hot water drilling and bore hole closure in cold ice drilling bore holes in deep cold ice masses by hot water methods and maintaining these holes with sufficient diameter to allow down hole experimentation poses a major obstacle to the investigation of conditions beneath ice sheets and ice streams closure of the water filled holes by refreezing is the dominant difficulty in this paper we describe calculations of heat transfer from the drilling system to the ice and the subsequent time dependent motion of the phase boundary defining the bore hole wall results are presented with the view of optimizing the bore hole radius at depth for a fixed drill performance and a variable rate of drilling calculation of melting refreezing rates at the bore hole wall requires the use of a one dimensional time dependent numerical heat flow model with a distorting mesh which follows the changing hole size the delay of hole closure is discussed with a view to keeping holes open long enough to allow instruments to be lowered to the glacier bed while realizing that drilling system performance may be marginal because of logisitical and or expenditure constraints the relative merits of drilling a large hole which is very time consuming with a small drill and the use of water soluble antifreezes which have a history of creating plugs of ice slush are discussed a method of creating a stable hole filled with antifreeze in which ice slush does not occur is described the recent application of these theoretical ideas to the planning and implementation of successful hot water drilling programs in antarctica and greenland is also presented

fire ecology of the carboniferous tropical zone abstract fossil charcoal fusain indicating the occurrence of wildfire is common in the carboniferous rocks of north america and europe during the carboniferous these regions lay on the southern margins of the laurasian continent and within the tropical zone this study examines the facies distribution and botanical identity of charcoal in order to investigate the influence of fire on carboniferous tropical ecology new data from charcoal bearing units in eastern canada poland and the british isles are presented and synthesised with previously published data of charcoal occurrence tournaisian visean charcoal bearing strata were deposited in volcanic lacustrine alluvial plain and coastal marine environments in these deposits charred floras are dominated by pro gymnospermous plants whilst uncharred compressed or permineralised floras are dominated by lycopsids uncharred lycopsid remains were probably derived from wetland communities growing close to the depocentres whilst charred gymnospermous remains may have been sourced from well drained extrabasinal settings based on the vertical distribution of charcoal layers in annually laminated lacustrine deposits it is estimated that fires occurred with high frequency approximately every 3 35 years palaeoclimatic analysis indicates that southern laurasia at this time was subject to a seasonal monsoonal tropical climate such environments today are characterised by tropical savannas with high fire frequencies and early carboniferous fire prone gymnospermous plant communities may have represented a comparable vegetation biome namurian stephanian charcoal bearing strata were deposited in alluvial plain coastal plain and coastal marine environments channelised sandstone units interpreted as river channel deposits contain charcoal derived from cordaitaleans and conifers this assemblage records fires in extrabasinal coniferopsid forests mudstone units containing coals are interpreted as the deposits of floodbasins and peat mires hollow uncharred lepidodendrid stumps occur in this facies and contain lepidodendrid charcoal in the stump bases and lepidodendrid pteridosperm coniferopsid and sphenopsid charcoal outside the stumps this assemblage records fires in wetland lepidodendrid dominated forests lepidodendrid trunks comprising of a spongy parenchymatous core surrounded by dense periderm became hollowed out during fire events an estimate of fire frequency based on the vertical spacing of charcoal layers in coals implies that fires occurred every 105 1085 years in the peat mires palaeoclimatic analysis indicates that southern laurasia was subject to a humid tropical climate during the late carboniferous such environments today are characterised by tropical rainforests where fires occur rarely and late carboniferous communities may have represented a comparable biome

shear resistance and continuity of subglacial till hydrology rules the field observations of g s boulton stimulated widespread interest in deformable beds shear resistance of till in its critical state is insensitive to strain rate and increases linearly with effective pressure during unsteady deformation pseudo viscous shear resistance can be caused by dilation of consolidated tills and resultant pore pressure decline this effect is probably uncommon however because susceptible tills of low hydraulic diffusivity are also those least likely to consolidate significantly during effective pressure transients stick slip motion at whillans ice stream antarctica indicates that its basal till must weaken during rapid slip and strengthen during longer periods of slower slip recurrence intervals for rapid slip episodes there 6 18 hours indicate that till strength variations if driven by changes in pore pressure either related or unrelated to basal freezing are focused in the uppermost several centimeters of the bed ploughing of grains at the bed surface and associated excess pore pressures in adjacent till can account for rate weakening during rapid slip with pore pressure decay causing strengthening between slip episodes by promoting shallow sluggish subglacial water flow and low effective pressure soft beds may help sustain themselves by slowing their own transport soft bed shear resistance kinematics and continuity are problems rooted in subglacial hydrology

borehole measurements indicate hard bed conditions kangerlussuaq sector western greenland ice sheet the hydrological processes and sliding dynamics of the greenland ice sheet are closely linked to the structural framework of its bed establishing whether the ice mass rests on bedrock relatively clear of rock debris a thick deformable till layer or some intermediate combination is therefore key to understanding the ice sheet response to changes in meltwater inputs here we report on direct observations of the ice bed interface along a flow line transect in the ablation zone of the western greenland ice sheet our measurements are derived from a network of 32 boreholes that vary from 100 m deep near the ice margin to 830 m deep 46 km upflow from the terminus we performed a suite of experiments and sampling techniques in the holes to investigate the bed conditions in contrast to previous geophysical and drilling studies elsewhere in greenland which have suggested that the ice rests on a thick layer of sediment we find no evidence for a thick sediment cover on the bed of the kangerlussuaq sector of the ice sheet our observations imply that this area has a relatively clean and hard bed and that this facilitates a basal hydraulic system governed by ice bedrock interactions the lack of sediment cover on the bed could be due to recent deglaciation and advance of this sector of the ice sheet and or variable rates of erosion and preferential routing of sediment through bedrock troughs

end member feldspar concentrations determined by ftir spectral analysis abstract feldspar mineralogy reported as concentrations of kalsi3o8 naalsi3o8 and caal2si2o8 can be determined from ftir spectroscopy in this study end member ftir spectra were constructed from sample spectra and their associated k na and ca feldspar concentrations using a least squares full spectrum program this was necessary because none of the samples have single phase pure end member composition the k na and ca feldspar concentrations are computed by fitting the sample ftir spectrum to the end member ftir spectra using a nonnegative least squares program for the feldspar samples examined we found that when the compositions determined from infrared spectroscopy are compared to the compositions deri ed from chemistry the standard error of estimate for k na and ca feldspar is 1 0 0 9 and 0 7 absolute mole respectively

the effect of the subglacial water pressure on the sliding velocity of a glacier in an idealized numerical model in order to interpret observed short term variations of the sliding velocity of a glacier the effect of a variable subglacial water pressure on the sliding velocity has been studied using an idealized numerical model in particular the transient stages of growing or shrinking water filled cavities at the ice bedrock interface were analysed it was found that the sliding velocity was larger when cavities were growing than when they had reached the steady state size for a given water pressure the smallest sliding velocities occurred while cavities were shrinking when cavitation is substantial a small drop of water pressure below the steady state value e g by 0 5 bar can temporarily cause backward sliding a limiting water pressure at which sliding becomes unstable is derived the consequences of more realistic assumptions than those of the model are discussed

transitional changes in arborescent lignophytes at the devonian carboniferous boundary abstract it is usually considered that after the extinction of the devonian tree archaeopteri s no new arborescent lignophytes were established before the late tournaisian a reassessment of this pattern is presented here based on a three fold approach a re evaluation of the taxic diversity of tournaisian lignophyte trees based on descriptions of new plants from palaeotropical latitudes a study of the patterns of phenotypic changes occurring among early lignophytes using a principal coordinate analysis and a phylogenetic analysis of the affinities of the arborescent taxa the best supported results indicate that a substantial taxonomic and phenotypic diversity of arborescent lignophytes was already established in the first part of the tournaisian including some taxa that persisted until the serpukhovian two genera may have originated in the late devonian and crossed the devonian carboniferous boundary fewer originations and a decrease in phenotypic diversity occurred in the visean the phenotypic distinctiveness of tree stems compared with those of other growth forms in the lignophytes is assessed we propose a scenario in which the presence of lignophyte trees is continuous across the devonian carboniferous boundary with arborescent taxa distinct from archaeopteris already present in the latest devonian possibly in upland floras and diversifying significantly soon after the devonian carboniferous boundary supplementary material a list of taxa characters and matrices used in the principal coordinate analysis and phylogenetic analysis is available at http www geolsoc org uk sup18447

seismic reflection evidence for a deep subglacial trough beneath jakobshavns isbrae west greenland seismic reflection methods were used to determine the ice thickness and basal topography of jakobshavns isbrae a large fast moving ice stream outlet glacier in west greenland a method of data analysis was developed which involves the pointwise migration of data from a linear seismic array and a single explosive source the method yields the depth horizontal position and slope of the basal reflector a deep u shaped subglacial trough was found beneath the entire length of the well defined ice stream the trough is incised up to 1500 m into bedrock and its base lies 1200 1500 m below sea level for at least 70km inland center line ice thickness along most of the channel is about 2500 m or about 2 5 times that of the surrounding ice sheet this prominent bedrock trough was not apparent in existing radio echo sounding data reflection coefficients indicate that much of the basal interface is probably underlain by compacted non deforming sediment the large ice thickness coupled with relatively steep surface slopes leads to high basal shear stresses 200 300 kpa along the ice stream the large shear stresses and lack of a deformable bed imply that internal deformation plays a dominant role in the dynamics of jakobshavns isbrae

physical conditions at the base of a fast moving antarctic ice stream boreholes drilled to the bottom of ice stream b in the west antarctic ice sheet reveal that the base of the ice stream is at the melting point and the basal water pressure is within about 1 6 bars of the ice overburden pressure these conditions allow the rapid ice streaming motion to occur by basal sliding or by shear deformation of unconsolidated sediments that underlie the ice in a layer at least 2 meters thick the mechanics of ice streaming plays a role in the response of the ice sheet to climatic change

temperature distribution and thermal anomalies along a flowline of the greenland ice sheet englacial and basal temperature data for the greenland ice sheet gris are sparse and mostly limited to deep interior sites and ice streams providing an incomplete representation of the thermal state of ice within the ablation zone here we present 11 temperature profiles at five sites along a 34 km east west transect of west greenland these profiles depict ice temperatures along a flowline and local temperature variations between closely spaced boreholes a temperate basal layer is present in all profiles increasing in thickness in the flow direction where it expands from 3 of ice height furthest inland to 100 at the margin temperate thickness growth is inconsistent with modeled heat contributions from strain heating heat conduction and vertical extension of the temperate layer we suggest that basal crevassing facilitated by water pressures at or near ice overburden pressure is responsible for the large temperate ice thicknesses observed high temperature kinks at 51 85m depth are likely remnants from the thermal influence of partially water filled crevasses up ice sheet steep horizontal temperature gradients between closely grouped boreholes suggest the recent thermal influence of a moulin these profiles demonstrate the ability of meltwater to rapidly alter ice temperatures at all depths within the ablation zone

seasonal speedup of the greenland ice sheet linked to routing of surface water we use interferometric synthetic aperture radar observations recorded in a land terminating sector of western greenland to characterise the ice sheet surface hydrology and to quantify spatial variations in the seasonality of ice sheet flow our data reveal a non uniform pattern of late summer ice speedup that in places extends over 100 km inland we show that the degree of late summer speedup is positively correlated with modelled runoff within the 10 glacier catchments of our survey and that the pattern of late summer speedup follows that of water routed at the ice sheet surface in late summer ice within the largest catchment flows on average 48 faster than during winter whereas changes in smaller catchments are less pronounced our observations show that the routing of seasonal runoff at the ice sheet surface plays an important role in shaping the magnitude and extent of seasonal ice sheet speedup

mechanisms of fast flow in jakobshavn isbrae west greenland part iii measurements of ice deformation temperature and cross borehole conductivity in boreholes to the bedrock at a site on the ice sheet adjacent to the jakobshavn ice stream in west greenland ice deformation rates and temperatures have been measured in boreholes to the bedrock at 830 m depth enhanced deformation rates were recorded just below the holocene wisconsin transition at 680 m depth a 31 m layer of temperate ice and the temperature minimum of 22 c at 520 m depth were detected the good agreement of these data with results of a two dimensional thermomechanically coupled flow model implies that the model input is adequate discrepancies between modelled and measured temperature profiles on a flowline at the ice stream centre have been attributed to effects not accounted for by the model we have suggested that the convergent three dimensional flow leads to a vertical extension of the basal ice entering the stream a thick basal layer of temperate and wisconsin ice would explain the fast flow of this ice stream as a test of this hypothesis the new core borehole conductivity cbc method has been used to compare conductivity sequences from the ice stream to those of the adjacent ice sheet the correlation thus inferred suggests that the lowest 270 m of the ice sheet correspond to the lowermost 1700 m of the stream and consequently that the lower part of the ice stream has experienced a very large vertical extension

a new serpukhovian mississippian fossil flora from western argentina paleoclimatic paleobiogeographic and stratigraphic implications an uppermost mississippian serpukhovian fossil flora from western argentina is described for the first time its particular composition includes both warm climate plants typical from the pennsylvanian of gondwana namely pteridosperms sphenophytes as well as arboreous lycopsids and small lycopsids characteristic of cooler climates of pre serpukhovian times a warm temperate climate is inferred for this association which fills a time gap between those pennsylvanian and mississippian classic floras previously known the presence of tomiodendron nothorhacopteris kellaybelenensis and paracalamites allow the recognition of the paraca floral realm in argentina supporting the existence of a nonglacial paleoclimate period developed just before of the bashkirian moscovian gondwanan glaciation and after a latest visean glaciation it likewise would indicate the paleogeographic position of south west gondwana which would have acceded to a warm temperature latitudinal belt during serpukhovian times the recognition of this floral assemblage has relevant biostratigraphic and lithostratigraphic implications for the western margin of gondwana it defines a new zone for western argentina herein named frenguellia eximia nothorhacopteris kellaybelenensis cordaicarpus cesarii fnc zone which is recorded in the oldest known lithostratigraphic unit from the paganzo basin the loma de los piojos formation nom nov

frasnian plants from the dra valley southern anti atlas morocco anatomically preserved plant fragments are reported from devonian marine deposits exposed in the dra valley of southern anti atlas morocco associated conodont and tentaculite faunas indicate that the sediments yielding plants which consist of black shales with intercalated calcareous concretions are early frasnian in age and most probably represent zone 2 of the conodont zonation this is the first record of frasnian plants in north africa the specimens found all correspond to decorticated portions of axes six are referable to callixylon the organ genus corresponding to anatomically preserved axes of the progymnosperm tree archaeopteris based on wood characters especially ray structure they are assigned to the species c henkei formerly described from the famennian of europe one single specimen is compared to xenocladia a cladoxylopsid genus previously known from the middle devonian of europe usa and kazakhstan interestingly archaeopteridales and cladoxylopsida are two groups that dominate the younger plant assemblages of famennian age recently described from the eastern anti atlas callixylon henkei type axes occur both in the frasnian and in the famennian deposits of the anti atlas and they are all devoid of growth rings these results are in accordance with a close position of gondwana and euramerica during late devonian times

basal drainage system response to increasing surface melt on the greenland ice sheet surface meltwater reaching the bed of the greenland ice sheet imparts a fundamental control on basal motion sliding speed depends on ice bed coupling dictated by the configuration and pressure of the hydrologic drainage system in situ observations in a four site transect containing 23 boreholes drilled to greenland s bed reveal basal water pressures unfavorable to water draining conduit development extending inland beneath deep ice this finding is supported by numerical analysis based on realistic ice sheet geometry slow meltback of ice walls limits conduit growth inhibiting their capacity to transport increased discharge key aspects of current conceptual models for greenland basal hydrology derived primarily from the study of mountain glaciers appear to be limited to a portion of the ablation zone near the ice sheet margin

late palaeozoic terrestrial habitats and biotas the effect of changing climates abstract the 2009 lyell meeting held at the geological society london reviewed various aspects of the interrelationship between late palaeozoic habitats biotas and climates the following five papers are based on some of the presentations given at the meeting

characteristics of the bed of the lower columbia glacier alaska an unplanned but unique experiment has given an in situ measurement of the strength of deforming subglacial till under the central region of a major valley glacier we report on both planned and unplanned borehole investigations of the subglacial shear zone of columbia glacier southeast alaska basal samples coring and down hole water samples show that the fiord filling lower reach of the glacier is underlain by a thin 7 cm veneer of rock debris fluidized debris intruded at least a meter up the borehole at a higher site 13 km from the terminus and above the fiord probing samples and the bending of a drill stem which was stuck in the basal zone for 5 days showed that the basal till layer was 65 cm thick horizontal velocity of the till decreased monotonically downward from the ice till interface till at the interface moved with the ice velocity plastic deformation of the drill stem gave an estimate of the strength of the basal till which is normally described as a viscoplastic material if the till is assumed to be either perfectly plastic or newtonian viscous then the strengths are as follows the plastic yield strength of the till was 5 5 10 3 pa 0 055 bar with an upper bound of 1 3 10 4 pa 0 13 bar while the nominal viscosity was of the order of 2 10 8 pa s 2 10 9 poise with an upper bound of 5 10 8 pa s in neither case is the till strength enough to supply the bulk basal shear stress to resist the glacier flow

palaeozoic landscapes shaped by plant evolution fluvial landscapes diversified markedly over the 250 million years between the cambrian and pennsylvanian periods the diversification occurred in tandem with the evolution of vascular plants and expanding vegetation cover in the absence of widespread vegetation landscapes during the cambrian and ordovican periods were dominated by rivers with wide sand beds and aeolian tracts during the late silurian and devonian periods the appearance of vascular plants with root systems was associated with the development of channelled sand bed rivers meandering rivers and muddy floodplains the widespread expansion of trees by the early pennsylvanian marks the appearance of narrow fixed channels some representing anabranching systems and braided rivers with vegetated islands we conclude that the development of roots stabilized the banks of rivers and streams the subsequent appearance of woody debris led to log jams that promoted the rapid formation of new river channels our contention is supported by studies of modern fluvial systems and laboratory experiments in turn fluvial styles influenced plant evolution as new ecological settings developed along the fluvial systems we suggest that terrestrial plant and landscape evolution allowed colonization by an increasingly diverse array of organisms

the holocene sedimentary history of the kangerlussuaq fjord valley fill west greenland abstract west greenland has been intensively studied to reconstruct and better understand past relative sea level changes and deglacial history this study extends these efforts by linking sea level and deglacial history to the sedimentary infill successions of kangerlussuaq fjord and associated landward valleys based on published and new land and sea based geophysical data radiocarbon dates and geological observations we have characterized the infill and reconstructed the sedimentation history during the holocene based on a revised sea level curve and data presented in this paper we defined three depositional phases phase i 7000 yr bp is represented by dominant glaciomarine deposition associated with a tide water glacier system as the greenland ice sheet gis continued to retreat it became land based during phase ii 7000 1500 yr bp two separate depocenters formed keglen delta depocenter arose from a temporary stabilization phase of the gis and prograded rapidly over the glaciomarine deposits of phase i further inland proglacial lake formation and subsequent sedimentary infill associated with the ongoing gis retreat is represents the second depocenter the watson river connected both depocenters by a flood plain which transferred sediment from the gis to the keglen delta ongoing sea level fall due to glacio isostastic uplift combined with a gradually cooler and dryer climate resulted in terrace formation along the watson river flood plain around 4000 yr bp the gis margin reached its most landward location and began to advance to its present location the final phase phase iii

hydraulics of subglacial cavities modele theorique du comportement a l etat stationnaire des cavites remplies d eau et interconnectees sur le lit du glacier

implications for deglaciation chronology from new ams age determinations in central west greenland abstract new evidence has been obtained for the age of the umivit keglen and orkendalen moraine systems close to the present ice sheet margin in central west greenland the umivit keglen moraine system is dated at 7500 to 6500 14 c yr b p which is older than the previously assumed date of 7300 to 6000 14 c yr b p the orkendalen system is now dated at 6200 to 5600 14 c yr b p against earlier estimates of 300 to 700 14 c yr b p the new age is based on ams radiocarbon dated organic material within depressions between morainic ridges belonging to the orkendalen system a major implication of the new age is that ice margin positions prevailed for about 6000 years behind the present ice sheet margin the retreat behind the present margin could be substantial and in the light of deglaciation rates prior to the orkendalen phase may be ca 10 s of kilometers rather than kilometers circumstantial evidence is found for the retreat of the ice sheet margin behind its present position during the holocene climatic optimum the results placed into a time frame of deglaciation since the last glacial maximum enable comparison with greenland ice sheet models and ice core records

evolution of fixed channel alluvial plains in response to carboniferous vegetation the establishment of terrestrial plants during the palaeozoic era was one of the most significant changes to the earth system during the phanerozoic eon the continuing evolution and expansion of land plants irrevocably altered the alluvial landscape the broad unconfined and unconsolidated blankets of coarse sediment found at the start of the cambrian period were replaced by a diverse array of braided and meandering channel styles and stable floodplains by the end of the devonian period here we show that the first appearance of a sedimentary facies suite attributed to low energy organic rich river systems with multiple channels and stable alluvial islands known as anabranching or anastomosing rivers occurred during the carboniferous period our field studies and literature review demonstrate that the appearance of these rivers coincides with the continuing evolution of tree like plants we suggest that increased floodplain stability and new triggers for channel avulsion were provided by the increase in complexity and diversity of root assemblages density of floodplain forests and production of woody debris associated with expansion of arborescence we conclude that the expansion of tree habitats led to the crossing of a threshold in vegetative control of floodplain and river morphology during the carboniferous

hydrogeological analysis of slug tests in glacier boreholes slug testing allows estimation of subglacial hydraulic properties by evaluating the response of a coupled borehole subglacial flow system to an artificial displacement of its steady state hydraulic head however existing models developed specifically for application to slug test data collected in glacier boreholes are challenging to apply in practice here we demonstrate that conventional linear methods which are relatively readily applicable and widely used in groundwater studies can also be used to estimate subglacial hydraulic properties overdamped underdamped and critically damped slug test data were recorded in fluctuating boreholes drilled to the bed of haut glacier d arolla valais switzerland we find that non linear effects in the data are negligible supporting the application of conventional hydrogeological methods results suggest that the hydraulic conductivity of the unconsolidated sediments within the area influenced by a major subglacial drainage channel is enhanced several 10 2 ms 1 typical of gravelly sand compared to areas outside the zone of influence 0 1 10 2 ms 1 typical of silty sand a distance to a flow boundary within the subglacial aquifer inferred on the basis of slug test analysis was found to coincide with the actual location of the subglacial channel sensitivity analyses reveal that uncertainties in borehole and filter radii as well as the storage coefficient of the subglacial aquifer are more likely to affect the accuracy of the hydraulic and distance estimates than uncertainties regarding the repeatability of the slug test responses and curve fitting procedures involved in the conventional hydrogeological methods

the plant fossil record reflects just two great extinction events five great taxonomic extinctions the so called big five mass extinctions are widely recognized in life history at the end of the ordovician frasnian late devonian permian triassic and cretaceous all of them were originally identified in the marine fossil record and have been interpreted as the result of abrupt global environmental changes previous evidence has suggested that terrestrial biota were also subjected to ecological disruption during these events but it is unknown whether they suffered the same level of large scale taxonomic disruption as marine organisms here we show that the plant fossil record in fact only provides evidence of two mass taxonomic extinction events one through the carboniferous permian transition the other during middle late permian times this differs significantly from the mass extinctions recognized in the marine realm and suggests that vascular plants have a special capacity for surviving abrupt environmental changes

considering river structure and stability in the light of evolution feedbacks between riparian vegetation and hydrogeomorphology river ecological functioning can be conceptualized according to a four dimensional framework based on the responses of aquatic and riparian communities to hydrogeomorphic constraints along the longitudinal transverse vertical and temporal dimensions of rivers contemporary riparian vegetation responds to river dynamics at ecological timescales but riparian vegetation in one form or another has existed on earth since at least the middle ordovician c 450 ma and has been a significant controlling factor on river geomorphology since the late silurian c 420 ma on such evolutionary timescales plant adaptations to the fluvial environment and the subsequent effects of these adaptations on fluvial sediment and landform dynamics resulted in the emergence from the silurian to the carboniferous of a variety of contrasted fluvial biogeomorphic types where water flow morphodynamics and vegetation interacted to different degrees here we identify several of these types and describe the consequences for biogeomorphic structure and stability i e resistance and resilience along the four river dimensions of feedbacks between riparian plants and hydrogeomorphic processes on contrasting ecological and evolutionary timescales

comparison of quantitative mineral analysis by x ray diffraction and fourier transform infrared spectroscopy abstract accurate description of mineralogy bears on oilfield operations and can be used to calibrate downhole logs and develop petrophysical models for oilfield exploration and development x ray diffraction xrd is the industry standard for quantitative mineral analysis but the accuracy of the method varies substantially due to differences in sample preparation sample measurement and data analysis techniques this paper reviews the alternative transmission fourier transform infrared ftir spectroscopy technique for quantitative analysis of sedimentary formations including recent analytical improvements and examines the differences between xrd and ftir mineralogy in several case studies the ftir procedure has been modified to address two challenges namely cloudy pellets and the presence of adsorbed water in ftir spectra quantitative mineral analysis by ftir is enabled using a generalized least squares inversion against a library of mineral standards with unique ir spectra mineralogy results from ftir are compared with those obtained using xrd techniques commonly practiced by commercial xrd laboratories on over one hundred sedimentary samples spanning carbonate sandstone and shale lithologies accuracy of the mineralogy is evaluated using whole rock chemistry bulk major element si ca al k na mg fe and s concentrations are reconstructed from the mineralogy by assigning chemical compositions to each mineral and are then compared against measured elemental concentrations obtained on identical splits of the samples using independent and validated chemical analysis techniques conformance between the reconstructed and measured elemental concentrations is assessed by quantifying the difference between the two for the sets of samples examined here ftir results are consistently better than those from xrd using this conformance criterion the data indicate that ftir can provide quantitative and accurate mineral analysis of sedimentary formations which can be used for example to calibrate and validate quantitative petrophysical interpretations in oilfield operations

modeling channelized and distributed subglacial drainage in two dimensions 1 we present a two dimensional glacier drainage system model glads that couples distributed and channelized subglacial water flow distributed flow occurs through linked cavities that are represented as a continuous water sheet of variable thickness channelized flow occurs through rothlisberger channels that can form on any of the edges of a prescribed unstructured network of potential channels water storage is accounted for in an englacial aquifer and in moulins which also act as point sources of water to the subglacial system solutions are presented for a synthetic topography designed to mimic an ice sheet margin for low discharge all the flow is accommodated in the sheet whereas for sufficiently high discharge the model exhibits a channelization instability which leads to the formation of a self organized channel system the random orientation of the network edges allows the channel system geometry to be relatively unbiased in contrast to previous structured grid based models under steady conditions the model supports the classical view of the subglacial drainage system with low pressure regions forming around the channels under diurnally varying input water flows in and out of the channels and a rather complex spatiotemporal pattern of water pressures is predicted we explore the effects of parameter variations on the channel system topology and mean effective pressure the model is then applied to a mountain glacier and forced with meltwater calculated by a temperature index model the results are broadly consistent with our current understanding of the glacier drainage system and demonstrate the applicability of the model to real settings

instruments and methods direct measurement of sliding at the glacier bed sliding at the base of trapridge glacier yukon territory canada was measured using a drag spool we describe this simple and inexpensive instrument as well as its installation and operation from 1990 to 1992 seven sites were instrumented with drag spools at six of the sites basal sliding during the period of observation accounted for 50 70 of the total flow observed at the glacier surface the contribution from ice creep is known to be small so most of the remaining surface motion must be attributed to subglacial sediment deformation for the seventh site the observed sliding rate was 90 of the total flow an indication that the sliding contribution varies spatially across the bed diurnal variations in the response of one of our instruments appear to be correlated to subglacial water pressure fluctuations and are interpreted in terms of changes in sliding velocity rather than the opening and closing of basal cavities

subglacial permafrost evidencing re advance of the greenland ice sheet over frozen ground abstract greenland ice sheet gris covers an area of 1 7 million km2 it has been an important source of climate information and the air temperature history of greenland is well known however the thermal history and temperature conditions of the greenland bedrock are poorly known there are only few records on the temperature of the proglacial bedrock and no records on bedrock temperature underneath the ice sheet the greenland analogue project gap recently investigated hydrological hydrogeological and geochemical processes in kangerlussuaq west greenland because permafrost has a major hydrological impact in arctic regions the cryogenic structure of the bedrock was an important research topic from previous studies it was already known that kangerlussuaq is located within the zone of continuous permafrost temperature profiling in a new research borehole extending horizontally 30 m underneath the ice sheet revealed that permafrost is 350 m deep at the ice margin this result raised the question how far the permafrost extends under the ice sheet in order to investigate the thermal properties we made a series of electromagnetic em soundings at the ice margin area on proglacial area and on the ice sheet and detected that subglacial permafrost extends at least 2 km from the ice margin to inland we also observed a patchy unfrozen sediment layer between the ice and the frozen bedrock possible existence of subglacial sediments and their role in ice dynamics has been debated in many recent papers our successful campaign shows that geophysics can be used for bedrock investigations through thick ice which is known to be challenging for electromagnetic methods our results provide the first direct evidence supporting the proposed holocene ice re advance over frozen ground and contribute to the discussion on the rapid climate changes in past to the future of the ice sheet under warming climate and hydrogeology at the ice margin

late devonian and early carboniferous alpha diversity ecospace occupation vertebrate assemblages and bio events of southeastern morocco abstract the late devonian was a time of dramatic environmental perturbations affecting marine ecosystems both the kellwasser latest frasnian and the hangenberg crises latest famennian are primarily reported as phases of drastic decreases in marine diversity while the hangenberg crisis is also described as a bottleneck in vertebrate evolution fossil bearing localities with upper devonian strata are of great interest to assess variations in the effects of environmental perturbations on biodiversity for this purpose we examined changes in alpha diversity and ecospace utilization of 21 famennian late devonian and early tournaisian early carboniferous invertebrate associations containing 9828 specimens from madene el mrakib and aguelmous southern maider basin northeastern anti atlas morocco where some layers yield exceptionally preserved gnathostome remains both the invertebrate and vertebrate associations contain predominantly opportunistic and pelagic taxa indicating oxygen depletion near the seafloor in this region nevertheless the ecospace extension was fluctuating and correlated with regional and or global sea level changes and oxygenation of bottom waters in the maider basin the ecospace was depleted after and during several bio events such as the kellwasser and hangenberg crises the annulata event middle famennian as well as during the early tournaisian abiotic as well as biotic changes instability of the invertebrate ecosystem are considered to have influenced famennian vertebrate diversity because they were more or less directly dependent on invertebrates as a food source

caterpillar like ice motion in the ablation zone of the greenland ice sheet current understanding of ice dynamics predicts that increasing availability and variability of meltwater will have an impact on basal motion and therefore on the evolution and future behavior of the greenland ice sheet we present measurements of ice deformation subglacial water pressure and surface velocity that show periodic and episodic variations on several time scales seasonal multiday and diurnal these variations observed with gps and sensors at different depths throughout the ice column are not synchronous but show delayed responses of ice deformation with increasing depth and basal water pressure in antiphase with surface velocity with the help of a full stokes ice flow model these observations are explained as ice motion in a caterpillar like fashion caused by patches of different basal slipperiness horizontal stress transfer through the stiff central part of the ice body leads to spatially varying surface velocities and ice deformation patterns variation of this basal slipperiness induces characteristic patterns of ice deformation variability that explain the observed behavior ice flow in the ablation zone of the greenland ice sheet is therefore controlled by activation of basal patches by varying slipperiness in the course of a melt season leading to caterpillar like ice motion superposed on the classical shear deformation

famennian charcoal of belgium abstract charcoal results from an incomplete combustion of biological material in anoxic conditions and has a high potential for three dimensional cellular preservation most of the belgian upper devonian flora is known through compression fossils mainly from the siliciclastic evieux formation no charcoal bearing layers had been reported to date we have recently identified organic rich beds from three late famennian localities val dieu quarry trooz quarry and arbre quarry the three localities are described from the sedimentological point of view the arbre and trooz quarries contain allochthonous specimens of charcoalified wood they are identified as callixylon in arbre in trooz the specimen belongs either to an undescribed species of callixylon or to another taxon of woody pro gymnosperm the val dieu quarry by contrast yielded a more diverse charcoalified assemblage including leafy remains branches and fertile axes related to ferns sphenopsids and pro gymnosperms this material experienced moderate transportation before burial the val dieu assemblage is exceptional for late devonian deposits as it represents a moderately disturbed litter interpreted as representing a swamp environment and its proximal margins this assemblage is an illustration that the fossil charcoal record can provide a unique opportunity to study in fine detail the evolutionary history and past diversity of life

quaternary relief generation by polythermal glacier ice the juxtaposition of wet based erosive ice in valleys and cold based non erosive ice atop felsenmeer covered interfluve plateaus has generated relief in the torngat mountains of northeastern canada measurements of in situ terrestrial cosmogenic nuclide tcn concentrations from 31 bedrock sites coupled with soils and geomorphology indicate that erosion of the valleys has been 2 m during a single glacial interglacial cycle however on summit plateaus the long term over several glacial interglacial cycles erosion rate is 1 4 m ma 1 tcn ratios reveal that the exposure plus ice cover history retained on some summit surfaces probably spans more than 800 ka despite complete ice cover as recently as 11 ka a thermodynamic ice sheet model with a basal water calculation is used to calculate the sliding distance normalized by the duration of ice cover for the region we formulate a general glacial erosion rule for the torngat mountains which correlates tcn derived erosion rates for terrain once partially covered by cold based ice with modelled average ice basal sliding velocities erosion rates vary linearly with average sliding velocity by a glacial erosion coefficient of 5 10 7 due to the significant distribution of cold based ice cover in this high latitude region our estimates of net regional glacial erosion and glacial erosion coefficient are orders of magnitude lower than a previously published value copyright 2005 john wiley sons ltd

measured basal water pressure variability of the western greenland ice sheet implications for hydraulic potential the gradient of the hydraulic potential field at the ice bedrock interface beneath the greenland ice sheet gris dictates the routing and energetics of subglacial water thereby influencing drainage system characteristics and sliding dynamics in the ablation zone of the gris variable water pressure due to an active subglacial drainage system and basal topography with high relief potentially interact to drive unknown spatial patterns and temporal changes in the hydraulic potential field here we present a suite of water pressure measurements collected in 13 boreholes along a 46 km transect on the western gris to investigate the role of spatial and temporal basal water pressure adjustments in hydraulic potential gradient dynamics all borehole sites show pressures with similar seasonality having relatively steady and high values during winter variable and irregular behavior during spring and fall and diurnal cycles that can persist for multiple weeks during the peak melt season despite much higher variability during the melt season the median pressure of the summer period is nearly the same as the median pressure of the winter period however time variability of water pressure due to basal drainage processes can force changes in the magnitude and orientation of the hydraulic potential field over diurnal periods we find that the basal water pressure across the transect generally mimics the ice thickness field but with superimposed large pressure gradients that develop at shorter scales within the basal drainage system this leads to a complex hydraulic potential field across regions of similar ice thickness

mechanisms of fast flow in jakobshavns isbrae west greenland part i measurements of temperature and water level in deep boreholes several holes were drilled to depths of 1500 1630 m along a profile across jakobshavns isbrae 50 km upstream from the calving front drilling was by hot water and required approximately 20 h the holes were rapidly closed by refreezing but it was possible to instrument them with thermistors and tilt sensors before this occurred near the margins of the ice stream the holes reached the bed and connected with the subglacial drainage system water level changes recorded in these holes are discussed in terms of the basal hydraulic system the temperature measurements show that the glacier is temperate based moreover extrapolation of a measured temperature profile and its curvature suggests that a temperate layer of substantial thickness may exist at the bed near the center of the ice stream there is a striking difference in the shapes of temperature profiles measured at different locations beneath the center line the temperature minimum is at a considerably smaller relative depth than near the margins but it is nearly the same in magnitude 22 1 c this may indicate a disproportionately large vertical stretching of the basal ice in the center of the ice stream since the basal ice is warmer and much less viscous than the ice above a thickening of that layer would cause a corresponding increase of surface velocity we presume that this mechanism contributes to the fast flow of jakobshavns isbrae

short term variability in greenland ice sheet motion forced by time varying meltwater drainage implications for the relationship between subglacial drainage system behavior and ice velocity 1 high resolution measurements of ice motion along a 120 km transect in a land terminating section of the gris reveal short term velocity variations 1 day which are forced by rapid variations in meltwater input to the subglacial drainage system from the ice sheet surface the seasonal changes in ice velocity at low elevations 1000 m are dominated by events lasting from 1 day to 1 week although daily cycles are largely absent at higher elevations reflecting different patterns of meltwater input using a simple model of subglacial conduit behavior we show that the seasonal record of ice velocity can be understood in terms of a time varying water input to a channelized subglacial drainage system our investigation substantiates arguments that variability in theduration and rate rather than absolute volume of meltwater delivery to the subglacial drainage system are important controls on seasonal patterns of subglacial water pressure and therefore ice velocity we suggest that interpretations of hydro dynamic behavior in land terminating sections of the gris margin which rely on steady state drainage theories are unsuitable for making predictions about the effect of increased summer ablation on future rates of ice motion

melt induced speed up of greenland ice sheet offset by efficient subglacial drainage fluctuations in surface melting are known to affect the speed of glaciers and ice sheets but their impact on the greenland ice sheet in a warming climate remains uncertain although some studies suggest that greater melting produces greater ice sheet acceleration others have identified a long term decrease in greenland s flow despite increased melting here we use satellite observations of ice motion recorded in a land terminating sector of southwest greenland to investigate the manner in which ice flow develops during years of markedly different melting although peak rates of ice speed up are positively correlated with the degree of melting mean summer flow rates are not because glacier slowdown occurs on average when a critical run off threshold of about 1 4 centimetres a day is exceeded in contrast to the first half of summer when flow is similar in all years speed up during the latter half is 62 16 per cent less in warmer years consequently in warmer years the period of fast ice flow is three times shorter and overall summer ice flow is slower this behaviour is at odds with that expected from basal lubrication alone instead it mirrors that of mountain glaciers where melt induced acceleration of flow ceases during years of high melting once subglacial drainage becomes efficient a model of ice sheet flow that captures switching between cavity and channel drainage modes is consistent with the run off threshold fast flow periods and later summer speeds we have observed simulations of the greenland ice sheet flow under climate warming scenarios should account for the dynamic evolution of subglacial drainage a simple model of basal lubrication alone misses key aspects of the ice sheet s response to climate warming

cyclic changes in pennsylvanian paleoclimate and effects on floristic dynamics in tropical pangaea abstract wetland floras narrowly define perceptions of pennsylvanian tropical ecosystems the so called coal age such wetlands reflect humid to perhumid climate leading to characterizations of pennsylvanian tropics as everwet swampy these views are biased by the high preservation potential of wetlands sedimentation patterns paleosols and fossil floras indicate the presence of vegetation tolerant of subhumid to dry subhumid perhaps semi arid climate in basins between peat formation times understanding the significance of this seasonally dry vegetation has suffered from conceptual and terminological confusion a clearer view has emerged as models for framing the data have improved basinal floras typical of seasonally dry conditions relatively low soil moisture regimes are well documented but mainly from isolated deposits some of the earliest dominated by primitive pteridosperms flozfern floras occur in clastic rocks between european early pennsylvanian coal beds later early pennsylvanian fern cordaitalean vegetation different from coal floras is preserved in marine goniatite bullions conifers are first suggested by late mississippian potoniesporites pollen about the same time in north america broadleaf foliage lesleya and megalopteris occur in basin margin settings on drought prone limestone substrates the best known xeromorphic floras found between coal beds appear in the middle through late pennsylvanian containing conifers cordaitaleans and pteridosperms the middle pennsylvanian appearances of this flora are mainly allochthonous though parautochthonous occurrences have been reported parautochthonous assemblages are mostly late pennsylvanian the conifer flora became dominant in western and central pangaean equatorial lowlands in earliest permian location of the humid perhumid wetland flora during periods of relative dryness though rarely discussed is as or more perplexing than the spatial location of seasonally dry floras through time wetland plants had few migratory options and possibly survived in small refugia within and outside of basins coupled oscillations in climate sea level and vegetation were driven most likely by glacial interglacial fluctuations perhaps controlled by orbital cyclicity

seasonal changes in ice sheet motion due to melt water lubrication abstract a numerical model is used to calculate how the motion of an idealized ice sheet margin is affected by the subglacial drainage of melt water from its surface the model describes the evolution of the drainage system and its coupling with ice flow through a sliding law that depends on the effective pressure the results predict ice acceleration during early summer when the inefficient drainage system is temporarily overwhelmed the growth of a more efficient drainage system leads to a subsequent slowdown of the ice very close to the margin but high water pressure and ice velocity are maintained through much of the summer further inland annual mean ice velocity increases with the total quantity of melt water except close to the margin where it is almost insensitive to the amount of melting short term variability of melt water input leads to rapid changes in ice velocity that result in a slight increase in the mean velocity relative to a smoother input linked cavity and poroelastic models for the distributed drainage system are compared and their relative merits discussed two different sliding laws are considered and the need for a holistic description of hydraulically controlled sliding is highlighted

formation and dynamics of vegetated fluvial landforms follow the biogeomorphological succession model in a channelized river feedback between hydrogeomorphological processes and riparian plants drives landscape dynamics and vegetation succession in river corridors we describe the consequences of biogeomorphological feedback on the formation and dynamics of vegetated fluvial landforms based on observations from the channelized isere river in france the channel was laterally confined with embankments and mostly straightened from the beginning of the 1970s to the end of the 1990s alternate bars were progressively but heavily colonized by vegetation this context presented an exceptional opportunity to analyse temporal adjustments between fluvial landforms and vegetation succession from bare gravel bars to mature upland forest as the consequence of biogeomorphological interactions based on a gis analysis of aerial photographs between 1948 and 1996 we show that the spatiotemporal organization of vegetated bars within the river channel observed in 1996 resulted from a bioconstruction and biostabilization effect of vegetation and interactions between bars of varying age size and mobility field measurements in 1996 reflected how a strong positive feedback between sedimentary dynamics and riparian vegetation succession resulted in the construction of the vegetated bars a highly significant statistical association of geomorphological and vegetation variables rv of co inertia analysis 0 41 p 0 001 explained 95 of the variability in just one axis supporting the existence of very strong feedback between geomorphological changes i e the transformation of small bare alternate bars to fluvial landforms covered by mature upland forest and vegetation succession such dynamics reflect the fluvial biogeomorphological successions model as described by the authors earlier 2020 john wiley sons ltd

deformation of till beneath ice stream b west antarctica the behaviour and possible instability of the west antarctic ice sheet depend fundamentally on the dynamics of the large ice streams which drain it model calculations show that most ice stream velocity arises at the bed1 2 and radar sounding has shown the bed to be wet3 but the basal boundary condition is not well understood seismic evidence from the upstream b camp upb on the siple coast of west antarctica4 shows that the ice stream there rests on a layer of unconsolidated sediment averaging 5 or 6 m thick in which the water pressure is only 50 kpa less than the overburden pressure because this thin layer occurs well inland beneath an active ice sheet and rests on a surface showing flutes4 characteristic of glacial erosion5 we presume that it is glacial till we propose here that deformation within the till is the primary mechanism by which the ice stream moves and we discuss implications of this hypothesis

upland ecology of some late carboniferous cordaitalean trees from nova scotia and england abstract permineralised logs and charcoal fragments composed of dadoxylon type wood and derived from cordaitalean trees are described from the upper carboniferous westphalian of nova scotia and england they exclusively occur in sandstone bodies interpreted as the deposits of braided meandering and anastomosing river channels the architecture and ecology of this type of cordaitalean has not yet been satisfactorily described estimates of tree height using an allometric approach suggest that the largest trees attained an approximate height of ca 45 m the absence of true growth rings in the logs indicate that they grew under non seasonal humid tropical conditions however the presence of charred wood fragments implies that droughts of sufficient intensity to permit wildfire did occasionally occur the charcoal fragments are usually associated with incised poorly sorted chaotically bedded channel facies interpreted as flood deposits dramatic increases in runoff and sediment discharge are known to follow the destruction of vegetation in modern wildfire events and the high energy charcoal bearing channel facies described may represent a similar geomorphic response to cordaitalean vegetation fires geomorphic sensitivity to fire is greatest for steeply sloping terrains and it is therefore probable that the cordaitaleans described in this paper occupied upland settings this palaeoecological interpretation is supported by occurrence of the cordaitalean remains in river channel deposits immediately downstream of regions of palaeo upland and by the palynological record the presence of upland forests in late carboniferous times has important implications for numerical modelling of global geochemical cycles

amplified melt and flow of the greenland ice sheet driven by late summer cyclonic rainfall intense rainfall events significantly affect alpine and alaskan glaciers through enhanced melting ice flow acceleration and subglacial sediment erosion yet their impact on the greenland ice sheet has not been assessed here we present measurements of ice velocity subglacial water pressure and meteorological variables from the western margin of the greenland ice sheet during a week of warm wet cyclonic weather in late august and early september 2011 we find that extreme surface runoff from melt and rainfall led to a widespread acceleration in ice flow that extended 140 km into the ice sheet interior we suggest that the late season timing was critical in promoting rapid runoff across an extensive bare ice surface that overwhelmed a subglacial hydrological system in transition to a less efficient winter mode reanalysis data reveal that similar cyclonic weather conditions prevailed across southern and western greenland during this time and we observe a corresponding ice flow response at all land and marine terminating glaciers in these regions for which data are available given that the advection of warm moist air masses and rainfall over greenland is expected to become more frequent in the coming decades our findings portend a previously unforeseen vulnerability of the greenland ice sheet to climate change

thick sediments beneath greenland s ablation zone and their potential role in future ice sheet dynamics the geological nature of glacier beds plays a key role in ice sheet dynamics whereas little is known about greenland s subglacial geology the presence of basal sediments is a necessary condition for fast flowing antarctic ice streams such sediments sustain subglacial till layers which if water saturated and under high pore water pressure provide little resistance to ice flow using receiver function modeling of teleseismic p waves we report a thick at least tens of meters sediment layer beneath a site in greenland s ablation zone 15 km away from the western ice sheet margin although we do not discuss the origin or detailed nature of these subglacial sediments we suggest that they are capable of sustaining a till layer due to the prevalence of an inefficient pressurized subglacial drainage system this till layer would typically be under high pore pressures and fail at the shear stresses transmitted from the overlaying ice ice flow resistance is thus focused on regions where till is consolidated or absent or where form drag over obstacles takes place in contrast to antarctica greenland s surface melt now affects practically all latitudes and efficient hydraulic connections between ice sheet surface and bed are pervasive throughout the ablation zone this implies that rapid melt induced changes in subglacial water pressure are possible the time required for basal till strength to react to these changes depends on the till s properties we estimate that formation and destruction of flow resistance can occur on time scales of less than a few years this could lead to changes in ice flow that are currently difficult to predict

calibrating a glaciological model of the greenland ice sheet from the last glacial maximum to present day using field observations of relative sea level and ice extent we constrain a three dimensional thermomechanical model of greenland ice sheet gris evolution from the last glacial maximum lgm 21 ka bp to the present day using primarily observations of relative sea level rsl as well as field data on past ice extent our new model huy2 fits a majority of the observations and is characterised by a number of key features i the ice sheet had an excess volume relative to present of 4 1 m ice equivalent sea level at the lgm which increased to reach a maximum value of 4 6 m at 16 5 ka bp ii retreat from the continental shelf was not continuous around the entire margin as there was a younger dryas readvance in some areas the final episode of marine retreat was rapid and relatively late c 12 ka bp leaving the ice sheet land based by 10 ka bp iii in response to the holocene thermal maximum htm the ice margin retreated behind its present day position by up to 80 km in the southwest 20 km in the south and 80 km in a small area of the northeast as a result of this retreat the modelled ice sheet reaches a minimum extent between 5 and 4 ka bp which corresponds to a deficit volume relative to present of 0 17 m ice equivalent sea level our results suggest that remaining discrepancies between the model and the observations are likely associated with non greenland ice load differences between modelled and observed present day ice elevation around the margin lateral variations in earth structure and or the pattern of ice margin retreat

arborescent lignophytes in the tournaisian vegetation of queensland australia palaeoecological and palaeogeographical significance abstract a middle tournaisian flora comprising several taxa of arborescent lignophytes is documented for the first time in australia it challenges earlier hypotheses considering that the early mississippian vegetation of australia was impoverished and dominated by small to medium sized arborescent lycopsids until the serpukhovian when climatic conditions became favorable to the thriving of the famous lignophyte dominated rhacopteris flora recorded in australia but also south america the present account is based on anatomically preserved fragments of trunks and branches from two localities of queensland in the broken river province and the burdekin basin three taxa are recognized dameria hueberi gen et sp nov the putative progymnosperm species protopitys buchiana goeppert 1850 and a taxon of uncertain affinities characterized by a pitus type of wood but which differs from the latter genus by anatomical traits relative to its primary body the possible occurrence of subtle growth rings in some of the woods from the burdekin basin and the conifer like traits of the dameria wood are interpreted as ecological clues suggesting that these trees may have inhabited drier settings than the wetland habitats generally inferred for the lycopsids this difference in habitats is suggested to explain the rarity of arborescent lignophytes compared to lycopsids in the australian record of plants of early mississippian age the three taxa reported in this paper represent the earliest record of arborescent lignophytes in australia after the global events that affected the vegetation at the devonian carboniferous boundary and the extinction of archaeopteris they show that the successional pattern of arborescent lignophytes around the devonian carboniferous boundary is comparable to that observed in western europe with the evidence of a diversification occurring as early as the middle tournaisian the palaeogeographic and stratigraphic distribution of protopitys and dameria indicates the occurrence of extensive floral exchanges between southern laurussia and north eastern gondwana in the late devonian to mississippian

devonian plants from colombia with discussion of their geological and palaeogeographical context plant fossils are described from the cuche formation eastern cordillera colombia in the area of floresta those identified as colpodexylon cf deatsii banks and cf archaeopteris sp suggest an earliest late devonian frasnian age for the formation these or similar taxa are also found in contemporaneous deposits in western venezuela and other elements of the venezuelan flora are found in a geographically intermediate locality all three devonian plant localities in the northwest of south america are within the colombian eastern cordillera and its northern extension the venezuelan perija range an area that has been integrated as a part of the so called eastern andean terrane or central andean province supposedly accreted to the autochthonous block of the guyana shield during the early jurassic or before although both invertebrates and plants from this terrane have strong affinities to north american and european assemblages and might be interpreted as implying a laurussian origin for the eastern andean terrane the evidence is not yet unequivocal with some authors postulating an in situ development of this province

the sedimentary record of carboniferous rivers continuing influence of land plant evolution on alluvial processes and palaeozoic ecosystems abstract evidence from modern rivers and the deep time geological record attests to the fundamental importance of plant life for the construction of physical habitats within fluvial environments data from an extensive literature review and original fieldwork demonstrates that many landforms and geomorphic features of modern river systems appear in the palaeozoic stratigraphic record once terrestrial vegetation had adopted certain evolutionary advances for example stable point bars are associated with the onset of rooted plants in the siluro devonian and avulsive and anabranching fluvial systems become common at the same time as extensive arborescent vegetation in the carboniferous in this paper we demonstrate a correlation between the diversification of physical fluvial environments and the expansion of terrestrial fauna and flora with an emphasis on the culmination of these trends within carboniferous alluvial systems many extrinsic factors have been considered as possible controls on the evolutionary timelines of terrestrialization for organisms however a fundamental prerequisite for achieving terrestrial biodiversity was the variety of physical habitats especially riparian systems available for newly evolved organisms in association with abundant lowland meandering systems the widespread appearance across carboniferous alluvial plains of fixed channel and anabranching reaches created further physical landforms for colonization and would have promoted increasingly complex hyporheic flow regimes furthermore the associated increase in arborescent vegetation and supply of large woody debris to inland and coastal rivers would have created a wealth of microhabitats for continental organisms we argue that the expanding extent and diversity of physical alluvial niches during the palaeozoic is an underappreciated driver of the terrestrialization of early continental life the study of the deep time fossil and stratigraphic record also illustrates that vegetation is a fundamental prerequisite for the creation of biogeomorphic alluvial landforms and physical habitats and microhabitats

evolution of drainage system morphology at a land terminating greenlandic outlet glacier 1 the influence of meltwater on the dynamics and geomorphic impact of the greenland ice sheet is strongly controlled by the morphology of the ice sheet s drainage system however this system and its evolution through the melt season remain poorly understood here we present the results of an intensive programme of dye tracing experiments undertaken along the lower 14 km of a land terminating greenlandic outlet glacier over a period of four months during the 2010 melt season these data are interpreted in conjunction with observations of proglacial discharge englacial water storage surface melt rates and ice velocity to produce a detailed picture of the changing hydrology of the glacier following the onset of melt in the spring inputs to the drainage system regularly exceed outputs causing the englacial water level to rise to the ice sheet surface during this time there is a rapid transition from distributed to channelized drainage in those parts of the drainage system closed by ice deformation over winter as the melt season progresses channel efficiency increases and englacial storage and ice velocity decrease high velocity events continue to be observed following the channelization of the drainage system however indicating that hydrological forcing of ice velocity occurs despite the existence of channels during periods when meltwater inputs exceed the capacity of the subglacial drainage system

a conifer dominated palynological assemblage from pennsylvanian late moscovian alluvial drylands in atlantic canada implications for the vegetation of tropical lowlands during glacial phases abstract new research suggests that pennsylvanian coal forests were commonly replaced by conifer dominated vegetation during seasonally dry glacial phases here we describe palynological assemblages from stacked sequences of the middle pennsylvanian late moscovian sydney mines formation of nova scotia canada which lends some support to this hypothesis one critical sample from a widespread redbed succession below the harbour coal is dominated by conifer pollen 55 together with abundant representatives of cordaitaleans other coniferopsids and rare pteridosperms ferns and lepidodendrids it differs markedly from 13 other samples obtained from coals their roof shale limestone and associated channel bodies which are dominated by lepidodendrids marattialean tree ferns cordaitaleans and or calamiteans the latter beds represent coastal wetlands and are attributed to late transgressive and highstand systems tracts whereas the conifer bearing sample represents a dryland alluvial plain and may be attributed to lowstand or earliest transgressive systems tracts three additional samples from grey shale below a sequence boundary late highstand and between a redbed succession and major coal seam early to mid transgressive deposits contain transitional palynofloras with a high proportion of herbaceous gleicheniaceous and sphenopteroid ferns herbaceous lycopsids and sphenophylls interspersed with cordaitaleans and or lepidodendrids the dominance of conifer pollen within the dryland components of well defined sequences which have been linked to relative sea level change promoted by gondwanan glaciation supports the view that pennsylvanian tropical biomes responded to the beat of glacial interglacial cycles

paleozoic vegetation and the siluro devonian rise of fluvial lateral accretion sets a long standing hypothesis links the increased prominence of meandering rivers in the middle paleozoic to the colonization of terrestrial environments by vegetation this hypothesis is tested using a data set of cambrian to devonian fluvial literature and field examination of key stratigraphic units according to some researchers cambrian to mid silurian river systems were braided in planform with a sharp increase in the abundance of meandering rivers during the silurian devonian although meandering systems were largely identified on the basis of thick mudstones and organized channel deposits the data set record of lateral accretion sets appears to be a robust proxy for the abundance of meandering river point bars lateral accretion is first recorded from pridolian lochkovian strata but is noted in nearly 40 of fluvial case studies by the famennian this trend matches the known record of rooted vegetation suggesting that vegetation progressively stabilized river banks and promoted single thread channels however the presence of precambrian and extraterrestrial meandering systems indicates that vegetation is not essential for meandering and the lack of evidence for cambrian to silurian ludlow point bars is surprising if originally present they may largely have been destroyed by extreme floods chute cut offs in coarse grained meandering systems and eolian activity

new precipitation and accumulation maps for greenland annual total precipitation and the annual accumulation on the greenland ice sheet are evaluated and presented in two maps the maps are based on accumulation measurements of 25 1 pits and cores obtained from the upper accumulation zone and precipitation measurements made at 35 meteorological stations in the coastal region to construct the accumulation map the annual precipitation was split into solid and liquid precipitation components annual total precipitation exceeding 2500 mm w e occurs on the southeastern tip of greenland while the minimum precipitation is estimated to occur on the northeastern slope of the ice sheet the mean annual precipitation for all of greenland is 340 mm w e the largest annual accumulation of about 1500 mm w e is found on the glaciers in the southeastern corner of greenland while the smallest accumulation is found on the northeastern slope of the ice sheet west of danmarkshavn the mean accumulation on the greenland ice sheet is estimated at 310 mm w e the regional difference in accumulation is examined with respect to the 850 hpa m bar level circulation the present surface topography is found to play an important role in determining regional accumulation on the ice sheet

subglacial till a physical framework for its properties and processes the continuum theory of mixtures provides a framework around which present knowledge of subglacial till can be organized the proposed framework is provisional in two senses the constitutive description of till will require improvement and not all potentially significant processes have been included till is treated as a three component mixture of water clasts coarse grained solids and fine grained matrix solids these components obey mass balance equations and their behavior is subject to constitutive relations that describe such processes as darcian water transport fine grained sediment transport consolidation shear deformation dilatancy and comminution five state variables uniquely determine the compressibility permeability shear strength and other physical properties numerical solutions of the state evolutions equations illustrate that the properties of till are highly responsive to changes in the subglacial environment

using fourier transform infrared spectroscopy to determine mineral phases in sediments abstract in paleoenvironmental studies the mineralogical composition of sediments is an important indicator in combination with other indicators they contribute to the understanding of changes in sediment sourcing as well as in weathering and depositional processes fourier transform infrared spectroscopy ftirs spectra contain information on mineralogical composition because each mineral has a unique absorption pattern in the mid ir range although easily obtained ftir spectra are often too complex to infer mineral concentrations directly in this study we use a calibration set of ca 200 sediment samples conventionally measured using x ray diffraction xrd in order to develop multivariate partial least squares pls regression models relating mineral contents to sediment spectra good correlations were obtained for the most common minerals e g quartz k feldspar illite plagioclase smectite calcite correlation coefficients ranged from 0 85 to 0 92 coefficients for the validation varied from 0 64 to 0 80 the number of latent variables pls regression components in the models ranged between 3 and 7 and the range of variation of the rmsecv gradient was from 15 28 to 5 7