forest soil paludification and mid holocene retreat of jack pine in easternmost north america evidence for a climatic shift from fire prone to peat prone conditions soil paludification is the main ecosystem process initiating the formation and development of most peatlands in the northern hemisphere sandy podzolic soils developed on coarse deposits are among

conceptual models of the evolution of transgressive dune field systems abstract this paper examines the evolutionary paths of some transgressive dune fields that have formed on different coasts of the world and presents some initial conceptual models of system dynamics for transgressive dune sheets and dune fields various evolutionary pathways are conceptualized based on a visual examination of dune fields from around the world on coasts with high sediment supply dune sheets and dune fields tend to accumulate as large scale barrier systems with little colonization of vegetation in arid hyper to arid climate regimes and as multiple active discrete phases of dune field and deflation plain couplets in temperate to tropical environments active dune fields tend to be singular entities on coasts with low to moderate sediment supply landscape complexity and vegetation richness and diversity increases as dune fields evolve from simple active sheets and dunes to single and multiple deflation plains and basins precipitation ridges nebkha fields and a host of other dune types associated with vegetation e g trailing ridges slacks remnant knobs gegenwalle ridges and dune track ridges tree islands and bush pockets three principal scenarios of transgressive dune sheet and dune field development are discussed including dune sheets or dune fields evolving directly from the backshore development following foredune and or dune field erosion and development from the breakdown or merging of parabolic dunes various stages of evolution are outlined for each scenario knowledge of evolutionary patterns and stages in coastal dune fields is very limited and caution is urged in attempts to reverse change and or modify dune fields to restore some perceived loss of ecosystem or dune functioning

lithological anomalies in a relict coastal dune geophysical and paleoenvironmental markers 1 ground exposures of migration surfaces slipfaces of a relict holocene coastal dune along the southeastern baltic sea coast provide an ideal opportunity for establishing the causes of prominent reflections on geophysical profiles high amplitude reflections on high resolution ground penetrating radar gpr images correlate well with two major lithological anomalies 1 paleosols developed on dune slipfaces and 2 slipfaces consisting of heavy mineral concentrations hmcs paleosols serve as indicators of dune stability represent datable chronostratigraphic surfaces and help reconstruct dune paleo morphology hmcs have substantially higher magnetic susceptibility values than background quartz rich sands and where they are well developed can be also used for spatial correlation based on their occurrence at the study site these enriched horizons likely represent periods of increased wind activity storminess multiple hmcs upwind of paleosol p1 800 670 cal years bp likely reflect periods of intensified wind activity along the southeast baltic region during the medieval warm period

holocene carbon accumulation rates from three ombrotrophic peatlands in boreal quebec canada impact of climate driven ecohydrological change understanding the processes controlling peatland carbon c sequestration is critical to anticipate potential changes in the global c cycle in response to climate change although identification of these factors may be relatively straightforward on seasonal timescales at centennial to millennial timescales complexities arise because of interactions between climate vegetation hydrology and long term ecological processes to better understand the factors controlling long term c accumulation holocene rates of c sequestration were quantified from three pristine ombrotrophic peatlands in boreal quebec northeastern canada 52 n 75 76 w bulk density and loss on ignition analyses combined with radiocarbon dating and age depth modelling were used to estimate long term apparent rates of carbon accumulation past changes in vegetation and water table depth were obtained from plant macrofossil and testate amoeba analysis earliest regional peat accumulation started 7520 cal bp with long term rates of c s

inland aeolian deposits of south west france facies stratigraphy and chronology archaeological investigations undertaken along a proposed highway together with the compilation of available geological and pedological data made it possible to give a first overview of the distribution of pleistocene aeolian deposits in south west france a chronological framework for deposition has been obtained using both radiocarbon n 24 and luminescence n 26 dating it shows that aeolian transport was very active during the late pleniglacial between 15 and 23 ka leading to sand emplacement over a 13 000 m 2 area at the centre of the basin the pleniglacial coversands are typified by extensive fields of small transverse to barchanoid ridges giving way to sandsheets to the east subsequent aeolian phases at ca 12 ka younger dryas and 0 8 0 2 ka little ice age correspond to the formation of more localized and higher mainly parabolic dunes at the southern and eastern margins of the coversand area aeolian dust accumulated to form loess deposits the thickness of which reaches 3 m on the plateaus luminescence dates together with interglacial ranking palaeoluvisols between the loess units clearly indicate that these accumulations built up during the last two glacial interglacial cycles the chronology of sand and loess deposition thus appears to be consistent with that already documented for northern europe this suggests that it was driven by global climate changes in the northern hemisphere the relatively thin aeolian deposits and particularly loess in south west france is thought to reflect both a supply limited system and a moister climate than in more northern and continental regions copyright 2011 john wiley sons ltd

late pleistocene fire in the ili basin central asia and its potential links to paleoclimate change and human activities abstract evidence of late pleistocene fire activity in central asia is important for understanding the underlying processes and controls of fire here two microcharcoal records from two separate loess sections covering the last 70 thousand years kyr in the ili basin are reported the results show that total microcharcoal concentrations are similar in both records and are correlated with insolation indicating consistent basin wide fire trends related to moisture changes driven by insolation in addition two anomalous fire events were identified at 45 35 ka and 6 0 ka we argue that these events are possibly related to ancient human activities rather than to pure natural factors such as sedimentation wind taphonomic change or climate change

niveo aeolian sand deposition in subarctic dunes eastern coast of hudson bay quebec canada aeolian sand transport during winter and the snow free season was assessed quantitatively by direct year round field measurements along transects on the lee side of parabolic dunes in subarctic quebec in 1987 1988 niveo aeolian deposition was more important than aeolian sedimentation in three of the four study sites and contributed 75 of the total annual accumulation in exposed sites and 25 in protected forest sites the maximum depth of interstratified snow and sand deposits 3 5 m was recorded in march semi permanent snow lenses may persist longer than 2 years in the aeolian sediments after dissipation of snow 22 cm of sand as a maximum accumulated on the slipface of the most active dunes whereas only minor sand accumulation occurred in distant areas from active sand erosion wind driven sand was dispersed over 7 4 km2 in the whapmagoostui kuujjuarapik area the acumulation of snow and sand during the snow season together with spring thaw and collapse of the niveo aeolian deposit caused different types of injuries to trees especially in 1985 and 1987 when a maximum of torn branches was recorded over the last 10 year period

drought drove forest decline and dune building in eastern upper michigan usa as the upper great lakes became closed basins current models of landscape response to holocene climate change in midcontinent north america largely reconcile earth orbital and atmospheric climate forcing with pollen based forest histories on the east and eolian chronologies in great plains grasslands on the west however thousands of sand dunes spread across 12 000 km 2 in eastern upper michigan eum more than 500 km east of the present forest prairie ecotone present a challenge to such models we use 65 optically stimulated luminescence osl ages on quartz sand deposited in silt caps n 8 and dunes n 57 to document eolian activity in eum dune building was widespread ca 10 8 ka indicating a sharp sustained decline in forest cover during that period this decline was roughly coincident with hydrologic closure of the upper great lakes but temporally inconsistent with most pollen based models that imply canopy closure throughout the holocene early holocene forest openings are rarely recognized in pollen sums from eum because faint signatures of non arboreal pollen are largely obscured by abundant and highly mobile pine pollen early holocene spikes in nonarboreal pollen are recorded in cores from small ponds but suggest only a modest extent of forest openings osl dating of dune emplacement provides a direct spatially explicit archive of greatly diminished forest cover during a very dry climate in eastern midcontinent north america ca 10 8 ka

origin chronology and environmental significance of holocene aeolian and alluvial sands at blue mountain falkland islands extensive and thick sand accumulations containing organic rich horizons at blue mountain falkland islands are most probably derived from weathering of local bedrock under late pleistocene periglacial conditions weathering and subsequent deflation produced several shallow basins that are now occupied by lakes sand morphology sedimentary structures and site characteristics indicate that the sand deposits are predominantly aeolian although some alluvial sands are also present deflation occurred either before the lakes existed or at times of lower lake levels sixteen 14c dates from organic rich horizons show that some sand accumulated in the early holocene or late pleistocene but that most is of mid to late holocene age landscape stability instability phases were not synchronous between sites and cannot be explained by the regional trends of holocene climate change a period of significantly lower lake levels and major aeolian erosion at c 5000 4500 bp is proposed but is not supported by regio

macrofossil and tree ring evidence for a long term forest succession and mid holocene hemlock decline abstract paludified dune fields in southern quebec provided a unique opportunity to analyze a mid holocene forest succession ranging from xero mesophilous forests to treed peatlands which registered the hemlock decline a major biostratigraphic event in eastern north america our fossil tree chronology established from 66 radiocarbon dates of tree stems indicates that white pine and hemlock were present at the study site about 6000 5700 yr b p hemlock reached a maximum 4900 4800 yr b p and then declined between 4600 and 3800 yr b p the species recovered around 3700 yr b p and then decreased when white pine and eastern latch dominated the site after 3000 yr b p and between 2600 and 2200 yr b p respectively tree ring signatures of fossil hemlocks suggest the continuous influence of biotic factors possibly insect defoliators throughout the record as shown by recurrent suppressed growth pattern microscopic examination of the hemlock fossil stems disclosed no evidence of fungal disease the hemlock decline was probably caused by regional posthypsithermal climatic changes toward moister conditions

the central scandinavian dolerite group protracted hotspot activity or back arc magmatism constraints from u pb baddeleyite geochronology and hf isotopic data the central scandinavian dolerite group csdg occurs in five separate complexes in central sweden and sw finland u pb baddeleyite ages of dolerite dikes and sills fall into three age intervals 1

deflation and redeposition of sand dunes in finnish lapland abstract deflation and redeposition of aeolian sands in finnish lapland have been studied by analysis of their sedimentology and stratigraphy by dating buried charcoal layers and by obtaining tl dates the thickness of redeposited sands on buried soils ranges from a few decimetres to more than two metres original dune formation after deglaciation finished around 7000 bp subsequent aeolian activity has been mainly destructive in nature deflation started in some regions about 4800 bp continuing with several breaks until the present some deflation basins have stayed active for at least 1300 years however it is too early to draw general conclusions for the whole area forest fires have been important reactivators of aeolian sand drift but tend to be rather local events change in the ground water table is a basic factor affecting deflation at present human impact and overgrazing by reindeer seem to increase deflation

archean synsedimentary tectonic deformation a comparison with the quaternary observations from the 3 55 3 3 ga barberton greenstone belt indicate an important phase of shortening synchronous with the deposition of alluvial sediments the structural style is remarkably similar in scale and geometry to that now occurring on land in the convergent plate boundary zone in the north island of new zealand

late holocene inland dune activity in the uk a case study from breckland east anglia inland dune fields found in breckland east anglia uk have previously been correlated with the widespread late devensian coversands of the region and a seventeenth century sandflood which is known to have inundated the village of santon downham a programme of optically stimulated luminescence and radiocarbon dating undertaken on the dunes at wangford warren and santon downham reveals that episodic aeolian activity has taken place during the last 7000 years five sand depositional phases on breckland dunes are identified c 6500 c 1600 1100 c 500 c 400 335 and from c 200 30 years before present between c 2120 1840 years ago and within the period 1100 300 years ago quiescent periods allowed the development of fen peat and soils local controlling factors on aeolian activity in breckland appear to be related to anthropogenic activities and livestock sheep and rabbits reducing vegetation cover and decreased precipitation and sea levels which led to lowering of water tables breckland aeolian activity when compared to the national and sub continental holocene aeolian activity record shows a high level of concordance the underlying forcing factor for late holocene dune activity in the uk and elsewhere in europe appears to be climatic instability in the north atlantic associated with both the little ice age and previous similar events which led to increased storminess climatic variability and lower temperatures

reactivation of supply limited dune fields from blowouts a conceptual framework for state characterization aeolian dune fields mantle the earth in both vegetated stable and unvegetated active states changes in state are poorly understood in particular little is known about reactivation devegetation from a vegetated state available evidence indicates that dune reactivation can be driven by changes in aridity increased wind speed fire biogenic disturbance human disturbance or a combination of the previous how these controls fit together and define the reactivation potential of dune fields is presently unknown here we develop a framework to describe reactivation potential for a specific case presently vegetated supply limited dune fields that develop blowouts under a unidirectional wind we first define a conceptual model of blowout expansion and then split the functions of vegetation in a stable dune field into i maintenance of a protective skin and ii blowout suppression we model reactivation as disturbance breaking through the protective skin which forms a blowout that is either i suppressed by colonizer species or ii capable of advancing downwind and reactivating part of the dune field the capacity for disturbance to break through the protective skin is a function of disturbance magnitude area and resistance of the skin the blowout suppression capacity of a dune field is a function of sediment flux blowout depth related to geomorphology and colonizer species vitality by plotting a given dune field with two variables protective skin breach rate and blowout suppression capacity we define four states i stable ii blowout dominated iii reactivating or iv stable but disturbance susceptible we reinforce the conceptual model with qualitative examples and discussion of experiments on grassland stabilized dunes in canada overall our framework provides a starting point for quantifying the reactivation potential of vegetated dune fields

holocene environmental history of a peatland in the lena river valley siberia a 3 86 m core of peat and organic lake mud from a polygonal peatland in the lena river valley of siberia was radiocarbon dated and analyzed for pollen plant macrofossils chrysophyte stomatocysts stable isotopes and charcoal at around 7200 bp a shallow lake or open water wetland supported diverse aquatic macrophytes the site had transformed initially into a richer fen with carex comarum palustris and drepanocladus and later a poorer fen with sphagnum which persisted until around 3000 bp fire may have been responsible for silt being blown onto the peatland which changed the hydrological and geochemical conditions for development of the poor fen ice accretion led to an increase in the height of the centre of the polygon and expansion of sphagnum peatland 18 o values become progressively more enriched which reflects more direct input of summer precipitation waters and less groundwater during this period finally the peatland surface was elevated sufficiently to limit water and nutrient supply thereby allowing ericaceae and betula to grow at the coring site fire burned the peatland surface and may have exaggerated the extremely slow rate of peat accumulation fire may also be a factor in maintaining the open larix dahurica forest in the region today while climate may be contributing to reducing postfire regeneration fire and climate together may be controlling the character and composition of forests near tree line in the lena river valley of this part of siberia resume une carotte de tourbe et de boue organique lacustre diune longueur de 3 86 m prolevoe dans une tourbire polygonale dans la valloe de la rivire lena en siborie a oto datoe au radiocarbone et analysoe pour les pollens plantes

buried soils in a perched dunefield as indicators of late holocene lake level change in the lake superior basin abstract a stratigraphic analysis of buried soils within the grand sable dunes a dune field perched 90 m above the southern shore of lake superior reveals a history of eolian activity apparently linked with lake level fluctuations over the last 5500 yr a relative rise in the water plane of the nipissing great lakes initially destabilized the lakeward bluff face of the grand sable plateau between 5400 and 4600 14 c yr b p this led to the burial of the sable creek soil by eolian sediments derived from the bluff face subsequent episodes of eolian activity appear to be tied to similar destabilizing events high lake levels may have initiated at least four and perhaps eleven episodes of dune building as expressed by soil burials within the dunes intervening low lake levels probably correlate with soil profile development which varies from the well developed sable creek spodosol catena to thin organic layers containing in place stumps and tree trunks paleoecological reconstructions available for the area do not imply enough climatic change to account for the episodic dune activity burial of soils by fine fraction sediments links dune building episodes with destabilization of the lower lake facing bluff which is rich in fines

thrust tectonics thin skinned or thick skinned and the continuation of thrusts to deep in the crust abstract the paper analyses the geometry of thin skinned thrust zones where the thrusts shallow out at depth and of thicker skinned fault zones where much of the crust is involved and where the thrusts are frequently observed to become steeper downwards in the interiors of many orogenic belts the steep dip of faults is not original but due to the folding above lower decoupling zones the energy involved in the internal deformation of hanging wall rocks may prohibit many faults becoming more shallow upwards such shallowing upwards faults may occur in more ductile rocks to maintain compatibility between zones which have experienced different deformation intensities but displacements on the faults are unlikely to be large another mechanism for producing faults which steepen downwards is proposed for the major thrusts which form the southern margin to the himalayas these carry large thicknesses 30 to 100 km of crustal and upper mantle rocks to the south causing flexuring and isostatic depression of the indian plate the steeply dipping thrusts are not footwall ramps these may be some distance behind the steepened zone this thrust induced isostatic bending of the crust has important implications when considering regional seismic interpretations as well as thrust mechanics and kinematics

holocene changes in seasonal precipitation highlighted by fire incidence in eastern canada postglacial fire history has been reconstructed for eastern canada from charcoal influx anomalies from 30 sites taken from a lacustrine charcoal database the reconstruction exhibits coherent patterns of fire occurrence in space and time the early holocene is characterised by high fire incidence there is a major change to much lower occurrence slightly after 8 ka bp a return to more fire appears after 3 ka bp this sequence does not fit with the hydro climatic reconstruction deduced from lake level reconstructions for northeastern north america which indicates a dry early and mid holocene and a wet late holocene fire occurrence however closely matches summer relative humidity inferred from 18o the differences between fire frequency and lake level history are due to changes in the seasonality of precipitation and drought frequency lake levels are essentially controlled by winter precipitation while summer precipitation controls fire occurrence the early holocene before 8 7 5 ka bp experienced dry summers due to higher solar radiation and dry adiabatic winds from the residual laurentide ice sheet the middle holocene was dominated by wet summers due to stability of the atlantic air mass over eastern canada after 2 5 ka bp summers became drier albeit not as fire conducive as during the early holocene late holocene summers conducive to fire are explained by more frequent incursions of dry cool pacific or cold arctic air masses over eastern canada

regional aridity in north america during the middle holocene increased aridity throughout the great plains and rocky mountain region during the middle holo cene has been documented from pollen records aeolian proxy variables in lake cores and active sand dune migration varve calibration provided by a continuously varved record of the holocene from a core from elk lake northwestern minnesota shows that the influx of aeolian clastic material increased beginning about 8 ka and ended about 3 8 ka with peak aeolian activity at about 6 ka if aeolian influx to elk lake corresponds in time to aeolian influx in other lakes and to maximum dune activity in minnesota dune fields then the varve calibration in elk lake provides precise time calibration of periods of peak aeolian activity in minnesota palaeowind studies from the minnesota dune fields show that the dominant wind direction when the dunes were active was from the northwest the same as the dominant wind direction in dune fields throughout the great plains and rocky mountains if the mid holocene aeolian act

deciphering the tectonic evolution of archaean greenstone belts the importance of contrasting histories to the distribution of mineralization in the yilgarn craton western australia abstract the distribution of archaean metallic mineral deposits reflects tectonic controls operating during the evolution of granitoid greenstone terranes tectonic analysis of these terranes not only allows recognition of parameters that may be important in interpreting the tectonic histories of greenstone belts but also the resultant tectonic control on mineral deposit distribution in the yilgarn craton of western australia the late archaean 2 7 ga norseman wiluna belt is most intensely mineralized with both komatiite associated ni cu deposits and epigenetic gold deposits this belt is dominated by 2 7 ga supracrustal successions and its tectonic history is that of an orogenic belt at an obliquely convergent craton or proto craton margin tectonostratigraphic associations preserved resemble younger volcanic arc and back arc basin crust and many represent the remains of a volcanic arc and back arc basin complex developed in response to westward dipping subduction these sequences were deformed metamorphosed and intruded by granitoids relatively soon 30 ma after the major period of volcanism with gold mineralization occurring late in the orogenic event possibly during uplift in contrast greenstone belts in the murchison and southern cross provinces are dominated by older supra crustal successions that contain 2 9 ga volcanosedimentary associations characterized by extensive oxide facies banded iron formations bifs bifs appear to have been deposited in shelf or platform environments in intra oceanic or passive craton margin settings komatiite associated ni cu mineralization and volcanogenic cu zn mineralization are locally hosted by favourable tectonostratigraphic associations the main period of deformation metamorphism and gold mineralization in these provinces was broadly synchronous with that in the norseman wiluna belt as was regional granitoid emplacement during this event strain was probably transmitted from the eastern margin of the craton via a yilgarn wide system of shear zones faults and fold belts gold mineralization is developed best in greenstone belts such as the meekathara mt magnet belt that contain large scale fault systems and internal granitoids similar tectonic controls on the distribution of mineral deposits can also be recognized in other archaean cratons and the heterogeneous distribution of archaean mineral deposits probably reflects a range of tectonic settings as well as different stages in the evolution of individual cratons

permineralization process promotes preservation of holocene macrofossil charcoal in soils the use of macrofossil soil charcoal as a palaeoecological tool to reconstruct past vegetation climate or fire history has gained much interest in recent years yet little is known about taphonomy of charcoal in soils here we assessed the putative loss of palaeoecological information due to charcoal fragmentation after burial we found no significant loss of charcoal mass with time instead we found a significant positive relationship between the mass of charcoal particles and their age permineralization of charcoal particles older than ca 5200 a explained the increased charcoal mass with time in mineral soils the permineralization process increased the density of charcoal particles resulting in a twofold particles mass increase and thus offers a protection against subsequent degradation our results suggest high stability of palaeoecological information from charcoal macrofossils buried in mineral soils at least over the holocene timescale copyright 2011 john wiley sons ltd

evaluating long term regional climate variability in the maritime region of the st lawrence north shore eastern canada using a multi site comparison of peat based paleohydrological records this study presents paleohydrological reconstructions from ombrotrophic peatlands bogs along the north shore of the estuary and the gulf of st lawrence in eastern canada past water table depths were reconstructed based on testate amoebae analyses within four peatlands from two maritime ecoclimatic regions boreal and subarctic using a new transfer function the comparison of multiple peat based paleohydrological records was used to distinguish climate driven changes from variations related to site specific factors coherence between the water table reconstructions at the regional scale suggests a common climatic influence on bog paleohydrology but there are inconsistencies which also suggest an influence of non climatic factors e g internal peatland processes and feedbacks the surface drying and increased hydrological variability after 3000 cal a bp in the studied bogs coincide with the transition from the holocene climatic optimum to the neoglacial cooling documented by proxy climate records in eastern canada the bogs of havre st pierre have experienced major drying during the late holocene indicating important annual to centennial water deficits at the peatland surface regional differences in the magnitude of the hydrological fluctuations may result from distinctive climatic conditions or could indicate that bog surface wetness in the gulf of st lawrence was more sensitive to past climate changes copyright 2014 john wiley sons ltd

constraining the timing of brittle deformation and sedimentation in southern finland implications for neoproterozoic evolution of the eastern fennoscandian shield abstract sheared sedimentary clay was found in a faulted fracture in crystalline bedrock in a tunnelling site at 60 m depth in southern finland brittle faults are numerous in the fennoscandian palaeoproterozoic bedrock but only some of them have relative age constraints while absolute ages are nearly lacking sedimentary rocks altogether are uncommon in finland and only sparsely dated by micropaleontological studies this study reports k ar data of fresh non weathered authigenic illite and constrains a time framework for the local faulting and sedimentation the neoproterozoic tonian to cryogenian ages derived from the grains in diminishing grain size order are c 967 947 809 and 697 ma results indicate that the formation of the extension fracture is related to the collapse of sveconorwegian orogeny c 1000 ma clay and mature quartz sand were deposited in this extension fracture in shallow water in an intracratonic basin followed by early diagenetic processes and neocrystallization of illite around 967 947 ma the neoproterozoic 1000 700 ma sedimentation documented in this study is rare in the fennoscandian shield as a whole neocrystallization of authigenic illite in the finest 0 4 and

brittle tectonothermal evolution in the forsmark area central fennoscandian shield recorded by paragenesis orientation and 40ar 39ar geochronology of fracture minerals in this paper we show how studies of fracture mineral paragenesis their orientation and ar 40 ar 39 geochronology can be applied in order to recognise the brittle tectonothermal evolution in an area samples were selected from nearly 18 km of drill cores from the upper i km of the fennoscandian shield obtained during the site investigation for a repository of spent nuclear fuel in forsmark central sweden four major events of fracturing and or reactivation of fractures associated with fracture mineralisation have been distinguished the first event was characterised by precipitation of epidote quartz and chlorite along preferably sub horizontal and gently dipping fractures or steep wnw ese to nw se fractures precipitation occurred between 1 8 and 1 1 ga possibly during the late stage of the svecokarelian orogeny close to 1 8 1 7 ga the second event is associated with precipitation of hematite stained adularia and albite prehnite laumontite calcite and chlorite preferably along steep ene wsw to nne ssw and nnw sse fractures precipitation occurred around 1107 7 to 1034 3 ma probably due to effects from the sveconorwegian orogeny this event was followed by a period with dissolution of fracture minerals and subsequent precipitation of mainly calcite quartz pyrite and asphaltite during the palaeozoic the formation fluid emanated from an overlying organic rich sedimentary cover precipitation occurred during reactivation of proterozoic fractures but formation of new fractures is also inferred possibly due to far field effects of the caledonian orogeny or elevated hydrostatic pressure due to its foreland basin the latest event is dominated by clay minerals chlorite and calcite along hydraulically conductive fractures these minerals are prominent along sub horizontal and gently dipping fractures but also occur in sets of steeply dipping fractures it is inferred that the hydraulically conductive fractures are proterozoic structures in which mineral precipitation has occurred during a long period however some of the near surface sub horizontal fractures may be quaternary in age c 2009 elsevier b v all rights reserved less

palaeoecology of a palsa and a filled thermokarst pond in a permafrost peatland subarctic quebec canada radiocarbon dating and macrofossil data from a palsa and a filled thermokarst pond within a subarctic permafrost peatland were used to reconstruct their evolution and to distinguish between allogenic and autogenic processes that had been involved in their development peat began to accumulate in the peatland basin shortly after 6000 cal bp the initial stage was a shallow bay or a salty marsh followed by a wet marsh triggered by a relatively rapid drop in sea level related to a rapid isostatic uplift of land by 5640 cal bp the site had transformed into a rich fen a high rate of peat accumulation led to the establishment of a short lived intermediate fen by 4610 cal bp and to a poor fen from 4200 cal bp until 1760 cal bp low water tables associated with decreased precipitation occurred between 5170 and 4610 cal bp and 3100 and 1760 cal bp between 1760 and the little ice age there was ombrotrophication of the site largely as a result of a thick peat accumulation during this period autogenic processes had controlled the general hydrosere while allogenic processes mainly precipitation had influenced species composition permafrost established during the little ice age leading to palsa formation and it has been melting in response to recent climate warming and precipitation increases macrofossil results from the filled thermokarst pond show that plant succession used the followed hydrosere calliergon giganteum and sphagnum riparium when the pond s depth was at a maximum s riparium and c giganteum when the pond was partly filled in and s lindbergii and s riparium since the pond has been completely filled in

distinguished multiple events of fracture mineralisation related to far field orogenic effects in paleoproterozoic crystalline rocks simpevarp area se sweden detailed investigations of fracture minerals have been carried out in the simpevarp area se sweden in order to reveal the low temperature evolution of the site and to discern different events of deformation especially in the brittle regime the study is part of the site characterisation programme for a potential deep seated repository for spent nuclear fuel the bedrock in the area is composed of generally un metamorphosed 1 8 ga crystalline rocks detailed sem investigations of cross cutting fracture mineralisations have revealed several generations of fillings formed at gradually lower temperatures during repeated events of fracturing and reactivation from the paleoproterozoic until the quaternary ar 40 ar 39 geochronology and fracture orientation analyses have been used to relate each fracture filling generation to geological events such as far field effects from orogenies as well as more local effects related to intrusions fracturing and formation of different fracture mineral parageneses during at least four different orogenies have been indicated the waning stages of the svecokarelian orogeny 1 75 ga the danopolonian orogeny similar to 1 47 1 44 ga the sveconorwegian orogeny similar to 1 1 0 9 ga and the caledonian orogeny similar to 0 5 0 4 ga the fracture minerals and greisen related to the danopolonian orogeny mainly formed in relation to the intrusion of two indicatively danopolonian related granites nearby furthermore periods of extension are indicated in the area by the presence of late sveconorwegian dolerites fractures filled with lower cambrian sandstone are plausibly formed in relation to far field extensional effects of the opening of the iapetus ocean fracture minerals of paleozoic age or younger show influence of loading and unloading cycles the youngest fracture minerals identified indicate precipitation from waters of similar composition as the present groundwater c 2008 elsevier b v all rights reserved less

recent dynamics of subarctic dunes as determined by tree ring analysis of white spruce hudson bay quebec the radial growth patterns of white spruce were studied on a number of trees growing in subarctic dunes along the eastern coast of hudson bay to calculate the rates of accumulation erosion and migration of cold climate sand dunes the average rate of sand accumulation in sheltered dunes forest sites was 2 5 to 3 3 cm yr which is two to three times lower than in highly exposed dunes with a rate of sedimentation of 7 65 cm yr the average erosion rate was 1 4 1 7 cm yr about two times lower than the accumulation rate the migration rate of sheltered dunes was 18 to 30 cm yr three to five times lower than for an exposed dune which advanced at a speed of 74 cm yr this migration rate established for highly exposed dunes in the subarctic with tree ring methods is about 10 times lower than that established for a barchan in the sahara with other methods

a relationship between dunes fire and climate recorded in the holocene deposits of quebec during the past 5 000 yr bp the tropics have experienced an increase in aridity and aeolian activity in both maritime and continental areas1 4 in contrast the onset and subsequent development of post hypsithermal climates in northern latitudes were primarily conducive to global cooling it is suggested here that aeolian activity in cold environments represents a direct response to this long term cooling trend that began after 6 000 5 000 yr bp at the end of the climatic optimum5 9 this study establishes the holocene chronology of sand dunes near the outer forest limit in northern quebec fig 1 i show here that fires initiate the aeolian activity and that the fire dune relationship is typical of cooling period on this basis a palaeoclimatic reconstruction since the climatic optimum is proposed

isolation and water level fluctuations of lake kachishayoot northern quebec canada this study combines different methods including grain size macrofossil and pollen analyses to reconstruct paleogeographical and paleoclimatological conditions for periods before during and after the isolation of a small lake lake kachishayoot in northern quebec after the retreat of the laurentide ice sheet around 8000 14c yr b p the area was submerged by the tyrrell sea the transition from marine to lacustrine environment occurred about 5400 yr b p two major periods of water level fluctuations were inferred from organic and mineral sediments a high water level that occurred after 3200 yr b p and a low water level that started before 2200 yr b p our chronological data for the first period are consistent with those from nearby lac des pluviers and from other lakes in east central canada and in the northeastern united states during the low water level period however there is no evidence for minor fluctuations whereas other lakes in northern quebec and east central canada underwent several brief lowerings long term changes in atmospheric circulation caused by changing global boundary conditions likely explained long term water level fluctuations of lake kachishayoot

craton scale distribution of archean greenstone gold deposits predictive capacity of the metamorphic model genetic models should not only attempt to explain features of archean gold mineralization on the scale of mines or districts but should also explain its marked spatial and temporal heterogeneity in greenstone belts the application of genetic models developed with such a philosophy can have predictive capacity in gold exploration the metamorphic model one of a number of current genetic models for archean gold deposits involves generation of auriferous h 2 o co 2 fluids by devolatilization of the stratigraphically lowermost greenstones during metamorphism and broadly synchronous synkinematic granitoid intrusion crustal scale fault shear systems are required to induce channeled fluid flow and to focus ore fluids toward suitable host rocks and structural sites declining temperature below the amphibolite greenschist transition combined with sulfidation of fe rich host rocks is a particularly efficient au depositing mechanism the model suggests that the major controlling factors in declining order of importance are 1 high temperature low pressure generally low strain metamorphic regimes 2 crustal scale fault systems 3 unaltered fe rich rocks tholeiites banded iron formation at a suitable stratigraphic metamorphic level and 4 abundant au enriched komatiites and s rich sediments in source regions the low pressure metamorphic conditions combined with the occurrence of elongate high strain zones in most if not all generally low strain greenstone belts may explain the ubiquitous occurrence of gold deposits in archean terranes all four favorable parameters appear to act in concert to produce the largest gold deposits and most abundant gold mineralization in 2 7 or 0 1 b y old rift phase greenstone belts interpreted to have formed under conditions of high crustal extension and extensive crustal thinning i e with predicted high geothermal gradients high fault density limited synvolcanic alteration and abundant komatiites and sulfidic sediment horizons more widespread commonly older platform phase greenstone belts which formed under conditions of lesser crustal extension and thinning are less mineralized as predicted by the metamorphic model the ability of the model to explain the regional distribution of known archean gold deposits lends credence to its predictive capacity for example 1 greenstone belts in any one craton can be broadly ranked in order of likely relative gold potential 2 the likelihood of discovery of large deposits in poorly exposed or poorly explored belts of known type can be estimated 3 areas with the highest potential can be defined in rift phase greenstone belts by the coincidence of critical parameters such as specific host rock sequences and metamorphic facies 4 prospective structural sites for gold mineralization can be postulated in platform phase greenstone belts affected by diapiric tectonics and 5 the possible spacing of large deposits can be estimated further the potential use of the model in exploration emphasizes serious gaps in our knowledge of parameters crucial to understanding greenstone belt metallogeny including alteration patterns metamorphic p t paths and regional scale structural regimes

late cenozoic fire enhancement response to aridification in mid latitude asia evidence from microcharcoal records fire provides an important indicator of paleoclimatic change however little information relating to late cenozoic fire history has been gathered in mid latitude asia including inner asia and east asia a key region for understanding the development of the arid monsoon climate system as well as the driving forces behind it here we first report the records of microcharcoal concentrations mc covering the holocene 10 0 ica and late pleistocene 0 8 0 ma which we use to analyze the fire activity patterns at an orbital time scale then we compile the late cenozoic mc record to investigate the long term fire history by analyzing four cores from the yangtze river delta yrd area east asia representing 8 0 ma and three sites in inner asia representing 18 2 ma the results show that the i mc remained higher during the relatively dry late holocene glacial stages than that during the humid middle holocene interglacial stages at individual sites ii mc increased with time in both inner asia and east asia after 18 and 8 ma respectively and iii mc always remained higher in the dry inner asia than in the contemporaneous wet east asia all these characteristics imply that late cenozoic fire occurrence in mid latitude asia experienced a gradual increasing trend along with the global temperature ice volume change and indicates a continuous aridification trend across mid latitude asia the global cooling rather than the tibetan plateau uplift might have played a key role in this observed trend c 2016 elsevier ltd all rights reserved

late holocene paleoecohydrology and carbon accumulation estimates from two boreal peat bogs in eastern canada potential and limits of multi proxy archives abstract the stratigraphy of four peat sequences collected in two peat bogs located in the eastmain river watershed 52 n 76 w james bay lowlands quebec canada was investigated to reconstruct past hydroclimatic conditions of peat accumulation and associated carbon dynamics during the late holocene analyses of macrofossils testate amoebae peat humification c n ratio and bulk density were performed at high resolution along each peat core allowing the potential of each proxy indicator under varying nutrient status and hydroclimatic conditions to be evaluated some synchronous changes were recorded both within and between peatlands suggesting the influence of allogenic factors in the development of these peatlands other reconstructed changes have highlighted autogenic succession processes related to the local geomorphic and hydrologic context highest peat carbon accumulation rates lorca were correlated with either wet conditions or high woody debris percentages suggesting that residence time of the biomass in the acrotelm and the nature of plant material can both influence carbon accumulation rates in peat bogs this study provides the first high resolution paleoecohydrological reconstructions from the mid boreal ecoregion of eastern canada a region in which peatlands occupy 30 to 60 of the land surface

holocene development of parabolic dunes in the central st lawrence lowland quebec abstract stabilized parabolic dunes in the central st lawrence lowland are oriented ne sw in the postulated direction of dune building winds coming from anticyclonic air circulation induced by the retreating laurentide ice sheet about 10 000 yr ago the eolian chronology reconstructed from several sections in mixed dune peatland environments indicates that postglacial plant colonization characterized by a fortuitous assemblage of arctic subarctic and boreal elements preceded dune formation during champlain sea regression around 10 000 yr b p confined peatlands and small forests were buried by eolian sands between 10 000 and 7500 yr b p under dry and temperate conditions this eolian episode lasted about 2500 14 c yr and ended when cyclonic air circulation similar to the present humid climatic regime was established following the breakup and disappearance of the laurentide ice sheet over hudson bay and peripheral areas dune stabilization through paludification of well drained eolian sands about 7500 yr b p suggests a major shift in climate toward wetter conditions that have been characteristic during most of the holocene in eastern north america minor eolian erosion induced by wildfire was recorded during late holocene time about 1250 yr b p anthropogenic perturbation logging and agriculture practice was also responsible for recent very local eolian activity

early holocene dune activity linked with final destruction of glacial lake minong eastern upper michigan usa abstract the early holocene final drainage of glacial lake minong is documented by 21 osl ages on quartz sand from parabolic dunes and littoral terraces and one radiocarbon age from a lake sediment core adjacent to mapped paleoshorelines in interior eastern upper michigan we employ a simple model wherein lake level decline exposes unvegetated littoral sediment to deflation resulting in dune building dunes formed subsequent to lake level decline prior to stabilization by vegetation and provide minimum ages for lake level decline optical ages range from 10 3 to 7 7 ka 15 ages on dunes adjacent to the lowest lake minong shoreline suggest final water level decline 9 1 ka the clustering of optical ages from vertically separated dunes on both sides of the nadoway gros cap barrier around 8 8 ka and a basal radiocarbon date behind the barrier 8120 40 14 c yr bp 9 1 cal ka bp support the hypothesis that the barrier was breached and the final lake level drop to the houghton low occurred coincident with 1 high meltwater flux into the superior basin and 2 an abrupt negative shift in oxygen isotope values in lake huron

holocene environmental change in subarctic aeolian dune fields the chronology of sand dune re activation events in relation to forest fires palaeosol development and climatic variations in finnish lapland sand dune stratigraphy radiocarbon dated charcoal layers palaeosol development and luminescence dating are used to reconstruct the holocene environmental history of the dune fields in finnish lap

reconstruction of the long term fire history of an old growth deciduous forest in southern quebec canada from charred wood in mineral soils charcoal particles are widespread in terrestrial and lake environments of the northern temperate and boreal biomes where they are used to reconstruct past fire events and regimes in this study we used botanically identified and radiocarbon dated charcoal macrofossils in mineral soils as a paleoecological tool to reconstruct past fire activity at the stand scale charcoal macrofossils buried in podzolic soils by tree uprooting were analyzed to reconstruct the long term fire history of an old growth deciduous forest in southern quebec charcoal fragments were sampled from the uppermost mineral soil horizons and identified based on anatomical characters spruce picea spp fragments dominated the charcoal assemblage along with relatively abundant wood fragments of sugar maple acer saccharum and birch betula spp and rare fragments of pine pinus cf strobus and white cedar thuja canadensis ams radiocarbon dates from 16 charcoal fragments indicated that forest fires were widespread during the early holocene whereas no fires were recorded from the mid holocene to present the paucity of charcoal data during this period however does not preclude that a fire event of lower severity may have occurred at least eight forest fires occurred at the study site between 10 400 and 6300 cal yr b p with a dominance of burned conifer trees between 10 400 and 9000 cal yr b p and burned conifer and deciduous trees between 9000 and 6300 cal yr b p based on the charcoal record the climate at the study site was relatively dry during the early holocene and more humid from 6300 cal yr b p to present however it is also possible that the predominance of conifer trees in the charcoal record between 10 400 and 6300 cal yr b p created propitious conditions for fire spreading the charcoal record supports inferences based on pollen influx data labelle c richard p j h 1981 vegetation tardiglaciaire et postglaciaire au sud est du parc des laurentides quebec geographie physique et quaternaire 35 345 359 of the early arrival of spruce and sugar maple in the study area shortly after deglaciation we conclude that macroscopic charcoal analysis of mineral soils subjected to disturbance by tree uprooting may be a useful paleoecological tool to reconstruct long term forest fire history at the stand scale d 2005 university of washington all rights reserved

geology of the golden grove prospect western australia a volcanogenic massive sulfide magnetite deposit potentially economic deposit stratabound two phases of sulfide precipitation separated by a major phase of fe oxide development metamorphosed under lower greenschist facies hydrothermal alteration of host rocks fe oxide abundance is due to either sea floor weathering or to a change with time in the trend of the ore solution seawater mixing path modified journal abstract

a revised chronology for aeolian activity in subarctic fennoscandia during the holocene detailed sedimentological studies and parallel sampling for 14c and infra red stimulated luminescence age assays were undertaken at six sites lying beyond and below the tree line with the objective of establishing the historical development of aeolian landforms in lapland the main issues were a the timing of dune activity and processes of stabilization b the specific processes responsible for the past and contemporary activity new data indicate that many of the primary dunes were active for several millennia after deglaciation diachronous stabilization at both local and regional scales appears likely initial stabilization occurred in local interdune areas and where regional dune fields were colonized by pine generally before 7 ka local large dunes and some regional dunefields only became stable around 4 3 ka when the regional groundwater table rose and late pine colonization was possible the latest episode of aeolian activity dates from ad 1100 1650 across the area a unique deflation trigg

terrestrial sensitivity to abrupt cooling recorded by aeolian activity in northwest ohio usa article i nfo article history received 7 may 2010 available online 21 february 2011 optically stimulated luminescence dated sand dunes and pleistocene beach ridges in northwest ohio are used to reconstruct landscape modification more than 5000 yr after deglaciation four of the osl ages 13 3 11 1 ka cluster around the younger dryas cold event five ages 10 8 8 2 ka cluster around the preboreal one young age 0 9 0 7 ka records more recent aeolian activity and one age of 15 1 13 1 ka dates a barrier spit in lake warren in northwest ohio both landscape instability recorded by aeolian activity and a vegetation response recorded by pollen are coeval with the younger dryas however the climate conditions during the preboreal resulting in aeolian activity are not recorded in the available pollen records from this we conclude that aeolian dunes and surfaces susceptible to deflation are sensitive to cooler drier episodes of climate and can complement pollen data younger dryas and preboreal aged aeolian activity in northwestern ohio coincides with aeolian records elsewhere in the great lakes region east of the prairie forest ecotone

holocene history of the great kobuk sand dunes northwestern alaska abstract located just north of the arctic circle the great kobuk sand dunes gksd are an inland dune field that is closely surrounded by boreal forest the history of the gksd tells us about changes in aridity a climatic parameter whose history is poorly understood at high latitudes vegetated dunes in several states of geomorphic preservation surround the active dune field today evidencing a complex history of holocene activity small lakes in the forest bordering the dunes accumulate wind blown sand we use 14 c dated lake sediment cores to reconstruct a continuous history of sand influx over the last 8000 yr the validity of this record is supported by limiting ages obtained from stratigraphic sections within the dune field the extent of the gksd underwent a fluctuating shrinkage coincident with neoglaciation this downsizing trend was interrupted by periods of increased sand deposition into lakes occurring 4800 4200 3300 2600 1300 700 and 300 100 calendar years ago aridity in the kobuk valley during the holocene probably was controlled by the frequency of north pacific storms entering the region in late summer our results describe the first continuous history of changing moisture balance for central beringia during the holocene and comprise a baseline against which future records of climatic and ecological change in this region can be compared

peatland development at the arctic tree line quebec canada influenced by flooding and permafrost in this study we documented the holocene history of a peat plateau at the arctic tree line in northern quebec using stratigraphic and macrofossil analyses to highlight the effects of geomorphic setting in peatland development paludification of the site began about 6800 cal yr bp from 6390 to 4120 cal yr bp the peatland experienced a series of flooding events the location of the peatland in a depression bounded by two small lakes likely explains its sensitivity to runoff the proximity of a large hill bordering the peatland to the south possibly favored the inflow of mineral laden water the onset of permafrost aggradation in several parts of the peatland occurred after 3670 cal yr bp uplifting of the peatland surface caused by permafrost stopped the flooding according to radiocarbon dating of the uppermost peat layers permafrost distribution progressed from the east to the west of the peatland indicating differential timing for the initiation of permafrost throughout the peatland most of the peatland was affected by permafrost growth during the little ice age picea mariana macroremains at 6450 cal yr bp indicate that the species was present during the early stages of peatland development which occurred soon after the sea regression

the holocene evolution of permafrost near the tree line on the eastern coast of hudson bay northern quebec permafrost evolution in postglacial marine silts near the tree line was reconstructed using landform analysis 14c dating and palynostratigraphic analysis of peat sections in the forest tundra below the tree line four sites in peat plateaus have a stratigraphic sequence indicating an alluvial plain environment from 6000 to 4800 bp followed by a wetland supporting trees and shrubs with deep snow accumulation and without permafrost ground heave occurred between 1900 and 1200 bp as peat plateaus and palsas were formed in the shrub tundra above the tree line three permafrost sites with buried peat beds suggest that climatic conditions were cold enough for discontinuous permafrost in the surrounding landscape starting from land emergence about 5800 bp however fen expansion and sedge peat accumulation continued over unfrozen ground until 2300 1560 and 1400 bp at these dates the sites were buried with silt probably as a result of mass wasting on nearby permafrost mounds and then permafrost aggrad

a late mesoproterozoic 40ar 39ar age for a melt breccia from the keurusselka impact structure finland field investigations in the eroded central uplift of the 30 km keurusselka impact structure finland revealed a thin dark melt vein that intersects the autochthonous shatter cone bearing target rocks near the homestead of kirkkoranta close to the center of the impact structure the petrographic analysis of quartz in this melt breccia and the wall rock granite indicate weak shock metamorphic overprint not exceeding 8 10 gpa the mode of occurrence and composition of the melt breccia suggest its formation as some kind of pseudotachylitic breccia 40ar 39ar dating of dark and clast poor whole rock chips yielded five concordant late mesoproterozoic miniplateau ages and one plateau age of 1151 10 ma 11 ma 2 mswd 0 11 p 0 98 considered here as the statistically most robust age for the rock the new 40ar 39ar age is incompatible with 1 88 ga svecofennian tectonism and magmatism in south central finland and probably reflects the keurusselka impact followed by impact induced hydrothermal chloritization of the crater basement in keeping with the crosscutting relationships in the outcrop and the possible influence of postimpact alteration the late mesoproterozoic 40ar 39ar age of 1150 ma should be treated as a minimum age for the impact the new 40ar 39ar results are consistent with paleomagnetic results that suggested a similar age for keurusselka which is shown to be one of the oldest impact structures currently known in europe and worldwide

holocene palaeoecological reconstruction of three boreal peatlands in the la grande riviere region quebec canada pollen and macrofossil analyses from central peat cores along with 23 radiocarbon dates were used in palaeoecological reconstructions for three peatlands lg1 lg2 and lg3 within the lower la grande riviere watershed in northern boreal quebec basal ages from lg3 and lg2 indicate up to an 1100 years later and possibly more abrupt tyrrell sea retreat in the lg3 area compared with the timeline for the region both autogenic and allogenic factors were found to have influenced local vegetation succession and rates of peat accumulation internal autogenic factors such as peat accumulation were key elements for the general peatland developmental pathway that followed the classic hydrosere sequence pond fen bog regional climate and hydrography are the main external factors associated with changes in vegetation assemblages surface wetness and consequently rates of peat accumulation the lg2 and lg3 peatlands began developing shortly after 7000 cal bp as shallow ponds with herbaceous freshwater aquatic and e

holocene changes in tropical wind intensity and rainfall evidence from southeast ghana abstract remnants of a fixed aeolian dune ridge occur along the southeast coast of ghana just behind the present shoreline aeolian sands also cover extensive areas of the accra plains no dunes are present here the sands mainly occurring as sheets which blanket an early holocene landscape the sediments are of mid holocene age and were deposited during the interval 4500 b p 3800 yr b p when the southwesterly winds were stronger than they are at present and much of tropical africa seems to have been subject to marked aridity the onset of drier windier conditions around 4500 yr b p brought to an end the more equable climates than had characterized much of west africa during the earlier holocene aridity intensified winds and desert expansion between 4500 and 3800 yr b p parallel environmental conditions in tropical continental areas at the height of the late pleistocene glaciation

the quaternary coversands of southwest france detailed stratigraphic analysis and numerical dating osl irsl esr 14c of pleistocene coversands in southwest france enable the construction of a renewed chronostratigraphic framework for sand deposition the chronological data obtained from sandsheet units testify to the development of transgressive dunefields since at least the middle pleistocene mis 10 three main phases of accumulation occurred during the last glacial the oldest one 64 42 ka is associated with wet sandsheet facies histic horizons and zibar type dune fields which reflect deposition in a context strongly influenced by the groundwater table the late pleniglacial 24 14 ka corresponds to the main phase of coversand extension in a drier context silty gley horizons suggest however local interruptions of sand drifting during gs 2 1 lateglacial stabilization of the coversands may not have occurred before gi 1c allerod which was typified by the development of cumulic arenosols these were covered by parabolic dunes during the younger dryas the variations in extent of the emerged continental shelf during the glacial interglacial cycles may explain the uneven geographical distribution of sand deposition through time because of coastline retreat up to 100 km north of 45 n during the lgm lowstand the coversands were unable to reach the northern part of the basin comparison with other european regions highlights stronger affinities of the french record with portugal than with the netherlands and great britain probably because of reduced influence of permafrost

a 1 2 myr record of isotopic changes in a late pliocene rift lake ethiopia the hadar fluvio lacustrine formation ethiopia contains an original hominid fossil australopithecus afarensis and an abundant vertebrate faunal assemblage1 2 the formation3 4 consists of a 150 300 m thick sequence of fine to coarse detrital sediments originating from the ethiopian plateau escarpment with some interbedded pyroclastic layers the three lower members of the formation were formed in a lacustrine environment which was occasionally interrupted by fluvial drainage the upper member is quite distinct and formed as an alluvial fan delta this sedimentary sequence was deposited at the end of the pliocene between 3 9 and 2 7 myr as indicated by magnetostratigraphy5 the palaeomagnetic record spans the gilbert gauss transition period k ar dating6 7 and biostratigraphy8 we consider here the oxygen and carbon isotope variations observed throughout the formation and their palaeo hydrological implications

late holocene atmospheric dust deposition in eastern canada st lawrence north shore dust deposition in two ombrotrophic peatlands baie and ile du havre peatland idh bogs of the estuary and gulf of the st lawrence in eastern canada was reconstructed using elemental geochemistry the rare earth elements rees and other lithogenic element concentrations were measured by icp oes and q icp ms along two peat cores spanning the last 4000 years principal component analyses on the geochemical profiles show that rees display the same behavior as al ti sc and zr all conservative elements which suggests that rees are immobile in the studied peat bogs and can be used as tracers of dust deposition plant macrofossils were also used to infer past environmental and humidity changes the dust fluxes were reconstructed using the sum of rees ree the range of dust deposition varies from 0 2 to 3 8 g m 2 yr 1 in the baie bog while the idh bog shows lower fluxes ranging between 0 1 and 1 2 g m 2 yr 1 the highest dust fluxes in the baie bog were recorded from 1750 1000 cal bp to 600 100 cal

assessing the effects of climate change and land use on northern labrador forest stands based on paleoecological data abstract we reconstructed the late holocene vegetation of the nain region northern labrador northeastern canada in order to assess the influence of climate and historic land use on past shifts in forest composition chronostratigraphy was used in combination with macrofossil and pollen data from monoliths sampled from four peatlands paleoecological reconstructions produced a vegetation history spanning 4900 years for the nain region that is largely concordant with other studies in labrador an initial open forest tundra phase was followed by an increase in tree cover at around 2800 cal yr bp paludification began 200 cal yr bp a decline in picea and its subsequent disappearance from most of the sites occurred 170 cal yr bp ad 1780 in a period of relatively mild conditions during the little ice age this event was followed by the establishment of larix laricina in the region local anthropogenic factors are likely responsible for these later developments as they were not observed in other regional studies the period around ad 1780 corresponds to the establishment of the moravian missionaries on the labrador coast which increased the need for fuel and lumber we conclude that changes in land use are reflected in the patterns of vegetation and hydrological change at the study sites

late proterozoic tectonic events in southern finland constrained by 40ar 39ar incremental heating and single spot fusion experiments on k feldspars the post svecofennian tectonic development of southern finland is controlled by intrusion of rapakivi granites and associated rocks reactivation of svecofennian wrench zones formation of sedimentary basins and successive intrusion of olivine dolerite dykes and sills relative age determinations have revealed that fault reactivation acted before simultaneously and after intrusion of the rapakivi granites results of

the impact of fire on sand dune stability surface coverage and biomass recovery after fires on western australian coastal dune systems from 1988 to 2016 abstract this study aims to determine the common response of coastal sand dunes in western australia wa to fire on decadal time scales in terms of ecological geomorphic climatic interactions to test the hypothesis that fire plays a role in coastal dune destabilisation fires are commonly suggested to have contributed to widespread dune reactivation in australia and globally a hypothesis that is relatively untested we used data from the landsat thematic mapper enhanced thematic mapper plus and operational land imager missions to monitor changes in surface coverage on coastal sand dunes in south west wa after fires we analysed 31 fire scars from 1988 to 2016 in two landsat scenes on the west and south coast of wa recovery ratios derived from the normalised difference vegetation index ndvi were used to monitor patterns in post fire biomass and surface cover recovery ratios are correlated with indices of burn severity and meteorological data to investigate relationships we also used maximum likelihood classification to monitor changes in bare sand area results suggest that recovery followed a strongly consistent pattern and is characterised by rapid vegetation cover re establishment within six to twelve months prior to this some aeolian activity may have occurred but without substantial surface changes initial germination and or resprouting were followed by steady growth up to seven years where ndvi typically neared pre fire values some variation in early recovery occurred between the west and south coast possibly owing to relative proportions of reseeding and resprouting plants a log regression explained 75 of the recovery pattern 79 on the south coast precipitation had some ability to explain recovery up to nine months post fire r 2 0 29 to 0 54 no relationships were observed between estimates of burn severity and recovery after nine months the biggest cause of spatial variation in recovery was the pre fire community composition and related seedbank or resprouting density image classification did not identify any new blowout features except where fires were not the primary cause results suggest that fires are not presently contributing to the destabilisation of coastal dunes in south west wa

geomorphology of high latitude coastal dunes a review the purpose of this review is to assess if there are any specific processes and morphologies distinguishing coastal dunes developed in cold climate conditions in order to illustrate how climate can exert a control on coastal dune morphologies in the arctic availability of sand supply and the duration of winter conditions are limiting factors for the development of large coastal dunes they are small in size and embryo dunes including nebkha are the dominant and often only coastal dune type in milder subarctic settings characterized by a longer surficial ice free season a greater variety of coastal dunes are found mainly foredunes blowouts and parabolic dunes in subarctic areas as along the se coast of hudson bay niveo aeolian processes actively affect coastal dune development these processes do not generally imprint permanent morphologies although some distinctive sedimentary structures owing to the melting of snow are observed the coastal dunes of the arctic regions differ from the dunes of subarctic and temperate regions mainly because of their limited spatial and morphological development extreme climatic conditions low precipitation extreme cold and very limited vegetation growing season combined with low sediment supply explain the fact that only embryo dunes develop in arctic environments

the himalayas a modern analogue for archaean crustal evolution abstract present crustal evolution models fail to account for the generation of the large volumes of continental crust in the required time intervals if the oceanic crust was appreciably thicker in the archaean as geothermal models would indicate then oceanic crustal collision on the scale of the present day himalayan continental collision zone may have been a frequent occurrence in the archaean resulting in extensive partial melting of the hydrous underthrust oceanic crust to produce voluminous tonalite melts leaving a depleted stabilised basic residuum

evidence for structural repetition in the greenstones of the kalgoorlie district western australia abstract regional mapping and air photographic interpretation of an area of about 20 000 km 2 centred on kalgoorlie provided compelling evidence that some previously published polycyclic stratigraphies cannot be substantiated large areas of rocks formerly proposed as younger cycles represent repetition mainly by faulting of a somewhat simpler stratigraphic sequence the main lines of support are 1 the similarity of older and younger mafic ultramafic successions 2 the tendency of younger sequences to merge with older ones when traced along strike and 3 the abundant evidence of faulting along critical contacts the subtle concordant nature of some of the faulting is consistent with an origin by thrusting at an early stage in the tectonic history especially where repeat sequences are folded around major upright structures later reactivation of sheared contacts and initiation of new ones during upright folding and faulting and transcurrent shearing is believed to have widely occurred gravitational gliding is proposed as a possible mechanism for thrust generation this being consistent with evidence of earlier instability in the sedimentation style of turbidites debris flows and olistostromes however conclusive evidence of a mechanism is lacking due to incomplete field evidence the repetition is viewed as a rearrangement of recognisable elements of the local stratigraphy rather than the result of a major collisional event at a plate margin this tends to favour an intracratonic rather than an oceanic setting for the local greenstones though the characteristic geological features of modern continental rifts have not been observed

the genesis and tectonic control on archaean gold deposits of the western australian shield a metamorphic replacement model abstract gold deposits occur in greenstone belts world wide and contribute to anomalously high gold production from archaean terranes as in other cratons archaean gold mineralization of western australia represents a complex array of deposit styles despite this most deposits are clearly epigenetic and large deposits have a number of features in common including their strong structural controls distinctive wallrock alteration fe sulphide k mica albite ca mg fe carbonates consistent metal associations au ag as sb w b low base metals commonly fe rich host rocks great depth extension and lack of appreciable vertical zonation these shared characteristics combined with their ubiquitous occurrence indicate that archaean gold deposits had a common origin related to the tectonic evolution of greenstone belts auriferous hydrothermal systems were broadly synchronous with regional metamorphism and emplacement of synkinematic granitoids and felsic porphyry intrusions although these gold systems involved low salinity lowdensity reduced near neutral h 2 o co 2 fluids carrying gold as reduced sulphur complexes the origin of the fluids is equivocal most timing evidence and stable isotope data cannot distinguish metamorphic from magmatic granitoid or felsic porphyry orggins but the lack of consistent spatial relationships between specific volumetrically significant intrusive phases and large gold deposits in a number of cratons strongly favours metamorphic derivation of fluids the metamorphic replacement model for gold mineralization involves devolatilization of the lower portions of the greenstone pile with high geothermal gradients inhibiting significant melting co 2 possibly formed by the decarbonation of early alteration related to mantle degassing along crustal scale synbasinal fault zones auriferous fluids were channelled along greenstone scale faults in part developed during reactivation of crustal scale faults in a strike slip regime gold deposition occurred largely under greenschist facies conditions about 300 400 c 1 2 kb in response to decreasing gold solubility with declining temperature however a major control on gold deposition was fluid wallrock interaction many large deposits formed by sulphidation of fe rich host rocks with synchronous deposition of fe sulphides and gold however the variable nature of gold depositing reactions including lowering of fo 2 and ph allowed a multitude of small and some large deposits to form wherever that fluid circulation occurred in consequence several of the relatively small deposits currently worked from open pit are hosted by ultramafic and felsic rocks there are few constraints on the source of components au s k co 2 added to gold deposits but even giant deposits such as the golden mile kalgoorlie could have formed from a realistic greenstone source volume ca 8 8 5 km convective circulation of fluids could have contributed to the generation of high fluid rock ratios on the regional scale the markedly heterogeneous distribution of large gold deposits gold productivity and host rocks to deposits can be accommodated by the metamorphic replacement model the most favourable conditions for development of auriferous hydrothermal systems operated in younger ca 2 7 0 1 ga rift phase greenstones where greatest extension and crustal thinning produced high geothermal gradients crustal scale synbasinal faults and rapid extrusion and burial of volcanics including abundant komatiites iron rich tholeiitic basalts and dolerites were preferred host rocks for large gold deposits the least favourable conditions existed in older ca 3 5 3 4 ga platformphase greenstones where gentle sagging on submerged continental crust produced eruption of mainly mafic volcanics with few komatiites commonly in very shallow water environments this allowed intense synvolcanic alteration of both gold source rocks and potential host rocks the generally smaller gold deposits formed mainly in ultramafic or greywacke hosts younger ca 3 0 ga platform phase greenstones appear intermediate in nature but unlike other greenstones have significant epigenetic gold deposits in originally oxide facies bif which were deposited on relatively deep water platforms similar controls appear to exist on a world scale with gold mineralization peaking at ca 2 7 0 1 ga in response to development of major rift zones in thickened relatively mature continental crust interestingly the giant witwatersrand goldfield formed at about the same time

a continuous record of holocene eolian activity in west greenland eolian landforms are widespread alongside proglacial valley sandurs in west greenland and comprise low relief sand sheets climbing dunes and upland loess sedimentary facies mainly reflect distance to outwash source zones and the influence of vegetation cover the sediments show stratification types typical for poorly to moderately vegetated sand sheets alternately laminated silt peat sequences and unstratified loess twenty five accelerator mass spectrometry 14c dates provide the basis for the chronostratigraphy of the inland eolian deposits 14c dates from interstratified sand sheets suggest that the bulk of eolian sands were deposited prior to 3400 cal yr b p and after 550 cal yr b p this two phase formation for the inland dunes most likely reflects local changes in proglacial floodplain development and meltwater rerouting associated with a significant recession of the greenland ice sheet during the mid holocene climate optimum subsequent floodplain regeneration and renewed sand sheet formation after 550 cal yr b p followed when the ice margin readvanced to its present position in contrast atmospheric deposition of regionally derived silt in upland peat mires has been continuous since at least 4750 cal yr b p silt influx data demonstrate a strongly episodic history of the intensity of eolian activity over the past five millennia which tentatively reflects alternating periods of winter aridity associated with the variable incursion of maritime air masses over the interior ice free areas of west greenland

holocene relict woodlands at the eastern canadian treeline abstract we present direct evidence for the relict nature of lichenspruce woodlands thriving at treeline using 14c dated stands growing in the humid climate of eastern hudson bay in northern quebec black spruce picea mariana mill bsp forms two groups of relict stands a neoglacial group of postfire origin dating between 2000 and 900 yr b p and a pre neoglacial group most likely established between 4500 and 3200 yr b p the latter group shows no evidence of fire absence of charcoal under topsoil organic horizon the stands are exceptional because they probably are the direct lineages of the primeval forests that colonized the land sometime after deglaciation the structure of the relict lichen spruce communities gives strong support to the current thesis that considers lichen spruce woodland as a self perpetuating open forest typical of the subarctic environment

holocene solifluction climate variation and fire in a subarctic landscape at pippokangas finnish lapland based on radiocarbon dated buried charcoal a large number of radiocarbon dates from charcoal layers buried beneath stacked solifluction lobes at pippokangas in the northern boreal zone of finnish lapland are used to reconstruct a holocene history of solifluction although the site is surrounded by scots pine forest the solifluction lobes occur on the lower slopes of a kettle hole the microclimate of which prevents the growth of trees samples from the upslope end of charcoal layers have enabled the recognition of four synchronous phases of solifluction lobe initiation 7400 6700 4200 3400 2600 2100 and 1500 500 cal yr bp rates of lobe advance are shown to be lobe dependent and age dependent initially average rates were commonly 0 14 0 19 cm yr 1 later falling to 0 02 0 07 cm yr 1 or less as the lobes approached the bottom of the slope the absence of charcoal prior to 8000 cal yr bp together with single irsl and tl dates indicate a relatively stable early holocene landscape the onset of solifluction around 7400 cal yr bp appears to have followed the immigration of pine around the site which increased the frequency of forest fires phases of solifluction activity seem to have been triggered by millennial scale variations in effective moisture the climatic hypothesis rather than episodic burning of the surface vegetation cover the geoecological hypothesis although climate may also have affected fire frequency and severity copyright 2005 john wiley sons ltd

shifting zonal patterns of the southern boreal forest in eastern canada associated with changing fire regime during the holocene this research aims at uncovering the stand scale holocene fire history of balsam fir forest stands from two bioclimatic zones of the boreal forest and assessing the existence of a sub continental shift in past fire activity that could have triggered a change in the holocene zonal pattern in eastern canada the extant closed crown boreal forest corresponds to two ecological regions separated along 49 n the northern black spruce zone and the southern balsam fir zone we sampled balsam fir stands from the southern fir zone n 7 and among the northernmost patches of fir forest located far beyond the fir zone boundary into the spruce zone n 6 macrofossil analysis of charcoal in mineral soils was used to reconstruct both the stand scale and regional holocene fire histories data were interpreted in the context of published palaeoecological evidence stands of the balsam fir zone were submitted to recurrent fire disturbances between c 9000 and 5000 cal yr b p local fire histories suggested that four sites within the fir zone escaped fire during the holocene such fire protected sites allowed the continuous maintenance of the balsam fir forest in the southern boreal landscape stands of the spruce zone have been affected by recurrent fires from 5000 cal yr b p to present local fire histories indicated that no site escaped fire in this zone published palaeoecological data suggested that balsam fir migrated to its current northern limit sometime between 7300 and 6200 cal yr b p a change of the fire regime 5000 years ago caused the regional decline of an historical northern balsam fir forest and its replacement by black spruce forest the consequence was a sub continental reshuffling of the fir and spruce zones within the closed crown boreal forest the macrofossil analysis of charcoal in mineral soils was instrumental to the reconstruction of stand scale holocene fire history at sites where no other in situ fire proxies were available

the late holocene record of aeolian and fire activity in northern quebec canada a set of 196 14c dates was used to reconstruct late holocene aeolian activity in the hudson bay area along a south north transect crossing the northern boreal forest the forest tundra and the shru

holocene fire on the northeast tibetan plateau in relation to climate change and human activity abstract a series of holocene charcoal concentrations cc records from a slope sedimentary section in gonghe basin northeast tibetan plateau are analyzed to investigate fire characteristics e g frequency or magnitude and their linkages with paleoclimate change and ancient human activities the results reveal that changes in fire indicators are well correlated with paleoclimatic change during the past 10 0 ka bp this pattern is characterized by lower cc in the warm and humid middle holocene and higher total cc in the cold dry climate of the early and late holocene meanwhile an event characterized by abnormally high cc values at 3 6 ka bp distinct from the above trend indicates an anomalously high fire frequency which cannot easily be explained as the result of a climatic event alternatively this event is noted to correspond closely with the time of rapid human occupation of the high elevation tibetan plateau many basic domestic and agricultural activities e g slash and burn farming cooking or heating have required fire in the hostile environment of the tibetan plateau this is reflected in the higher cc following the spread of human habitation the analysis of cc might be a useful alternative method for investigating human activities when no direct evidence is available in the holocene tibetan plateau records

sphagnum δ13c values as indicators of palaeohydrological changes in a peat bog late holocene peat stratigraphy of a canadian boreal peat bog was examined to evaluate the poten tial of sphagnum 13 c values as surface moisture proxy indicators isotopic measurements were compared to tes tate amoebae inferred water table depth reconstructions plant macrofossil assemblages and past decompo sition levels inferred by colorimetric humification ams radiocarbon dates were coupled with 210 pb dates to establish peat chronology although the mechanisms underlying carbon fractionation processes in peatlands are not well understood we demonstrate that sphagnum 13 c values have potential for palaeohydrological recon structions since variations presented by the isotopic values can generally be correlated with the other proxy records especially during drier episodes

impacts of holocene climatic variations on alluvial fan activity below snowpatches in subarctic quebec abstract in the lake guillaume delisle area of subarctic quebec storm generated alluvial fans have been active sporadically throughout the holocene in this study we propose that the persistence of late lying snowpatches in fan catchments during holocene cold episodes promoted alluvial fan activity by lowering the precipitation threshold required to trigger a torrential event this hypothesis was tested by characterizing the depositional processes responsible for alluvial fan formation below snowpatches and by reconstructing the holocene alluvial fan activity stratigraphic and sedimentary analyses conducted on seven alluvial fans revealed that they were deposited by torrential activity leading to waterlaid transient or hyperconcentrated deposition the chronology of the storm generated alluvial fans based on 22 radiocarbon dates indicates that torrential activity was enhanced during the cooler late holocene i e after ca 3500 cal yr bp snowier winters and cooler summers were beneficial to nival activity allowing the persistence of larger snowpatches throughout the summer and fall seasons rainfall induced thaw of such snowpatches during rainstorm events is inferred to have contributed to alluvial fan activity by increasing water availability three peaks of alluvial activity occurred during the late holocene 2950 2750 1900 1400 and 800 300 cal yr bp and are indicative of increased storminess resulting in higher fan activity increased fan activity during cooler episodes was concurrent with increased runoff activity in the immediate pronival area this stresses the importance of nivation below snowpatches and pinpoints the role of nivation in enhancing geomorphological activity during period of cooler and more humid climate in subarctic environments

foredune development along a subarctic emerging coastline eastern hudson bay canada abstract a study of sedimentary processes and evolution of subarctic foredunes along a rapidly emerging coastline in southeastern hudson bay showed that niveo eolian sedimentation is a significant process contributing to the formation of these foredunes the fall storm berm and the sand laden ice foot are the prime sedimentary sources for the niveoeolian deposits which are generally coarser grained than the eolian sand deposited during summer the annual sedimentation in the backshore zone is less than in typical mid latitude regions the development of established foredunes in this subarctic environment seems to require a longer period of time than in other climatic zones the short term backshore evolution 1954 1990 shows that sediment supply appears to be a major factor controlling foredune morphology and dynamics phases of sediment surplus seem to correspond to rapid seaward progradation and formation of low foredune terraces or low foredune ridges with a beach ridge like morphology conversely high foredunes probably develop during periods of lower sediment supply and slower beach progradation on a longer time scale the relative sea level fall controls coastline progradation and results in the formation of raised coast parallel relict foredune ridges

increased atmospheric dust deposition during the neoglacial in a boreal peat bog from north eastern canada abstract dust deposition in north eastern canada was estimated from the geochemical signature of a boreal peat bog from the james bay lowlands the rare earth elements and other lithogenic elements as well as nd isotopes were measured by q icp ms icp oes and mc icp ms respectively along a 4 20 m peat core covering the last 7000 years a principal component analysis performed on the geochemical dataset shows that rees display the same chemical behavior as other lithogenic elements such as al and ti which suggests that they are immobile in the peat column and can be used as tracers of dust deposition after 4000 cal yr bp peaks in dust deposition associated with greater variability in testate amoebae assemblages and plant macrofossil composition as well as a change in nd values are observed between 7000 and 4100 cal yr bp the nd values varied from 36 to 29 while they gradually increased from 4100 cal yr bp until 1500 cal yr bp suggesting proportionally less dust from local source s is deposited in favor of more regional source s from 1500 cal yr bp nd values remained relatively stable around 15 and 12 most of the dust peaks correspond to documented cold and dry periods likely linked to intrusion of arctic air masses a migration of the polar front might explain the more frequent intrusion of arctic air masses in the region and the greater variability in the lg2 record over the last 4000 years

sand incursion into temperate lithuania and tropical the bahamas maritime vegetation georadar visualization of target rich aeolian lithosomes abstract interaction of windblown sand with maritime vegetation either as dune migration or episodic grain transport is a common phenomenon along many sandy coasts vegetation introduces antecedent surface roughness especially when scaled to the landform height but its role may be concealed if overwhelmed by aeolian incursion and burial where field observations and cores lack detail for characterizing this complex process ground penetrating radar gpr offers continuous visualization of aeolian sequences along the curonian spit lithuania dune reactivation phases resulted in massive invasion of siliciclastic sand triggered by natural perturbations and land clearance massive 30 m high dunes entombed mature pine oak and alder stands and this process is ongoing mid frequency 200 mhz georadar surveys reveal landward dipping lateral accretion surfaces interrupted by high amplitude point source anomalies produced by recently buried trees in tropical regions dense vegetation and potential for rapid lithification of carbonate sand results in more complex internal structures along the windward coast of san salvador island the bahamas a massive dune has buried several generations of maritime scrubland resulting in highly chaotic reflection pattern and high target density on a nearby little exuma island numerous reentrants in aeolianites promoted formation of blowouts and incursion of windblown sand 10 25 m into a silver thatch palm forest high frequency 800 mhz gpr images resolve diffractions from trunks and roots buried by 2 m of oolitic sand basal refection morphology helps differentiate the irregular dune beachrock surface from a smooth palm frond mat aside from detecting and mapping buried vegetation geophysical images capture its effect on sediment accumulation this has the potential for differentiating its effect from other discordant structures within dunes clasts dissolution voids trunk molds burrows and cultural remains

the archaean whim creek belt an ensialic faultbounded basin in the pilbara block australia abstract the whim creek belt in the western pilbara block australia is an elongate structural basin 80 km long and up to 15 km wide it contains a c 2950 ma old sequence of bimodal volcanics volcaniclastics and terrigenous sediments which unconformably overlies granitoids and older deformed and metamorphosed supracrustal sequences the volcano sedimentary sequence was deposited in terrestrial to marine environments in a fault bounded basin with approximately the same configuration as the present whim creek belt alluvial and subaqueous fanglomerate facies were deposited along the northern margin of the basin with submarine fan and basinal facies deposited longitudinally in the centre of the basin the basin margin faults are now part of a regional pattern of strike slip faults which were active both prior to and after basin formation and probably had a significant lateral component during basin evolution the whim creek belt is thus interpreted as an archaean rift or pull apart basin similar basins containing bimodal volcanics and terrigenous sediments occur at the head of the present gulf of california e g salton trough although a direct tectonic analogy cannot be assumed this interpretation implies that the archaean tectonic pattern in the western pilbara involved externally imposed deformation and was not solely the result of gravity driven uprise of granitic batholiths