impact of the late glacial eruption of the laacher see volcano central rhineland germany abstract within a period of a few weeks toward the end of the allerod interstadial the major plinian eruption of the laacher see volcano produced some 20 km3 of eruptiva covering and preserving the late glacial landscape in the german central rhineland over an area of more than 1000 km2 correlation of terrestrial archives with the greenland ice core records and improved calibration of the radiocarbon timescale permit a precise accurate age determination of the laacher see event some 200 yr before the onset of the younger dryas cold episode carbonized trees and botanical macrofossils preserved by laacher see tephra permit detailed regional paleoenvironmental reconstruction and show that open woodland were typical for the cool and humid hemiboreal climatic conditions during the late allerod this woodland provided the habitat for a large variety of animal species documented at both paleontological and final paleolithic archeological sites preserved below laacher see deposits of special interest are numerous animal tracks intercalated in middle laacher see deposits at the south of the neuwied basin this knowledge may help to evaluate possible supraregional impacts of this volcanic event on northern hemispheric environment and climate during the late allerod

lateglacial early holocene fluvial reactions of the jeetzel river elbe valley northern germany to abrupt climatic and environmental changes abstract mechanisms of climatic control on river system development are still only partially known palaeohydrological investigations from river valleys often lack a precise chronological control of climatic processes and fluvial dynamics which is why their specific forces remain unclear in this multidisciplinary case study from the middle elbe river valley northern germany multiple dating of sites palynostratigraphy radiocarbon and osl dating and high resolution analyses of environmental and climatological proxies pollen plant macro remains and ostracods reveal a continuous record of the environmental and fluvial history from the lateglacial to the early holocene biostratigraphical correlation to northwest european key sites shows that river system development was partially out of phase with the main climatic shifts the transition from a braided to an incised channel system predated the main phase of lateglacial warming 14 6 ka bp and the meandering river did not change its drainage pattern during the cooling of the younger dryas period environmental reconstructions suggest that river dynamics were largely affected by vegetation cover as a vegetation cover consisting of herbs dwarf shrubs and a few larger shrubs seems to have developed before the onset of the main lateglacial warming and pine forests appear to have persisted in the river valley during the younger dryas in addition two phases of high fluvial activity and new channel incision during the middle part of the younger dryas and during the boreal were correlated with changes from dry towards wet climatic conditions as indicated by evident lake level rises lateglacial human occupation in the river valley which is shown by numerous palaeolithic sites forming one of the largest settlement areas of that period known in the european plain is assigned to the specific fluvial and environmental conditions of the early allerod

stable isotopic biogeochemistry of carbon and nitrogen in a perennially ice covered antarctic lake lake hoare 77 degrees 38 s 162 degrees 53 e is an amictic oligotrophic 34 m deep closed basin lake in taylor valley antarctica its perennial ice cover minimizes wind generated currents and reduces light penetration as well as restricts sediment deposition into the lake and the exchange of atmospheric gases between the water column and the atmosphere the biological community of lake hoare consists solely of microorganisms both planktonic populations and benthic microbial mats lake hoare is one of several perennially ice covered lakes in the mcmurdo dry valleys that represent the end member conditions of cold desert and saline lakes the dry valley lakes provide a unique opportunity to examine lacustrine processes that operate at all latitudes but under an extreme set of environmental conditions the dry valley lakes may also offer a valuable record of catchment and global changes in the past and present furthermore these lakes are modern day equivalents of periglacial lakes that are likely to have been common during periods of glacial maxima at temperate latitudes we have analyzed the dissolved inorganic carbon dic of lake hoare for delta 13c and the organic matter of the sediments and sediment trap material for delta 13c and delta 15n the delta 13c of the dic indicates that 12c is differentially removed in the shallow oxic portions of the lake via photosynthesis in the anoxic portions of the lake 27 34 m a net addition of 12c to the dic pool occurs via organic matter decomposition the dissolution of caco3 at depth also contributes to the dic pool except near the canada glacier where a substantial amount of allochthonous organic matter enters the lake the organic carbon being deposited on the lake bottom at different sites is isotopically similar suggesting an autochthonous source for the organic carbon preliminary inorganic carbon flux calculations suggest that a high percentage of the organic carbon fixed in the water column is remineralized as it falls through the water column at nearby lake fryxell the substantial relative to lake hoare glacial meltstream input overprints fryxell s shallow water biological delta 13c signal with delta 13c depleted dic in contrast lake hoare is not significantly affected by surface water input and mixing and therefore the delta 13c patterns observed arise primarily from biological dynamics within the lake organic matter in lake hoare is depleted in 15n which we suggest is partially the result of the addition of relatively light inorganic nitrogen into the lake system from terrestrial sources

paleoecology of a 90 000 year lacustrine sequence from fog lake baffin island arctic canada a 137 cm sediment core from fog lake a small upland basin that was not glaciated during the late wisconsinan reveals the following stratigraphic succession i basal diamicton ii laminated silts iii compacted dewatered gyttja iv stratified minerogenic sediments and v overlying gyttja units i iii and most of unit iv were deposited prior to the holocene unit v represents approximately the last 8000 14c years alternate luminescence dating techniques tl and irsl place unit iii in latter oxygen isotope stage ois 5 74 000 years bp a suite of 20 ams 14c dates suggests that much of the post ois 5 paleoenvironmental record is characterized by either extremely low continuous sediment accumulation or by one or more episodes of more rapid sedimentation diverse pollen and spore assemblages have concentrations that are unexpectedly high throughout the pre holocene sediments 10 000 grains cm 3 by comparison to the holocene 5000 grains cm 3 exceedingly low sediment accumulation rates appear to have resulted in the concentration of atmospherically derived pollen and spores diatom assemblages record the evolution of the lake s chemistry and past algal production several abrupt changes occurred synchronously in both the terrestrial and aquatic components of the system and these appear to represent ecological responses to pre holocene climatic variability the sediments of fog lake provide the first integrated paleoecological record older than holocene for a vast region of the canadian arctic thereby refining our understanding of long term arctic ecosystem ontogeny 2000 elsevier science ltd all rights reserved

high resolution ground penetrating radar profiles of perennial lake ice in the mcmurdo dry valleys antarctica horizon attributes unconformities and subbottom penetration abstractground penetrating radar gpr is not commonly used to study lake ice and in general the ground based use of radar frequencies greater than 500 mhz in cryosphere geophysics is rare due to a general interest in deeper stratigraphy and the difficulty of extensive profiling over rough snow surfaces our goal was to find further information on the origin of the deposition and formation of intra ice layers bottom topography and subbottom deposits using gpr with pulses centered near 850 mhz on two permanently ice covered lakes in the mcmurdo dry valleys antarctica the profiles were obtained using a one person sled operation over lake bonney which is typical of lakes in the region having an ice thickness that ranges between 3 and 5 m and lake vida where the maximum ice depth is at least 27 m lake bonney exhibits a semicontinuous sediment horizon at approximately a 2 m depth and several minor horizons in contrast lake vida contains unconformably eroded and folded continuous reflection horizo

lateglacial calendar year chronology based on annually laminated sediments from lake meerfelder maar germany abstract annually laminated sediments from lake meerfelder maar mfm in the eifel germany provide an independent calendar year timescale for the last glacial interglacial transition changes in varve thickness and varve facies reflect significant environment variations during this period the general micro facies pattern confirms that diatomaceous organic varves are favoured during warm climatic phases while cold periods generate higher allochthonous sediment fluxes an exception is the significant increase in diatom blooms at the beginning of the younger dryas six lateglacial biozones have been defined by litt and stebich quaternary international 1999 the sediment record comprises two tephra layers as chronomarkers the laacher see tephra 12 880 varve years bp is a continent wide correlation horizon while the ulmener maar tephra provides regional chronological links the beginning of the lateglacial warming is dated at 14 450 varve years vyrs bp which is regarded as the minimum age three abrupt cold spells interrupted the lateglacial interstadial at 13 800 vyrs bp oldest dryas 13 540 vyrs bp older dryas and 12 680 vyrs bp younger dryas the oldest dryas 130 years and the older dryas 190 years were rather short while the younger dryas lasted much longer 1090 years the mfm chronology was compared with ice core timescales from gisp2 and grip there is a good agreement between these timescales with the grip model age ss09 providing the best match to the mfm chronology

bio and chronostratigraphy of the lateglacial in the eifel region germany abstract in recent years enormous success has been achieved in varve counting of the eifel maar lakes but a detailed correlation with the biostratigraphy has been missing in this paper we present new palynological results of the lateglacial sequences from holzmaar lake and meerfelder maar lake based on annually laminated sediments in particular the meerfelder maar has great potential because in contrast to the holzmaar the sequence between the ulmener maar tephra 11 000 varve years bp and the laacher see tephra 12 880 varve years bp including the younger dryas is undisturbed and complete therefore we currently use the meerfelder maar chronology brauer et al 1999b as an independent varve calendar for the biostratigraphy of the lateglacial the palynological signals of both maar lakes are in good agreement and can easily be correlated with one another and with type sections type regions in northwestern germany and jutland the sequences of the eifel maar lakes have the quality of hypostratotypes with regional biozones based on an absolute time scale

evolution and environmental impacts of the eruption of laacher see volcano germany 12 900 a bp abstract laacher see volcano lsv 40 km south of bonn explosively erupted ca 6 3 km 3 of chemically strongly zoned phonolite magma probably during spring 12 900 years ago the resulting eruption column having reached at least 20 km in height the bulk of the laacher see tephra lst was deposited east of the volcano within the neuwied basin lst ashes form the most important stratigraphic marker in lateglacial deposits over much of central europe a minimum of 2 mt total s was calculated to have been released during the eruption by comparing pre and posteruptive volatile concentrations in glass inclusions and pumice matrix glasses because a separate s bearing vapor phase was probably present in the magma prior to eruption as indicated by the high melt h 2 o contents close to saturation level the actual amount of s released during the eruption could have significantly exceeded 2 mt the sulfuric acid aerosol layer resulting from the massive stratospheric s input probably resided in the stratosphere for years and most likely had a significant impact on climate and thus the environment increased precipitation in central europe and or impairment of the vegetation cover for several years is suggested by several proxies especially increased sediment supply into lakes proximal to the eruptive center major environmental impacts include an initial blast that felled trees up to 4 km away from vent fast deposition of huge tephra volumes led to the complete disruption of rhine river within the lower neuwied basin and the damming up of a lake ca 140 km 2 in areal extent sudden collapse of the temporary tephra dam caused a catastrophic flood wave downstream whose deposits are recognized as far north as bonn reworking of unconsolidated tephra deposits over several 100 km 2 was widespread and extensive generating abundant lahars and flood plain deposits a braided river system established in neuwied basin probably persisted up to several years recent reports for a second eruption of lsv are not confirmed

mineralogical and geochemical analyses of antarctic lake sediments a study of reflectance and mossbauer spectroscopy and c n and s isotopes with applications for remote sensing on mars abstract we analyzed lake bottom sediments from the dry valleys region of antarctica to study the influence of water chemistry on the mineralogy and geochemistry of these sediments as well as to evaluate techniques for remote spectral identification of potential biomarker minerals on mars lakes from the dry valleys region of antarctica have been investigated as possible analogs for extinct lake environments on early mars sediment cores were collected in the present study from perennially ice covered lake hoare in the taylor valley these sediments were taken from a core in an oxic region of the lake and another core in an anoxic zone differences between the two cores were observed in the sediment color fe ii fe iii ratio the presence of pyrite the abundance of fe s and some trace elements and the c n and s isotope fractionation patterns the results of visible infrared reflectance spectroscopy 0 3 25 m mossbauer spectroscopy 77 and 4 k and x ray diffraction are combined to determine the mineralogy and composition of these samples the sediments are dominated by plagioclase k feldspar quartz and pyroxene algal mats grow on the bottom of the lake and organic material has been found throughout the cores calcite is abundant in some layers of the sediment core from the shallow oxic region and pyrite is abundant in the upper sediment layers of the core from the deep anoxic region of lake hoare analysis of the spectroscopic features due to organics and carbonates with respect to the abundance of organic c and carbonate contents was performed in order to select optimal spectral bands for remote identification of these components in planetary regoliths carbonate bands near 4 and 6 8 m 2500 and 1500 cm 1 were detected for carbonate abundances as low as 0 1 wt co2 organic features at 3 38 3 42 and 3 51 m 2960 2925 and 2850 cm 1 were detected for organic c abundances as low as 0 06 wt c the 13c and 15n trends show a more complex organic history for the anoxic region sediments than for the oxic region sediments the biogenic pyrite found in the core from the anoxic zone is associated with depleted 34s values and high organic c levels and could be used as a potential biomarker mineral for paleolakes on mars

the permanent ice cover of lake bonney antarctica the influence of thickness and sediment distribution on photosynthetically available radiation and chlorophyll a distribution in the underlying water column the thick permanent ice cover on the lakes of the mcmurdo dry valleys antarctica inhibits spatial lake sampling due to logistical constraints of penetrating the ice cover to date most sampling of these lakes has been made at only a few sites with the assumption that there is a spatial homogeneity of the physical and biogeochemical properties of the ice cover and the water column at any given depth to test this underlying assumption an autonomous underwater vehicle auv was deployed in lake bonney taylor valley measurements were obtained over the course of 2 years in a 100 100 m horizontal sampling grid at a 0 2 m vertical resolution additionally the auv measured the ice thickness in water equivalent and collected images looking up through the ice which were used to quantify sediment distribution on the surface and within the ice satellite imagery was used to map sediment distribution on the surface of the ice we present results of the spatial investigation of the sediment distribution on the ice cover and its effects on biological processes with particular emphasis on photosynthetically active radiation par the surface sediment is a secondary controller of the ice cover thickness which in turn controls the depth integrated par in the water column our data revealed that depth integrated par was negatively correlated with depth integrated chlorophyll a r 0 88 p 0 001 n 83 which appears to be related to short term photoadaptation of phytoplanktonic communities to spatial and temporal variation in par within the water column

antarctic paleolake sediments and the search for extinct life on mars evidence of lakes in mars history is substantial the proposed similarities between the ancient martian environment and certain modern environments on earth have led exobiologists to study antarctic lakes as analogs to those purported to have existed on mars we have investigated modern sedimentation processes especially with respect to 13c of carbonate and organic matter in lakes in the mcmurdo dry valleys region of east antarctica and assessed various paleolake deposits with respect to their utility as martian analogs and targets for future mars exobiology missions three main types of paleolake deposit were identified and assessed strand lines perched deltas and lacustrine sand mounds deltas are usually identified as good targets but our research shows that authigenic carbonates are not readily identifiable in the sediments large deltas although most likely to attract attention through remote sensing generally are difficult sites for discovery of paleobiological matter and 13c signals follow no coherent pattern lacustrine sand mounds on the other hand contain abundant authigenic carbonate and freeze dried organic matter and appear to be excellent records of paleolimnological conditions the advantage of studying lake bottom deposits versus lake edge deposits is retrieval of a stable lake wide signal deltas are therefore most useful in that they are generally large scale features capable of drawing attention to a region of potential for the discovery of smaller lacustrine sand mounds

late cenozoic paleoenvironment in southern victoria land antarctica based on a polar glaciolacustrine deposit in western victoria valley situated in the transantarctic mountains western victoria valley is in a key position to test the late cenozoic stability of the east antarctic ice sheet as well as that of the surrounding landscape surface victoria drift which covers most of western victoria valley represents a peculiar yet common type of deposit in the region the sedimentology of victoria drift is dominated by loose sorted material which preserves lacustrine algae quite unlike tills in the dry valleys ridges characterize its morphology extraordinarily old ridges and mounds as well as fresh features and unweathered and perched boulders occur without apparent order accelerator mass spectrometry ams radiocarbon dates of algae from within victoria drift range from 11 th054 95 to 45 th000 14 c yr b p and are not arrayed in chronological order across the drift sheet resting on a miocene erosion surface victoria drift is the only widespread deposit in western victoria valley younger than ca 14 ma one hypothesis is that the drift consists of moraines the strength of this hypothesis is that it explains the arcuate form of many ridges however it does not explain the sedimentology weathering characteristics or radiocarbon dates a second hypothesis is that victoria drift is a unique polar glaciolacustrine sediment facies deposited by a lake ice conveyer the morphologic features sedimentology weathering characteristics and radiocarbon dates of the drift are all consistent with deposition in a perennially ice covered lake this second hypothesis implies polar glacial conditions during deposition of the drift sheet in order to maintain a permanently ice covered proglacial lake

glacier fluctuations of muztagh ata and temperature changes during the late holocene in westernmost tibetan plateau based on glaciolacustrine sediment records late holocene glacier variations in westernmost tibetan plateau were studied based on the analysis of grain size magnetic susceptibility and elements from an 8 3 m long distal glaciolacustrine sediment core of kalakuli lake our results show that there are four glacier expansion episodes occurring in 4200 3700 calibrated years cal years b p 2950 2300 cal years b p 1700 1070 cal years b p and 570 100 cal years b p and four glacier retreat periods of 3700 2950 cal years b p 2300 1700 cal years b p 1070 570 cal years b p and 50 cal years b p present the four glacier expansion episodes are generally in agreement with the glacier activities indicted by the moraines at muztagh ata and kongur shan as well as with the late holocene ice rafting events in the north atlantic over the last 2000 years our reconstructed glacier variations are in temporal agreement with reconstructed temperature from china and the northern hemisphere indicating that glacier variations at centennial time scales are very sensitive to temperature in western tibetan plateau

light transmission and reflection in perennially ice covered lake hoare antarctica we have investigated the transmission and albedo of the perennial ice cover on lake hoare antarctica our database consists of year round measurements of the photosynthetically active radiation 400 700 nm under the ice measurements of the spatial variation of the under ice light in midsummer and spectrally resolved measurements from 400 to 700 nm of the albedo and transmission of the ice cover in early november and in midsummer january our results show that the transmission decreases in the first part of summer dropping by a factor of 4 from november to january we suggest that this is due to heating in the upper layers of the ice cover and the formation of tyndall figures later in the summer when a significant liquid water fraction occurs within the ice cover the transmission increases in the fall when the ice cover freezes solid the transmission drops markedly the spectrally resolved measurements from 400 to 700 nm show that 2 5 of the incident light in this spectral region penetrates the 3 5 m thick ice cover we have analyzed the spectral data using a two stream scattering solution to the radiative transfer equation with three vertical layers in the ice cover a surficial glaze of scattering ice 1 cm thick overlies a layer of sandy bubbly ice about a meter thick and below this is a thick layer of sand free ice with bubbles we find that the ice cover is virtually opaque at wavelengths longer than 800 nm the net transmission of solar energy is 2 significant changes in the thickness of the ice cover have been reported at lake hoare these are due primarily to changes in the thickness of the bottom layer only because this layer is relatively clear the effect on the transmission through the ice cover from these changes is less than would be predicted assuming a homogeneous ice cover

paleo environment and radiocarbon calibration as derived from lateglacial early holocene tree ring chronologies abstract we present an overview of the extended hohenheim oak chronology hoc and the dendrochronologically dated preboreal pine tree ring chronology ppc both provide an absolute annual time frame of the holocene extending into the younger dryas yd back to 11 919 bp two floating pine and larch chronologies are 14 c dated covering large parts of the lateglacial dendro ecological parameters such as ring width and stable isotope variation are used to infer past environmental conditions 14 c analyses on decadal sections provide a high precision high resolution data set for calibration of the radiocarbon time scale based on a marked change in ring width and growth pattern the yd termination is clearly identified in the german pine chronology its absolute age of 11 570 bp appears synchronous within the errors of the respective chronologies to related signals in the greenland ice cores grip gisp2 and in lacustrine varve sequences the 14 c age of the laacher see tephra lst is determined from a series of decadal tree ring samples to 11 063 12 14 c bp the calibrated range is 13 010 13 200 cal bp the climatic impact of the lst is reflected in the growth pattern of our tree ring chronologies

impact of antarctic climate during the late quaternary records from zub lake sedimentary archives from schirmacher hills east antarctica abstract the antarctic continental margin is marked with ice free areas which are host to numerous freshwater lakes these lacustrine systems are rich in sedimentary deposits which archive in them the regional and general climatic variations these lakes respond to the seasonal variations in climate over glacial interglacial timescales and can be inferred from the sedimentary proxies in this study a 79 cm long radiocarbon dated sediment core retrieved from a peri glacial lake is analysed for elementary corg norg isotopic 13com 15nom and particle size sand silt clay the radiocarbon dated sections 0 65 cm extends up to 43 kyr bp the time series of sedimentary organic matter om proxies corg 3 5 3 c natomic ratio 11 3 and 13com 14 4 indicate that the om in this lake sedimentary record is an admixture of terrestrial and lacustrine biomass distinctly higher lower values during the holocene lgm suggests presence of terrestrial and aquatic aquatic biomass indicating ice free ice cover and warm cold holocene glacial conditions which would result in an increased decreased lake productivity and fluvial wind input of sand and clay silt higher sand content 30 24 and 15 kyr bp silt content 24 kyr bp corg and norg 24 kyr bp within the last glacial stage lgs indicates intermittent warming period in coherence with the antarctic isotope maximum aim the transition in values corg norg c n ratio 13com sand content starting at 16 6 kyr bp closely following antarctic deglaciation to reach holocene optimum values at 11 3 kyr bp documents the influence of antarctic climate on regional areas

a critical assessment of subglacial mega floods a case study of glacial sediments and landforms in south central alberta canada the existing subglacial megaflood explanation of glacial sediment deposition and landform production in south central alberta relies upon four sets of observations and associated interpretations 1 a subglacial genesis for all glacilacustrine sediments lying stratigraphically below a local melt out till or ice stagnation facies 2 a melt out genesis for the ice stagnation facies 3 a syn depositional status for the glacitectonic disturbance visible in most exposures due to periodic ice bed re coupling and 4 a subglacial megaflood origin for a truncation surface and clast lag that occurs at the top of the sedimentary exposures and the carving of hummocky terrain and flutes in the area we provide alternative interpretations of the sediment landform assemblages of the area and demonstrate that alternative simpler interpretations of the evidence can be proposed specifically we propose 1 a proglacial rather than subglacial origin of glacilacustrine sediments 2 a glacilacustrine origin for the melt out till and its subsequent glacitectonic disturbance by minor glacier readvances 3 postdepositional rather than syn depositional glacitectonic disturbance due to a significant advance by glacier ice after the accumulation of a thick sequence of glacilacustrine sediments 4 that some linear chains of hummocks are the morphological expression of glacitectonic folding and thrusting 5 that the use of the truncation surfaces to propose a subglacial fluvial origin for hummocky moraine is flawed logic because they do not constitute the tops of hummocks but rather occur on the interfluves that separate the numerous small coulees incised into the valley sides during postglacial time truncation surfaces and clast lags occur locally on the beds of spillway tracts and can be explained as the products of erosion by subaerial spillway water the mega flood explanation of flutings and hummocky moraine in the region is also questioned because these landforms record a regional ice flow imprint of mis aligned and cross cutting flow sets terminating at series of inset and locally cross cutting and lobate transverse ridges moraines these landform associations preclude a subglacial flood origin for the flutings and demonstrate that the transverse ridges are more appropriately interpreted as recessional push moraines the similarity of the glacial landforms of this region to the active temperate glacial landsystem produced by historical glacier recession in modern glacierized catchments where sheetfloods have not been influential in subglacial landform production allows us to apply a modern analogue to landscape interpretation that does not include subglacial sheetflooding

lake hoare antarctica sedimentation through a thick perennial ice cover lake hoare in the dry valleys of antarctica is covered with a perennial ice cover more than 3 m thick yet there is a complex record of sedimentation and of growth of microbial mats on the lake bottom rough topography on the ice covering the lake surface traps sand that is transported by the wind in late summer vertical conduits form by melting and fracturing making the ice permeable to both liquid water and gases cross sections of the ice cover show that sand is able to penetrate into and apparently through it by descending through these conduits this is the primary sedimentation mechanism in the lake sediment traps retrieved from the lake bottom indicate that rates of deposition can vary by large amounts over lateral scales as small as 1 m this conclusion is supported by cores taken in a 3 x 3 grid with a spacing of 1 5 m despite the close spacing of the cores the poor stratigraphic correlation that is observed indicates substantial lateral variability in sedimentation rate apparently sand descends into the lake from discrete highly localized sources in the ice that may in some cases deposit a large amount of sand into the lake in a very short time in some locations on the lake bottom distinctive sand mounds have been formed by this process they are primary sedimentary structures and appear unique to the perennially ice covered lacustrine environment in some locations they are tens of centimetres high and gently rounded with stable slopes in others they reach approximately 1 m in height and have a conical shape with slopes at angle of repose a simple formation model suggests that these differences can be explained by local variations in water depth and sedimentation rate rapid colonization of fresh sand surfaces by microbial mats composed of cyanobacteria eukaryotic algae and heterotrophic bacteria produces a complex intercalation of organic and sandy layers that are a distinctive form of modern stromatolites

a systematic classification of glacial and periglacial environments facies and deposits abstract several aspects of the deposits formed in the glacial and periglacial environments are presented in order to establish a framework that can be used in various disciplines dealing with sedimentation under glacial and periglacial conditions the almost unlimited number of different deposits are grouped into 37 types that are all described briefly most of them are also illustrated by field examples mainly from poland these 37 types are grouped within 23 facies belonging to 3 continental glacial 3 continental periglacial and 3 marine periglacial subenvironments all environments subenvironments facies and deposits are defined and presented with a hierarchic code that enables unambiguous definition attention is paid to both the general characteristics of the various deposits as they have been described by previous investigators and to specific deposits that have been studied by the present authors the factors influencing peri glacial sedimentation are discussed briefly

surficial geology and geomorphology of eastern and central wright valley antarctica abstract surficial deposits in eastern and central wright valley antarctica record multiple inland incursions of grounded ice from the ross sea embayment glacial geologic mapping coupled with 42 ams 14 c dates of lacustrine algae and 10 40 ar 39 ar dates of basalt erratics indicate westward ice expansion at least eight times during the pliocene and quaternary the most extensive westward incursion resulted in an advance of at least 21 km beyond the margin of present day wright lower glacier accompanied by ice thickening of 500 m at the location of the present day wilson piedmont glacier in the eastern valley mouth large proglacial lakes and glaciolacustrine sedimentation coincide with at least some of these advances

optimization of a sea ice model using basinwide observations of arctic sea ice thickness extent and velocity a stand alone sea ice model is tuned and validated using satellite derived basinwide observations of sea ice thickness extent and velocity from the years 1993 to 2001 this is the first time that basin scale measurements of sea ice thickness have been used for this purpose the model is based on the cice sea ice model code developed at the los alamos national laboratory with some minor modifications and forcing consists of 40 yr ecmwf re analysis era 40 and polar exchange at the sea surface poles data three parameters are varied in the tuning process ca the air ice drag coefficient p the ice strength parameter and the broadband albedo of cold bare ice with the aim being to determine the subset of this three dimensional parameter space that gives the best simultaneous agreement with observations with this forcing set it is found that observations of sea ice extent and velocity alone are not sufficient to unambiguously tune the model and that sea ice thickness measurements are necessary to locate a unique subset of parameter space in which simultaneous agreement is achieved with all three observational datasets

volatile composition of the phonolitic laacher see magma 12 900 yr bp implications for syn eruptive degassing of s f cl and h 2 o a volatile rich and chemically zoned phonolitic magma reservoir was tapped successively during the eruption of laacher see volcano ca 12 900 years bp and produced a tephra sequence consisting of phenocryst poor highly evolved phonolite at the base and phenocryst rich more mafic phonolite at the top the stratospheric volatile loading was estimated by comparing pre and post eruptive s f cl and h2o contents of undegassed glass inclusions and partially degassed matrix glasses glass inclusions 150 1490 ppm s and host matrix glasses 150 820 ppm s both document a strong s decrease during progressive magmatic differentiation which is interpreted to be partially caused by crystallization of hauyne the s6 stotal ratio of the pre eruptive melt increased with differentiation from 8 to 71 as indicated by s k wavelength shift measurements in glass inclusions sulfate rich highly evolved phonolitic magma was erupted during plinian and sulfide rich more mafic phonolitic magma during late phreatomagmatic phases f and cl became enriched during late stages of differentiation glass inclusions 690 4060 ppm f 1770 4400 ppm cl matrix glasses 680 3660 ppm f 2130 4330 ppm cl the most differentiated melts maximum 13 wt na2o occur only as matrix glass and are extremely f enriched 5080 8780 ppm but cl depleted 460 2820 ppm suggesting that f was retained in the melt whereas some cl was lost during pre and or syn eruptive degassing the h2o contents of glass inclusions increase irregularly with differentiation 2 5 5 7 wt matrix glasses are h2o depleted 0 2 2 8 wt compared to most glass inclusions showing that most h2o was released to the atmosphere by explosive degassing a mass balance calculation yields a syn eruptive volatile release of 1 9 tg stotal 6 6 tg cl and 403 tg h2o from the melt this is a minimum estimate since s and cl could have accumulated in a separate fluid phase as indicated by fluid inclusions in hauyne and pre eruption h2o contents close to saturation level at the likely pressure temperature conditions in the laacher see magma reservoir we estimate that at least ca 20 tg so2 were injected into the stratosphere causing a significant negative climate forcing as reflected by several paleoclimate proxies and as shown by recent modeling

sedimentation in ice covered lake hoare antarctica the sedimentation mechanisms that occur in ice covered lake hoare antarctica are examined to determine how sediment enters the lake and how the sedimentation pattern affects blue green algal growth at the lake bottom the 3 m thick ice cover contains pebbly sand as much as 2 m below the surface sediment with similar texture and mineralogy is found at the lake bottom this evidence together with the lack of sediment in the inflowing stream and the markedly different texture of sediment from the other terrains around the lake suggest that most of the sediment at the lake bottom comes in through the ice cover sand grains intermittently migrate through porous ice on the surface water filled vertical gas channels penetrating two thirds of the ice cover and possibly through cracks in the ice that act as conduits the algae at the lake bottom are able to survive in part because sediment that comes through the ice cover does not obliterate them

microorganisms in the malan ice core and their relation to climatic and environmental changes 1 a 102 m long ice core retrieved from the malan ice cap on the tibetan plateau provides us with a historical record of the microorganisms trapped in the ice the microorganisms in the malan ice core are identified as and proteobacteia and the lgc hgc and cfb group by means of the results of 16s rrna sequence analysis and physiological characteristics while the eukaryotes in the ice core are mainly composed of chlamydomonas sp and pseudochlorella sp based on the phylogenetic examination of the 18s rrna gene the microbial populations show observable differences at different depths in the ice core reflecting the effects of climatic and environmental changes on the distribution of the microorganisms in the glacier examination of the malan ice core shows four general periods of microbial concentration which correspond to four phases of temperature revealed by 18o values in the core observations also indicate that microorganism concentrations tend to be negatively correlated with the temperature at a relatively long timescale and to some extent positively correlated with mineral concentrations the present study demonstrates that more microorganisms are associated with colder periods while fewer microorganisms are associated with warm periods which provides us with a new proxy for the reconstruction of past climatic and environmental changes by means of ice core analysis

lake ice ablation rates from permanently ice covered antarctic lakes in the mcmurdo dry valleys of antarctica three large permanently ice covered closed basin lakes exist along the floor of taylor valley lake ice ablation loss of ice mass is calculated as the sum of sublimation and surface melt and is the driver of ice cover turnover in these systems in taylor valley both manual and automated lake ice ablation rates have been calculated from 2001 to 2011 results indicate relatively consistent winter ablation of 0 07 0 21 m 0 2 0 7 mm w e d 1 summer ablation of lake ice is more variable and ranges from 0 25 to 1 62 m 5 31 mm w e d 1 over an average 51 day period previous to this study ablation rates have been cited as 0 35 m a 1 in the dry valleys from sublimation modeling based on meteorological variables we show that this value has significantly underestimated mean ablation and ice cover turnover on the taylor valley lakes

catchment and lake controls over the formation of varves in monomictic nicolay lake cornwall island nunavut on the basis of thin section sedimentology 137cs and 210pb profiles and the pronounced seasonality of runoff and sediment delivery sediments from nicolay lake cornwall island nunavut 77 46 n

varve chronology and palynology of the lateglacial in northwest germany from lacustrine sediments of hamelsee in lower saxony abstract the hamelsee is a dolina from a collapse over permian salt that occurred at the end of the pleniglacial it is more than 21 m deep and contains 18 m of lacustrine sediments the lateglacial sediments in the central part of the lake consist of 2 7 m from 15 to 17 7 m of sapropelic and silty muds which are mostly laminated and partly bioturbated minor slumps occur mainly during colder phases the subdivision of the lateglacial is based on pollen zones multidisciplinary studies of the microfacies from thin sections geochemistry pollen analysis and rotifer analysis allow environmental and palaeoclimatological interpretations to be made the biozones of the lateglacial and their boundaries are marked by rapid climatic changes though covering comparatively short periods of time they are not monotonous but characterized by minor internal climatic fluctuations the sediments of the meiendorf and oldest dryas are not laminated the allerod sediment is seasonally varved without interruption and encompasses 625 yr the eruption of the laacher see volcano 12 900 cal bp had an impact on the climate during the following 10 yr the transition from the allerod to the younger dryas took some 50 yr and it occurred 200 yr after the eruption of the laacher see volcano the abrupt change at the end of the lateglacial 11 560 cal bp occurred within less than 10 yr however many proxies reacted with a time lapse of 15 to 30 yr

holocene glacial history and sea level changes on james ross island antarctic peninsula a reconstruction of deglaciation and associated sea level changes on northern james ross island antarctic peninsula based on lithostratigraphical and geomorphological studies shows that the initial deglaciation of presently ice free areas occurred slightly before 7400 14 c yr bp sea level in connection with the deglaciation was around 30 m a s l a glacier readvance in brandy bay of at least 7 km with the initial 3 km over land reached a position off the present coast at ca 4600 yr bp the culmination of the advance was of short duration and by 4300 yr bp the coastal lowlands again were ice free a distinct marine level at 16 18 m a s l was contemporaneous with or slightly post dates the brandy bay advance thus indicating the relative sea level around 4600 4500 yr bp our results from james ross island confirm that over large areas in this part of antarctica the last deglaciation occurred late 1997 by john wiley sons ltd

nature and classification of waterlain glaciogenic sediments exemplified by pleistocene late paleozoic and late precambrian deposits this study of waterlain glaciogenic sediments is designed to present both a review and new information on glaciogenic subaquatic deposits of differing age in a number of localities in north and south america and south africa the late paleozoic glaciogenic deposits of the parana basin in brazil and the karoo basin of south africa are singled out for special attention as they show a reasonably complete lateral sequence of terrestrial to off shore glaciogenic sedimentation although the environment of subaquatic glaciogenic sedimentation varies from one area to the next certain common elements are found which can be used to develop a generalized model for both glaciomarine and glaciolacustrine sedimentation for descriptive purposes the model is divided into two broad categories a shelf facies and a basinal facies the shelf facies is marked by massive diamicton ite which may be 200 m or more in thickness and which is frequently overlain by a complex of clastic sediments consisting primarily of gravity and fluid flows the basinal facies is marked by products of subaquatic slumps and more distal turbidites and glaciomarine sediments new terminology is introduced the massive diamicton ite which is diagnostic of the shelf facies probably represents deposition from the base of active ice in a subaquatic environment and is termed undermelt diamicton ite the gravity and fluid flows which are usually found overlying undermelt diamicton ite and in the basinal facies are subdivided into six categories glaciogenic subaquatic outwash glaciogenic suspension flow glaciogenic chaotic debris flow glaciogenic subaquatic debris flow glaciogenic slurry flow and glaciogenic turbidity flow the relative abundance of undermelt diamicton ite and the various types of gravity and fluid flows can be used to define inner shelf outer shelf inner basin and outer basin facies of glaciomarine sedimentation

changes in ice cover thickness and lake level of lake hoare antarctica implications for local climatic change we report results from 10 years of ice thickness measurements at perennially ice covered lake hoare in southern victoria land antarctica the ice cover of this lake had been thinning steadily at a rate exceeding 20 cm yr 1 during the last decade but seems to have recently stabilized at a thickness of 3 3 m data concerning lake level and degree days above freezing are presented to show the relationship between peak summer temperatures and the volume of glacier derived meltwater entering lake hoare each summer from these latter data we infer that peak summer temperatures have been above 0 c for a progressively longer period of time each year since 1972 we also consider possible explanations for the thinning of the lake ice the thickness of the ice cover is determined by the balance between freezing during the winter and ablation that occurs all year but maximizes in summer we suggest that the term most likely responsible for the change in the ice cover thickness at lake hoare is the extent of summer melting consistent with the rising lake levels

models of glaciomarine sedimentation and their application to the interpretation of ancient glacial sequences abstract this paper argues that glaciomarine environments can be regarded as special glacially influenced types of continental margin environments e g continental shelf slope rise and basin plain knowledge of the stratigraphic architecture and typical sedimentary sequences of non glacial margins is becoming well known but remains limited for those that have been glacially modified the principal influences on sedimentation in these environments relate to the glacial sediment input controlled by relief of basin margin glacier thermal regime and ice flow dynamics and depositional environments influence of traction currents substrate relief and proximity to nearby ice margins typical ranges of sedimentation rates can be established for glacially influenced continental margin environments and these may provide a framework for ancient sequences starvation of sediment supply to glacially influenced continental margins is common the nature of sub ice shelf sedimentation a model that has been applied to many ancient glacial sequences is critically reviewed the significance of such sedimentation in the rock record has probably been exaggerated because of oversimplistic interpretations of diamictite sequences existing process models of glaciomarine sedimentation derived from study of modern environments are sometimes difficult to employ in investigation of ancient sedimentary sequences because simple lithofacies criteria and typical vertical profiles are not available to aid in interpretation in addition compositional data emphasized by many workers for distinguishing glaciomarine from continental glacial diamict ite s frequently fingerprint sediment source and not mode of deposition the importance of facies analysis methods for isolating depositional environments is illustrated by three examples of ancient glaciomarine sequences these are the early proterozoic gowganda formation 2 3 ga of northern ontario canada the late proterozoic port askaig formation 670 ma of scotland and ireland and the late cenozoic yakataga formation 20 ma to recent of the gulf of alaska these examples illustrate the significance of detailed genetic studies of ancient glacial rocks in the interpretation of palaeogeographic and tectonic settings diamictite units in ancient glaciomarine sequences cannot be easily interpreted in terms of climatic or ice advance retreat cycles because of the varied controls on diamict accumulation and diamictite preservation in marine basins

reflectance spectroscopy and geochemical analyses of lake hoare sediments antarctica implications for remote sensing of the earth and mars abstract visible to infrared reflectance spectroscopic analyses 0 3 25 m have been performed on sediments from the dry valleys region of antarctica sample characterization for these sediments includes extensive geochemical analyses and x ray diffraction xrd the reflectance spectra and xrd indicate major amounts of quartz feldspar and pyroxene in these samples and lesser amounts of carbonate mica chlorite amphibole illite smectite and organic matter calcite is the primary form of carbonate present in these lake hoare sediments based on the elemental abundances and spectroscopic features the particle size distribution of the major and secondary components influences their detection in mixtures and this sensitivity to particle size is manifested differently in the volume scattering and surface scattering infrared regions the christiansen feature lies between these two spectral regimes and is influenced by the spectral properties of both regions for these mixtures the christiansen feature was found to be dependent on physical parameters such as particle size and sample texture as well as the mineralogy semiquantitative spectroscopic detection of calcite and organic material has been tested in these quartz and feldspar rich sediments the relative spectral band depths due to organics and calcite correlate in general with the wt c from organic matter and carbonate the amounts of organic matter and carbonate present correlate with high br and u abundances and high ca and sr abundances respectively variation in the elemental abundances was overall minimal which is consistent with a common sedimentary origin for the forty two samples studied here from lake hoare

scarp bounded benches in gorgonum chaos mars formed beneath an ice covered lake 1 level bench like platforms edged with scarps facing the interior of the martian gorgonum chaos basin may have formed in conjunction with an ancient ice covered lake these benches however lack the typical features of shorelines associated with wave and current transport and erosion such as crescentic embayments spits barrier islands and wave cut cliffs rather the basin facing platform edges are commonly rounded and cumulate in planform often evenly encircling buttes protruding above the level of the benches the benches are postulated to have been formed by outward growth in a quiescent environment possibly by deformative lateral flow of sediment below the ice water interface in a perennially frozen lake due to the weight of the ice overburden

increased mud deposition reduces stromatolite complexity microbial mat growth can produce diagnostic delicate structures in low energy environments but mat morphology and thus preservation of delicate structures as morphological biosignatures is affected by mud accumulation in lake joyce antarctica varying rates of siliciclastic mud deposition affected the morphology of partially calcified microbial mats these mats were characterized along a shore parallel transect from higher to lower sedimentation regions of the lake mats with high mud accumulation rates were predominantly flat with sparse pinnacles at lower sedimentation rates mats developed more pinnacles and more delicate features including vertical webs of biofilm suspended between pinnacles morphological transitions suggest that mud deposition disrupts growth of delicate microbial structures like biofilm webs and inhibits pinnacle growth at higher accumulation rates the simplification of mat morphology with increasing mud accumulation has important implications for the distribution of stromatolite types in the rock record stromatolites with intricate biofilm structures are rare possibly due to the paucity of appropriate environments rather than the intrinsic properties of microbial communities communities capable of forming delicate microbialites likely produced morphologically simpler pinnacles and flat mat in environments with significant siliciclastic mud or micrite influx thus delicate mats have narrow environmental ranges for growth and temporal or spatial variations in siliciclastic mud or micrite sedimentation rates bias the record of microbial activity preserved in stromatolites

paleoclimatic reconstruction and the response of carbonate minerals during the past 8000 years over the northeast tibetan plateau abstract the climatic significance of the carbonate content and composition of lake sediments remains unclear in this study we analyzed the glycerol dialkyl glycerol tetraethers and mineral contents of alake lake sediments to reconstruct temperature and moisture changes over the northeast tibetan plateau since 8000 cal yr bp we identified warm cold and wet dry conditions during the roman warm period and holocene climate optimum early neoglacial cooling period accompanied by a dominance of aragonite monohydrocalcite based on our results and previous laboratory experiments we suggest that monohydrocalcite is predominantly deposited in colder drier and higher mg ca conditions relative to that of aragonite the carbonate mineral composition should therefore be fully considered when sediment carbonate contents are used to reconstruct paleotemperature moisture changes

temperature gradients in northern europe during the last glacial holocene transition 14 914c kyr bp interpreted from coleopteran assemblages late glacial and early holocene climatic conditions have been reconstructed for northern europe using the mutual climatic range mcr palaeoclimate method based on fossil coleopteran assemblages altogether beetle faunas from 77 sites have been analysed ranging from ireland in the west to poland and finland in the east and mcr estimates calculated the results are plotted on 16 maps each representative of a selected time slice covering the period from 14 5 14c kyr bp to 9 0 14c kyr bp eight of the maps show the mcr estimates of tmax mean temperature of the warmest month derived from each site for which data are available while the remainder show estimated tmax isotherms interpolated from these values it can be demonstrated that at times the thermal climate was fairly uniform throughout the study area whereas at others temperature gradients were much steeper than they are in the region today there also appears to be a distinct contrast between cold periods when contours trended nw se and warmer periods when contours trend w e or even ne sw the pattern of climatic changes that emerges is shown to be very different from the traditional view that has been used up to now as a template for classifying late glacial climatic events on a wide even global scale the suddenness and intensity of changes in the thermal climate may have been partially responsible for an apparent lack of equilibrium between the flora and fauna of the time and the physical environment in which they lived 1998 john wiley sons ltd

laacher see tephra a widespread isochronous late quaternary tephra layer in central and northern europe a late quaternary tephra layer widespread in central and northern europe resulted from explosive plinian and phreatomagmatic eruptions of the laacher see volcano 11 000 yr b p the tephra is distinguished from other late quaternary andesitic rhyolitic airfall tuff layers in northern europe and from basaltic or trachytic tuff deposits in southern europe by its phonolitic composition and abundance of sanidine plagioclase clinopyroxene amphibole and sphene the proximal tephia sequence at laacher see is divided into three main deposits the predominantly plinian deposits of lower and middle laacher see tephra llst and mlst and phreatomagmatic deposits of the upper laacher see tephra ulst the mlst member is further subdivided into beds a b and c1 c2 and c3 the chemical composition of the magma is highly differentiated phonolite in the llst to mlst b sections but mafic phonolite in the mlst c1 to ulst sections all deposits are considered to be isochronous the frequency maximum of 16 radiocarbon datings indicating an eruption about 11 000 50 yr b p distal ash was deposited in three main fans directed to the northeast lst traced up to 1 100 km distance south lst traced up to 600 km and southwest lst traced up to 100 km tephrostratigraphic correlation of the distal ash deposits is based on a the major element composition of glass shards b lithology and c heavy mineral analyses the northeastern fan consists of deposits from llst mlst b and mlst c1 eruptive phases the southern fan comprises mlst a mlst c2 and ulst deposits and the southwestern fan consists exclusively of ash from the ulst eruptive phase northeastern transport of ash during eruptive phases with high plinian eruption columns but southern and southwestern transport of ash along phases of relatively low eruption columns are interpreted in terms of prevailing southwesterly paleowinds at high altitudes tropopause level but northerly winds dominating in the lower atmosphere the laacher see eruption columns were emplaced into an atmosphere vertically zoned with respect to paleowind directions which also explains the near vent shifting of llst mlst b and mlst c1 iso pach axes from east southeast to northeast within the first 20 km of transport

boundary conditions for damming of a large river by fallout during the 12 900 bp plinian laacher see eruption germany syn eruptive rhine damming ii abstract the rhine river germany the largest river in western europe was dammed by pyroclastic material multiple times during the major plinian laacher see eruption 12 900 bp dams formed both upstream and downstream of the broad tectonic lower neuwied basin lnb which interrupts the narrow rhine canyon here we document upstream damming of the rhine river at the entrance to the lnb close to the present city of koblenz due to overloading with tephra fall into the rhine and its major tributaries the moselle and the lahn the dam was formed repeatedly during rapid pumiceous tephra fall events and breached during breaks in eruptive activity causing extensive high energy flooding throughout the entire basin the ephemeral koblenz dams differed significantly from normal volcanically induced dams by consisting principally of washed together pumice clasts and some driftwood the porous nature of pumice and its ability to absorb water were crucial factors thus a large volume percentage of the tephra that had fallen into the rhine floated submerged within the upper part of the water column or swam at the surface moreover the absorption of the river water by the pumice clasts increased the sediment water ratio of the two phase flow considerably we here present a model of dam formation resembling the formation of ice jams we visualize the koblenz dams to have been elongate partly floating and partly grounded permeable plugs many kilometers long and rising no higher than the flood plain damming was most plausibly initiated in the lnb within the area of maximum tephra loading and propagated upstream in a chain reaction comparable to the formation of traffic jams a major dam was finally accumulated at the bottleneck entrance to the lnb a site combining several favorable conditions the upstream multi channel rhine was confined to a single channel change of flow direction by 125 extremely low gradient 0 19 starting already 24 km upstream of the bottleneck constant decrease of flow velocity over many kilometers towards the bottleneck and the moselle river largest tributary of the rhine within the lnb and an important conveyor of additional tephra masses entered the rhine only 700 m upstream of the bottleneck we assume that the koblenz dams could only have formed and been stabilized by an extremely long foot region that extended many kilometers downstream and that was possibly connected to one or several low rise secondary jams dams the backwater of lake brohl that was dammed by pyroclastic flows 7 km downstream of the lnb about halfway through the eruption extended further and further upstream into the lnb during the second plinian stage of the laacher see eruption and was probably a major factor contributing to the formation and large size of koblenz dam no 4 the koblenz dams were probably not completely sealed most of the time this way the major pre eruptive rhine channel received some water an equilibrium condition was established that enabled the dams to remain stable as long as tephra fell into the rhine relatively continuously

the association of sulphate evaporites stromatolitic carbonates and glacial sediments examples from the proterozoic of australia and the cainozoic of antarctica abstract carbonate sediments are often considered diagnostic of warm water environments and thus the occurrence of dolomite and limestone beds within and immediately overlying many late proterozoic glacial deposits tillites has long been a source of controversy stromatolites are also conventionally thought to be warm water indicators we describe two examples of stromatolitic dolomite occurring together with barite at the top of late proterozoic glacial sequences in the amadeus and ngalia basins of central australia problems of interpretation may be largely resolved after examination of published data on antarctic lakes antarctic lakes of high salinity occupy enclosed glacial basins in both the vestfold hills and the taylor and wright dry valleys lake bonney is the most comprehensively described example carbonate sediments sulphate evaporites and even stromatolites are common components of cold arid climate lakes the stromatolitic mats and their constructing cyanobacteria are similar to those described from warmer climates the tundra plains and lakes and coastal lagoons of northern canada and siberia are better geomorphic analogues for the proterozoic deposits and these too seem to contain analogous sediments but only brief descriptions are available we suggest that environments such as these provide modern analogues of the association of proterozoic glacial sediments with carbonates evaporites and stromatolites

hydrodynamic behaviour of taupo 1800a pumice implications for the sedimentology of remobilized pyroclasts large scale explosive eruptions from silicic caldera volcanoes can generate huge volumes of pyroclastic material in terrestrial and marine environments on land erosion remobilization and redeposition of this debris is predominantly carried out by running water in the form of precipitation run off conversely in the submarine realm both primary emplacement and subsequent remobilization are influenced by the presence of water as a transporting medium despite this and the number of studies devoted to volcaniclastic sedimentation relatively little attention has been paid to the hydrodynamic behaviour of the particles themselves which ought to underpin any assessment of transport or depositional process this is crucial as many volcanic particles exhibit variable density according to composition and as functions of differing degrees of vesiculation and the extent to which pore space is filled by water and or gaseous phases during transport and deposition investigation of the physical and hydrodynamic properties of taupo 1800a pumice with reference to sedimentary facies developed during the eruption aftermath shows that although buoyant when dry when sufficiently waterlogged cool pumice clasts will sink and behave more like quartzo feldspathic material saturation is apparently achieved by a combination of rapid capillary flooding of large interconnected vesicles and slower diffusional air water exchange in smaller pores low saturated pumice densities result in lower settling velocities and easier entrainment by tractional currents than those for equivalent sized quartzo feldspathic or crystal lithic particles fine grained pumice is conversely harder to entrain because of the frictional interlocking of angular particles these unusual properties of temporary buoyancy variable saturation low density and size dependent cohesion complicate interpretations of the depositional setting and energy of pumiceous sediments and give rise to several unique facies these findings have implications not only for the analysis of remobilized pyroclastic facies in terrestrial and marine environments but also for primary depositional processes during subaqueous explosive volcanism

the record of density induced underflows in a glacial lake as part of an overall study of sedimentation processes in a proglacial lake an effort was made to compare field results with some of the general equations for density flows the results suggest that in relatively small glacial lakes the occurrence of underflows with lower sediment loads involves a complex interplay between thermal and sediment effects which is extremely sensitive to varying hydrologic and climatic conditions in terms of actual transport mechanics the results i indicate that a higher value of 0 6 or 0 7 gives a closer agreement between the measured velocity values and the established equations on moderately shallow slopes ii provide field support for the experimentally derived relationship of britter linden 1980 for the velocity of underflows and suggest the equation may be applicable in situations below 5 slopes and iii support the relationship between velocity of the front and body of a continuous underflow for moderate slope situations suggested by middleton 1966b finally the velocity values measured by electromagnetic current meters stationed in the lake the grain size data obtained from mapping core data and the application of other criteria support the concept that in this environment the underflows are capable of erosion

glacial and postglacial sedimentation in the fryxell basin taylor valley southern victoria land antarctica abstract a 9 14 m long sediment sequence was recovered from lake fryxell taylor valley southern victoria land antarctica and investigated for its chronology and sedimentological mineralogical and biogeochemical changes the basal part of the sequence is dominated by coarse clastic matter i e mainly sand the sediment composition suggests that a lake existed in fryxell basin during the middle weichselian by ca 48 000 cal year bp after a short period of lake level lowstand ca 43 000 cal year bp lower taylor valley became occupied by the proglacial lake washburn which was at least partly supplied by meltwater and sediments from the ross ice sheet that was advanced to the mouth of taylor valley evaporation of lake washburn to lower levels started during the last glacial maximum at ca 22 000 cal year bp long before the ross ice sheet retreated significantly lake level lowering was discontinuous with a series of high and low stands from ca 4000 cal year bp environmental conditions were similar to those of today and lower fryxell basin was occupied by a small lake this lake evaporated to a saline or hypersaline pond between ca 2500 and 1000 cal year bp and refilled subsequently

dating quaternary lacustrine sediments in the mcmurdo dry valleys antarctica abstract reports of erroneously old 14c dates for modern antarctic materials have thrown doubt into 14c chronologies the carbon reservoir effect purported to exist in quaternary lacustrine sediments of the mcmurdo dry valleys was investigated by studying 14c distribution and testing alternate dating techniques our results show that the carbon reservoir effect is not pervasive stream and near shore microbial mats and dissolved inorganic carbon dic in the surface waters of lake fryxell are in equilibrium with modern 14co2 the surface waters of lake hoare and lake bonney however have dic 14c ages of 1650 and 2080 yr b p respectively these older age estimates are suggested to be due to the direct input of large amounts of glacial melt with relict dic on the other hand lake fryxell receives only a minor component of its inflow directly from a glacier while a large component must travel long distances in numerous shallow ephemeral streams after leaving local valley glaciers this mode of melt water input allows the water to equilibrate with modern co2 before entering the lake bottom water 14c ages for lake hoare closely match surface sediment ages supporting the widely published period 1200 yr b p after a 1650 yr reservoir correction when most dry valley lakes apparently evaporated to small brine ponds and or disappeared completely lake bonney bottom water is 8000 yr b p carbon dating is shown to be a viable technique for lake edge deposits and possibly lake bottom deposits where a correction to the sediment surface age can be obtained however we conclude that deep water paleolake deposits can not be reliably dated using 14c alone because of an inability to determine the age of the reservoir correction i e accounting for the initial carbon reservoir plus the age of the bottom water a suite of alternative and complimentary dating techniques were tested on modern and late holocene lacustrine deposits these include thermoluminescence tl 210pb 137cs and paleomagnetism of these techniques tl or the more sensitive optically stimulated luminescence holds the most promise for correcting lake sediment 14c ages tl dating of the modern lake hoare sediments showed an 1000 yr relict signal this signal is unaffected by the age of the lake water both 210pb and 137cs occurred in very low levels in the sediments and do not appear to be viable dating techniques for the perennially ice covered lakes of the mcmurdo dry valleys paleomagnetism was not suited to the coarse grained nature of lake hoare bottom sediments but could be a useful alternative given a finer sediment type

trapping of aeolian sediments and build up of the ice cover of a dry based antarctic lake among the perennially frozen lakes of the dry valleys of south victoria land antarctica some are dry based i e frozen to the bottom one of these is studied here by a multiparametric investigation isotopic composition in da nd 18 o ions gas and ice texture analyses a sediment layer about 10 cm thick appearing at a depth of 3 5m is also studied by grain size x ray diffraction and scanning electron microscope analyses the information retrieved indicates that this ice block lake results from a build up in two steps and explains how aeolian sediments were included as a layer into the ice copyright 2002 john wiley sons ltd

lake heimtjonna at dovre mid norway reveals remarkable late glacial and holocene sedimentary environments and the early establishment of spruce picea abies alder alnus cf incana and alpine plants with present centric distributions abstract two and a half meters of sediments from lake heimtjonna in the scandes mountains reveal changes in the vegetation climate and sediment environment since deglaciation the lake was deglaciated in the late glacial lg perhaps as early as 16 18 ka cal bp after deglaciation the sediment environment at the heimtjonna coring point was extraordinary and challenging to interpret the genesis of the 1 7 m basal unsorted sediments including large stones is discussed concluding that the layer was rafted by lake ice after the lg deglaciation the younger dryas yd established a semi perennial lake ice that stopped the deposition of the ice rafted stone rich sediments in the early holocene the unstratified and well sorted clayey silt shows fluvial origin in late holocene strong flood activity including the major flood disaster stor ofsen in ad 1789 caused a sediment hiatus at the coring point from ca 9 5 ka cal bp to ca 250 a cal bp the lg interstadial warming initiated the succession from pioneer plants on mineral soils towards local dwarf shrub heath july temperatures reached at least 7 8 oc in the lg and early holocene papaver radicatum artemisia norvegica and campanula cf uniflora today occurring at dovre and with centric scandinavian distributions locally established all have previously been connected to weichselian survival on nunatak refugia continuous pollen curves of spruce picea abies support the much debated lg and early holocene presence of spruce in the scandes mountains for the first time it is shown that both grey alder alnus incana and armeria occurred in the scandes in the lg and early holocene due to dating errors lg ages is exclusively based on stratigraphical correlations and considerations the lg chronology must be thoroughly tested by future studies providing reliable ams 14c dates of terrestrial fossils

plio pleistocene pumice floods in the ancestral rio grande southern rio grande rift usa abstract at least four times during the late pliocene and early pleistocene pyroclastic eruptions in the jemez volcanic field northern rio grande rift flooded the ancestral rio grande with gravel sized pumice following as much as 400 km of fluvial transport the pumice was deposited in beds 0 2 to 2 0 m thick in the camp rice formation of the southern rio grande rift a combination of reversal magnetostratigraphy and single crystal sanidine 40 ar 39 ar dating constrains the ages of pumice clast conglomerates at 3 1 2 0 1 6 and 1 3 ma the coarsest pumice beds cobbles boulders were deposited as antidune like bedforms in a fluvial channel and as a crevasse splay sheet granule and pebble sized pumice was deposited as dune bedforms in fluvial channels and as ripple bedforms on the floodplain the abundance of pumice clasts in the gravel fraction 60 100 suggests very rapid transport downriver probably in a few days or weeks the two older pumice clast conglomerates correlate with the puye formation in the jemez volcanic field whereas the younger two are coeval to the lower bandelier tuff and cerro toledo rhyolite