holocene glacial activity and climatic variations in the swiss alps reconstructing a continuous record from proglacial lake sediments cores recovered from proglacial lake silvaplana swiss alps were investigated to examine the influence of holocene glaciers on lacustrine sedimentation during times of glacial activity in the catchment the sedimentation in the lake is dominated by the input of silt and clay sized material delivered by glacial meltwaters the deposition of fine grained material and the formation of varves reflect the existence of glaciers in the catchment and can therefore be used for the reconstruction of glacial history sedimentation rates are up to nine times higher in the varved than in the non varved sediments indicating significantly higher erosion rates under glaciated catchment conditions glacial varves were deposited in lake silvaplana during glacial retreat in the latest pleistocene and early holocene until 9400bp non varved deposits having a higher organic content and coarser grain sizes accumulated at lower rates when glacial activity was absent or negligible within the catchment between 9400 and 3300 bp

contrasting types of grenvillian granulite facies aluminous gneisses insights on protoliths and metamorphic events from zircon morphologies and ages abstract zircon morphology internal texture u pb age distributions and th u ratios are used to characterize aluminous gneisses in the canyon domain manicouagan area central grenville province from two contrasting supracrustal sequences metamorphosed at granulite facies one a package of paragneiss and the other a dominantly bimodal felsic mafic volcanic sequence the aluminous paragneisses yielded zircon with fragmental igneous cores overgrown by metamorphic rims these cores show a spread in ages between 1500 ma and 2700 ma consistent with a supply of detritus from the adjacent canadian shield in contrast a felsic gneiss with aluminous nodules inferred to represent a hydrothermally altered felsic volcanic rock of the bimodal sequence yielded well preserved igneous zircon dated at 1238 13 ma an age that integrated with previously published data links this volcanic sequence to a major episode of crustal extension in the central grenville province metamorphic zircon grains and rims from the paragneisses gave two groups of pre grenvillian ages that demonstrate the effect of major magmatic events on the country rocks in the canyon domain a 1391 1408 ma coeval with the emplacement of an older layered mafic to intermediate volcanic suite and b 1217 1260 ma coeval with the development of the 1238 ma bimodal felsic mafic volcanic sequence in addition metamorphic zircon from all the investigated aluminous gneisses records the high grade grenvillian metamorphism 1080 1040 ma

derivation of isotope ratios errors and error correlations for u pb geochronology using 205pb 235u 233u spiked isotope dilution thermal ionization mass spectrometric data a comprehensive treatment of the derivation of u pb isotope ratios and their corresponding uncertainties from isotope dilution thermal ionization mass spectrometric measurements is presented standard parametric statistical methods of error propagation are utilized to convolve uncertainties associated with instrumental mass fractionation tracer subtraction blank pb and u subtraction and initial common pb correction derivations include errors and error correlations for total sample u pb and pb isotope ratios including radiogenic and initial common pb for two and three dimensional isochron calculations radiogenic u pb and pb isotope ratios for concordia and radiogenic model age calculations and the propagation of model age errors from radiogenic isotope ratios

a 500 year long record of tephra falls from redoubt volcano and other volcanoes in upper cook inlet alaska abstract volcanic ash layers preserved in glacial lacustrine sediments at skilak lake on the kenai peninsula of southcentral alaska constitute a record of eruptions at redoubt volcano and other alaskan volcanoes which affected the upper cook inlet area during the last 500 years high resolution magnetic susceptibility profiling delineates similar sequences of tephra layers in several 1 m long lake sediment cores electron microprobe analyses of glass shards from the tephras indicate correlation of some ash layers with known reference tephras from the source volcanoes while other ash layers record previously unknown prehistoric eruptions skilak lake cores contain ash from the historic 1912 katmai eruption the 1902 redoubt eruption and the 1883 mount st augustine eruption as well as prehistoric ash layers erupted from crater peak at mt spurr ca 250 350 years ago from redoubt volcano at ca 300 400 years ago and again at ca 350 450 years ago and a 500 year old ash from mount st augustine still older tephras from redoubt volcano and crater peak at mt spurr are found lower in the cores the cores indicate that volcanoes in the cook inlet area have erupted every 10 35 years during the 20th century and ash falls have occurred at skilak lake at least once every 50 100 years for the last 500 years with redoubt spurr and augustine volcanoes being the most important sources of tephra

docking of the central metasedimentary belt to laurentia in geon 12 evidence from the 1 17 1 16 ga chevreuil intrusive suite and host gneisses quebec the chevreuil intrusive suite 1 17 1 16 ga represents a chronological field marker of regional extent that intruded the central metasedimentary belt in the western grenville province of quebec after peak metamorphism style and site of magma emplacement and extent of deformation of chevreuil plutons and dykes permit unravelling of the early grenvillian evolution of the belt with respect to cratonal north america the suite comprises a series of vertically layered gabbro stocks and monzonite diorite gabbro sheet intrusions and a swarm of microdiorite dykes that cut across gneisses the dykes display systematic variations in extent of deformation across the belt we targeted u pb geochronology on gneisses within the identified strain windows they preserve the record of a ca 1 20 ga high pressure temperature p t metamorphic event the sheet intrusions define magmatic corridors all along and concordant with the western northern and eastern tectonic boundaries of the belt the concordant and elonga

new insights on the 1 7 1 0 ga crustal evolution of the central grenville province from the manicouagan baie comeau transect abstract integrated field relationships and u pb geochronology of rocks exposed along the southern part of the manicouagan reservoir central grenville province quebec provide insights into protolith formation and thermal events that range in age from ca 1 7 to 0 9 ga and share common features with the rest of the grenville province and beyond from presently lower to higher structural levels main findings include the recognition of a ca 1 70 1 75 ga granitic magmatism and metamorphism in the southern part of the parautochthonous gagnon terrane correlative in age with late stages of magmatism in the makkovik orogen to the northeast b a ca 1 69 gabbro anorthosite suite island domain which is inferred to represent the southwesternmost exposure of labradorian crust in the central grenville province c a 1 4 ga volcaniclastic sequence and associated plutonic rocks canyon domain which based on lithological association and age is inferred to represent the nne extension of the montauban island arc and d a ca 1 2 ga bimodal felsic mafic volcanic to intermediate volcaniclastic sequence banded complex inferred to have originated in an intra continental rift system contemporaneously with the composite arc belt southwestern grenville province and with widespread extensional magmatism elsewhere in the canadian shield in addition 1 3 ga granitoid plutons are documented to intrude labradorian units at the nw boundary of canyon domain the significance of these plutons is ambiguous as they may represent either stitching plutons marking the accretion of the 1 4 ga canyon domain to the laurentian margin or the first stage in the development of the ca 1 2 ga continental rift system the hinterland units island domain canyon domain and banded complex were metamorphosed under medium pressure granulite facies conditions during the culmination of the grenvillian orogeny between 1 08 and 1 04 ga this metamorphism was accompanied by ca 1 07 ga a type granitic magmatism in canyon domain in addition locally abundant ca 0 98 ga late tectonic felsic pegmatite and ultrapotassic dykes occur in canyon domain this event is coeval with titanite ages documented in a wide range of units the data on the grenvillian evolution suggest mantle derived magmatism and associated metamorphism in the hinterland during both the culmination and the waning stages of the grenvillian orogeny

pinwarian to grenvillian magmatic evolution in the central grenville province new constraints from id tims u pb ages and coupled lu hf s mc icp ms data understanding the magmatic evolution of the rocks once comprising the hinterland of the grenville orogen through their mesoproterozoic formation is a key to understanding the grenvillian orogeny as a whole in this contribution we present high precision isotope dilution thermal ionization mass spectrometry id tims u pb and coupled solution multicollector inductively coupled plasma mass spectrometry s mc icp ms lu hf zircon data from magmatic rocks occurring in the allochthonous belt of the grenville orogen in the central part of the grenville province we document the presence of a large tract of pinwarian crust represented by a 1497 5 ma granitic gneiss as well as large late geon 14 to early geon 13 1434 7 11 1413 12 1393 8 1383 1 ma magmatic complexes one grenvillian plutonic suite of 1015 2 ma that cross cuts the host rock metamorphic fabric has also been dated this age provides a minimum age of ottawan metamorphism in the region the hf isotopic data show that the magmatic roc

the human occupation of the northwestern pyrenees in the late glacial new data from the arudy basin lower ossau valley excavated since the 1860s the arudy basin has yielded a number of rich magdalenian sites that enable us to address the question of the human reoccupation of the lower pyrenean valleys at the end of the last glacial maximum until the 1990s it was considered that at arudy this reoccupation started ca 16 000 cal bp in the middle magdalenian and continued into the upper magdalenian until ca 14 000 cal bp however since the mid 2000 s this picture has been modified through a series of new analyses excavations caves of laa 2 and tastet 14c dates and reassessment of ancient collections evidence of human occupation ca 20 000 19 000 cal bp although limited has been identified at laa 2 and tastet consistent with numerous data obtained at pyrenean scale showing a deglaciation of the north pyrenean foothills as early as the end of the global lgm the number of sites with evidence of magdalenian has increased showing that human presence in the basin was more intensive than previously thought the middle and upper magdalenian occupations have been redated to at least 18 000 17 500 cal bp to 15 000 14 500 cal bp with the transition between the two phases probably occurring ca 16 600 16 200 cal bp the faunal records of these sites document an emphasis on horse hunting which is not common in the northern pyrenees but also witness an evolution over time in the range of species hunted furthermore the pyrenean affinities of the arudy groups and their relations with neighboring regions such as spain and the northern part of the aquitaine basin can be addressed through new evidence in particular lithic and osseous raw materials and specific types of projectile tips these results significantly change our view of the nature rhythm and chronology of the late glacial settlement in this area

correlation of alaskan varve thickness with climatic parameters and use in paleoclimatic reconstruction the thickness of varves in the sediments of skilak lake alaska are correlated with the mean annual temperature r 0 574 inversely correlated with the mean annual cumulative snowfall r 0 794 and not correlated with the mean annual precipitation r 0 202 of the southern alaska climatological division for the years 1907 1934 a d varve thickness in skilak lake is sensitive to annual temperature and snowfall because skilak glacier the dominant source of sediment for skilak lake is sensitive to these climatic parameters trends of varve thickness are well correlated with trends of mean annual cumulative snowfall r 0 902 of the southern alaska climatological division and with trends of mean annual temperature of the southern r 0 831 and northern r 0 786 alaska climatological divisions trends of varve thickness also correlate with trends of annual temperature in seattle and north head washington r 0 632 and 0 850 respectively comparisons of trends of varve thickness with trends of annual temperature in california oregon and washington suggest no widespread regional correlation trends of annual snowfall in the southern alaska climatological division and trends of annual temperature in the southern and northern alaska climatological divisions are reconstructed for the years 1700 1906 a d climatic reconstructions on the basis of varve thickness in skilak lake utilize equations derived from the regression of series of smoothed climatological data on series of smoothed varve thickness reconstruction of trends of mean annual cunulative snowfall in the southern alaska climatological division suggests that snowfall during the 1700s and 1800s was much greater than that during the early and mid 1900s the periods 1770 1790 and 1890 1906 show marked decreases in the mean annual snowfall reconstructed trends of the annual temperature of the northern and southern alaska climatological divisions suggest that annual temperatures during the 1700s and 1800s were lower than those of the early and mid 1900s two periods of relatively high annual temperatures coincide with the periods of low annual snowfall thus determined

dendrohydroclimate reconstructions of july august runoff for two nival regime rivers in west central british columbia lengthy records of river discharge are necessary to comprehensively assess the long term connection between synoptic climate forcings and nival regime systems in british columbia a regional multispecies network of tree ring width and ring density chronologies was built for west central british columbia with the intention of dendrohydrologically extending short runoff records in this area extended records of july august mean discharge anomalies for the skeena and atnarko rivers were reconstructed back to ad 1660 low flow events represented during the late 1600s early 1700s and late 1800s lie beyond those experienced during the recent instrumental period for these basins the documentation of extreme events of this magnitude necessitates consideration when planning for future water resources in this region supplementary dendroclimatic reconstructions of the winter pacific north american pna pressure anomaly pattern and records of mean summer temperature and end of winter snow water equivalent were also constructed these ancillary climate records provide insight into the long term climate drivers of annual discharge dynamics within these nival basins correlation and wavelet analyses confirm the persistent relationship of synoptic climate regimes described by the southern oscillation index nino 3 4 pacific decadal oscillation and pna indices on runoff in west central british columbia copyright 2012 john wiley sons ltd

climate record in varved sediments of the eocene green river formation three time series of varves from the eocene green river formation in colorado consisting of 1469 1869 and 4158 annual thickness measurements were analyzed by a variety of statistical techniques to characterize climate variations the analyses reveal that the time series are lognormal after adjustment for a trend moreover the analyses suggest that the time series are generally nonstationary and are noiselike in structure fourier spectra and maximum entropy spectra of the time series are reddish indicating the importance of nonoscillatory changes in varve thickness at time scales ranging from tens to hundreds of years there are no statistically significant peaks in fourier spectra for the entire time series however one segment of one of the three time series displays statistically significant peaks corresponding to periods of 10 8 and 5 4 years overall the time series are suggestive of a nonperiodic and weakly predictive climate during the time periods corresponding to deposition of the varves

repeated crustal thickening and recycling during the andean orogeny in north chile 21 26 s posttectonic granitoids 2 lower crustal p wave velocities of 7 3 7 7 km s 1 compatible with underplated mafic crust and 3 results from recent experimental petrologic work showing garnet stability in mafic mineralogies 12 kbar 40 km crustal thickness analogous to older andean magmatic episodes in north chile newly underplated basaltic crust may account for the remaining deficit in neogene crustal thickening similar evolutionary patterns in geochemistry and initial sr and nd isotopic characteristics of andean 200 ma to present magmatic rocks suggest that the andean orogeny in this region evolved by a combination of processes of repeated arc migration tectonic and magmatic crustal thickening and igneous recycling which was controlled by periodically changing plate convergence rates and obliquity and corresponding changes in the rheologic behavior of the continental crust index terms 1020 geochemistry composition of the crust 1030 geochemistry geochemical cycles 0330 8159 evolution of the earth rheology crust and lithosphere 9360 information related to geographic region south america keywords andean orogeny continental crust recycling adakite ttg crustal thickening

paleoseismic potential of sublacustrine landslide records in a high seismicity setting south central alaska abstract sublacustrine landslide stratigraphy is considered useful for quantitative paleoseismology in low seismicity settings however as the recharging of underwater slopes with sediments is one of the factors that governs the recurrence of slope failures it is not clear if landslide deposits can provide continuous paleoseismic records in settings of frequent strong shaking to test this we selected three lakes in south central alaska that experienced a strong historical megathrust earthquake the 1964 m w 9 2 great alaska earthquake and exhibit high sedimentation rates in their main basins 0 2 cm yr 1 1 0 cm yr 1 we present high resolution reflection seismic data 3 5 khz and radionuclide data from sediment cores in order to investigate factors that control the establishment of a reliable landslide record seismic stratigraphy analysis reveals the presence of several landslide deposits in the lacustrine sedimentary infill most of these landslide deposits can be attributed to specific landslide events as multiple landslide deposits sourced from different lacustrine slopes occur on a single stratigraphic horizon we identify numerous events in the lakes eklutna lake proximal basin 14 events eklutna lake distal basin 8 events skilak lake 7 events and kenai lake 7 events the most recent event in each basin corresponds to the historic 1964 megathrust earthquake all events are characterized by multiple landslide deposits which hints at a regional trigger mechanism such as an earthquake the synchronicity criterion this means that the landslide record in each basin represents a record of past seismic events based on extrapolation of sedimentation rates derived from radionuclide dating we roughly estimate a mean recurrence interval in the eklutna lake proximal basin eklutna lake distal basin skilak lake and kenai lake at 250 yrs 450 yrs 900 yrs and 450 yrs respectively this distinct difference in recording can be explained by variations in preconditioning factors like slope angle slope recharging sedimentation rate and the sediment source area faster slope recharging and a predominance of delta and alluvial fan failures increase the sensitivity and lower the intensity threshold for slope instability also the seismotectonic setting of the lakes has to be taken into account this study demonstrates that sublacustrine landslides in several alaskan lakes can be used as reliable recorders of strong earthquake shaking when a multi lake approach is used and can enhance the temporal and spatial resolution of the paleoseismic record of south central alaska

a 1500 year record of temperature and glacial response inferred from varved iceberg lake southcentral alaska we present a varve thickness chronology from glacier dammed iceberg lake in the southern alaska icefields radiogenic evidence confirms that laminations are annual and record continuous sediment deposition from a d 442 to a d 1998 varve thickness is positively correlated with northern hemisphere temperature trends and more strongly with a local 600 yr long tree ring width chronology varve thickness increases in warm summers because of higher melt runoff and sediment transport as expected but also because shrinkage of the glacier dam allows shoreline regression that concentrates sediment in the smaller lake varve thickness provides a sensitive record of relative changes in warm season temperatures relative to the entire record temperatures implied by this chronology were lowest around a d 600 warm between a d 1000 and a d 1300 cooler between a d 1500 and a d 1850 and have increased dramatically since then combined with stratigraphic evidence that contemporary jokulhlaups which began in 1999 are unprecedented since at least a d 442 this record suggests that 20th century warming is more intense and accompanied by more extensive glacier retreat than the medieval warm period or any other time in the last 1500 yr

varve studies at hector lake alberta canada and the relationship between glacial activity and sedimentation glacial lake sedimentary records from hector lake in banff national park alberta are examined with the aim of clarifying the relationship between glacial activity and outwash sedimentation rhythmic couplets in lake bottom sediments provide a method for accurate documentation and dating of recent sedimentation chronology as analysis of 137cs content indicates that the couplets are of annual periodicity i e varves a comparison of sedimentation rate records with recent regional glacial history indicates that high sedimentation rates of one to a few decades duration occur either during and immediately following periods of moraine deposition ie maximum ice stands or during periods of rapid ice recession comparison of sedimentary records with somewhat longer term glacial and vegetation records indicates that sedimentation rate variations of several centuries duration closely parallel changes in upvalley ice extent over this time scale high sedimentation rates occur during periods of relatively increased ice extent low rates during periods of reduced ice extent within this general pattern however sedimentation rates may remain very high for nearly a century following maximum ice stands due to the exposure of unstable glaciogenic deposits to fluvial reworking during ice recession

a routine high precision method for lu hf isotope geochemistry and chronology a method for chemical separation of lu and hf from rock meteorite and mineral samples is described together with a much improved mass spectrometric running technique for hf this allows i geo and cosmochronology using the176lu 176hf decay scheme and ii geochemical studies of planetary processes in the earth and moon chemical yields for the three stage ion exchange column procedure average 90 for hf chemical blanks are 0 2 ng for lu and hf from 1 g of hf a total ion current of 0 5 10 11 ampere can be maintained for 3 5 h yielding 0 01 0 03 precision on the ratio176hf 177hf normalisation to179hf 177hf 0 7325 is used extensive results for the johnson matthey hf standard jmc 475 are presented and this sample is urged as an international mass spectrometric standard suitable aliquots prepared from a single batch of jmc 475 are available from denver lu hf analyses of the standard rocks bcr 1 and jb 1 are given the potential of the lu hf method in isotope geochemistry is assessed

varve formation during the past three centuries in three large proglacial lakes in south central alaska the sediments stored in the large deep proglacial lakes of south central alaska are largely unstudied we analyzed sediments in 20 cores up to 160 cm long from eklutna kenai and skilak lakes using a combination of repeated lamination counting radionuclide dating event stratigraphy and tephrochronology we show that the characteristically rhythmic layers were deposited annually most of these glacial varves consist of one coarse grained base and a fine grained top but varves composed of multiple coarse grained turbidite pulses are common too they are likely related to successive episodes of high sediment discharge during flooding and they become more frequent in all three lakes along with increased sedimentation rates during the nineteenth century late phase of the little ice age these flood turbidites were generated by rain events and intense melting of snow and ice other mega turbidites are a result of earthquake triggered slope collapses e g a d 1964 some event layers are present in all three lakes in addition the annual time series of varve thickness normalized annual sedimentation rate are significantly correlated among the three lakes p 0 27 p 0 001 differences between the varve thickness records can be attributed partly to the dam construction at eklutna lake and outbursts from an ice dammed lake at skilak lake geomorphologic differences among the catchments result in further differences in sedimentation patterns in the three lakes

post younger dryas seasonality in the north american midcontinent region as recorded in lake huron varved sediments a sediment core from northwestern lake huron contains a sequence of red and gray layered sediments that are postglacial and early holocene glaciolacustrine varves two hundred and sixty four couple

subduction dynamics and the origin of andean orogeny and the bolivian orocline the building of the andes results from the subduction of the oceanic nazca plate underneath the south american continent however how and why the andes and their curvature the bolivian orocline formed in the cenozoic era 65 5 million years myr ago to present despite subduction continuing since the mesozoic era 251 0 65 5 myr ago is still unknown three dimensional numerical subduction models demonstrate that variations in slab thickness arising from the nazca plate s age at the trench produce a cordilleran morphology consistent with that observed the age dependent sinking of the slab in the mantle drives traction towards the trench at the base of the upper plate causing it to thicken thus subducting older nazca plate below the central andes can explain the locally thickened crust and higher elevations here we demonstrate that resultant thickening of the south american plate modifies both shear force gradients and migration rates along the trench to produce a concave margin that matches the bolivian orocline additionally the varying forcing along the margin allows stress belts to form in the upper plate interior explaining the widening of the central andes and the different tectonic styles found on their margins the eastern and western cordilleras the rise of the central andes and orocline formation are directly related to the local increase of nazca plate age and an age distribution along the margin similar to that found today the onset of these conditions only occurred in the eocene epoch this may explain the enigmatic delay of the andean orogeny that is the formation of the modern andes

characteristics of sedimentary varve chronologies a review abstract we constructed a varve data base vdb to study the worldwide distribution of varved sediment records and the fidelity of their varve chronologies clusters of lakes with varved sediments exist in central north america in the canadian arctic and in northern and central europe among the 108 sites included in the vdb varved records are typically 200 500 cm long and cover a period of 1000 2000 years their varve chronologies are often based on counting of annual layers from fresh sediment surfaces and photographs or from epoxy embedded sediment blocks and thin sections the vdb indicates that chronological errors associated with counting sedimentary varves fall generally between 1 and 3 but only 57 of published records are providing quantitative error estimations for their chronologies with a careful documentation of varves and by applying radiometric dating methods to surface sediments as well as using historical events as time markers there is the potential of having centennial long varved records with a very precise age depth control however it is unrealistic to expect errors significantly below 1 from several millennia long sections we found no indication that varve chronologies would have been substantially more accurate and precise in some parts of the world than in others or statistically dependent on varve thickness or temporal extension of a varved sequence according to the vdb close to 90 of the published varve chronologies have been cross checked with some independent dating methods

the central metasedimentary belt grenville province as a failed back arc rift zone nd isotope evidence abstract nd isotope data are presented for granitoid orthogneisses from the central metasedimentary belt cmb of the grenville province in order to map the extent of juvenile grenvillian age crust within this orogenic belt that is composed mostly of older crustal terranes the data reveal a 150 km wide belt of juvenile crust in ontario but this belt contains a block of pre grenvillian crust containing the elzevir pluton which yields an estimated crustal formation age of 1 5 ga the recognition of an older block within the cmb has profound implications for its structure and tectonic evolution because it implies that juvenile grenvillian crust apparently forming a wide ne sw belt is in fact distributed in two narrower segments with approximately n s strike we suggest that the cmb comprises an en echelon series of ensimatic rift segments created by back arc spreading behind a continental margin arc these rift segments extend southwards in the subsurface into the northeastern unites states the rift segments contain abundant marble outcrops consistent with marine incursion into the rift zone and these deposits also continue northwards into a marble domain of the cmb in quebec however crustal formation ages in the latter domain are largely pre grenvillian implying that the quebec rift segment was ensialic hence we interpret the cmb in ontario and quebec as the northern termination of a failed back arc rift zone

varve formation and the climatic record in an alpine proglacial lake calibrating annually laminated sediments against hydrological and meteorological data processes leading to the formation of varves in proglacial oeschinensee switzerland are investigated the aim is to calibrate annually laminated sediments of the last three decades against hydrological and meteorological instrumental data results from water samples and sediment traps show that the suspended sediment in the lake is mainly distributed by underflows during the time of the largest sediment input from may to mid august this leads to the deposition of the basal silt layers of the varves settling of fine grained suspension from interflows dominates sedimentation between august and october forming the final layer of fine grained material at the end of the annual deposition cycle the median grain size at the top of the varves is always below 5 m and thus defines the varve boundaries varve thickness is a function of the annual discharge of suspended load from the catchment this is supported by evidence from hydrological and meteorological data compiled for a glaciated catchment loetschen

a long lacustrine record from the pianico sellere basin middle late pleistocene northern italy abstract the stratigraphical succession of the pianico sellere basin northern italy represents an exceptionally well preserved sedimentary assemblage which formed in a closed lake basin during the middle upper pleistocene these deposits are grouped into the hereby proposed pianico formation this includes four lacustrine fine grained laminated lithostratigraphical units containing a 10 5 m thick interval of well preserved varved carbonates the lacustrine units are coeval and laterally heteropic to lake marginal talus cone fan delta debris flow deposits accumulated within the lake the stratigraphical study and sedimentary facies analysis throughout the lacustrine succession combined with a preliminary pollen and microstratigraphical investigation provide evidence of a complex environmental and climatic evolution which occurred during the lacustrine deposition the pianico formation shows multiple changes in sedimentary processes which indicate a transition from a peri proglacial to a temperate lacustrine environment within forested phases a complex evolution is evident main changes in vegetational patterns from conifer to broad leaved warm temperate forests correspond to changes in sediment composition from distal sand silt turbidites to a regular continuous succession of endogenic calcite rich annual varves an increased rate of erosional processes on the surrounding slopes is also indicated by debris flow deposits stratigraphically their frequency within the fine grained basinal sediments increases upwards which would indicate increasing subaerial erosion processes at the end of the sedimentation of the pianico formation these data highlight the sensitivity of the pianico sellere basin sedimentation in recording minor climatic fluctuations and related environmental changes which occurred before the last glacial maximum probably during oxygen isotope stage 5 7 or 9

solar signature in sedimentary cycles from the late precambrian elatina formation australia climatic cyclicity is recorded by regular variations in the thickness of varves in the elatina formation a late precambrian periglacial lake deposit in south australia earlier conclusions that the climatic cycles reflect solar variability are strongly supported by a complexity of periods revealed through study of drill cores of the varved sequence the new data promise to contribute significantly to our understanding of solar processes

solar periodicities expressed in varves from glacial skilak lake southern alaska a sequence of 236 varve thickness measurements by perkins and sims from proglacial skilak lake in southern alaska is shown to contain spectral features similar to those of the sunspot index in general the varve spectrum qualitatively mimics that of the sunspot index with discrepancies perhaps arising from the misinterpretation of random summer layers as annual increments varves these discrepancies may be largely removed through maximization of the sunspot index varve cross correlation whereby a time scale factor increment is applied to the varve series measurements varve thickness is positively correlated with the sunspot index and with vanishing lag insofar as can be resolved as varve thickness and meteorological variables have previously been shown to be strongly correlated a direct link between the sunspot index and varve thickness is suggested by way of climate response to solar variations

dust transport and palaeoclimate during the oldest dryas in central europe implications from varves lake constance this paper evaluates evidence for seasonal loess deposits in peri alpine lake constance at the end of the last glacial oldest dryas chronozone the usefulness of such lacustrine deposits for palaeoclimatic interpretations is discussed the sedimentology of laminated couplets comprising yellow and grey silts has been investigated to test the hypothesis that the couplets are varves i e annual rhythmites comprising alternations of loess and glacial silt and clay the laminae are mostly less than 1 mm thick and include from bottom to top 1 a matrix of well sorted non graded fine yellow silt with sand size intraclasts 2 coarsening upward grey silt with a cap of fining upward silt to clay the latter is typical for varves in modern proglacial lakes and reflects summer and winter deposits silt and clay respectively we propose that the lack of grading and the matrix supported fabric is indicative of aeolian transport and therefore interpret the yellow laminae as loess deposits volcanic glass intraclasts in the loess layers are probably derived from volcanic terrain to the west of the lake indicating an easterly palaeowind direction deposition of loess in the lake occurred regularly at the beginning of each annual cycle suggesting that the palaeowinds were associated with winter and or spring conditions two transport scenarios are suggested to explain the sand grains scattered in this deep water lacustrine record 1 the grains may have been transported as bedload over the annual winter ice cover of the lake under moderate wind strengths frozen into the ice and released for deposition during spring melt 2 the sand grains were blown directly out onto the lake water by very strong winds during spring the first scenario is contrary to the general view that loess was transported during summer and that loess deposits thus reflect summer conditions only loess input to the lake shows a transitional decrease after ca 14 3 kyr bp and cessation at ca 14 kyr bp probably as a result of a change of wind behaviour increased humidity and or vegetational changes during the oldest dryas in central europe