holocene coastal glaciation of alaska holocene uctuations of the three cirque glaciers on the seward peninsula and ve groups of tidewater and land terminating glaciers along the northernmost gulf of alaska provide a proxy record of late holocene climatic change furthermore the movements of the coastal glaciers were relevant to late holocene native american migration the earliest expansion was recorded about 6850 yr bp by hubbard glacier at the head of yakutat bay in the gulf of alaska however its down fjord advance to the bay mouth was delayed until 2700 bp similarly expansions of the icy bay bering and mccarty glaciers occurred near their present termini by 3600 3000 bp compatible with marked cooling and precipitation increases suggested by the alaskan pollen record decrease in glacier activity 2000 bp was succeeded by advances of gulf coastal glaciers between 1500 and 1300 bp correlative with early medieval expansions across the northern hemisphere a medieval optimum encompassing at least a few centuries prior to ad 1200 is recognized by general retreat of land terminating glaciers but not of all tidewater glaciers little ice age advances of land based glaciers many dated with the precision of tree ring cross dating were centered on the middle 13th or early 15th centuries the middle 17th and the last half of the 19th century a d strong synchrony of these events across coastal alaska is evident 2000 elsevier science ltd all rights reserved

little ice age glacial activity in peter lougheed and elk lakes provincial parks canadian rocky mountains dendrochronological lichenometric and i4c studies at 14 glacier sites in peter lougheed and elk lakes provincial parks were used to develop a chronology of little ice age glacial events the earliest indications of glacial activity are represented by moraines deposited prior to the 16th century a major glacial expansion in the 17th century is recorded at three sites where i4c dates show glaciers reached their maximum down valley positions lichenometric dates and tree growth suppression records show a phase of glacial activity early in the 18th century for which there is only sparse morainic evidence most moraines in the area date from a glacial advance culminating in the mid 19th century and moraine formation was complete everywhere by the late 1800 s recessional moraines are rare in the study area and indicate that ice front retreat has been relatively continuous since the 19th century the glacial chronology developed in this work is comparable to that reconstructed for both the main ranges of the canadian rockies and the coast ranges of the southern cordillera resum6 les ctudes dendrochronologique 1ichcnomctrique et radiomktrique au i4c de 14 sites rcalisces dans les parcs provinciaux de peter lougheed et de elk lakes ont servi a ctablir une chronologie des cvbnements glaciaires survenus durant le petit bge glaciaire les plus anciens indices de l activitk glaciaire sont reprcsentcs par les moraines dcposces anttrieurement au xvie sibcle une expansion glaciaire majeure durant le xviie sibcle est enregistrke sur trois sites ou les dates au 14c rcvklent la prksence de glaciers avec leurs positions de progression maximale vers le bas de la vallce les datations fondces sur la 1ichcnomctrie et sur les registres de cessation de la croissance des arbres montrent la prcsence d une phase d activitk glaciaire au debut du xviiie sibcle qui a iaissc peu de dcp8ts morainiques dtcelables la plupart des moraines qui apparaissent dans la rcgion datent d une avancce glaciaire qui avait atteint son apogce d extension au milieu du xixe sikcle et leur construction fut complctce vers la fin des annces 1800 les moraines de rkcession sont rares dans la rcgion ctudik cependant elles indiquent que depuis le xixe sibcle il y a eu un retrait relativement continu du front glaciaire la chronologie glaciaire ktablie dans la prcsente ctude est analogue i celle reconstruite pour les chaines principales des rocheuses du canada et pour le domaine c8tier de la cordillbre mkridionale traduit par la raaction

the sedimentary record of moose lake implications for glacier activity in the mount robson area british columbia the postglacial sedimentary environment of moose lake was investigated using 3 5 khz subbottom profiles and cores from the sediment surface a late phase in the deglaciation of the upper fraser river valley involved a valley glacier that flowed east to west and that terminated near the present day outlet of moose lake the overdeepened fraser valley was infilled with ice contact sediments including terminal and recessional moraines thereby damming westward drainage and forming moose lake eastward glacier retreat resulted in the deposition of ice blocks in the shallow west zone of the lake where subsequent melting disturbed conformable glaciolacustrine deposits the main moose lake basin records a transition from proximal to distal proglacial environments however late glacial and postglacial sediments are dominated by settling from suspension coarse but localized sediment inputs are derived from the thunder creek fan delta and avalanche activity on the north facing slope of the south shore depths

reply to miller et al 2013 substantial agreement on the timing and magnitude of late holocene ice cap expansion between east greenland and the eastern canadian arctic a commentary on lowell et al 2013

dendrochronology and late holocene history of bering piedmont glacier alaska fluctuations of the piedmont lobe of bering glacier and its sublobe steller glacier over the past two millennia are reconstructed using 34 radiocarbon dates and tree ring data from 16 sites across the glaciers forelands the general sequence of glacial activity is consistent with well dated fluctuations of tidewater and land terminating glaciers elsewhere along the gulf of alaska extensive forested areas along 25 km of the bering ice margin were inundated by glacio lacustrine and glacio fluvial sediments during a probable ice advance shortly before 500 cal yr a d regrowth of forests followed the retreating ice as early as the 7th century a d with frequent interruptions of tree growth due to outwash aggradation forests overrun by ice and buried in outwash indicate readvance about 1080 cal yr a d retreat followed with ice free conditions maintained along the distal portions of the forefield until the early 17th century after which the ice advanced to within a few kilometers of its outer neoglacial moraine ice reached this position after the mid 17th century and prior to 200 yr ago since the early 20th century glacial retreat has been punctuated by periodic surges the record from forests overrun by the nonsurging steller lobe shows that this western ice margin was advancing by 1250 a d reaching near its outer moraine after 1420 cal yr a d since the late 19th century the lobe has dominantly retreated

glacier fluctuations during the past millennium in garibaldi provincial park southern coast mountains british columbia the little ice age glacier history in garibaldi provincial park southern coast mountains british columbia was reconstructed using geomorphic mapping radiocarbon ages on fossil wood in glacier forefields dendrochronology and lichenometry the little ice age began in the 11th century glaciers reached their first maximum of the past millennium in the 12th century they were only slightly more extensive than today in the 13th century but advanced at least twice in the 14th and 15th centuries to near their maximum little ice age positions glaciers probably fluctuated around these advanced positions from the 15th century to the beginning of the 18th century they achieved their greatest extent between a d 1690 and 1720 moraines were deposited at positions beyond present day ice limits throughout the 19th and early 20th centuries glacier fluctuations appear to be synchronous throughout garibaldi park this chronology agrees well with similar records from other mountain ranges and with reconstructed n

cratering and modification of wet target craters projectile impact experiments and field observations of the lockne marine target crater sweden marine impacts are one category of crater formation in volatile targets at target water depths exceeding the diameter of the impactor the zones of vaporization melting and excavation of the standard land target cratering model develop partially or entirely in the water column the part of the crater that has a potential of being preserved seafloor crater may to a great extent be formed by material emplacement and excavation processes that are very different from land target craters these processes include a high energy water jet driven excavation flow at greater water depths the difference in strength of the target layers causes a concentric crater to evolve the crater consists of a wide water cavity with a shallow excavation flow along the seabed surrounding a nested deeper crater in the basement the modification of the crater is likewise influenced by the water through its forceful resurge to fill the cavity in the water mass and the seafloor the resurge flow is strongly erosive and incorporates both ejecta and rip up material from the seabed surrounding the excavated crater a combination of field observations and impact experiments has helped us analyze the processes affecting the zone between the basement crater and the maximum extent of the water cavity the resurge erosion is facilitated by fragmentation of the upper parts of the solid target caused by a spallation and b vibrations from the shallow excavation flow and subsequently c the vertical collapse of the water cavity rim wall in addition poorly consolidated and saturated sediments may collapse extensively possibly aided by a violent expansion of the pore water volume when it turns into a spray during passage of the rarefaction wave this process may also occur at impacts into water saturated targets without an upper layer of seawater present our results have implications for impacts on both earth and mars and possibly anywhere in the solar system where volatiles exist have existed in the upper part of the target

glacier fluctuation and tree ring records for the last millennium in the canadian rockies tree ring series and records of alpine glacier fluctuations provide complementary evidence to reconstruct decade to century climate fluctuations over the last millennium in the canadian rockies tree line ring width chronologies in this area are temperature sensitive and long ca 900 years series from sites adjacent to bennington and athabasca glaciers show synchronous declines in ring width during the periods ca 1170 1180 1280 1290 1330 1350 1430 1450 1530 1540 1690 1705 and 1810 1825 a d the latter two events are replicated in many shorter tree ring chronologies and immediately precede the two major periods of moraine development ca 1700 1725 and 1825 1875 a d during the little ice age dendrochronological dating of glacially overridden trees 0 5 1 0 km upvalley of 18th century maximum positions indicate that robson and peyto glaciers were advancing between 1150 and 1350 a d during the earliest phase of the little ice age in the canadian rockies available tree ring data suggest that the level and pattern of climate variability during the 18th and 19th centuries extends back over the last milennium it is also hypothesised that glaciers attained their maximum holocene extent during the little ice age because of the interaction between these decade to century scale fluctuations and the progressive long term decline of incoming summer solar radiation in the northern hemisphere over the last 10 000 years

late holocene expansion of istorvet ice cap liverpool land east greenland abstract the greenland ice sheet is undergoing dynamic changes that will have global implications if they continue into the future in this regard an understanding of how the ice sheet responded to past climate changes affords a baseline for anticipating future behavior small independent ice caps adjacent to the greenland ice sheet hereinafter called local ice caps are sensitive indicators of the response of greenland ice marginal zones to climate change therefore we reconstructed late holocene ice marginal fluctuations of the local istorvet ice cap in east greenland using radiocarbon dates of subfossil plants 10 be dates of surface boulders and analyses of sediment cores from both threshold and control lakes during the last termination the istorvet ice cap had retreated close to its maximum holocene position by 11 730 cal yr bp radiocarbon dates of subfossil plants exposed by recent recession of the ice margin indicate that the istorvet cap was smaller than at present from ad 200 to ad 1025 sediments from a threshold lake show no glacial input until the ice cap advanced to within 365 m of its holocene maximum position by ad 1150 thereafter the ice cap remained at or close to this position until at least ad 1660 the timing of this the most extensive of the holocene expansion is similar to that recorded at some glaciers in the alps and in southern alaska however in contrast to these other regions the expansion in east greenland at ad 1150 appears to have been very close to if not at a maximum holocene value comparison of the istorvet ice cap fluctuations with holocene glacier extents in southern hemisphere middle to high latitude locations on the antarctic peninsula and in the andes and the southern alps suggests an out of phase relationship if correct this pattern supports the hypothesis that a bipolar see saw of oceanic and or atmospheric circulation during the holocene produced asynchronous glacier response at some localities in the two polar hemispheres

geomorphic and climatic change over the past 12 900 yr at swiftcurrent lake glacier national park montana usa abstract glaciated alpine landscapes are sensitive to changes in climate shifts in temperature and precipitation can cause significant changes to glacier size and terminus position the production and delivery of organic mass and in the hydrologic energy related to the transport of water and sediment through proglacial environments a sediment core representing a 12 900 yr record collected from swiftcurrent lake located on the eastern side of glacier national park montana was analyzed to assess variability in holocene and latest pleistocene environment the spectral signature of total organic carbon content toc since 7 6 ka matches that of solar forcing over 70 500 yr timescales periodic inputs of dolomite to the lake reflect an increased footprint of grinnell glacier and occur during periods when sediment sinks are reduced glacial erosion is increased and hydrologic energy is increased grain size carbon nitrogen c n ratios and toc broadly define the termination of the younger dryas chronozone at swiftcurrent lake as well as major holocene climate transitions variability in core parameters is linked to other records of temperature and aridity in the northern rocky mountains over the late pleistocene and holocene

the marine lockne impact structure jamtland sweden a review the lockne impact structure in jamtland 63 00 20 n 14 49 30 e formed in the middle ordovician at approximately 455 ma the structure is a concentric crater with a total diameter of 13 5 km the impact took place in a marine environment seawater played an important role in the cratering process and in crater morphology and the amount of melt remaining in the structure seawater rushed back into the crater in a resurge eroding and redepositing the ejecta among the resurge deposit seawater furthermore facilitated the hydrothermal system which was driven by the residual heat in the structure the lockne structure hosts shocked quartz and an iridium anomaly the rim wall round the crater collapsed in the modification stage of the crater and was annihilated by the resurge the fractured basement and the impact breccia were initially rich in open cavities these became partly filled with dominantly calcite the filling contributed to a low density contrast generating a negative gravity anomaly of 22 gu the gravity model indicates a central uplift and a nw directed tilt of the structure this tilt is also seen in the magnetic models the apparent absence of any impact melt is probably real and related to the environment of impact

early modification stage preresurge sediment mobilization in the lockne concentric marine target crater sweden lockne is a concentric impact structure due to a layered target where weak sediments and seawater covered a crystalline basement a matrix supported sedimentary breccia is interlayered between the crystalline breccia lens and the resurge deposits in the crater infill as the breccia is significantly different from the direct impact breccia and the resurge deposit we propose a separate unit name tramsta breccia based on the type locality i e the loc02 drilling at tramsta we use granulometry and a novel matrix line log method to characterize the sedimentology of the tramsta breccia the obliquity of impact combined with the layered target caused an asymmetric concentric transient crater which upon its collapse controlled the deposition of the breccia on the wide brimmed downrange side of the crater where the sedimentary target succession was removed during crater excavation wide overturned basement crater ejecta flaps prevented any slumping of exterior sediments instead the sediments most likely originated from the uprange side where the brim was narrow and the basement crater rim was poorly developed sediment rich and relatively unstable here the water cavity wall remained in closer proximity to the basement crater and aided by the pressure of the collapsing water wall unconsolidated black mud would flow back into the crater the absence of interlayered resurge deposits in the tramsta breccia and the evidence for reworking at the contact between the overlying resurge deposits and the tramsta breccia indicate that the slumping was a rapid process 75 s terminating well before the resurge entered the crater

subglacial methanogenesis a potential climatic amplifier 1 subglacial environments are a previously neglected component of the earth s global carbon cycle a reflection of the view held until recently that they are dominated by abiotic and oxic conditions here we provide a realistic assessment of the theory that the basal regions of the ice sheets that formed over north america and europe during glaciations were host to significant populations of anaerobic microorganisms including methanogens able to metabolize organic carbon sequestered during interglacials and overridden during quaternary glacials in doing so we review the current evidence for subglacial methane release during deglaciation estimate the size of the subglacial reservoir of organic carbon soc and assess the amount of soc available to subglacial microbes and the likely pathways and rates of carbon turnover we then discuss the fate of subglacial methane and the potential impact of its release on atmospheric methane concentrations we calculate that the soc equates to 418 610 pg c and includes carbon from terrestrial soils vegetation peatlands lake and marine sediments the soc that is potentially available for microbial conversion to methane is smaller than this estimate due to 1 glacial erosion 2 accumulation of recalcitrant organic carbon compounds over time 3 conversion to carbon dioxide by aerobic anaerobic respiration and 4 incomplete conversion of labile organic matter to methane we estimate that the total soc available for conversion to methane is 63 pg c our estimates of methane production potentials span a wide range because of the current uncertainty surrounding subglacial metabolic rates we believe however that there is a strong likelihood that subglacial microbes could convert 63 pg of soc to methane during a glacial cycle if this were the case release of this methane from the ice sheet margins during retreat would need to be episodic in order to significantly impact atmospheric methane concentrations our findings suggest that it may well be important to consider subglacial environments as active components of the earth s carbon cycle conclusive determination of the potential impact of subglacial methane production on atmospheric methane concentrations during deglaciation however awaits more precise determination of the ability of subglacial microbes to degrade organic carbon components and their associated rates of metabolism under in situ conditions

sedimentological analysis of resurge deposits at the lockne and tvaren craters clues to flow dynamics the lockne and tvren craters formed about 455 million years ago in an epicontinental sea where seawater and mainly limestones covered a crystalline basement the target water depth for tvaren apparent basement crater diameter d 2 km was probably not over 150 m and for lockne d 7 5 km recent best fit numerical simulations suggest the target water depth of 500 700 m lockne has crystalline ejecta that partly cover an outer crater 14 km diameter apparent in the target sediments tvren is eroded with only the crater infill preserved we have line logged cores through the resurge deposits within the craters in order to analyze the resurge flow the focus was clast lithology frequencies and size sorting we divide the resurge into resurge proper with water and debris shooting into the crater and ultimately rising into a central water plume anti resurge with flow outward from the collapsing plume and oscillating resurge not covered by the line logging due to methodological reasons with decreasing flow in diverse directions at lockne the deposit of the resurge proper is coarse and moderately sorted whereas the anti resurge deposit is fining upwards and better sorted the tvren crater has a smoothly fining up section deposited by the resurge proper and may lack anti resurge deposits at lockne the content of crystalline relative to limestone clasts generally decreases upwards which is the opposite of tvren this may be a consequence of factors such as crater size i e complex versus simple and the relative target water depth the mean grain size i e the mean phi value per meter and standard deviation i e size sorting for both craters can be expressed by the equation 0 60 1 25

a continuous holocene glacial record inferred from proglacial lake sediments in banff national park alberta canada abstract sediment cores from three proglacial lakes in northern banff national park alberta preserve a record of holocene glacial activity upvalley which is more continuous and better dated than available surficial records dating of the cores is based on tephrochronology and 16 ams14c ages of terrestrial macrofossils all cores contain a threefold sequence of lacustrine sediments overlying a late pleistocene diamicton basal lacustrine sediments 10 10014c yr old contain little organic matter sediment composition indicates a large glacigenic contribution a sharp increase in organic content marks the beginning of the altithermal interval at all three lakes this transition occurred abruptly at about 10 10014c yr b p at crowfoot lake and possibly more gradually at the other lakes altithermal sediments contain relatively little glacigenic material and during most of the altithermal glaciers may have been absent above crowfoot and bow lakes glaciers draining into hector lake appear to have persisted through the altithermal a subsequent decrease in organic content in each lake reflecting increased clastic sedimentation marks the end of the altithermal and the onset of neoglacial ice advances the transition took place between about 5800 and 400014c yr b p and may be time transgressive beginning earlier in hector lake than in crowfoot lake changing neoglacial clastic sedimentation rates through the neoglacial interval indicate two main periods of increased glacier extent between ca 3000 and 1800 varve yr ago ca 2900 190014c yr b p and during the last several hundred years during the intervening period glaciers were less extensive but much more extensive than during the recessions of the altithermal interval

identification of peneplains by multi parameter assessment of digital elevation models the concept of peneplains has existed since the end of the nineteenth century typical peneplains are elevated geomorphological features with a low relief surface on top they may be tilted due to tectonic activity or intersected by evolving erosion until now neither a standardized definition for peneplains nor an established procedure to identify and quantify well preserved peneplains as prominent landforms existed at present the global availability of homogeneous digital elevation models dems provides an accurate characterization of the morphology of the earth surface in this study a new numerical dem based fuzzy logic approach is presented for the delineation of peneplains solely from a morphological perspective the approach is based on a morphometric analysis of the 90 arcsec shuttle radar topography mission srtm dem four critical parameters are employed which are implemented within a geographic information system gis the parameters for the correct and unambiguous description of a flat top mountain are i slope ii curvature iii terrain ruggedness index and iv relative height the approach was developed using a test area in the central tibetan plateau which is characterized by representative and well preserved peneplains and for which additional field data were collected in order to verify the method peneplains were delineated in different regions with various geological settings for which potential peneplains were already described in the literature the results from the appalachian mountains andes massif central and new zealand confirm the robustness of the proposed approach copyright 2015 john wiley sons ltd

geophysical signature of malingen the minor crater of the lockne malingen doublet impact structure malingen is the 0 7km wide minor crater associated to the 10 times larger lockne crater in the unique lockne malingen doublet the craters formed at 458ma by the impact of a binary asteroid related

neoglacial history of robson glacier british columbia as glaciers in the canadian rockies recede glacier forefields continue to yield subfossil wood from sites overridden by these glaciers during the holocene robson glacier in british columbia forme

the holocene history of the columbia icefield canada abstract the columbia icefield is the largest icefield in the canadian rockies and feeds eight major glaciers that drain to three different oceans previous glacier studies have focused on athabasca and saskatchewan glaciers primarily due to their easy access this paper reviews evidence of the holocene history from all eight glaciers maximum holocene glacier extent was during the little ice age lia with dating based mainly on minimum tree ring estimates from trees growing on the moraines or from trees scarred tilted or killed by the glaciers the lia maximum advance was during the 19th century at athabasca 1843 4 dome 1846 saskatchewan 1862 and castleguard 1271 and detrital wood from lateral moraines at columbia ca 0 8 0 7ka two overridden stumps at columbia glacier indicate a previously unidentified advance ca 1500 a d these four phases of lia coincide with major reductions in summer temperatures reconstructed at the icefield there are also undated pre 1600 possibly pre lia moraines at kitchener glacier less extensive neoglacial glacier events are documented by an in situ forest bed buried by the saskatchewan glacier ca 2 90 3 4 ka equivalent to the peyto advance and stumps buried by till ca 4 2ka at boundary glacier detrital wood recovered from till at columbia glacier indicates at least one glacier advance ca 2 0 2 2ka till exposed between the bridge river and mazama tephras at stutfield glacier includes detrital wood dating 2 22 2 70 ka that possibly indicates a glacier advance immediately prior to the bridge river tephra regional paleoenvironmental data indicate warmer conditions and higher treelines in the early holocene detrital wood washed out of dome and athabasca glaciers indicates trees were present in these valleys ca 6 7 and 9ka upvalley of present glacier snouts evidence from castleguard cave indicates upstream entrances below the present icefield were probably ice free ca 9 5ka indicating the icefield was much reduced in extent at that time the detrital wood may represent wood killed and reworked by limited glacier advances from the icefield far upstream of present glacier fronts at these times

neoglaciation in the southern coast mountains of british columbia chronology prior to the late neoglacial maximum moraine stratigraphy and morphology radiocarbon dates from klinaklini franklin tiedemann gilbert and bridge glaciers and related information from elsewhere in the coast mountains are used to construct a chronology for glacier fluctuations the garibaldi phase of glacier expansion 6000 5000 14c years bp at the end of the early holocene xerothermic interval is indicated by overridden tree stumps the mid neoglacial tiedemann advance 3300 1900 14c years bp is represented by moraines till and meltwater sediments at three glaciers but only tiedemann glacier attained its greatest holocene extent at this time late neoglacial expansion commenced before 900 14c years bp and continued without notable interruption until glaciers achieved their maximum post pleistocene expansion during the eighteenth and nineteenth centuries evidence for the garibaldi and tiedemann events is scarce within the coast mountains because of the more extensive late neoglacial advance however correlative advances have been

evidence for 1 82 ga transpressive shearing in a 1 85 ga granitoid in central sweden implications for the regional evolution abstract two crustal scale shear zone systems the storsjon edsbyn deformation zone and the hassela shear zone join in the western part of central sweden and form an anastomosing pattern of ductile shear zones several of these up to 1 km wide zones truncate an intrusion previously defined as a component of the major ca 1 80 1 77 ga magmatic suite the revsund granitoids in north central sweden however within the southern part of the intrusion titanites that are components of the fabric in a pervasively deformed shear zone forsaan have a u pb tims age of 1816 2 ma zircon porphyroclasts in the same fabric yield a u pb sims age of 1849 14 ma overlapping with the u pb tims age of 1851 2 ma for titanites from an undeformed granitoid these results are interpreted to define the ages of ductile shearing and magma emplacement respectively this interpretation is supported by microstructures as well as the regional structural pattern characterised by shear zones enveloping virtually undeformed pods of the granitoid previously reported and locally existing magmatic flow structures indicate some syn emplacement deformation the kinematic results characterised by a high proportion of pure shear within the granitoid and oblique dextral shearing along its margin reflect strain partitioning under transpressive conditions the kinematic and geochronological results fit into the regional framework of late orogenic localised deformation along crustal scale shear zones recent absolute datings of shear fabrics defines ca 1 82 1 80 ga as a period of shear zone activity in central sweden temporally this period overlaps with the emplacement of s type granites and granitoids derived from deeper crustal levels a similar situation exists in southern finland structural geochronological and geophysical data suggest that the crustal scale shear zones in central sweden and southern finland may be related temporally and spatially the age and the post tectonic nature on a regional scale of the dated 1 85 ga granitoid have important regional implications as both the age of the intrusion and the ductile shearing are older than the established age range 1 80 1 77 ga of the revsund granitoids either an extended intrusive history for the suite is indicated or the granitoids in this part of the type areas should be excluded from the revsund suite their post tectonic nature implies that the pervasive svecokarelian deformation in the area occurred earlier than generally assumed 1 85 1 80 ga on the other hand approximately coeval calc alkaline granitoids to the south east of the investigated area are folded and foliated pervasively indicating a later svecokarelian evolution in that area i e that the granitoids are located in domains with separate orogenic evolutions

ground surface temperatures in canada spatial and temporal variability 1 past changes in the earth s surface energy balance are recorded in the ground as perturbations of the subsurface thermal regime here we reconstruct ground surface temperature histories gsth from temperature versus depth profiles measured at 246 sites distributed across canada we show that the ground has warmed about 0 7 k in the last 100 years spatial variability is significant and indicates that the largest warming is in the southern areas of canada the apparent signal for the little ice age lia does not appear to be homogeneous across canada

post impact structural crater modification due to sediment loading an overlooked process post impact crater morphology and structure modifications due to sediment loading are analyzed in detail and exemplified in five well preserved impact craters mjolnir chesapeake bay chicxulub montagnais and bosumtwi the analysis demonstrates that the geometry and the structural and stratigraphic relations of post impact strata provide information about the amplitude the spatial distribution and the mode of post impact deformation reconstruction of the original morphology and structure for the mjolnir chicxulub and bosumtwi craters demonstrates the long term subsidence and differential compaction that takes place between the crater and the outside platform region and laterally within the crater structure at mjolnir the central high developed as a prominent feature during post impact burial the height of the peak ring was enhanced and the cumulative throw on the rim faults was increased the original chicxulub crater exhibited considerably less prominent peakring and inner ring crater rim features than the present crater the original relief of the peak ring was on the order of 420 570 m currently 535 575 m the relief on the inner ring crater rim was 300 450 m currently 700 m the original bosumtwi crater exhibited a central uplift high whose structural relief increased during burial current height 101 110 m in contrast to the original height of 85 110 m whereas the surrounding western part of the annular trough was subdued more that the eastern part exhibiting original depths of 43 68 m currently 46 m and 49 55 m currently 50 m respectively furthermore a quantitative model for the porosity change caused by the chesapeake bay impact was developed utilizing the modeled density distribution the model shows that compared with the surrounding platform the porosity increased immediately after impact up to 8 5 in the collapsed and brecciated crater center currently 6 due to post impact compaction in contrast porosity decreased by 2 3 currently 3 to 4 5 due to post impact compaction in the peak ring region the lateral variations in porosity at chesapeake bay crater are compatible with similar porosity variations at mjolnir crater and are considered to be responsible for the moderate chesapeake bay gravity signature annular low of 8 mgal instead of 15 mgal the analysis shows that the reconstructions and the long term alterations due to post impact burial are closely related to the impact disturbed target rock volume and a brecciated region of laterally varying thickness and depth varying physical properties the study further shows that several crater morphological and structural parameters are prone to post impact burial modification and are either exaggerated or subdued during post impact burial preliminary correction factors are established based on the integrated reconstruction and post impact deformation analysis the crater morphological and structural parameters corrected from post impact loading and modification effects can be used to better constrain cratering scaling law estimates and impact related consequences

multi proxy record of holocene glacial history of the spearhead and fitzsimmons ranges southern coast mountains british columbia abstract evidence from glacier forefields and lakes is used to reconstruct holocene glacier fluctuations in the spearhead and fitzsimmons ranges in southwest british columbia radiocarbon ages on detrital wood and trees killed by advancing ice and changes in sediment delivery to downstream proglacial lakes indicate that glaciers expanded from minimum extents in the early holocene to their maximum extents about two to three centuries ago during the little ice age the data indicate that glaciers advanced 8630 8020 6950 6750 3580 2990 and probably 4530 4090 cal yr bp and repeatedly during the past millennium little ice age moraines dated using dendrochronology and lichenometry date to early in the 18th century and in the 1830s and 1890s limitations inherent in lacustrine and terrestrial based methods of documenting holocene glacier fluctuations are minimized by using the two records together

facies distribution of post impact sediments in the ordovician lockne and tvaren impact craters indications for unique impact generated environments the lockne and tvaren craters formed in the late ordovician baltoscandian epicontinental sea both craters demonstrate similarities concerning near synchronous age target seabed and succeeding resurge deposits however the water depths at the impact sites and the sizes of the craters were not alike the post impact sedimentary succession of carbonates i e the dalby limestone deposited on top of the resurge sediments in the two craters is nevertheless similar at least three main facies of the dalby limestone were established in the lockne crater depending on sea floor topography location with respect to the crater and local water currents the dominating nodular argillaceous facies showing low values of inorganic carbon ic was distributed foremost in the deeper and quiet areas of the crater floor and depressions at the crater rim consisting of crushed crystalline basement ejecta a rim facies with a reef like fauna was established most certainly due to topographical highs and substrate derived nutrients between these facies are occurrences of a relatively thick bedded calcilutite rich in cephalopods cephalopod facies in tvaren the lower part of the succession consists of an analogous argillaceous facies also showing similar low ic values as in lockne followed by calcareous mudstones with an increase of ic occasionally biocalcarenites with a distinctive fauna occur in the tvaren succession probably originating as detritus from a facies developed on the rim they are evident as peaks in ic and lows in organic carbon corg the fauna in these biocalcarenites corresponds very well with those of erratic boulders derived from tvaren moreover they correspond to the rim facies of lockne except for the inclusion of photosynthesizing algae indicating shallower water at tvaren than lockne consequently we suggest equivalent distribution patterns for the carbonates of the dalby limestone in lockne and tvaren

calendar dated glacier variations in the western european alps during the neoglacial the mer de glace record mont blanc massif holocene glacier records from the western european alps are still sparse although a number of sites are well suited to constraining pre and early little ice age lia glacier advances the present study provides the first dendrochronologically based and calendar dated neoglacial glacier chronology for the mont blanc massif french alps it is based on the analysis of over 240 glacially buried pinus cembra subfossil logs and wood remains found either embedded in till or as detrital material in the mer de glace right lateral moraine only a few of the samples were found to be formally in situ but we show that some logs were virtually in situ not rooted but showing little or no evidence of reworking and could be used to accurately reconstruct past glacier margin behavior in space and time uncertainties regarding the other samples may relate to original growth location and or to outer wood decay the resulting dates followed by a were therefore considered maximum limiting ages for glacier advances the main burial events interpreted as glacier advances occurred between ca 1655 and 1544 bc between ca 1230 and 1105 bc between ca 1013 and 962 937 bc at ca 802 777 bc after 608 bc between 312 and 337 ad between ca 485 ad and 606 ad between 1120 and 1178 ad between ca 1248 and 1278 1296 ad and after 1352 ad these advances predate the late lia maxima known from historical sources the magnitude of the advances gradually increased to culminate in three near neoglacial maxima during the 7th 12th and 13th centuries ad followed by a first lia neoglacial maximum in the second half of the 14th century ad the pattern of neoglacial events described here is coherent with central and eastern alpine glacier chronologies this indicates marked synchronicity of late holocene glacier variability and forcing at a regional scale although occasional differences could be detected between western and eastern records the mer de glace record also confirms the link between the timing of sediment erosion in a high elevation glaciated alpine catchment and subsequent deposition in the sub alpine lake bourget

wobbly ocean conveyor circulation during the holocene abstract compared to the last glacial period the climate of the holocene has been quite stable however the record does suggest that at high latitudes in the north temperatures have cooled at least since the middle holocene and that this cooling has been modulated by millennial duration fluctuations that culminated in the medieval warm little ice age oscillation in this paper we explore the possibility that these variations were associated with concurrent changes in the strength of the atlantic s conveyor circulation three lines of evidence are considered one involves records that relate directly to ocean operation a second involves the tie between sea ice extent in the northern atlantic and the extent of mountain glaciers in the european alps and in the cordillera of western north america and a third involves evidence for a bipolarity in climate changes in the northern and southern polar regions in addition we look into clues provided by the atlantic multidecadal oscillation amo although at this point no firm conclusion can be drawn the case for ocean involvement is sufficiently strong to merit further attention

the geology of the malingen structure a probable doublet to the lockne marine target impact crater central sweden the malingen structure is an approximately 700 m wide rimmed sediment filled circular depression in precambrian crystalline basement approximately 16 2 km from the concentric marine target lockne crater inner basement crater diameter approximately 7 5 km total diameter in sedimentary strata approximately 13 5 km we present here results from geologic mapping a 148 8 m deep core drilling from the center of the structure detailed biostratigraphic dating of the structure s formation and its age correlation with lockne chemostratigraphy of the sedimentary infill and indication for shock metamorphism in quartz from breccias below the crater infill the drill core reveals from bottom to the top approximately 33 m of basement rocks with increased fracturing upward approximately 10 m of polymict crystalline breccia with shock features approximately 97 m of slumped cambrian mudstone approximately 4 7 m of a normally graded polymict sedimentary breccia that in its uppermost part grades into sandstone and siltstone cf resurge deposits and approximately 1 6 m of secular sediments the combined data set shows that the malingen structure formed in conjunction with the lockne crater in the same marine setting the shape and depth of the basement crater and the cored sequence of crystalline breccias with shocked quartz slumped sediments and resurge deposits support an impact origin the stratigraphic and geographic relationship with lockne suggests the lockne and malingen craters to be the first described doublet impact structure by a binary asteroid into a marine target setting

dendroglaciological evidence for holocene glacial advances in the todd icefield area northern british columbia coast mountains accelerated glacial recession and downwasting in pacific north america is exposing land surfaces and fea tures buried by glacial advances that in many locations predate the recent little ice age lia dendrochronologic analyses of increment core samples from living trees abies lasiocarpa tsuga mertensiana and samples of subfossil wood collected in the todd icefield area boundary ranges british columbia coast mountains provide the basis for a dendroglaciological and radiocarbon based reconstruction of late holocene glacier activity five intervals of glacier ex pansion were recorded by trees killed or buried by advancing glaciers 1 an advance prior to 3000 14 c years bp 2 an advance at 3000 14 c years bp that coincides with the regional tiedemann advance 3 an unattributed advance at 2300 14 c years bp 4 a two phase advance at 1700 and 1450 14 c years bp that corresponds with the regional first millennium advance 5 an advance with three phases of expansion that began prior to 750 14 c bp and is con sistent with the regional early lia interval and a two phase interval of late lia expansion culminating after 240 and 100 years bp this chronology of late holocene glaciation matches that emerging from similar investigations in the coastal cordillera of pacific north america and provides additional support for the regional significance of both the tiedemann and the first millennium advances resume une recession et une fonte glaciaire accelerees dans l ocean pacifique en amerique du nord exposent des sur faces de terrain et des traits caracteristiques enfouis sous des avancees glaciaires lesquelles dans bien des cas datent d avant le recent petit ge glaciaire des analyses dendrochronologiques d echantillons proportionnels de carottes pris

western canadian glaciers advance in concert with climate change circa 4 2 ka 1 disparate climate proxies from the northern hemisphere record a climate event at 4 2 3 8 ka here we show that glaciers throughout the mountain ranges of western canada advanced at about this time this conclusion is based on 1 new and previously reported radiocarbon ages on in situ stumps logs branches and soils exposed by recent retreat in glacier forefields and 2 clastic rich sediment intervals in cores retrieved from four montane lakes these glacier and lacustrine data indicate a period of several decades to century length when climate conditions cool summers wet winters or both favoured glacier nourishment and advance across western canada

evolution of the moose lake delta british columbia implications for holocene environmental change in the canadian rocky mountains abstract reconstruction of the geomorphic history of the moose lake delta is used to infer environmental change in the uppermost fraser river watershed british columbia delta top changes are interpreted from surface channel morphology riverbank exposures hand auger data vibracores and other borehole records river channel and overbank sediments are related to source area contributions in terms of granule lithology and fine

role of water in the formation of the late cretaceous wetumpka impact structure inner gulf coastal plain of alabama usa the effect of shallow marine water 30 100 m deep in the late excavation and early modification stages of a marine target crater 5 km in diameter as exemplified by the late cretaceous wetumpka impact structure in alabama usa is manifest in the early collapse of a weak part of the rim excavation flow and connate marine water are interpreted to be factors in this collapse this partial rim collapse catastrophically emplaced an upper structure filling unit of broken and redistributed sedimentary target formations which presently mantles the deeper fallback breccia deposits within the structure furthermore rim collapse flow facilitated the formation of a structurally modified extrastructure terrain which is located outside and adjacent to the collapsed rim segment this extrastructure terrain appears to be the product of extensive slumping of poorly consolidated target sedimentary formations

climatic variability in the northwestern alps france as evidenced by 600 years of terrigenous sedimentation in lake le bourget cores recovered from periglacial lake le bourget deep basin northwestern alps were investigated to examine the ine uence of the little ice age lia on terrigenous lacustrine sedimentation growing glaciers in the regional watershed induced catastrophic rhone river e oods and major undere ow deposits in the deep basin during the early e fteenth the sixteenth and the mid eighteenth centuries the lia is characterized by a decrease in deposition from intere ows from ad 1550 to 1740 and an increase in deposition from undere ows from ad 1550 to 1800 on one hand spectral analyses of the laminations in intere ow deposits reveal 4 5 years cyclicities from ad 1440 to 1550 as well as 7 8 and 13 14 years cyclicities from ad 1740 to 1870 on the other hand spectral analyses of a clay mineral ratio ree ecting undere ow deposits highlight 45 50 years cyclicities from ad 1550 to 1800 these pluriannual decadal and pluridecadal periods are typical of the north atlantic oscillation nao a nao like period in our data would be a consequence of periodical variations in rainfall and snow accumulation during late autumn and winter over lake le bourget s watershed

evolution of glacier dammed lakes through space and time brady glacier alaska usa abstract glacier dammed lakes and their associated jokulhlaups cause severe flooding in downstream areas and substantially influence glacier dynamics brady glacier in southeast alaska is well suited for a study of these phenomena because it presently dams 10 large 1 km 2 lakes our objectives are to demonstrate how brady glacier and its lakes have co evolved in the past and to apply this knowledge to predict how the glacier and its lakes will likely evolve in the future to accomplish these objectives we georeferenced a variety of maps airphotos and optical satellite imagery to characterize the evolution of the glacier and lakes we also collected bathymetry data and created bathymetric maps of select lakes despite small advances and retreats the main terminus of brady glacier has changed little since 1880 however it downwasted at rates of 2 3 m y between 1948 and 2000 more than the regional average the most dramatic retreat 2 km and downwasting 120 m have occurred adjacent to glacier dammed lakes and are primarily the result of calving brady glacier is a former tidewater glacier with continued downwasting brady glacier may return to a tidewater regime and enter into a phase of catastrophic retreat the situation at brady glacier is not unique and the lessons learned here can be applied elsewhere to identify future glacier dammed lakes jokulhlaups and glacier instability

holocene glacier fluctuations in the canadian cordillera alberta and british columbia abstract although the record of holocene glacier fluctuations in british columbia and alberta is still very fragmentary much recent progress has been made in their study dating of end moraines has been supplemented by studies of lateral moraine stratigraphy and dating of glacially overridden organic matter upstream of end moraines dates from sites close to contemporary glaciers indicate that ice had retreated to about its present limits before 10 ka bp prior to deposition of mazama tephra a minor pre hypsithermal readvance the crowfoot advance left deposits in the rockies and the interior of british columbia the earliest known neoglacial advances occurred 5 6 ka bp in the coast mountains and shortly after 4 ka bp in the rockies an advance culminating ca 4 3 ka bp has been reported from bugaboo glacier while evidence of another advance culminating in the period ca 2 5 1 8 ka bp the tiedemann advance is reported from more than one site following a recession the little ice age expansion the cavell advance began shortly after 900 bp this advance culminated in most cases in the 18th or 19th centuries the crowfoot tiedemann and little ice age advances were apparently of roughly the same magnitude the latter was most extensive in most cases but at several sites crowfoot moraines lie slightly farther downvalley than little ice age moraines during the present century ice fronts have generally retreated particularly rapidly in the period 1920 1950 a d although rates of retreat have decreased in the last three decades and some glaciers have readvanced slightly

holocene and latest pleistocene fluctuations of stutfield glacier canadian rockies the holocene and late glacial history of fluctuations of stutfield glacier are reconstructed using moraine stratigraphy tephrochronology and dendroglaciology stratigraphic sections in the lateral moraines contain tills from at least three glacier advances separated by volcanic tephras and paleosols the oldest pre mazama till is correlated with the crowfoot advance dated elsewhere to be younger dryas equivalent a neoglacial till is found between the mazama tephra and a paleosol developed on the bridge river tephra a log dating 2400 bp from the upper part of this till indicates that this glacier advance correlated with the peyto advance culminated shortly before deposition of the bridge river tephra radiocarbon and tree ring dates from overridden trees exposed in moraine sections indicate that the initial cavell little ice age lia advance overrode this paleosol and trees after a d 1271 three subsequent phases of the cavell advance were dated by dendrochronology the maximum glacier extent occurred in the mid 18th century predating 1743 on the southern lateral although ice still occupied and tilted a tree on the north lateral in 1758 subsequent glacier advances occurred ca 1800 1816 and in the late 19th century the relative extent of the lia advances at stutfield differs from that of other major eastward flowing outlets of the columbia icefield which have maxima in the mid late 19th century this is the first study from the canadian rockies to demonstrate that the large morphologically simple lateral moraines defining the lia glacier limits are actually composite features built up pro gressively but discontinuously over the holocene and contain evidence of multiple holocene and crowfoot age gla cier advances resume la stratigraphie des moraines la tephrochronologie et la dendroglaciologie des moraines ont servi a recons truire les fluctuations a l holocene et au cours de l histoire glaciaire tardive du glacier stutfield les sections stratigra phiques dans les moraines laterales contiennent des tills d au moins trois avancees glaciaires separees par des tephras volcaniques et des paleosols le plus ancien le till pre mazama est correle a l avancee crowfoot dont on a determine l ge ailleurs comme etant un equivalent du dryas recent un till de l epoque neo glaciaire se retrouve entre le tephra mazama et un paleosol developpe sur le tephra de bridge river un billot date 2400 bp provenant de la partie supe rieure de ce till indique que cette avancee glaciaire correlee a l avancee de peyto a culmine peu de temps avant la deposition du tephra de bridge river des datations au 14 c et des series chronlogiques provenant d arbres recouverts puis exposes dans des sections de moraine indiquent que l avancee cavell initiale petit ge glaciaire a chevauche ce paleosol et les arbres apres l an 1271 la dendrochronologie a permis la datation de trois phases subsequentes de l avancee cavell l etendue glaciaire maximale eut lieu au milieu du 18e siecle avant 1743 sur le cote sud bien que la glace fut encore presente sur le cote nord et y ait bascule un arbre en 1758 des avancees glaciaires subsequentes ont eu lieu vers 1800 1816 et vers la fin du 19e siecle l etendue relative des avancees du petit ge glaciaire a stutfield differe de celles d autres glaciers majeurs du champ de glace columbia s ecoulant vers l est et qui ont eu leur maxi mum dans la deuxieme moitie du 19e siecle cette etude est la premiere provenant des rocheuses canadiennes a de monter que les grandes moraines laterales morphologiquement simples definissant les limites du glacier au petit ge glaciaire sont en fait des elements composites developpes progressivement mais de facon discontinue tout au cours de l holocene et qu elles contiennent des evidences d avancees glaciaires multiples d ge holocene et crowfoot

rb sr dating of detrital feldspar a new method to study till late wisconsin till in the midwestern u s a contains feldspar concentrated in the sand size fractions 0 0 to 4 0 phi the feldspar originated almost exclusively from the igneous and metamorphic rocks of the precambrian shield of north america ice flow directions support the hypothesis that feldspar in late wisconsin till of ohio and indiana is a mixture of grains derived from the superior structural province 2 70 b y by the huron ice lobe and from the grenville structural province 1 07 b y by the erie and ontario lobes feldspar is well suited for dating by the rb sr method and such dates can therefore be used to study regional variations in its provenance the k feldspar plagioclase ratios of feldspar and their rb sr ratios increase with grainsize feldspar size fractions from two till samples form a linear array of data points on the rb sr isochron diagram the slope of this line is related to the proportion of mixing and is expressed as a provenance date of 1 70 pm 0 52 b y feldspa

tree ring dated little ice age histories of maritime glaciers from western prince william sound alaska tree ring studies at 13 glacier forefields in western prince william sound show little ice age glacial fluctuations were strongly synchronous on decadal timescales cross dated glacially overrun trees at eight sites indicate ice margins advanced in the early late twelfth through thirteenth centuries and middle seventeenth to early eighteenth centuries little ice age tree ring dates of 22 moraines at 13 glaciers show two main periods of stabilization the earlier of these in the first decades of the eighteenth century overlaps with the second period of glaciers overrunning trees and marks culmination of this middle little ice age expansion stabilization of moraines on nine of the study forefields in the latter part of the nineteenth century delineates a third interval of little ice age glacial advance the detailed little ice age record from land terminating glaciers in western prince william sound is consistent on a timescale of decades with four other tree ring dated glacial histories from across the northern gulf of alaska this coastal northeastern pacific glacial record reveals the structure of the little ice age in the region and provides a strong basis for comparison with other proxy climate records spanning the past 1000 years

latest pleistocene and holocene glacier fluctuations in western canada we summarize evidence of the latest pleistocene and holocene glacier fluctuations in the canadian cordillera our review focuses primarily on studies completed after 1988 when the first comprehensive review of such evidence was published the cordilleran ice sheet reached its maximum extent about 16 ka and then rapidly decayed some lobes of the ice sheet valley glaciers and cirque glaciers advanced one or more times between 15 and 11 ka by 11 ka or soon thereafter glacier cover in the cordillera was no more extensive than at the end of the 20th century glaciers were least extensive between 11 and 7 ka a general expansion of glaciers began as early as 8 4 ka when glaciers overrode forests in the southern coast mountains it culminated with the climactic advances of the little ice age holocene glacier expansion was not continuous but rather was punctuated by advances and retreats on a variety of timescales radiocarbon ages of wood collected from glacier forefields reveal six major periods of glacier advance 8 59 8 18 7 36 6 45 4 40 3 97 3 54 2 77 1 71 1 30 ka and the past millennium tree ring and lichenometric dating shows that glaciers began their little ice age advances as early as the 11th century and reached their maximum holocene positions during the early 18th or mid 19th century our data confirm a previously suggested pattern of episodic but successively greater holocene glacier expansion from the early holocene to the climactic advances of the little ice age presumably driven by decreasing summer insolation throughout the holocene proxy climate records indicate that glaciers advanced during the little ice age in response to cold conditions that coincided with times of sunspot minima priority research required to further advance our understanding of late pleistocene and holocene glaciation in western canada includes constraining the age of late pleistocene moraines in northern british columbia and yukon territory expanding the use of cosmogenic surface exposure dating techniques using multi proxy paleoclimate approaches and directing more of the research effort to the northern canadian cordillera

the target peneplain of the lockne impact the lockne impact crater in central sweden with a diameter of about 7 km formed in the mid ordovician in a marine environment that was deeper than present shelf seas the present dip of the so called sub cambrian peneplain in the target area of the impact is about 0 85 toward the northwest the peneplain is cut by a set of northwest striking nearly vertical faults with a throw of up to just over 100 m collectively the identification of the peneplain and its deformation by faulting allows us to infer that the part of the crater that is exposed to the east of lake locknesjon has been lowered by about 100 m relative to parts exposed to the west of the lake and that it has therefore been spared from significant erosion therefore the preservation of the whole crater is even better than was assumed in previous work the peneplain extends to 600 700 m from the rim of the inner crater hence the structural uplift of the rim is quite subdued compared to the craters that formed on land

pre little ice age glacier fluctuations in garibaldi provincial park coast mountains british columbia canada holocene glacier fluctuations prior to the little ice age in garibaldi provincial park in the british columbia coast mountains were reconstructed from geomorphic mapping and radiocarbon ages on 37 samples of growth position and detrital wood from glacier forefields glaciers in garibaldi park were smaller than at present in the early holocene although some evidence exists for minor short lived advances at this time the first well documented advance dates to 7700 7300 14c yr bp subsequent advances date to 6400 5100 4300 4100 2900 and 1600 1100 14c yr bp some glaciers approached their maximum holocene limits several times during the past 10 000 years periods of advance in garibaldi park are broadly synchronous with advances elsewhere in the canadian cordillera suggesting a common climatic cause the garibaldi park glacier record is also broadly synchronous with the record of holocene sunspot numbers supporting previous research that suggests solar activity may be an important climate forcing mec

mineralogy and oxygen isotope geochemistry of clays from surficial deposits in the athabasca tar sands area detailed clay mineralogical characterization was completed on four major glaciogenic surficial deposits in northeastern alberta the mineral species identified and quantified were mica montmorillonite beidellite kaolinite chlorite and vermiculite although there were quantitative differences in the amounts of mica kaolinite and chlorite in the legend unit the similarity of the mineral species in all deposits precluded their use for a definitive assessment of sediment provenance oxygen isotopic data for the clay separates served as a useful criterion for differentiation of deposits differences in isotopic signature were related to the inclusion of materials from the underlying cretaceous marine sediments and to the admixture of materials from preweathered shield sediments the difference in isotopic signature of the clay separates was specifically related to the formation conditions of the micaceous component

fire and vegetation history during the last 3800 years in northwestern montana abstract foy lake in northwestern montana provides a record of annual to decadal scale landscape change sedimentary charcoal and pollen analyses were used to document fire and vegetation changes over the last 3800 years which were then compared to similar records from ad 1880 to 2000 the long term record at foy lake suggests shifts between forest and steppe as well as changes in fire regime that are likely the result of climate change fire activity inferred from the frequency of charcoal peaks averaged 18 fire episodes 1000 years from 3800 to 2125 cal year bp and increased from 16 fire episodes 1000 years at 2125 cal year bp to 22 episodes 1000 years at 750 cal year bp a period when the pollen data suggest that steppe vegetation yielded to increasing patches of forest cover between 2125 and 750 cal year bp increased forest cover produced more background charcoal than before and after this period when vegetation was dominated by steppe between 750 and 75 cal year bp steppe has expanded and fire episode frequency averaged 33 episodes 1000 years increasing to a maximum of 40 episodes 1000 years at ca 300 cal year bp and then decreasing to present levels since ad 1880 the pollen record indicates an increase in shrubs and grasses from ad 1895 to 1960 as a result of vegetation changes associated with timber harvesting and livestock grazing no fires have been documented in the foy lake watershed since ad 1880 charcoal from the extralocal fires of ad 1910 burning over 4 111 249 ha in idaho montana and wyoming however is present in foy lake between ad 1970 and 2000 increased arboreal pollen in the record is consistent with observations that the forest has become more closed the activities of euro americans have led to a decline in forest cover between ad 1880 and 1970 followed by a recent increase as trees are now growing in areas previously occupied by steppe euro americans are likely the cause of a reduction in fire activity in watershed since ad 1880

recent glacier advances in the premier range british columbia aerial photography 1948 1985 and field investigations are used to reconstruct recent ice front fluctuations for 27 glaciers size range 0 63 17 9 km2 in the premier range british columbia rapid rates of frontal recession between ca 1930 and the mid fifties were followed by glacier readvance at many sites culminating in the 1973 1976 period when 90 of the monitored ice fronts were either advancing 68 or stable maximum downvalley advance was about 0 5 km median 90 m and 14 glaciers formed new terminal or lateral moraine ridges between 1970 and 1985 nine of these postdate 1976 one is dated to the 1980 1981 winter using tree rings the glacial advance is attributed to significant mass balance changes inferred from periods of increased winter precipitation ca 1951 1976 and low summer temperatures 1954 1968 measured at valemount warmer summers and reduced winter precipitation after 1976 account for the slight recession of ice fronts from maximum downvalley positions in the last few years

a lacustrine based neoglacial record for glacier national park montana usa abstract multi proxy study of sediment cores retrieved from lakes below modern glaciers supports the first detailed neoglacial chronology for glacier national park gnp montana analysis focused on sedimentary properties sensitive to the extent and activity of upstream glacier ice including water organic matter carbonate and biogenic silica content bulk density mass accumulation rate phosphorus fractionation magnetic susceptibility l a b color values and grain size distribution results indicate that alpine glaciers in gnp advanced and retreated numerous times during the holocene after the onset of neoglaciation ca 6500 bp the two oldest phases of glacier expansion were synchronous with the well documented garibaldi 5600 6900 bp and tiedemann peyto 1900 3700 bp phases in western canada younger phases correspond with the first millennium advance in western canada as well as glacier with advances in the sierra nevada the culminating little ice age lia advance was the most recent and extensive of a series of advance retreat cycles over the past millennium retreat from the lia maximum was the most dramatic episode of ice retreat in at least the last 1000 years

alpine glaciers and permanent ice and snow patches in western canada approach their smallest sizes since the mid holocene consistent with global trends most alpine glaciers in the northern hemisphere reached their maximum extents of the holocene between ad 1600 and 1850 since the late 1800s however glaciers have thinned and retreated mainly be

calendar dated early little ice age glacier advance at robson glacier british columbia canada dendrochronological studies at robson and bennington glaciers have provided the first calendar dating of an early little ice age glacier advance in north america dates derived from in situ stumps indicate that robson glacier began over riding forest between c ad 1142 and 1150 and continued until at least ad 1350 the highest rates of glacier advance c 3 8 m yr 1 occurred between ad 1214 and 1261 based on a series of kill dates from in situ stumps between c ad 1142 1214 and 1261 1350 rates were somewhat lower at c 2 2 5 m yr 1 this glacier advance terminated upvalley of the little ice age maximum position of robson glacier and there is no evidence at this site for glacial events between ad 1350 and 1783 however two smaller glaciers in the robson area and the main tongue of small river glacier have outermost little ice age moraines that date from the first decades of the ad 1700s all glaciers examined in the mount robson area have several well developed moraines dating from the period c

glacier fluctuations during the past 2000 years abstract a global compilation of glacier advances and retreats for the past two millennia grouped by 17 regions excluding antarctica highlights the nature of glacier fluctuations during the late holocene the dataset includes 275 time series of glacier fluctuations based on historical tree ring lake sediment radiocarbon and terrestrial cosmogenic nuclide data the most detailed and reliable series for individual glaciers and regional compilations are compared with summer temperature and when available winter precipitation reconstructions the most important parameters for glacier mass balance in many cases major glacier advances correlate with multi decadal periods of decreased summer temperature in a few cases such as in arctic alaska and western canada some glacier advances occurred during relatively warm wet times the timing and scale of glacier fluctuations over the past two millennia varies greatly from region to region however the number of glacier advances shows a clear pattern for the high mid and low latitudes and hence points to common forcing factors acting at the global scale globally during the first millennium ce glaciers were smaller than between the advances in 13th to early 20th centuries ce the precise extent of glacier retreat in the first millennium is not well defined however the most conservative estimates indicate that during the 1st and 2nd centuries in some regions glaciers were smaller than at the end of 20th early 21st centuries other periods of glacier retreat are identified regionally during the 5th and 8th centuries in the european alps in the 3rd 6th and 9th centuries in norway during the 10th 13th centuries in southern alaska and in the 18th century in spitsbergen however no single period of common global glacier retreat of centennial duration except for the past century has yet been identified in contrast the view that the little ice age was a period of global glacier expansion beginning in the 13th century or earlier and reaching a maximum in 17th 19th centuries is supported by our data the pattern of glacier variations in the past two millennia corresponds with cooling in reconstructed temperature records at the continental and hemispheric scales the number of glacier advances also broadly matches periods showing high volcanic activity and low solar irradiance over the past two millennia although the resolution of most glacier chronologies is not enough for robust statistical correlations glacier retreat in the past 100 150 years corresponds to the anthropogenic global temperature increase many questions concerning the relative strength of forcing factors that drove glacier variations in the past 2 ka still remain

1200 years of fire and vegetation history in the willamette valley oregon and washington reconstructed using high resolution macroscopic charcoal and pollen analysis article high resolution macroscopic charcoal and pollen analyses were used to reconstruct the fire and vegetation history of the willamette valley for the last 1200 years presented in this paper are three new paleoecological reconstructions from lake oswego porter lake and warner lake oregon and portions of previous reconstructions from battle ground lake washington and beaver lake oregon the reconstructions show that prior to euro american settlement vegetation and fire regimes were influenced by a combination of natural and anthropogenic factors battle ground lake shows a stronger influence from climate while lake oswego beaver lake porter lake and warner lake were more controlled by human activity however human set fires were also modulated by regional climate variability during the medieval climate anomaly and the little ice age fire reconstructions from battle ground lake lake oswego beaver lake and porter lake imply that fires were infrequent in the willamette valley 200 300 years prior to euro american settlement the decline of native american populations due to introduced disease may have led to this reduction in fire activity the prehistoric record from warner lake however indicates that fires in the foothills of the cascade range were more frequent than on the valley floor at least until ca ad 1800 the historic portions of the reconstructions indicate that euro american land clearance for agriculture and logging produced the most dramatic shifts in vegetation and fire regimes all five records indicate that few fires in the willamette valley have occurred since ca ad 1930 and fires today are predominantly grass fires 2010 elsevier b v all rights reserved

coupled effects of impact and orogeny is the marine lockne crater sweden pristine our current understanding of marine impact cratering processes is partly inferred from the geological structure of the lockne crater we present results of a mapping campaign and structural data indicating that this crater is not pristine in the western part of the crater pre impact impact and post impact rocks are incorporated in caledonian thrust slices and are subjected to folding and faulting a nappe outlier in the central crater depression is a relic of the caledonian nappe cover that reached a thickness of more than 5 km the overthrusted crater is gently deformed strike of strata and trend of fold axes deviate from standard caledonian directions northeast southwest radially oriented crater depressions which were previously regarded as marine resurge gullies formed when resurging seawater erosively cut through the crater brim are interpreted to be open synclines in which resurge deposits were better preserved the presence of the impact structure influenced orogenesis due to morphological and lithological anomalies of the crater i a raised crater brim zone acted as an obstacle during nappe propagation ii the occurrence of a central crater depression caused downward sagging of nappes and iii the lack of an appropriate detachment horizon alum shale within the crater led to an enhanced mechanical coupling and internal deformation of the nappe and the overthrusted foreland preliminary results of 3 danalogue experiments suggest that a circular high friction zone representing the crater locally hinders nappe propagation and initiates a circumferentially striking ramp fault that delineates the crater crustal shortening is also partitioned into the crater basement and decreases laterally outward deformation of the foreland affected the geometry of the detachment and could be associated with the activation of a deeper detachment horizon beneath the crater strain gradients both vertically and horizontally result in non plane strain deformation in the vicinity of the crater the strain tensors in the hanging and foot walls may deviate up to 90 from each other and rotated by up to 45 with respect to the standard regional orientation the observed deflection of strata and fold axes within the lockne crater area as revealed by field mapping is in agreement with the pattern of strain partitioning shown in the analogue models

ground warming patterns in the northern hemisphere during the last five centuries abstract changes in the earth s surface energy balance recorded underground were used to reconstruct the temperature of the ground surface for the last 500 years in the northern hemisphere we reconstructed ground surface temperature histories gsths from temperature versus depth profiles measured at 558 sites distributed between 30 and 60 n in the northern hemisphere we show that the ground has warmed about 0 5 k in the last 100 years spatial analysis reveals that spatial variability is important and that the weighted average northern hemisphere gsth shows some consistency with multiproxy and meteorological records reconstructions for the last two centuries

use of lacustrine sedimentary sequences as indicators of holocene glacial history banff national park alberta canada abstract bottom sediments from three lakes in the canadian rocky mountains were examined with the aim of evaluating the usefulness of downvalley sediment studies in reconstruction of holocene glacial histories analyses of organic carbon and carbonate contents of core sediments provide information on changing sedimentation rate and changing relative importance of glacial and non glacial sediment sources sedimentary histories of the three lakes are similar suggesting that they record regional glacial climatic forcing rather than localized events and thus that they may be useful in reconstructing holocene glacial history lacustrine sediments indicate a period of high sedimentation rates and relatively large glacial sediment contribution prior to 7500 7000 yr b p with much reduced rates and decreased glacial sediment contribution between about 6000 and 4000 yr b p possibly interrupted by a brief period of increased glacial sediment output shortly after 5000 yr b p sometime after 4000 yr b p sedimentation rates and glacial sediment output began to rise again reaching approximately present levels by 2750 2650 yr b p and have not since returned to low mid holocene levels in detail over the last 3000 yr there is some indication of a slight decrease in sedimentation rate for more than 1000 yr after about 2200 yr b p sedimentation rates and glacial sediment input into all three lakes rose between about 900 and 750 yr b p and have remained very high since if the lake sediments are interpreted as a proxy record of upvalley glacial activity they allow the development of a glacial chronology which is at once generally consistent with and more complete and easily datable than the surficial glacial record

the little ice age in the canadian rockies abstract this paper reviews the evidence and history of glacier fluctuations during the little ice age lia in the canadian rockies episodes of synchronous glacier advance occurred in the 12th 13th early 18th and throughout the 19th centuries regional ice cover was probably greatest in the mid 19th century although in places the early 18th century advance was more extensive glaciers have lost over 25 of their area in the 20th century selective preservation of the glacier record furnishes an incomplete chronology of events through the 14th 17th centuries in contrast varve sequences provide continuous annually resolved records of sediments for at least the last millennium in some highly glacierized catchments such records have been used to infer glacier fluctuations evaluation of recent proxy climate reconstructions derived from tree rings provides independent evidence of climate fluctuations over the last millennium most regional glacier advances follow periods of reduced summer temperatures reconstructed from tree rings particularly ca 1190 1250 1280 1340 1690s and the 1800s reconstructed periods of higher precipitation at banff alberta since 1500 are 1515 1550 1585 1610 1660 1680 and the 1880s glacier advances in the early 1700s the late 1800s and in places the 1950 1970s reflect both increased precipitation and reduced summer temperatures negative glacier mass balances from 1976 to 1995 were caused by decreased winter balances the glacier fluctuation record does not contain a simple climate signal it is a complex response to several interacting factors that operate at different timescales evaluation of climate proxies over the last millennium indicates continuous variability at several superimposed timescales dominated by decade century patterns only the 19th century shows a long interval of sustained cold summers this suggests that simplistic concepts of climate over this period should be abandoned and replaced with more realistic records based on continuous proxy data series the use of the term lia should be restricted to describing a period of extended glacier cover rather than being used to define a period with specific climate conditions

geology of the early palaeozoic lockne impact structure central sweden abstract the diameter of the crater at lockne as seen on topographic maps is 7 8 km the tandsbyn breccia the principal evidence of impact consists of strongly crushed local basement its distribution follows the crater margin on the north margin basement granite rests on an inverted sub cambrian erosion surface on the lowermost middle cambrian tangential faults occur at the periphery of the structure after the impact occurred under the sea during the middle ordovician there was a resurgence of ejecta loaded sea water which deposited a chaotic breccia lockne breccia which has the appearance of a debris flow the lockne breccia together with a less coarsely grained turbidite loftarsten which lies immediately above it predominantly consist of clasts of lower to middle ordovician limestone and mainly subordinate inclusions of tandsbyn breccia and isolated clasts of crystalline basement fragments of impact melt are important components of the turbidite a protective cover of sediments formed after the impact is in turn overlain by an outlier of a caledonian overthrust nappe which occupies the central and topographically deepest part of the crater shocked quartz has been identified in the loftarsten

neoglacial glacier fluctuations in the canadian rockies abstract the little ice age was the most extensive neoglacial glacier advance in the canadian rockies evidence of earlier less extensive neoglacial glacier advances is based on wood recovered from several glacier forefields wood flushed out of athabasca glacier 7550 8230 yr b p three dates and dome glacier 6120 6380 yr b p two dates indicates that forests occurred upvalley of present glacier termini during the hypsithermal detrital logs from peyto 14 dates saskatchewan 3 dates robson 3 dates and yoho 1 date glaciers plus in situ slumps at peyto and robson glaciers have yielded 14 c dates between 2490 and 3300 yr b p 12 dates between 2800 and 2990 this wood is derived from sources at or upvalley from present glacier termini and represents forests overridden by glaciers between ca 3100 and 2500 yr b p treeline was higher than present immediately prior to this advance this advance which did not extend beyond the little ice age maximum position is designated the peyto advance and correlated with the tiedemann advance in western british columbia earliest little ice age advances at peyto and robson glaciers are dated ca 800 600 yr b p at positions ca 500 m upvalley from little ice age limits

persistent millennial scale shifts in moisture regimes in western canada during the past six millennia inferences of past climatic conditions from a sedimentary record from big lake british columbia canada over the past 5 500 years show strong millennial scale patterns which oscillate between periods of wet and drier climatic conditions higher frequency decadal to centennial scale fluctuations also occur within the dominant millennial scale patterns these changes in climatic conditions are based on estimates of changes in lake depth and salinity inferred from diatom assemblages in a well dated sediment core after periods of relative stability abrupt shifts in diatom assemblages and inferred climatic conditions occur approximately every 1 220 years the correspondence of these shifts to millennial scale variations in records of glacial expansion recession and ice rafting events in the atlantic suggest that abrupt millennial scale shifts are important to understanding climatic variability in north america during the mid to late holocene unfortunately the spatial patterns and mechanisms behind these large and abrupt swings are poorly understood similar abrupt and prolonged changes in climatic conditions today could pose major societal challenges for many regions

early holocene glacier advance southern coast mountains british columbia canada abstract terrestrial and lake sediment records from several sites in the southern coast mountains british columbia provide evidence for an advance of alpine glaciers during the early holocene silty intervals within organic sediments recovered from two proglacial lakes are bracketed by ams 14 c dated terrestrial macrofossils and mazama tephra to 8780 6730 and 7940 6730 14 c yr bp 10 150 7510 and 8990 7510 cal yr bp radiocarbon ages ranging from 7720 to 7380 14 c yr bp 8630 8020 cal yr bp were obtained from detrital wood in recently deglaciated forefields of sphinx and sentinel glaciers these data together with previously published data from proglacial lakes in the canadian rockies imply that glaciers in western canada advanced during the early holocene the advance coincides with the well documented 8200 yr cold event identified in climate proxy data sets in the north atlantic region and elsewhere

nomenclature and resolution in holocene glacial chronologies most quaternary research in canada during the first half of the twentieth century focused on pleistocene glaciation given the dramatic shifts in climate during the pleistocene it is not surprising that the holocene was viewed as a time of benign climate holocene climate variability was first recognized around the middle of the century when paleoecologists found evidence that the early part of the epoch was warmer and drier than the later part in 1970s and 1980s another generation of geologists geographers and botanists began to recognize more complexity in holocene climate and vegetation in western canada several millennial scale glacier advances postdating the early holocene warm interval were defined including the garibaldi phase 6 9 5 6 ka the tiedemann peyto advance 3 5 1 9 ka and the little ice age ad 1200 1900 subsequently application of dendrochronological techniques and stratigraphic studies in glacier forefields showed that the little ice age was itself more complex than previously thought during that 700 year period glaciers repeatedly advanced and retreated in response to climatic variability on time scales ranging from centuries to decades recent work shows that the glacier record of the garibaldi phase and the tiedemann and peyto advances are similar in complexity to the little ice age with multiple advances of glaciers separated by intervals of more restricted ice cover researchers have also identified other times in the holocene when glaciers expanded from restricted positions 8 20 4 90 3 80 and 1 70 1 40 ka continued research undoubtedly will reveal additional complexities but with what is currently known the appropriateness of terms such as tiedemann advance peyto advance and little ice age can be questioned only short periods of time separate these episodes as currently defined and it seems likely that intervals of restricted glacier cover within each of these millennial length intervals are just as long as the intervals separating them

how element translocation by plants may stabilize illitic clays in the surface of temperate soils abstract it has been described several times that plant activity enriches the upper part of soil profiles in the inorganic elements they use for their growth si k ca mg this phenomenon called nutrient uplift or element translocation can counteract element loss via leaching in surface soils and may therefore impact clay mineral stability in upper soil horizons however apart from some studies in tropical ecosystems the link between element translocation and clay mineral stability has been poorly investigated yet the present work explores the consequences of element translocation on clay mineral stability in temperate grassland soils through the use of a geochemical model initially studies indicating that silicon and potassium translocation stabilizes 2 1 clay minerals and especially illitic clay minerals in surface soil were compiled using this analysis as a basis we propose a simple biogeochemical model linking plant primary productivity and clay mineral thermodynamic stability that allowed explaining how plant activity may stabilize clay minerals in the upper part of temperate grassland soils the influence of various parameters such as rainfall primary production elemental composition of plants or acidifying activity of roots was also investigated using the model the outputs of the model suggested that plant activity under certain conditions may well stabilize illitic clay in surface soils which opens wide perspectives for modellers and experimentalists

late holocene glacier expansion in the cariboo and northern rocky mountains british columbia canada abstract castle creek glacier in the cariboo mountains of british columbia remained close to its little ice age limit for most of the past 1500 years without significant recession until the 20th century this conclusion is based on radiocarbon dated detrital and in situ plant material overrun by the glacier and the sedimentary record from informally named on off lake which received clastic sediments only when castle creek glacier crossed a hydrologic divide 330 m upvalley of the little ice age limit plant macrofossils recovered from the transition between basal inorganic silt and overlying organic silty clay in a sediment core from the lake indicate that the glacier first retreated behind the divide ca 10 92 9 70 ka ages of 8 97 8 61 and 5 58 5 53 ka on detrital wood from the glacier s forefield may record earlier advances but the first unequivocal evidence of glacier expansion is from an overridden stump with an age of 4 96 4 45 ka continuous accumulation of gyttja within on off lake however indicates that castle creek glacier did not cross the hydrologic divide at any time during the first half of the holocene glacigenic sediments began to accumulate in the lake between 2 73 and 2 49 ka indicating that castle creek glacier expanded beyond the hydrologic divide at that time a coincident advance is also recorded in the northern rocky mountains of british columbia at kwadacha glacier which overran a vegetated surface at 2 69 2 36 ka clastic sedimentation in on off lake ceased soon after the bridge river volcanic eruption 2 70 2 35 ka indicating that castle creek glacier retreat to a position upvalley of the divide at that time sedimentation resumed before 1 87 1 72 ka when the glacier advanced again past the hydrologic divide following a second retreat castle creek glacier advanced across the divide a final time at ca 1 54 1 42 ka the snout of the glacier remained less than 330 m upvalley of the little ice age moraine until the early twentieth century when annual moraines indicate rapid frontal recession to a position upvalley of the hydrologic divide these data collectively indicate that glaciers in the cariboo mountains of british columbia nearly achieved their all time holocene limits as early as 2 73 2 49 ka and climatic conditions in the early 20th century abruptly ended a 1500 year period favoring glacier expansion

soil and sedimentary charcoal evidence for holocene forest fires in an inland temperate rainforest east central british columbia canada accelerator radiocarbon dating of 147 charcoal samples recovered from colluvial and alluvial fan deposits at 29 sites was used to reconstruct the holocene fire history of an inland temperate rainforest watershed in east central british columbia bc canada radiocarbon dates ranged from 182 to 9558 cal yr bp with prominent peaks in the probability distribution of calibrated dates at c 7100 3900 2300 1600 and 250 1000 cal yr bp the inferred median fire return interval fri was 800 1200 cal yr depending on the extent of inbuilt age errors resulting from charring of wood pre dating actual fire ages this fri is likely an overestimate as less severe events may not have created sufficient erosion and slope instability to preserve a record of charcoal in buried soils and slope deposits median time since fire was 467 cal yr based on ages of the uppermost charcoal found at each site but the severity of heart rots in the dominant redcedars thuja plicata donn ex d don prevented independent confirmation of stand ages by dendrochronology sites with multiple charcoal containing layers having similar radiocarbon ages can be explained with reference to contemporary post fire mass wasting processes peaks in fire related sedimentation probability coincided broadly with periods of higher fire frequency c 600 1000 1300 2400 and 3500 4500 cal yr bp inferred from sedimentary charcoal records at subalpine sites in southwestern bc correspondence with fire records from more distant sites in northwestern north america was less clear