high resolution particle size analysis of naturally occurring very fine grained sediment through laser diffractometry abstract in this paper we present results from a large number of experiments aimed at quantifying method and instrument uncertainty associated with laser diffraction analysis we analyzed the size distribution of fine grained sediment 24 hours prior to analysis and using 60 seconds of ultrasonication during analysis 2 obscuration a measure of the concentration of the suspension during analysis produced the most reproducible results at about 20 3 variations in refractive index settings can significantly alter estimated grain size distributions 4 assumed values for absorption the degree to which sediment grains absorb the light can have a profound effect on grain size results absorption settings near 0 resulted in unexpected bimodal grain size distributions for sediments in the 10 m size fraction and significantly skewed the fine grained tail of coarser samples probably because of sub optimal diffraction by particles with a diameter similar in size to the laser wavelength absorption settings closer to 1 produced very reproducible results and unimodal grain size distributions over a wide range of refractive indexes our study has shown that laser diffraction can measure very fine grained sediments 10 m quickly with high precision 5 at 2 standard deviations and without the need for extensive mineralogical determinations these results make possible a new generation of studies in which high resolution time series data sets of sediment grain size can be used to infer subtle changes in paleohydrology

anisotropic zonation in the lithosphere of central north america influence of a strong cratonic lithosphere on the mid continent rift we present shear wave splitting analyses of sks and skks waves recorded at sixteen superior province rifting earthscope experiment spree seismic stations on the north shore of lake superior as well as fifteen selected earthscope transportable array instruments south of the lake these instruments bracket the mid continent rift mcr and sample the superior penokean yavapai and mazatzal tectonic provinces the data set can be explained by a single layer of anisotropic fabric which we interpret to be dominated by a lithospheric contribution the fast s polarization directions are consistently ene wsw but the split time varies greatly across the study area showing strong anisotropy up to 1 48 s in the western superior moderate anisotropy in the eastern superior and moderate to low anisotropy in the terranes south of lake superior we locate two localized zones of very low split time 0 6 s adjacent to the mcr one in the nipigon embayment an mcr related magmatic feature immediately north of lake superior and the other adjacent to the eastern end of the lake at the southern end of the kapuskasing structural zone ksz both low splitting zones are adjacent to sharp bends in the mcr axis we interpret these two zones along with a low velocity linear feature imaged by a previous tomographic study beneath minnesota and the dakotas as failed lithospheric branches of the mcr given that all three of these branches failed to propagate into the superior province lithosphere we propose that the sharp bend of the mcr through lake superior is a consequence of the high mechanical strength of the superior lithosphere ca 1 1 ga

jurassic deep water microbial biostromes as flooding markers in carbonate sequence stratigraphy abstract carbonate microbial biostromes developed during the jurassic in open marine relatively deep water outer shelf slope environments they resemble the ammonitico rosso lithofacies are intercalated within shaly micritic deposits and reflect periods of extremely low sedimentation rates the biostromes are interpreted as condensed sections of depositional sequences and seem to be of potential use for delineation of marine flooding maxima the series examined here are from the upper jurassic of southeast france and the lower jurassic of the eastern central atlantic comparisons of results with the available sea level curves disclose both agreements and discrepancies this gives rise to questions about the reliability of correlations between distinct biochronologic subdivisions used control on depositional sequence development and validity of these comparisons

microbial carbonates the geological record of the calcified bacterial algal mats and biofilms summary deposits produced by microbial growth and metabolism have been important components of carbonate sediments since the archaean geologically best known in seas and lakes microbial carbonates are also important at the present day in fluviatile spring cave and soil environments the principal organisms involved are bacteria particularly cyanobacteria small algae and fungi that participate in the growth of microbial biofilms and mats grain trapping is locally important but the key process is precipitation producing reefal accumulations of calcified microbes and enhancing mat accretion and preservation various metabolic processes such as photosynthetic uptake of co2 and or hco3 by cyanobacteria and ammonification denitrification and sulphate reduction by other bacteria can increase alkalinity and stimulate carbonate precipitation extracellular polymeric substances widely produced by microbes for attachment and protection are important in providing nucleation sites and facilitating sediment trapping microbial carbonate microfabrics are heterogeneous they commonly incorporate trapped particles and in situ algae and invertebrates and crystals form around bacterial cells but the main component is dense clotted or peloidal micrite resulting from calcification of bacterial cells sheaths and biofilm and from phytoplankton stimulated whiting nucleation interpretation of these texturally convergent and often inscrutable fabrics is a challenge conspicuous accumulations are large domes and columns with laminated stromatolite clotted thrombolite and other macrofabrics which may be either agglutinated or mainly composed of calcified or spar encrusted microbes stromatolite lamination appears to be primary but clotted thrombolite fabrics can be primary or secondary microbial precipitation also contributes to hot spring travertine cold spring mound calcrete cave crust and coated grain deposits as well as influencing carbonate cementation recrystallization and replacement microbial carbonate is biologically stimulated but also requires favourable saturation state in ambient water and thus relies uniquely on a combination of biotic and abiotic factors this overriding environmental control is seen at the present day by the localization of microbial carbonates in calcareous streams and springs and in shallow tropical seas and in the past by temporal variation in abundance of marine microbial carbonates patterns of cyanobacterial calcification and microbial dome formation through time appear to reflect fluctuations in seawater chemistry stromatolites appeared at 3450 ma and were generally diverse and abundant from 2800 to 1000 ma inception of a proterozoic decline variously identified at 2000 1000 and 675 ma has been attributed to eukaryote competition and or reduced lithification thrombolites and dendrolites mainly formed by calcified cyanobacteria became important early in the palaeozoic and reappeared in the late devonian microbial carbonates retained importance through much of the mesozoic became scarcer in marine environments in the cenozoic but locally re emerged as large agglutinated domes possibly reflecting increased algal involvement and thick micritic reef crusts in the late neogene famous modern examples at shark bay and lee stocking island are composite coarse agglutinated domes and columns with complex bacterial algal mats occurring in environments that are both stressed and current swept products of mat evolution ecological refugia sites of enhanced early lithification or all three

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

climatic ups and downs in a disturbed jurassic world the tropical warm and equable climate of the jurassic world is regularly challenged by geoscientists especially since oxygen isotopes 18 o of fossil hardparts have been used to reconstruct the paleotemperature history of seawater by applying the innovative sizer sig nifi cant zero crossings of the derivatives statistical approach to a newly compiled 18 o data base for the jurassic we demonstrate the occurrence of major and multiscale 18 o changes mainly related to climate disturbances for the fi rst time two long term anomalies in 18 o are identifi ed during the toarcian and the late jurassic in conjunction with intensive volcanism in large igneous provinces these results support a strong infl uence of repeated volcanic pulses on the modulation of pco 2 temperatures and polar ice cap volumes over protracted periods at shorter time scales 13 relatively rapid 0 5 1 m y and signifi cant warming and cooling events are identifi ed the causes of which include transient fl uctuations in greenhouse gas con centrations related to still debated mechanisms

middle jurassic early cretaceous tectono sedimentary evolution of the southwestern iberian basin central spain major palaeogeographical changes in the geotectonic framework of the western tethys abstract the middle jurassic early cretaceous tectono sedimentary evolution of the southwestern part of the intraplate iberian basin spain was mostly controlled by the alto tajo montes universales atmu and landete teruel lt faults during the middle jurassic the atmu fault separated a western area dominated by shallow marine carbonates and an eastern area with open marine facies during the bathonian callovian the area located to the west of the atmu fault and north of the lt fault cuenca domain was progressively exposed and remained uplifted until the late barremian a widespread unconformity with a variable gap around the callovian to mid oxfordian has been related to the onset of an earlier synrift stage that includes a lower episode middle oxfordian kimmeridgian of carbonate ramp sedimentation and an upper episode latest kimmeridgian early berriasian with intense fault compartmentalization this fault activity involved the eventual uplift of the teruel javalambre and valencia highs separating the maestrazgo and valencia basins after a berriasian early barremian stratigraphic gap the upper synrift stage late barremian aptian marks the onset of the sedimentation in the cuenca basin west of the atmu and lt faults initial continental sedimentation occurred in small grabens bounded by nne ssw and wnw ese trending faults an early aptian transgressive event overcame the lt fault and connected cuenca and valencia basins successive episodes of stretching in the intracratonic iberian basins were not synchronous as shown by the offset of the distribution of the deformation between the cuenca valencia and maestrazgo basins the synrift sequences recorded in the studied intracratonic basins indicate that most of the accommodation created occurred in response to far field extension after the simultaneous evolution of three main rifts in the north and west iberian margins and in the alpine tethys ocean the heterogeneously distributed stretching indicates that the iberian intraplate realm can be interpreted as a constantly thinned domain in which coeval rift related deformation and rift drift transitions migrated significantly along space and time the comparison and the integration of the obtained results in a broader context make of this work a contribution to the knowledge of the jurassic cretaceous paleogeographic evolution of the iberian plate in the geotectonic evolution of the western tethys

holocene glacier fluctuations a global overview of glacier advances and retreats grouped by regions and by millennia for the holocene is compiled from previous studies the reconstructions of glacier fluctuations are based on 1 mapping and dating moraines defined by 14 c tcn osl lichenometry and tree rings discontinuous records time series and 2 sediments from proglacial lakes and speleothems continuous records time series using 189 continuous and discontinuous time series the long term trends and centennial fluctuations of glaciers were compared to trends in the recession of northern and mountain tree lines and with orbital solar and volcanic studies to examine the likely forcing factors that drove the changes recorded a general trend of increasing glacier size from the earlyemid holocene to the late holocene in the extra tropical areas of the northern hemisphere nh is related to overall summer temperature forced by orbitally controlled insolation the glaciers in new zealand and in the tropical andes also appear to follow the orbital trend i e they were decreasing from the early holocene to the present in contrast glacier fluctuations in some monsoonal areas of asia and southern south america generally did not follow the orbital trends but fluctuated at a higher frequency possibly triggered by distinct teleconnections patterns during the neoglacial advances clustered at 4 4e4 2 ka 3 8e3 4 ka 3 3e2 8 ka 2 6 ka 2 3e2 1 ka 1 5e1 4 ka 1 2e1 0 ka 0 7e0 5 ka corresponding to general cooling periods in the north atlantic some of these episodes coincide with multidecadal periods of low solar activity but it is unclear what mechanism might link small changes in irradiance to widespread glacier fluctuations explosive volcanism may have played a role in some periods of glacier advances such as around 1 7e1 6 ka coinciding with the taupo volcanic eruption at 232 5 ce but the record of explosive volcanism is poorly known through the holocene the compilation of ages suggests that there is no single mechanism driving glacier fluctuations on a global scale multidecadal variations of solar and volcanic activity supported by positive feedbacks in the climate system may have played a critical role in holocene glaciation but further research on such linkages is needed the rate and the global character of glacier retreat in the 20th through early 21st centuries appears unusual in the context of holocene glaciation though the retreating glaciers in most parts of the northern hemisphere are still larger today than they were in the early and or mid holocene the current retreat

holocene glaciation and climate evolution of baffin island arctic canada abstract lake sediment cores and cosmogenic exposure ce dates constrain the pattern of deglaciation and evolution of climate across baffin island since the last glacial maximum lgm ce dating of erratics demonstrates that the northeastern coastal lowlands became ice free ca 14 ka as the laurentide ice sheet lis receded from its lgm margin on the continental shelf coastal lakes in southeastern baffin island started to accumulate sediment at this time whereas initial lacustrine sedimentation was delayed by two millennia in the north reduced organic matter in lake sediment deposited during the younger dryas chron and the lack of a glacial readvance at that time suggest cold summers and reduced snowfall ice retreated rapidly after 11 ka but was interrupted by a widespread readvance of both the lis and local mountain glaciers 9 6 ka cockburn substage a second readvance occurred just before 8 ka during a period of unusually cold summers corresponding to the 8 2 ka cold event in the greenland ice sheet most local glaciers were behind their present margins before 7 ka and in some instances much earlier although the foxe dome of the lis continued to slowly retract toward the present day barnes ice cap throughout the holocene pollen in lake sediments is rare and dominated by exotic sources prior to 12 ka subsequently grass tundra became established followed by modern tundra vegetation ca 8 ka with subtle changes in pollen assemblages in the late holocene lake primary productivity peaked in the early holocene before terrestrial vegetation or marine surface waters reached their apparent thermal maxima lacustrine marine and glacial proxies all reflect significant late holocene cooling the onset of neoglaciation is well dated in lacustrine records at ca 6 ka with intensification after 2 5 ka the expansion of local glaciers during the little ice age represents the most extensive advance since 7 ka we suggest that the replacement of atlantic surface waters by cold low salinity arctic ocean water coupled with the steady reduction of summer insolation resulted in a significant positive sea ice feedback that produced a larger late holocene summer temperature depression over the baffin region than in the pacific sector of the arctic

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

recent glacier retreat exceeds internal variability glacier fluctuations exclusively due to internal variations in the climate system are simulated using downscaled integrations of the echam4 opyc coupled general circulation model gcm a process based modeling approach using a mass balance model of intermediate complexity and a dynamic ice flow model considering simple shearing flow and sliding are applied multimillennia records of glacier length fluctuations for nigardsbreen norway and rhonegletscher switzerland are simulated using autoregressive processes determined by statistically downscaled gcm experiments return periods and probabilities of specific glacier length changes using gcm integrations excluding external forcings such as solar irradiation changes volcanic or anthropogenic effects are analyzed and compared to historical glacier length records preindustrial fluctuations of the glaciers as far as observed or reconstructed including their advance during the little ice age can be explained by internal variability in the climate system as represented by a gcm however fluctuations comparable to the present day glacier retreat exceed any variation simulated by the gcm control experiments and must be caused by external forcing with anthropogenic forcing being a likely candidate

holocene environmental variability in southern greenland inferred from lake sediments abstract sediments from qipisarqo lake provide a continuous holocene paleoenvironmental record from southern greenland following deglaciation and glacio isostatic emergence of the basin from the sea 9100 cal yr b p proxies of lake paleoproductivity including biogenic silica and organic matter increased markedly until 6000 cal yr b p and thereafter remained stable over the ensuing warm three millennia subsequent decreases in these proxies most dramatically between 3000 and 2000 cal yr b p show the lake s responses to initial neoglacial cooling intervals of ameliorated limnological conditions occurred between 1300 and 900 and between 500 and 280 cal yr b p briefly interrupting the decreasing trend in productivity that culminated in the little ice age increased lake productivity during the latter half of the 20th century which reflects the limnological response to circum arctic warming still has not reached peak holocene values the neoglacial climate of the last 2000 yr includes the most rapid high amplitude environmental changes of the past nine millennia the norse thus migrated around the north atlantic ocean region in the most environmentally unstable period since deglaciation lacustrine sediment records provide a context with which to consider future environmental changes in the labrador sea region in particular any future warming will be superposed on a regional climate system that is currently exhibiting highly unstable behavior at submillennial timescales

identification and significance of tephras encountered in a core from mary lake yoho national park british columbia mary lake is a small subalpine lake located proximal 3 km to the continental divide near lake o hara in yoho national park british columbia a 1 25 m core recovered from surficial bottom sediments was found to contain both bridge river tephra 2350 years bp and mazama tephra 6800 years bp identification of the tephras was initially based on distinctive colour texture phenocryst assemblages and glass shard habits and was confirmed by electron microprobe analysis of the constituent glass shards the microprobe technique employed backscattered and secondary electron imagery and both energy dispersive and wavelength dispersive analyses mean annual sedimentation rates calculated from tephra depths in the mary lake core were found to be of the order of 0 15 mm year for the post bridge river time period and 0 02 mm year for the mazama bridge river interval the preservation of mazama tephra in mary lake lacustrine sediments indicates that deglaciation had proceeded upvalley from the mary lake basin

middle jurassic stromatactis mud mounds in the pieniny klippen belt carpathians a possible clue to the origin of stromatactis abstract four occurrences of jurassic stromatactis mud mounds were found in the czorsztyn unit of the pieniny klippen belt western carpathians in western slovakia slavnicke podhorie babina and in the transcarpathian ukraine priborzhavskoe and veliky kamenets their stratigraphic range is from bajocian to callovian the mounds consist of micropeloidal mudstones wackestones to packstones with a fauna including pelecypods brachiopods ammonites and crinoids spicules and skeletons of siliceous sponges are abundant in every section all of the mounds contain networks of stromatactis cavities that are partially filled with radiaxial fibrous calcite rfc and locally by internal sediments at slavnicke podhorie the sparry masses that fill stromatactis cavities are weathered out and show casts of sponges parallel study of the weathered casts and their cross sections in slabs showed that they bear all the signs of stromatactis relatively flat bottoms and digitate upper parts rfc initial fillings and eventual blocky calcite later filling almost no original sponge structures were preserved this strongly supports the possible sponge related origin for stromatactis cavities

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

the mesoproterozoic midcontinent rift system lake superior region usa abstract exposures in the lake superior region and associated geophysical evidence show that a 2000 km long rift system developed within the north american craton 1109 1087 ma the age span of most of the volcanic rocks this system is characterized by immense volumes of mafic igneous rocks mostly subaerial plateau basalts generated in two major pulses largely by a hot mantle plume a new ocean basin was nearly formed before rifting ceased perhaps due to the remote effect of the grenville continental collision to the east broad sagging subsidence combined with a system of axial half grabens separated along the length of the rift by accommodation zones provided conditions for the accumulation of as much as 20 km of volcanic rocks and as much as 10 km of post rift clastic sediments both along the rift axis and in basins flanking a central post volcanic horst pre rift mature quartzose sandstones imply little or no uplift prior to the onset of rift volcanism early post rift red bed sediments consist almost entirely of intrabasinally derived volcanic sediment deposited in alluvial fan to fluvial settings the exception is one gray to black carbon bearing lacustrine unit this early sedimentation phase was followed by broad crustal sagging and deposition of progressively more mature red bed fluvial sediments with an extra basinal provenance

facies and climate environmental changes recorded on a carbonate ramp a sedimentological and geochemical approach on middle jurassic carbonates paris basin france a detailed sedimentological geochemical and mineralogical study is carried out on the early bajocian to early callovian middle jurassic limestones of the paris basin objectives are to document and explain the facies changes in the context of the climate environmental evolution at the nw european scale deposits include 18 lithofacies which are stacked into 10 third order depositional sequences at a greater time scale 4 biosedimentary packages are distinguished by their allochems associations 1 an intracratonic carbonate environment with coral reefs and crinoid rich facies is typical of the early bajocian 2 a major facies change occurred at the early late bajocian transition with a shift from crinoid and coral rich facies to ooid rich facies during the late bajocian a southward dipping ooid ramp with successive progradational trends was emplaced 3 a large lagoon protected by ooid shoals developed during the bathonian in a muddy ramp setting 4 at the bathonian callovian boundary a second major change occurred with the lagoonal facies being superseded by an ooid bioclastic crinoids corals ramp associated with a waning of carbonate productivity retrogradational trend our geochemical study including a compilation of bibliographic data allows us to refine the existing sea surface palaeotemperature pattern a cooling from the latest early bajocian to the late bajocian and a subsequent warming from the earliest callovian to the early middle callovian transition are described using a proxy of sea surface temperatures together with 13c and mineralogical data our new 18o values suggest a palaeo climatic palaeo environmental control of facies in this shallow carbonate ramp environment

transgressive regressive cycles and jurassic palaeogeography of northeast iberia abstract a correlation and sequence stratigraphy study of jurassic successions has been carried out in the main sedimentary basins of northeast iberia i e asturias basque cantabrian and iberian basins based on the identification of transgressive regressive cycles the development and palaeogeographic evolution of the epicontinental carbonate platforms of northeast iberia were largely controlled by major tectonic activity at three main intervals at the beginning of the jurassic in the lower middle jurassic transition and during the uppermost jurassic respectively during early jurassic times northeast iberia was the site of a single and large carbonate ramp opened to the north this carbonate ramp suffered a progressive drowning evolving from an inner to hemipelagic ramp systems with the local development of suboxic environments in the deepest areas located to the north during the middle jurassic different open carbonate platforms were formed including the development of swells in intermediate areas during the upper jurassic the outer ramp areas were progressively moving to the east iberian basin and the ammonite faunas showing a markedly tethyan affinity thereafter three first order t r cycles bounded by major discontinuities associated with significant time gaps are identified they extend respectively from the latest rhaetian to the early aalenian from the middle aalenian to the early oxfordian and from the early oxfordian to the late berriasian major transgressive peaks occurred at the middle toarcian bifrons zone at the late bajocian upper niortense and garantiana zones and at the mid kimmeridgian divisum zone each of the first order cycles includes four second order t r cycles cycles 1 1 1 4 are identified in the northern basins cycles 2 1 2 4 display some differences in age of transgressive peaks from one basin to another cycles 3 1 3 4 are mainly identified in the iberian basin the correlation with other separated boreal and thethysian basins demonstrates that the number and age of t r cycles varies from one basin to another and are mainly controlled by the local or regional tectonic development the transgressive peaks may reflect episodes of eustatic rise during the jurassic however their different age from one basin to another is explained by different subsidence evolution

facies distribution and coral microbialite reef development on a low energy carbonate ramp chay peninsula kimmeridgian western france abstract the chay peninsula western france succession corresponds to a kimmeridgian shallow and low energy ramp system that developed in the northeast of the aquitaine basin the sedimentation shows a transition from a carbonate dominated to a mixed carbonate siliciclastic depositional environment that takes place at the base of a major third order sea level transgression facies partitioning and coral microbialite reef levels i e reef windows suggest higher frequency fourth order sea level oscillations reef growth phases i e high frequency reef windows are interpreted to have been controlled by fifth order sea level oscillations in the mixed siliciclastic carbonate system successive prograding units of shoreface sediments pass into thick marl limestone alternations over a distance of tens of metres such remarkable short distance lateral facies variations suggest a complex sedimentary system made of juxtaposed deposits that rapidly shift through time terrigenous fluxes in modifying the light intensity and the nutrient level in the water column strongly controlled the facies distribution and notably the reef composition and growth identified coral genera suggest mixed photo heterotrophic mode of nutrition and low mesotrophic conditions in marine waters for each reef growth phase nutrient increase favoured large amounts of microbialites to develop forming a crust that entirely capped the coral reef surface thus high frequency fluctuations in nutrient input in tune with fifth or higher order sea level fluctuations controlled the reef development at a millennial scale the chay peninsula reef distribution and development provide insight into understanding the response of reef communities under climatically induced environmental changes

mount mazama eruption calendrical age verified and atmospheric impact assessed geochemical identification of mount mazama ash in the greenland ice sheet project 2 gisp2 ice core gives a calendrical age of 7627 150 cal yr b p 5677 150 b c for the eruption thus providing a more accurate early holocene stratigraphic time line than previously available the gisp2 record of volcanically derived sulfate suggests a total stratospheric aerosol loading between 88 and 224 mt spread over an 6 yr period following the eruption of mount mazama taking into account the likelihood of some tropospheric aerosol transport to greenland realistic estimates of the resulting atmospheric optical depth range from 0 6 to 1 5 these values may have produced a temperature depression of 0 6 to 0 7 c at mid to high northern latitudes for 1 3 yr after the eruption these results indicate that the 5677 b c eruption of mount mazama was one of the most climatically significant volcanic events of the holocene in the northern hemisphere we also calculate a maximum stratospheric cl release of 8 1 mt by the eruption which may have led to substantial stratospheric ozone depletion

latest pleistocene and holocene glaciation of baffin island arctic canada key patterns and chronologies abstract melting glaciers and ice caps on baffin island contribute roughly half of the sea level rise from all ice in arctic canada although they comprise only one fourth of the total ice in the region the uncertain future response of arctic glaciers and ice caps to climate change motivates the use of paleodata to evaluate the sensitivity of glaciers to past warm intervals and to constrain mechanisms that drive glacier change we review the key patterns and chronologies of latest pleistocene and holocene glaciation on baffin island the deglaciation by the laurentide ice sheet occurred generally slowly and steadily throughout the holocene to its present margin barnes ice cap except for two periods of rapid retreat an early interval 12 to 10 ka when outlet glaciers retreated rapidly through deep fiords and sounds and a later interval 7 ka when ice over foxe basin collapsed in coastal settings alpine glaciers were smaller during the younger dryas period than during the little ice age at least some alpine glaciers apparently survived the early holocene thermal maximum which was several degrees warmer than today although data on glacier extent during the early holocene is extremely sparse following the early holocene thermal maximum glaciers advanced during neoglaciation beginning in some places as early as 6 ka although most sites do not record near little ice age positions until 3 5 to 2 5 ka alpine glaciers reached their largest holocene extents during the little ice age when temperatures were 1 1 5 c cooler than during the late 20th century synchronous advances across baffin island throughout neoglaciation indicate sub milankovitch controls on glaciation that could involve major volcanic eruptions and solar variability future work should further elucidate the state of glaciers and ice caps during the early holocene thermal maximum and glacier response to climate forcing mechanisms

detailed basin structure and tectonic evolution of the midcontinent rift system in eastern lake superior from reprocessing of glimpce deep reflection seismic data line f of the glimpce deep marine reflection seismic survey has been reprocessed according to a data dependent strategy aimed at enhancing the fine structural features of the midcontinent rift system in eastern lake superior the processing sequence was specially designed to attenuate first order water reverberations and to reduce the excessive oscillatory character of the basic wavelet a detailed examination of the final migrated stacked section reveals that beneath line f the midcontinent rift system is an almost perfectly symmetric syncline the structure appears to have formed in the beginning by the extrusion of lavas on a horizontal platform subsiding without major deformation the initial phase was followed by local crustal sagging in the centre the transition is marked by a major reflector which is hypothesized to correspond to the boundary between reverse and normal polarity volcanics in eastern lake superior integrating the results of several recent investigations a five stage evolutiona

facies architecture of a microbial siliceous sponge dominated carbonate platform the bajocian of moscardon middle jurassic spain extensive facies analysis of the outcrops located near moscardon iberian basin ne spain resultedin a precise reconstruction of thefacies architecture of a bajocian middlejurassic carbonate platform different types of microbialites occurred in the transitional area between the shallow and relatively deep carbonate platform domains located above and below wave base level respectively the most significant volume of the micorbialites is found in the platform slope located below wave base level in a depth range of around 30 50 m in the lower slope during stages of rapid accommodation gain the vertical aggradation of individual stratiform build ing blocks results in the formation of up to 25 m thick microbial siliceous sponge buildups during stages of sea level highstand the individual building blocks are dominated by lateral down slope progradational accretion resulting in flatter lens shaped buildups the transition between the upper slope and the shallow platform area is characterized by microbial encrusted intraclastic bioclastic packstones microbial crust development helped to stabilize the seafloor allowing the eventual accumulation and preservation of the sand sized grains above wave base organicbuildupswithvariableproportionsofmicro bialites grew in shallow to relatively deep domains of the jurassic carbonate platforms that developed

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

a complete record of holocene glacier variability at austre okstindbreen northern norway an integrated approach arctic glaciers are currently undergoing major changes but accurate knowledge about how they varied during the entire holocene is still scarce here we present a new complete glacier record from austre okstindbreen in nordland northern norway this reconstruction is based on a number of short and long cores retrieved from several downstream basins which have been analyzed by a suite of methods including geochemical elements xrf rock magnetic properties dry bulk density dbd and loss on ignition loi lake sediment distribution was surveyed and mapped prior to coring by the use of ground penetrating radar gpr independently lichen dated marginal moraines and historical information about the glacier frontal positions from old photographs and maps have made it possible to link the moraine sequence to the 210pb dated lake sediment chronology this integrated approach reveals that austre okstindbreen is the first known glacier in scandinavia to possibly have survived the holocene thermal optimum it also brackets the four largest glacier advances to c 7400 7000 1400 1200 900 700 and 300 150 years before ad 2000 b2k in contrast to most reconstructed glaciers in scandinavia the largest glacier advance was not associated with the little ice age but rather to an earlier period centred at 1300 b2k both the moraine chronology and the lacustrine records document this neoglacial advance compared to other glacier reconstructions from the northern hemisphere we identify near synchronous glacier advances occurring roughly at 4000 b2k 2700 b2k 1300 b2k and during the little ice age these correlative advances across the northern hemisphere suggest that these observed centennial scale events are a shared feature regardless of the large geographical distances separating them some minor discrepancies between different geographical areas may be caused by lack of precise dating but local climatic conditions may play a role as well

holocene and latest pleistocene alpine glacier fluctuations a global perspective abstract alpine glacier fluctuations provide important paleoclimate proxies where other records such as ice cores tree rings and speleothems are not available about 20 years have passed since a special issue of quaternary science reviews was published to review the worldwide evidence for holocene glacier fluctuations since that time numerous sites have been discovered new dating techniques have been developed and refined climatic hypotheses have been proposed that contribute to a better understanding of earth s climate system this special volume includes 12 papers on holocene and latest pleistocene alpine glacier fluctuations that update the seven review papers from 1988 major findings of these 12 papers include the following many but certainly not all alpine areas record glacier advances during the younger dryas cold interval most areas in the northern hemisphere witnessed maximum glacier recession during the early holocene with some glaciers disappearing although a few sites yield possible evidence for advances during the 8 2 ka cooling event in contrast some alpine areas in the southern hemisphere saw glaciers reach their maximum post glacial extents during the early to middle holocene in many parts of the globe glaciers reformed and or advanced during neoglaciation beginning as early as 6 5 ka neoglacial advances commonly occurred with millennial scale oscillations with many alpine glaciers reaching their maximum holocene extents during the little ice age of the last few centuries although the pattern and rhythm of these glacier fluctuations remain uncertain improved spatial coverage coupled with tighter age control for many events will provide a means to assess forcing mechanisms for holocene and latest pleistocene glacial activity and perhaps predict glacier response to future impacts from human induced climate change

holocene glacier fluctuations in alaska abstract this review summarizes forefield and lacustrine records of glacier fluctuations in alaska during the holocene following retreat from latest pleistocene advances valley glaciers with land based termini were in retracted positions during the early to middle holocene neoglaciation began in some areas by 4 0 ka and major advances were underway by 3 0 ka with perhaps two distinct early neoglacial expansions centered respectively on 3 3 2 9 and 2 2 2 0 ka tree ring cross dates of glacially killed trees at two termini in southern alaska show a major advance in the ad 550s 720s the subsequent little ice age lia expansion was underway in the ad 1180s 1320s and culminated with two advance phases respectively in the 1540s 1710s and in the 1810s 1880s the lia advance was the largest holocene expansion in southern alaska although older late holocene moraines are preserved on many forefields in northern and interior alaska tidewater glaciers around the rim of the gulf of alaska have made major advances throughout the holocene expansions were often asynchronous with neighboring termini and spanned both warm and cool intervals suggesting that non climatic factors were important in forcing these advances however climatic warming appears to have initiated most rapid iceberg calving retreats large glaciers terminating on the forelands around the gulf of alaska may have had tidewater termini early in the holocene but have progressively become isolated from the adjacent ocean by the accumulation and subaerial exposure of their own sediments

using proglacial threshold lakes to constrain fluctuations of the jakobshavn isbrae ice margin western greenland during the holocene abstract the future response of the greenland ice sheet gis and its potential contribution to sea level rise are uncertain rapid changes of greenland s outlet glaciers over the past decade have made it difficult to extrapolate ice sheet change into the future this significant short term variability highlights the need for longer term geologic e g holocene records of ice margin fluctuations however a major challenge with reconstructing the gis during the holocene stems from it having been smaller than it is at present thus traditional glacial geologic approaches are not suitable we use radiocarbon dated sediment sequences from seven proglacial threshold lakes spanning 50 km of the western gis margin near jakobshavn isbrae to constrain the timing of early holocene deglaciation the duration that this sector of the western gis was smaller than its present configuration and the timing of its advance during neoglaciation our reconstructions suggest deglaciation 7300 cal yr bp minimum ice extent 6000 5000 cal yr bp and smaller than present ice configuration until at least 2300 cal yr bp for the ice margin south of jakobshavn isbrae and until 400 cal yr bp for the ice margin north of jakobshavn isbrae one relatively large proglacial lake that became briefly ice free during the middle holocene lies in a catchment that likely extends 10s of km inland beneath the gis suggesting significant middle holocene retreat of this portion of the gis the overall pattern of ice sheet change is inconsistent with existing ice sheet model reconstructions for this region but is consistent with numerous paleoclimate proxy and relative sea level data these continuous lacustrine records corroborate but provide closer age control than existing non continuous records of radiocarbon dated reworked bivalves from historical moraines in the region reconstructing ice margin change from proglacial threshold lakes is one of few approaches with the potential to constrain smaller than present ice sheet extent

what do glaciers tell us about climate variability and climate change glaciers respond to long term climate changes and also to the year to year fluctuations inherent in a constant climate differentiating between these factors is critical for the correct interpretation of past glacier fluctuations and for the correct attribution of current changes previous work has established that century scale kilometre scale fluctuations can occur in a constant climate this study asks two further questions of practical significance how likely is an excursion of a given magnitude in a given amount of time and how large a trend in length is statistically significant a linear model permits analytical answers wherein the dependencies on glacier geometry and climate setting can be clearly understood the expressions are validated with a flowline glacier model the likelihood of glacier excursions is well characterized by extreme value statistics although probabilities are acutely sensitive to some poorly known glacier properties conventional statistical tests can be used for establishing the significance of an observed glacier trend however it is important to determine the independent information in the observations which can be effectively estimated from the glacier geometry finally the retreat of glaciers around mount baker washington state usa is consistent with but not independent proof of the regional climate warming that is established from the instrumental record

hybrid carbonates in situ abiotic microbial and skeletal co precipitates abstract abiotic bioinduced and biocontrolled carbonates are process based sediment categories they successively reflect increasing levels of biotic control over carbonate precipitation from aqueous solutions are often closely linked to depositional environment and change with time hybrid carbonates are intimate in situ combinations of two or more of these categories hybrid carbonates are widespread and diverse in the marine geological record and reflect large scale changes in carbonate precipitation through time they also occur in fluvial and lacustrine carbonates marine and non marine reef systems and methane seep deposits plots of hybrid carbonate composition in time and space reveal complex backtracking and looping patterns that reflect changes in environmental conditions and biological processes of carbonate production recognition of hybridity emphasizes the importance of distinguishing abiotic and bioinduced precipitates until they were diversified by skeletal carbonates in the late proterozoic precambrian hybrid carbonates were abiotic bioinduced combinations during the phanerozoic hybrid carbonates were conspicuous during periods of overlap or transition between intervals of microbial and skeletal carbonate abundance microbial skeletal dual hybrids are common during the cambrian mid ordovician late devonian mississippian and late jurassic early cretaceous abiotic microbial skeletal triple hybrids were common from late pennsylvanian to mid triassic shallow marine hybrid carbonates declined in abundance after the mid cretaceous although late cenozoic reefs contain some striking examples of microbial skeletal hybrids recognition of hybrid carbonates draws attention to fundamental processes underlying carbonate sedimentation and their patterns and drivers of change in time and space

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

annual push moraines as climate proxy 1 we reconstruct the terminus position of a mountain glacier in british columbia canada from annual push moraines formed between 1959 and 2007 our reconstruction represents the longest annually resolved record of length change for a north american glacier comparison of annual recession with climate records indicates that glacier recession is controlled by air temperatures during the ablation season and accumulation season precipitation during the previous decade analysis among records of glacier frontal variation and mass balance in western north america similarly reveals an immediate terminus reaction to summer and net balance and a delayed reaction to winter and net balance other mountain ranges may contain long series of push moraines that could be exploited as climate proxies and to improve understanding of glacier response to climate

new accelerator mass spectrometry radiocarbon ages for the mazama tephra layer from kootenay national park british columbia canada charcoal fragments recovered from the mazama air fall tephra layer in cores from dog and cobb lakes kootenay national park british columbia yielded accelerator mass spectrometry ages of 6720 70 and 6760 70 14c years bp respectively these two new ages together with other previously published radiocarbon ages on charcoal and twig fragments from mazama air fall deposits indicate that the climactic eruption of mount mazama occurred 6730 40 14c years bp

anomalous early 20th century sedimentation in proglacial green lake british columbia canada annually laminated sediments were recovered from green lake a proglacial lake in the southern coast mountains in british columbia to examine their potential as a temperature proxy varve thickness is moderately correlated with temperature anomalies a d 1900 1994 and annual maximum mean daily discharge of lillooet river a d 1930 1999 but these relations are not stable through time following a d 1977 the relation between varve thickness and annual maximum mean daily discharge is stronger prior to a d 1977 varve thickness is correlated with march to october air temperature which controls the intensity and duration of glacier runoff varve thickness is weakly correlated with reconstructed air temperature records for north america and the northern hemisphere for the period a d 1600 1976 less extensive glacier cover may explain the lack of a clear temperature signal in the varved sediment record prior to a d 1600 and following a d 1977 the period of highest lake sedimentation from a d 1920 to 1945 coincides with rapid retreat of glaciers in the watershed the lack of a similar level of sedimentation in the varve chronology suggests that glacier recession during the period 1920 1945 was higher than at any time in the past 600 years

estimating palaeo water depth from the physical rock record abstract palaeo water depth and its change with time is a key factor in environmental analysis and in sedimentology in general the literature published on this topic and on related subjects however is substantial albeit scattered within and between different communities geologists oceanographers engineers physicists etc here i focus on proxies for palaeo bathymetry as obtained from the physical rock record floral faunal and chemical evidence for palaeo water depth being equally important must be dealt with elsewhere an assessment of the main depth related parameters in actualistic settings is presented and their applicability to the fossil sedimentary record discussed the outcome reveals the full complexity of this topic there is for example no such thing as an average wave base depth applicable to a wide range of fossil case settings this because wave and current climates in general and particularly so in neritic and coastal settings are intriguingly complex furthermore observations from modern oceans are not a priori applicable to fossil ones acknowledging these problems and limitations critically evaluated quantitative proposals for depth indicative facies and features in the sedimentary record are presented and error bars discussed

expansion of alpine glaciers in pacific north america in the first millennium a d radiocarbon ages and lichen dated moraines from 17 glaciers in coastal and near coastal british columbia and alaska document a widespread glacier advance during the first millennium a d glaciers at several sites began advancing ca a d 200 300 based on radiocarbon dated overridden forests the advance is centered on a d 400 700 when glaciers along an 2000 km transect of the pacific north american cordillera overrode forests impounded lakes and deposited moraines the synchroneity of this glacier ad vance and inferred cooling over a large area suggest a regional climate forcing and to gether with other proxy evidence for late holocene environmental change during the me dieval warm period and little ice age provide support for millennial scale climate variability in the north pacific region

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

latest pleistocene and holocene glacier fluctuations on mount baker washington abstract glaciers on stratovolcanoes of the pacific northwest of north america offer opportunities for dating late pleistocene and holocene glacier advances because tephra and fossil wood are common in lateral moraines and in glacier forefields we capitalize on this opportunity by examining the holocene glacial record at mount baker an active stratovolcano in northwest washington earlier workers concluded that glaciers on mount baker during the early holocene were more extensive than during the little ice age and hypothesized that the explanation lay in unusual climatic or hypsometric effects peculiar to large volcanoes we show that the main argument for an early holocene glacier advance on mount baker namely the absence of ca 10 000 year old tephra on part of the south flank of the mountain is incorrect moreover a lake sediment core indicates that a small cirque moraine previously thought be of early holocene age is also likely older than the tephra and consequently of late pleistocene age lateral and end moraines and wood mats ca 2 km downvalley of the present snout of deming glacier indicate that an advance during the younger dryas interval was little more extensive than the climactic little ice age advance tephra and wood between tills in the left lateral moraine of easton glacier suggest that ice on mount baker was restricted in the early holocene and that neoglaciation began ca 6 ka a series of progressively more extensive neoglacial advances dated to about 2 2 1 6 0 9 and 0 4 ka are recorded by stacked tills in the right lateral moraine of deming glacier intervening retreats were long enough to allow establishment of forests on the moraine wood mats in moraines of coleman and easton glaciers indicate that little ice age expansion began before 0 7 ka and was followed by retreat and a readvance ca 0 5 ka tree ring and lichen data indicate glaciers on the south side of the mountain reached their maximum extents in the mid 1800s the similarity between glacier fluctuations at mount baker and those elsewhere in the cascades and in british columbia suggests a coherent history of holocene climate change over a broad area of the western cordillera we found no evidence that glaciers on stratovolcanoes behave differently than glaciers elsewhere

the iberian middle jurassic carbonate platform system synthesis of the palaeogeographic elements of its eastern margin spain abstract during the middle jurassic the domain of the iberian and catalan coastal ranges of eastern spain was occupied by a system of fault controlled carbonate platforms that flanked the iberian massif to the east this platform system marked the transition between the shelves of the alpine tethys and the central atlantic ocean the palaeogeographic reconstruction of the iberian middle jurassic platform system is based on more than 199 surface sections and 37 wells from southwest to northeast eight main palaeogeographic elements with associated characteristic facies are recognized these represent a system of horsts and grabens in the southwest the internal castilian platform is characterized by the frequently dolomitized oolitic and restricted facies of the yemeda formation to the northeast the nw trending open marine carbonate environments of the external castilian and aragonese platforms were separated by the fault controlled el maestrazgo high that is characterized mainly by the dolomitized rafales formation the external castilian and aragonese platforms consist from bottom to top of the microfilament mudstones to wackestones of the el pedregal formation the bioclastic and oolitic grainstones to packstones of the moscardon formation and the domeno formation that reflects a return to an open marine low energy wackestone to mudstone facies locally containing patches of oolitic grainstones the highly subsiding tortosa platform represented by the sant blai cardo and la tossa formations is bounded by the dolomitic facies deposited on the el maestrazgo and the tarragona highs and by the catalan massif where no middle jurassic deposits have been recorded the open marine facies and condensed sections of the beceite strait separated the aragonese and tortosa platforms a regional stratigraphical gap spanning the upper callovian lamberti zone to the lower oxfordian cordatum zone is evident a system of northwest and northeast trending normal faults controlled thickness and facies distribution data from the iberian carbonate platform system indicate that expanded sections were not necessarily associated with open marine environments condensed and expanded sections are developed in open and restricted marine facies even on such palaeogeographic highs as the el maestrazgo high restricted and shallow marine environments occasionally developed in parts of the external castilian platform

neritic carbonate crisis during the early bajocian divergent responses to a global environmental perturbation abstract the early bajocian witnessed a global environmental perturbation characterized by faunal and floral turnovers and a positive carbon isotope excursion in italy this environmental perturbation coincided with an eutrophication event and a carbonate crisis but this has so far not been adequately reported from other settings leaving doubt about the extent and nature of these phenomena in this paper we are reporting on an extensive neritic carbonate factory demise that occurs in the upper lower bajocian of morocco more precisely in the upper propinquans lower humphriesianum zones this demise coincided with the acme of the global carbon isotope perturbation recorded by a 3 positive carbon isotope excursion in the bulk organic matter of morocco but not in the micritic phase due to the fact that the moroccan carbonate 13c record is more sensitive to local rather than global influences furthermore we observe that the lower bajocian of morocco is relatively enriched in arenitic siliciclastic deposits suggesting increased weathering and nutrient levels along the northwestern margin of africa during the early bajocian however comparison with neighboring european basins highlights the non uniqueness and different timing of the response of shallow water carbonates to the early bajocian environmental perturbations as some regions present no sign of carbonate factory crisis hence we postulate that local factors were important in mediating the response of neritic carbonate factories to this global environmental perturbation we notably highlight the role of large early bajocian sea level fluctuation as a trigger for carbonate factory change and demise in morocco

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

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

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

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

carbonate production and offshore transport on a late jurassic carbonate ramp kimmeridgian iberian basin ne spain evidence from outcrops and computer modelling

late holocene glacial activity in manatee valley southern coast mountains british columbia canada the dendroglaciologic and lichenometric research methodologies employed in this study provide a perspective of glaciological conditions from 5 ka to present in a remote headwater area of the british columbia coast mountains since holocene ice fronts of four glaciers at this site periodically extended below treeline previous glacier advances overrode and buried forests beneath till deposits this study suggests that glaciers were expanding into standing forests at 4 76 and 3 78 ka following glacier expansion at 3 78 ka a period of recession ensued when glaciers withdrew upvalley long enough for the development of deep pedogenic surfaces and the growth of trees exceeding 300 years investigations at beluga and manatee glaciers benchmark a subsequent episode of significant glacial expansion at 2 42 ka referred to as the manatee advance this advance has regional correlatives and is distinguished from the tiedemann advance at manatee glacier by documentation of substantive ice front retreat between the

improved age estimates for the white river and bridge river tephras western canada new 14c ages date the eruptions that produced the white river and bridge river tephras two important holocene marker beds in western canada the 14c ages were obtained on trees in growth position buried in coarse tephra and a pyroclastic flow near the source vents the mean calendric age of the white river eruption based on four 14c ages is 1147 cal years bp calibrated years approximately equivalent to calendric years or ad 803 the 2 age range obtained from the two most precise 14c ages is 1014 1256 cal years bp or ad 694 936 the mean age of the bridge river eruption determined both from i the single most precise outer ring 14c age and ii the weighted mean of six outer ring 14c ages is 2360 cal years bp or 411 bc 2 age range 2349 2704 cal years bp or 755 400 bc