relationship to the geographical position of the site the sdf must be calibrated against at least two reliable and well dated palaeotemperature points the end product is a reconstruction of absolute cave and surface temperatures the technique is tested using a holocene speleothem from north norway sg93 dated by 12 tims u th dates the reconstructed temperature curve is presented and compared with the gisp2 ice core record and with the historic record in both cases the correlation with sg93 is impressive indicating the validity of the technique

on solar forcing of holocene climate evidence from scandinavia the focus of this study is the possible correlation between changes in the climate of scandinavian and changes in solar irradiation reliable information about holocene climatic change in sweden and norway is currently available from two main sources the 14c dating of pine wood retrieved from above the present pine tree limit and studies of glacier variations based on proglacial lacustrine sediments and on moraines the reconstructed alpine tree limit reveals that summer temperature in general was warmer during the early holo cene than it was during the late holocene superimposed on this general trend are several fluctuations of a few hundred years duration relatively cold periods with a duration of the order of 300 600 years occurred frequently during the holocene in this paper dates of the major climatic events are compared with an index of solar activity the so called 14c anomalies for most of the last 9000 years a good correspondence is demonstrated between the timing of cold events in scandi

contemporary sedimentation in the cocos keeling islands indian ocean interpretation using settling velocity analysis abstract textural parameters of grain size distributions derived from sieve analysis and component analysis have been used to the exclusion of other methods to examine sedimentary processes in modern reef environments however because these methods do not reflect the hydraulic behaviour of bioclastic sediment this study uses settling velocity analysis accounting for grain size density and shape variability and component analysis of separated settling velocity fractions to describe and differentiate bioclastic deposits and infer transport pathways in the cocos keeling islands an indian ocean atoll principal component and cluster analysis of settling 251 samples and component 90 samples characteristics discriminated eight settling velocity and five component classes a derived settling velocity classification reflecting the hydraulic properties of the sediments describes a lagoonward gradient from those with fast settling characteristics on the outer reef flat to those with moderate settling character on sand aprons the active sediment transport system is constrained between these zones component analysis of bulk samples identifies two broad sediment types 1 those with reef derived components found throughout the active transport zone reef flat to sand aprons and 2 those characterised by greater proportions of gastropod and halimeda fragments which are produced and deposited in situ in the lagoon component analysis of settling fractions further resolves details of sediment movement in the active transport zone sediment is transported from the productive reef flat to passage entrances which form initial depositional environments slower settling material is selectively transported from the entrances through the passage conduits to passage exit environments these form the main depositional areas under mean energy conditions during moderate to high energy events sediment is flushed from the passage to sand apron zones with slower settling grains deposited in the deep lagoon sinks results show that settling velocity analysis and component analysis of settling fractions can resolve the nature of sediment transport patterns in reef environments at a much finer scale than studies in which analysis is based on grain size distributions

human induced changes in sedimentary facies and depositional environments sarum area red sea coast saudi arabia this paper aims to study the environmental impact of the human inference on the coastal zone of sarum area red sea coast saudi arabia in the past the study area was occupied by coastal lagoons that were connected with the sea with several inlets change detection technique based on multi date satellite images in the last 44 years indicated the occurrence of environmental changes accompanied the construction of the main asphaltic road of the red sea that separated some coastal lagoons at the studied area from the red sea field investigation and litho and bio facies distribution indicated the existence of six lateral facies types gypsum microbial mats halite quaternary coral reef terrace bioclasts and siliciclastic sand sheets the lateral distribution of these facies is related to the following changes 1 disconnection between the coastal lagoons and the sea 2 extensive contraction of the coastal lagoons and formation of saline ponds 3 exposure of the submerged quaternary coral reef terrace 4 increasing of the salinity of the ponds up to 270 and 5 deposition of the evaporitic facies types gypsum and halite over intertidal and subtidal marine carbonates based on the above mentioned criteria the human activity leads to environmental changes in the sarum area from coastal lagoons dominated with carbonate deposits into hypersaline ponds dominated with evaporitic deposits

spinifex and swirling olivines in a komatiite lava lake munro township canada abstract spinifex veins and veins filled with swirling tabular olivine grains intrude the upper part of a 120 m thick lava lake in munro township ontario canada these veins are 20 200 cm wide tens of metres long and are oriented roughly parallel to the upper surface of the lava lake the spinifex texture differs from that found in simple layered komatiite flows rather than increasing downwards the size of skeletal olivine grains is greatest in the centres of the veins or varies irregularly upper contacts meander and veinlets penetrate overlying rock lower contacts are transitional the other type of vein contains 50 70 of 5 mm long hopper olivine grains whose orientation varies widely to produce a swirling contorted fabric both types of vein are believed to have formed when lava from the centre of the lake flowed into fractures in the solidified crust the lava lake has a dunitic lower portion and an olivine porphyry upper portion the composition of chill samples the compositions of olivine phenocrysts and variations in major element abundances throughout the unit are used to show that the lava originally was komatiite with about 22 mgo the lava lake is overlain by mafic scorias and breccias with moderate vesicularity and welding structures suggesting eruption in shallow water

controls of the eruption of mafic and ultramafic lavas ruth well ni cu prospect west pilbara the markedly bimodal early archean volcanic suite exposed near the ruth well ni cu prospect west pilbara shows the intimate interfingering and interlayering of spinilex textured komatiite mgo 30 20 and komatiitic basalt mgo 14 10 implying closely spaced and or closely timed eruptions of these two different extrusive products the favored hypothesis involves derivation of basalt from komatiite in transient magma chambers from which only the lower density basalt can be erupted parental komatiite is erupted directly from depth during periods of higher regional stress or in areas lacking magma chambers although metamorphic alteration of these magma products renders compositional constraints less firm derivation of basalt from komatiite in this particular case by fractional crystallization is supported by data for mgo ni ti and zr rare pyroclastic ultramafic rocks are not part of this sequence but may represent catastrophic mixing of parental and daughter products

a 11 000 yr palaeotemperature reconstruction from the southern boreal zone in finland abstract the ecotone between the boreo nemoral hemiboreal and the southern boreal vegetation zones constitutes the northern distributional limit of a number of thermophilous tree species in northern europe and is to a large extent controlled by climatic conditions we present a quantitative annual mean temperature reconstruction from a high resolution pollen stratigraphy in southern boreal finland using a pollen climate calibration model with a cross validated prediction error of 0 9 c our model reconstructs low but steadily rising annual mean temperature from 10 700 to 9000 cal yr bp at 8000 4500 cal yr bp reconstructed annual mean temperature reaches a period of highest values holocene thermal maximum with particularly high temperatures 2 0 1 5 c higher than at present at 8000 5800 cal yr bp from 4500 cal yr bp to the present day reconstructed annual mean temperature gradually decreases by ca 1 5 c comparison of present results with palaeotemperature records from the greenland ice cores notably with the northgrip 18 o record shows marked similarities suggesting parallel large scale holocene temperature trends between the north atlantic and north european regions the verification of the occurrence timing and nature of the short term temperature fluctuations during the holocene in the southern boreal zone in europe requires replicate high resolution climate reconstructions from the region

the marine record of deglaciation from the continental margin off nova scotia continental margin sediments off nova scotia accumulate at high rates up to 360 cm kyr 1 and contain a history of millennial scale environmental changes which are dominated by the proximity of the laurentide ice sheet during the latest quaternary using stable isotope ratios of oxygen accelerator mass spectrometer radiocarbon dating micropaleontology and sedimentology we document these changes in six piston cores ranging in water depth from 450 to 4300 m we find that maximum 18o in n pachyderma occurred about 15 ka and preceded the maximum abundance of this species in these cores by 1000 years between 13 and 14 ka we find a second peak in abundance of n pachyderma minimum 18o and two pulses of ice rafting the sediment lithology supports terrestrial studies which indicate that there was a general withdrawal of ice beyond the upper paleozoic and mesozoic red beds by 14 ka in southeastern canada so the ice rafting events between 13 and 14 ka probably reflect ice stream activity in the st lawrence valley the younger dry as event is recognized as a peak in abundance of n pachyderma and ice rafting dated as 11 3 ka but meltwater discharge to the gulf of st lawrence was either too small or occurred over too long a time to leave a distinct 18o minimum off nova scotia at 7 1 ka in the middle of holocene warming we find a third peak in abundance of n pachyderma and another 18o minimum but no ice rafting we interpret these data as evidence of a late occurring meltwater event which if correct could have originated in the great lakes in the labrador ungava region or in both the final millennial scale phenomenon off nova scotia is the onset of neoglaciation marked by increased ice rafting and increased n pachyderma beginning about 5 kyr ago

holocene temperature changes in northern fennoscandia reconstructed from chironomids using bayesian modelling the recently developed bayesian multinomial calibration model bummer was applied to the fossil chironomid assemblages of a lake situated at the present tree line in northern fennoscandia to reconstruct patterns in holocene climates the results are compared with inferences derived using non bayesian weighted averaging partial least squares regression the reconstruction exhibits both long term trends as well as a series of shorter term oscillations abrupt climatic excursions were particularly characteristic for the early holocene period with cooling episodes around 9200 8600 and 8200 cal yr bp the interval from ca 8000 to 5800 cal yr bp appeared to be warm and stable but was followed by a pronounced climatic cooling around 5800 cal yr bp leading to a relatively long lasting mid holocene temperature minimum between ca 5800 and 4000 cal yr bp the reconstruction during the latter part of the holocene is relatively featureless which may partly be due to gradual shallowing of the lake by sedimentation that may have affected chironomid compositions thereby masking the climate signal the major climatic patterns in our reconstruction agree well with inferences from greenland ice and marine sediments and are also in line with the previous reconstructions based on diatoms and pollen from the same core although the finer scale variations reflected by the three proxies do not always match the overall results provide evidence for climatic complexity during the holocene epoch and demonstrate that bayesian modelling is highly suitable for reconstruction purposes

holocene humidity changes in northern finnish lapland inferred from lake sediments and submerged scots pines dated by tree rings conclusive evidence for a rise in water levels has been found in connection with lake sediment studies undertaken partly in collaboration with the pine megafossil sampling and dendrochronological work in northern finnish lapland the change in lake level stands is shown by slow sedimentation rate in the early to mid holocene and an increase thereafter these data indicate a regional rise in water levels during the latter part of the holocene following a relatively dry period between 8000 and 4000 bp synchronous changes also indicating rising water levels have been observed in the diatom and cladoceran assemblages of the sediment cores subfossil scots pines pinus sylvestris l have been preserved in large quantities in small lakes in lapland because in many cases the rising water level has inundated the trunks after death the position of the subfossil trunks and stumps often indicates that the pines have been growing on dry land at the sides of the lakes in which they are now submerged traces of

wave and tidal current sorting of sand on a wide surf zone beach abstract experiments with fluorescent tracers have shown that on a wide surf zone beach selective transport of different grain size material may play an important role in the sorting of beach sediments by waves and tidal currents in the alongshore direction the results have shown that at the mid tide level small particles in general move more rapidly than coarse material although there is evidence to suggest that with increasing particle size the net rate of movement passes through a minimum such behaviour would be consistent with komar s 1977 observations and suggestion of a minimum corresponding to the transition from bedload to suspended load transport of sediment across the beach fluorescent tracer samples have shown onshore offshore sorting about the mean position of the breaker line with coarse material moving offshore and fine material moving onshore

pyroclastic rocks another manifestation of ultramafic volcanism on gorgona island colombia tertiary ultramafic volcanism on gorgona island colombia is manifested not only by komatiite flows but also by a more voluminous sequence of tuff breccias which is cut by comagmatic picrite dikes the ultramafic pyroclastic rocks are chaotic to stratified mixtures of angular to subrounded glassy picritic blocks and a fine grained volcaniclastic matrix that consists primarily of plastically deformed glassy globules the entire deposit is interpreted to have formed by an explosive submarine eruption of phenocryst laden picritic magma mgo contents of tuff breccias and picrite dikes range from 21 to 27 wt relative to nearby komatiite flows these rocks are mgo rich and feo tio2 and ni poor hree concentrations are very low seven times chondrite and similar to those of the komatiites whereas the lree are extremely fractionated ce sm n 0 2 indicating derivation from a more highly depleted mantle source region nd isotopic data suggest a cogenetic relationship between the picritic magma that formed the tuff breccia and associated dikes and that which produced the komatiite flows nevertheless pb isotopic data as well as whole rock geochemistry preclude such a connection either due to olivine fractionation accumulation or to different degrees of partial melting these ultramafic rock types crystallized from magmas which most likely were extracted from distinct mantle source regions

july mean temperature and annual precipitation trends during the holocene in the fennoscandian tree line area pollen based climate reconstructions july mean temperature and annual precipipation during the last 9900 cal yr bp were recon structed from pollen assemblages preserved in a sediment core from northern finland quantitative recon structions were performed using a modern pollen climate calibration model based on weighted averaging partial least squares regression the predictive ability of the model was evaluated against modern meteoro logical data using leave one out cross validation the prediction error for july mean temperature is c 1 0 c and for annual precipitation 340 mm the july mean temperatures during the earliest holocene were low c 1 1 0 c and annual precipitation was high c 600 800 mm between 8200 and 6700 cal yr bp july mean temperatures reached their maxima 12 5 13 0 c which are c 1 4 1 7 c higher than at present at the same time precipitation decreased during the late holocene july mean temperatures declined and the last 2000 years have been the coolest since the early holocene precipitation has slightly increased the spatial coherence between our results and of several other climate reconstructions from northern europe indicates that the holocene climate was strongly influenced by north atlantic oceanic and atmospheric circulation patterns we propose that the distinctly oceanic climate of the early holocene was due to enhanced westerly latitudinal airflow which was replaced at c 8200 cal yr bp by a more meridional flow pattern and by the development of predominantly anticyclonic summer conditions

the use of the textural parameters of sand in studying the characteristics and depositional processes of coastal sediments south of jeddah saudi arabia abstract the subtidal sediments of four coastal environments beach swash zone lagoon and nearshore bar south of jeddah have been studied in terms of their textural characteristics and depositional process the skeletal grains are composed mainly of fragments of corals benthic foraminifera and different types of shells together with sand sized rock fragments and quartz and feldspar grains the skeletal material of the sediments has been derived from the mechanical breakdown of the adjacent reefs while the small clastic portion was provided from the hinterland by rivers bimodal and polymodal grain size distributions are common and can be attributed to heterogeneity in the types of skeletal debris the size distribution of such sediments suggests that the various processes that are responsible for their transportation and deposition are wave current and wind action the different energy conditions and the morphology of each coastal environment seem to be reflected in the characteristics of the sediments in each environment

rapid hydrological changes during the holocene revealed by stable isotope records of lacustrine carbonates from lake igelsjon southern sweden a holocene sediment sequence from lake igelsjon south central sweden was studied by stable oxygen and carbon isotope analyses of different carbonate components the deposit which covers the time span from ca 11 500 cal bp to the present was laid down in a small kettle hole lake the hydrological balance of which is presently dominated by groundwater flow isotopic records obtained on bulk carbonates originating mainly from summer produced calcitic algal encrustations exhibit several rapid shifts of more than 2parts per thousand likely reflecting pronounced hydrological variations corresponding isotopic data obtained on calcitic gastropod opercula from parts of the profile show subdued responses to major climatic shifts probably related to an extended calcification season the isotopic records were complemented by studies of modern isotope hydrology and our interpretations are based on a simplistic climate hydrology model in which variations in groundwater generation within the lake catchment produce changes in groundwater level and related adjustments of lake level and surface volume ratio of the basin during the ice free season assumed periods of decreased lake volume in a relatively dry climate low lake level are characterised by enrichment in o 18 and c 13 resulting from increased evaporation inflow ratio and atmospheric equilibration respectively in clear contrast to this situation intervals of more humid climatic conditions give rise to increased lake volume high lake level possibly surface over flow and relatively depleted isotopic ratios relatively humid conditions which may correlate to a wide spread cooling event recorded by various proxies across the north atlantic region are indicated by distinct isotopic shifts at ca 8300 and 8000 cal bp bracketing a period of o 18 depletion the period between ca 8000 and 4000 cal bp was characterised by relatively dry and stable climatic conditions whereas the subsequent part of the holocene experienced a more humid and variable climate following marked and coherent depletions in o 18 and c 13 at ca 4000 cal bp c 2002 elsevier science ltd all rights reserved less

a new approach to calculating holocene winter precipitation by combining glacier equilibrium line altitudes and pine tree limits a case stud from hardangerjokulen central southern norway at hardangerjokulen central southern norway detailed knowledge of the number age and magnitude of holocene glacier fluctuations is used to reconstruct variations in equilibrium line altitude ela for the last 10 000 years present and past elas are based on an accumulation area ratio aar of 0 7 and are adjusted for land uplift a synchronous relationship between advanced glacier positions and the highest pine tree limits pinus sylvestris l is demonstrated for the early to mid holocene in southern scandinavia which indicates that warm summers were compensated for by high winter precipitation based on pine tree limit fluctuations as a measure of mean ablation season temperature holocene variations in winter precipitation at hardangerjokulen have been calculated by substitution in the close exponential relationship between mean ablation season temperature and winter precipitation at the ela of norwegian glaciers setting the winter precipitation during the period ad 1961 1990 at 100 mean values

irregular glacial interstadials recorded in a new greenland ice core the greenland ice sheet offers the most favourable conditions in the northern hemisphere for obtaining high resolution continuous time series of climate related parameters profiles of 18o 16o ratio along three previous deep greenland ice cores1 3 seemed to reveal irregular but well defined episodes of relatively mild climate conditions interstadials during the mid and late parts of the last glaciation but there has been some doubt as to whether the shifts in oxygen isotope ratio were genuine representations of changes in climate rather than artefacts due to disturbed stratification here we present results from a new deep ice core drilled at the summit of the greenland ice sheet where the depositional environ ment and the flow pattern of the ice are close to ideal for core recovery and analysis the results reproduce the previous findings to such a degree that the existence of the interstadial episodes can no longer be in doubt according to a preliminary timescale based on stratigraphic studies the interstadials lasted from 500 to 2 000 years and their irregular occurrence suggests complexity in the behaviour of the north atlantic ocean circulation

a detailed 31 000 year record of climate and vegetation change from the isotope geochemistry of two new zealand speleothems abstract uranium series dating and stable isotope analyses of two speleothems from northwest nelson new zealand record changes in regional climate and local forest extent over the past 31 000 years oxygen isotope variation in these speleothems primarily represents changes in the meteoric waters falling above the caves possibly responding to latitudinal changes in the position of the subtropical front in the tasman sea seven positive excursions can be identified in the oxygen isotope record which coincide with periods of glacier advance known to be sensitive to northward movement of the subtropical front four glacier advances occurred during oxygen isotope stage 2 with the most extreme glacial conditions centered on 19 000 cal yr b p 2 an excursion in the oxygen isotope record from 13 800 to 11 700 cal yr b p provides support for a previously identified new zealand glacier advance at the time of the younger dryas stade but suggests it began slightly before the younger dryas as recorded in greenland ice cores carbon isotope variations in the speleothems record changes in forest productivity closely matching existing paleovegetation records on the basis of vegetation changes stage 2 glacial climate conditions terminated abruptly in central new zealand from 15 700 to 14 200 cal yr b p evidence of continuous speleothem growth at one site suggests that depression of the local treeline was limited to 600 700 m below its present altitude throughout the last 31 000 years

reconstruction of temperature in the central alps during the past 2000 yr from a δ18o stalagmite record the precisely dated isotopic composition of a stalagmite from spannagel cave in the central alps is translated into a highly resolved record of temperature at high elevation during the past 2000 yr temperature maxima during the medieval warm period between 800 and 1300 ad are in average about 1 7 8c higher than the minima in the little ice age and similar to present day values the high correlation of this record to d 14 c suggests that solar variability was a major driver of climate in central europe during the past 2 millennia d 2005 elsevier b v all rights reserved

holocene climate variability although the dramatic climate disruptions of the last glacial period have received considerable attention relatively little has been directed toward climate variability in the holocene 11 500 cal yr b p to the present examination of similar to50 globally distributed paleoclimate records reveals as many as six periods of significant rapid climate change during the time periods 9000 8000 6000 5000 4200 3800 3500 2500 1200 1000 and 600 150 cal yr b p most of the climate change events in these globally distributed records are characterized by polar cooling tropical aridity and major atmospheric circulation changes although in the most recent interval 600 150 cal yr b p polar cooling was accompanied by increased moisture in some parts of the tropics several intervals coincide with major disruptions of civilization illustrating the human significance of holocene climate variability c 2004 university of washington all rights reserved

stable isotope variations in stalagmites from northwestern sweden document changes in temperature and vegetation during the early holocene a comment on sundqvist et al 2007a we offer an alternative palaeoenvironmental interpretation of oxygen isotope data obtained on two early holocene stalagmite records from caves in the scandes mountains of northern sweden korallgrottan and labrintgrottan and the well known soylegrotta norway sg93 record with which they are compared that differs in several respects from that proposed by the authors contrary to viewing these as inverted palaeotemperature records we suggest that they primarily reflect changes in the delta o 18 of local annual precipitation modified by secondary temperature dependent variation in water calcite oxygen isotope fractionation at each of the three sites this is supported by the striking similarity over the entire holocene between the sg93 calcite delta o 18 record and the lacustrine carbonate delta o 18 record from lake tibetanus northern sweden which implies straightforward transfer of annual precipitation delta o 18 signals into cave drip waters recent studies of drip waters in korallgrottan also support this model this further enhances the value of cave deposits as palaeoclimate archives in this region and provides additional evidence of the sensitivity of the precipitation isotope thermometer to changes in atmospheric circulation patterns less

holocene climatic change reconstructed from diatoms chironomids pollen and near infrared spectroscopy at an alpine lake sjuodjijaure in northern sweden the results of a multiproxy study reconstructing the climate history of the last 9300 years in northern sweden are presented it is based on diatom chironomid and pollen analyses as well as near

centennial scale climate cooling with a sudden cold event around 8 200 years ago the extent of climate variability during the current interglacial period the holocene is still debated temperature records derived from central greenland ice cores show one significant temperature anomaly between 8 200 and 8 100 years ago which is often attributed to a meltwater outflow into the north atlantic ocean and a slowdown of north atlantic deep water formation this anomaly provides an opportunity to study such processes with relevance to present day freshening of the north atlantic anomalies in climate proxy records from locations around the globe are often correlated with this sharp event in greenland but the anomalies in many of these records span 400 to 600 years start from about 8 600 years ago and form part of a repeating pattern within the holocene more sudden climate changes around 8 200 years ago appear superimposed on this longer term cooling the compounded nature of the signals implies that far field climate anomalies around 8 200 years ago cannot be used in a straightforward manner to assess the impact of a slowdown of north atlantic deep water formation and the geographical extent of the rapid cooling event 8 200 years ago remains to be determined

texture and mineralogy of the surface sediments of sharm obhur west red sea coast of saudi arabia abstract the present paper deals with the study of the grain size characteristics and the mineralogy of the bottom and beach sediments of sharm obhur most of the sediments are in digenous carbonates with little terrigenous material a major part of the sharm is covered with coarse to medium grained sediments heavy minerals make up 5 to 15 of the samples and are mainly composed of amphiboles pyroxenes biotite epidote and opaques the heavy mineral suite is apparently derived mainly from metamorphic source rocks with minor contribution from basalts the content of high mg calcite decreases landward in the sharm due to more inorganic precipitation of carbonate in the form of aragonite the high content of calcite in the beach sands from the shoreline of the sharm shows that the calcite rich old reef limestones that crop out along the sharm contribute considerable material of the beach sediments kaolinite mixed layer chlorite vermiculite and illite are the dominant clay minerals the alluvium derived from the low grade metamorphic rocks and basalts of the jeddah group forms the source of the clay minerals

complexity of holocene climate as reconstructed from a greenland ice core glaciochemical time series developed from summit greenland indicate that the chemical composition of the atmosphere was dynamic during the holocene epoch concentrations of sea salt and terrestrial dusts increased in summit snow during the periods 0 to 600 2400 to 3100 5000 to 6100 7800 to 8800 and more than 11 300 years ago the most recent increase and also the most abrupt coincides with the little ice age these changes imply that either the north polar vortex expanded or the meridional air flow intensified during these periods and that temperatures in the mid to high northern latitudes were potentially the coldest since the younger dryas event

enriched komatiitic basalts from newton township ontario their genesis by crustal contamination of depleted komatiite magma lree enriched komatiitic basalts are commonly found in association with lree depleted komatiites this association is found in a sequence of late archaean lavas from newton township ontario the komatiitic lavas at newton township differ from most late archaean examples in that both the komatiites and the komatiitic basalts are depleted in al and in the hree the close association and distinctive al and hree depletions of the two lava types strongly suggest a common origin despite their contrasting lree patterns a model is proposed whereby the lree depleted komatiites represent the parental magma to the lree enriched komatiitic basalts the two being linked by a combination of crystal fractionation and crustal assimilation the composition of the contaminant is estimated by comparing the lree enriched komatiitic basalts with the evolved part of a thick layered komatiite flow that has similar major element chemistry the contaminant composition coincides closely with taylor mclennan s estimate of the composition of the archaean upper crust it is concluded that lree enriched komatiitic basalts can be produced from lree depleted komatiite parent magmas by combined assimilation and fractionation and that such a process best explains the geochemistry and nd isotopic features of most komatiitic basalts

up down or sideways emplacement of magmatic fe ni cu pge sulfide melts in large igneous provinces the preferential localization of fe ni cu pge sulfides within the horizontal components of dike sill lava flow complexes in large igneous provinces lips indicates that they were fluid dynamic tra

stable isotope variations in stalagmites from northwestern sweden document climate and environmental changes during the early holocene this paper presents two early holocene 9 6 5 9 ka bp high resolution stable isotope records of stalagmites from two caves in northwestern sweden korallgrottan and labyrintgrottan close similarities between the swedish records and a previously presented norwegian stalagmite oxygen isotope record emphasize the potential of scandinavian stalagmites to provide high resolution regional palaeoclimatic information the stable oxygen isotope records are interpreted to reflect the temperature evolution during the early holocene with a gradual warming from c 9 6 ka bp interrupted by cooler conditions at 8 5 8 0 ka bp the results indicate that the cooler conditions were driven by two to three abrupt cold events rather than one 8 2 event only except for these cold events the stalagmite oxygen isotope records show that temperatures in northwestern sweden were warmer than today between 9 6 and 5 9 ka bp and that during this period the interval between 7 8 and 5 9 ka bp seems to have been the warmest the hig

late deglaciation of the central labrador coast and its implications for the age of glacial lakes naskaupi and mclean and for prehistory the age of the marine limit and associated deglaciation has been estimated from relative sea level curves for the hopedale and nain areas of the central labrador coast as approximately 7600 200 and 8500 200 yr ago respectively these ages indicate that the ice margin remained on the coast for up to 3000 yr longer than previously estimated because the central coast is due east of glacial lakes naskaupi and mclean the earliest the lakes could have formed was 8500 200 yr ago with their largest phases being fully established only after 7600 200 yr ago this suggests that the age of the lakes and associated deglaciation of the central labrador ungava region is younger by at least 1500 yr than previously estimated a late glacial marine based ice mass in ungava bay that dammed the lakes collapsed ca 7000 yr ago within this time frame therefore the glacial lakes only existed for 500 yr the persistence of the laurentide ice sheet margin on the central labrador coast until 7600 yr ago probably restricted the northward movement of early prehistoric people into northern labrador

quantitative multiproxy assessment of long term patterns of holocene environmental change from a small lake near abisko northern sweden quantitative reconstructions are made of holocene changes in climatic and environmental conditions from analyses of pollen chironomids and diatoms in identical stratigraphic levels of a sediment c

high resolution paleotemperature proxy record for the last interglaciation based on norwegian speleothems two speleothems from a coastal lowland and an alpine cave site in northern norway grew in isotopic equilibrium during termination ii and marine isotope stage 5 150 000 80 000 yr b p as dated by the u series technique the stable isotope record 18o 13c displays a time resolution down to 20 yr the 18oc signal in the two speleothems appears to be mainly dominated by the meteoric signal i e there is a positive relationship between 18oc and temperature 18oc t 0 the fm 2 couplet a younger dryas type two step structure in termination ii at 132 000 5000 and 129 000 5000 yr is prominent in the speleothem record the record correlates well with details and gross features of the grip ice core and confirms the time scale and the unstable climate proposed for substage 5e the isotopic response in termination ii is delayed relative to the devil s hole record and is in accord with the specmap chronology but cooling at the end of substage 5e seems to be synchronous between devil s hole and the norwegian flowstones

biomass effects on stalagmite growth and isotope ratios a 20th century analogue from wiltshire england increases in calcite deposition rates combined with decreases in 13c and 18o in three modern stalagmites from brown s folly mine wiltshire england are correlative with a well documented re vegetation above the mine increased soil pco2 resulted in greater amounts of dissolved caco3 in the drip waters which consequently increased annual calcite deposition rates the absence of deposition prior to 1916 28 years after the mine was closed indicates that vegetation had not yet sufficiently developed to allow higher pco2 values to form in the soil lower 13c values through time may reflect the increased input of isotopically light biogenic carbon to the total dissolved inorganic carbon dic 18o decreased synchronously with 13c reflecting the increased importance of isotopically light winter recharge due to greater biomass induced summer evapotranspiration this is the first empirical demonstration that vegetation density can control stalagmite growth rates 13c and 18o contributing critical insights into the interpretation of these climate proxies in ancient stalagmites

timing equilibrium line altitudes and climatic implications of two early holocene glacier readvances during the erdalen event at jostedalsbreen western norway following the younger dryas the e rst evidence of glacial activity in southern norway in response to climatic change occurred during the early holocene when terminal moraines from the erdalen event formed beyond the position of later little ice age moraines in front of present outlet glaciers on both sides of the jostedalsbreen ice cap sets of pre little ice age marginal moraines have been morphostratigraphicallycorre lated with the erdalen event the lithostratigraphyin a peat bog at hellemyrane in jostedalen western norway provides e rm evidence for a two phase erdalen event associated with two glacier readvances of nigardsbreen at the preboreal boreal transition radiocarbon dates from the peat bog give age estimates for the two phases the e rst erdalen event readvance took place between 10 100 and 10 050 cal bp while the second occurred close to 9700 cal bp the lowering of the equilibrium linealtitude ela during these readvances is estimated using the little ice age ratio lr approach to be about 230 m and 215 m respectively the e rst readvance is attributed to an increase in winter precipitation while the second readvance may have been primarily caused by a marked drop in summer temperature which reactivated already existing ice masses

effects of solar forcing and north atlantic oscillation on the climate of continental scandinavia during the holocene abstract 10 000 year long varved sediment records from lakes nautajarvi and korttajarvi finland provide evidence of climate and environment oscillations at multi decadal to millennial timescales we used two independent methods to extract periodic features from these time series of clastic laminae and assess their statistical reliability analyses revealed that seasonal sediment fluxes correspond to environmental changes with statistically significant periodicities of 1500 1800 1000 600 800 nearly 300 nearly 200 150 170 nearly 90 and 47 years showing variable coherency with different climate forcing factors and other palaeoproxy records in the northern hemisphere results indicate that the holocene winter climate in continental scandinavia was forced by a combination of several factors at least by solar variability and the north atlantic ocean atmosphere circulation patterns with varying influences through time

reconstruction of holocene glacier history from distal sources glaciofluvial stream bank mires and a glaciolacustrine sediment core near sota saeter breheimen southern norway this study attempts to reconstruct the holocene glacier history of breheimen southern norway from four stream bank mire sites and a downstream lake sediment core near sota saeter based on lithostr

sequence stratigraphy of the archaean supracrustal belts of the pilbara block western australia abstract the stratigraphic succession of the 3580 2770 m y old granite greenstone terrain of the pilbara block is re assessed by the first and second order sequence stratigraphic techniques that are the standard for phanerozic terrains with the view to testing the conformity of stratigraphic cause and response a holistic tectonostratigraphic framework is presented that pairs the supracrustal and crustal rock records the resulting sequence scheme is tested against the cause of first order sequence cycles viz global sea level responses to supercontinent breakup and assembly three first order inter regional unconformities divide the stratigraphic succession of the supracrustal belts into four units of first order megasequence status in order of decreasing age these are named the warrawoona gorge creek roebourne and mount negri megasequences a total of 17 second order supersequences are also named although some may represent supersequence sets the megasequences and or their genetic crustal equivalents represent the preserved rock record of four megacycles of forearc arc and or back arc geotectonic evolution associated with the convergent margins of a pilbara continent individual supersequences are the rock record of separate second order basins or basin phases and reflect the different geotectonic components of each megasequence the four megacycles had respective longevities from oldest to youngest of 150 m y 230 m y 160 m y and 180 m y they are identical in their stratigraphic successions and predicted first order sea level cycles to phanerozoic first order tectono eustatic cycles and are interpreted as the same response to global tectonic change the warrawoona and gorge creek megacycles and the roebourne and mount negri megacycles are tectonogenetic pairs of the east pilbara and the west pilbara megacycle sets respectively the east pilbara megacycle set evolved over a period of 380 m y from 3490 ma to 3110 ma whereas the west pilbara megacycle set evolved over a period of 340 m y from 3110 ma to 2770 ma the two megacycle sets are identical in their longevity geotectonic components and predicted sea level cycles to convergent margin wilson and supercontinent cycles and are thereby interpreted individually as the oldest established records of the supercontinent cycle the implication of this interpretation is that a steady state global tectonic regime has been in operation from early in earth s history which has important consequences for theoretical modelling of the earth s early tectonic style and secular changes in its geochemical regime

changes in continental and sea salt atmospheric loadings in central greenland during the most recent deglaciation model based estimates by fitting a very simple atmospheric impurity model to high resolution data on ice accumulation and contaminant fluxes in the gisp2 ice core we have estimated changes in the atmospheric concentrations of soluble major ions insoluble particulates and 10 be during the transition from glacial to holocene conditions for many species changes in concentration in the ice typically overestimate atmospheric changes and changes in flux to the ice typically underestimate atmospheric changes because times of increased atmospheric contaminant loading are also times of reduced snowfall the model interpolates between the flux and concentration records by explicitly allowing for wet and dry deposition processes compared to the warm preboreal that followed we estimate that the atmosphere over greenland sampled by snow accumulated during the younger dry as cold event contained on average four seven times the insoluble particulates and nearly seven times the soluble calcium derived from continental sources and about three times the sea salt but only slightly more cosmogenic 10 be

early mixed water dolomitization in the pleistocene reef limestones west coast of saudi arabia abstract raised pleistocene reef limestone characterizes the western coastal plain of jeddah on the eastern margin of the red sea soon after the mid pleistocene regression the subaerially exposed limestone was subjected to meteoric processes during which mg calcite was converted to stable low mg calcite and partial or complete dissolution of aragonite occurred at various depths early meteoric diagenesis through dissolution precipitation processes had produced sparry calcite in the voids formed by the dissolution of aragonite in the limestone following the late pleistocene holocene marine transgression dolomitization was initiated in the reef in a meteoric marine water mixing zone lack of correlation between dolomite and the evaporite minerals and the low sr concentrations argue against hypersaline solutions as agents of dolomitization mineralogical and chemical data suggest that most diagenetic dolomite is formed at the expense of primary aragonite vertical and lateral variations in the distribution of dolomite aragonite and calcite indicate that dolomitization processes have been affected by the fluctuating mixed water zone associated with sea level oscillations holocene rise in the sea level terminated dolomitization in the lower layers and shifted the dolomitizing front to the upper sections of the limestone dolomite is low in the upper horizons of the reef and occurs as scattered perfect rhombs while in the lower layers it is fine grained and subhedral

generation and crystallization of an amphibolite shear melt an investigation using radial friction welding apparatus a cylinder of amphibolite comprising the assemblage amphibole clinozoisite albite has been frictionally melted using radial friction welding apparatus this was achieved by rotating a steel ring at 750 rpm and a force of 98 kn for 10 s against a stationary steel casing which housed the rock sample the ring penetrated the casing then proceeded to rotate and compress the sample to 95 of its original volume until it cracked at right angles to its length this generated a whole rock silicate melt which injected the crack and on cooling produced glass crystallites and vesicles melting occurred in two stages an initial low pressure melting event with crystallization to augite fe rich anorthite followed by a high pressure melting event with crystallization to fassaitic clinopyroxene it is estimated that pressures of 0 5 gpa rising to 1 gpa were realized at the ring rock interface under these conditions fassaite superseded augite anorthite crystallization due to the increased solubility of ca tschermak s component in clinopyroxene the high pressure event provides a crude analogue for the frictional melting of basic rock at depths of 15 30 km in a seismogenic fault a situation realized along the slip zone between cold descending lithosphere and overlying mantle during subduction

palaeoclimate determination from cave calcite deposits calcite deposits formed in limestone caves have been found to be an excellent repository of palaeoclimatic data for terrestrial environments the very presence of a relict deposit indicates non glacial conditions at the time of formation and both 14c and uranium series methods can be used to date the deposit and hence the age of these climatic conditions variations in 13c and 18o content of the calcite in 2h and 18o content of fluid inclusions in trace element concentrations and more recently in pollen assemblages trapped in the calcite are all potentially available as synchronous palaeoclimatic indicators previous work has tended to concentrate mainly on abundance of deposits as a palaeoclimatic indicator for the last 300 000 years this literature is briefly reviewed here together with the theory and methods of analysis of the u series and stable isotopic techniques the combined use of u series ages and 13c and 18o variations in cave calcites illustrates the potential for palaeoclimate determination previously unpublished results of stable isotopic variations in dated calcites from caves in northern england indicate the level of detail of stable isotopic variations and time resolution that can be obtained and the complexity of interpretation that may arise tentative palaeoclimatic signals for the periods 90 125 ka and 170 300 ka are presented more comprehensive studies are needed in future work especially in view of the difficulty in obtaining suitable deposits and the ethics of cave deposits conservation

holocene climate reconstructions from the fennoscandian tree line area based on pollen data from toskaljavri due to its location on the eastern north atlantic seaboard the fennoscandian tree line area is an ideal area to use biological proxies to assess the relative roles of the scandinavian ice sheet and of oceanic atmospheric and astronomic forcings on regional climate history here we report pollen based july mean temperature tjul and annual precipitation pann reconstructions from a sediment core from a high altitude tree line lake in northwestern finland the reconstructions suggest that at 9600 8300 cal yr b p tjul values were low but steadily rising while pann was high the period of warmest summers with tjul values ca 1 8 1 6 c higher than at present occurred at ca 8000 6500 cal yr b p since then climate has become gradually cooler tjul values during the medieval warm period ca 1400 1000 cal yr b p were ca 0 8 c higher that at present but decreased rapidly to the low little ice age levels at 800 cal yr b p we compare these results with an earlier pollen based climate reconstruction from the same region the reconstructions indicate a similar general holocene tjul pattern with lower values in the reconstruction from the high altitude lake however most of the small scale variations are not synchronous suggesting that they may represent noise rather than signal in our data c 2002 university of washington

holocene glacier fluctuations of flatebreen and winter precipitation changes in the jostedalsbreen region western norvay based on glaciolacustrine sediment records the history of holocene glacier variations of flatebreen an independent glacier close to the sw part of the jostedalsbreen ice cap has been reconstructed from lacustrine sediments in the proglacial lake jarbuvatnet the sedimentary succession shows evidence of three maini episodes of holocene glacier expansion the first is recorded in the basal part of the core up to 370 cm according to the age depth relationship in the sediment core based on 12 ams radiocarbon dates this glacier expansion episode terminated about 10200 cal yr bp the second major glacier phase lasted from 8400 to 8100 cal yr bp while the third was initiated around 4000 cal yr bp and has continued up to the present at 43 cm in the core the medium silt content increases significantly accompanied by a minor increase in the sand content this textural change is interpreted as the first time that the tenninus of flatebreen extended inlto an upstream lake at 1083 m a s l the age model suggests that this event took place around