permafrost tectonics and past and future regional climate change yukon and adjacent northwest territories late tertiary changes in the general circulation of the atmosphere regionally enhanced by uplift of the wrangell saint elias and coast mountains were sufficient to promote permafrost development in the western arctic permafrost developed in yukon territory and adjacent northwest territories during early pleistocene glacial periods after continued tectonic activity led to further modification of regional climate but degraded in the interglacials permafrost has been present in northern parts of the region since the illinoian glaciation but most ground ice in central yukon formed in the late wisconsinan the present interglacial is the only one with widespread evidence of permafrost which is maintained in the valleys of central and southern yukon by the saint elias mountains blocking continental penetration of maritime air from the gulf of alaska this reduces snow depth in winter while cold air drainage in the dissected terrain of the yukon plateaus enhances the near surface inversion leading t

use of temperature logs in coal seam gas reservoirs application to the sydney basin australia this study examines the relationship between borehole temperature logs and gas distribution in coal seams both spatially and with depth temperature logs are often utilized in hydrogeology to monitor groundwater flow which can introduce methanogenic consortia into coal seams resulting in the generation and accumulation of coal seam gases areas of hydraulic connectivity characterized by open cleats and fractures provide a pathway for the meteoric influx whereas tight mineralized sections of strata prohibit vertical flow and have the potential to trap coal seam gases or to limit the influx of methanogens and the generation of secondary biogenic methane the combination of these concepts raises the possibility of utilizing temperature logs for mapping coal seam gas distributions and assisting exploration activities wireline temperature logs are inexpensive to obtain as part of any exploration production or monitoring program but provide information pertaining to flow regimes and in situ geological environments a case study is presented from the sydney basin of australia to demonstrate the types of analyses and interpretations relating to coal seam gas distribution that may be gleaned from temperature log datasets

milankovitch forcing of fluctuations in the level of tropical lakes from 18 to 0 kyr bp an atmospheric general circulation model has been used to simulate the climates of january and july at 3 000 yr intervals from 15 kyr bp onwards the model simulates a strengthened monsoon circulation and increased precipitation in the northern hemisphere tropics culminating at 9 6 kyr bp the computed hydrological budgets were used to estimate the area of closed lakes between 8 9 and 26 6 n giving with minor exceptions results in good agreement with geological evidence

variations in permafrost thickness in response to changes in paleoclimate solutions to the stefan problem for the motion of the base of ice bearing permafrost in response to changes in paleoclimate were obtained using perturbation finite difference and finite element methods paleotemperature models were used to investigate the thickness response to compare solution methods to determine the current state of the permafrost and to determine constraints on the models the perturbation and finite difference methods used the approximation of linear temperature profiles while the finite element method did not there was a transient thickness response of about 41 kyr implying that paleotemperature records of greater length are needed for models and that the permafrost loses its memory of past conditions for much longer times faster thawing rates slower freezing rates and greater variations in thickness were found for the perturbation and finite difference solutions compared to the finite element solution these results appear to be caused by the simplifying assumptions in the former solutions a lag about 20 kyr exists between changes in surface temperature and thickness response and a small thermal offset is apparent in the finite element solution small asymmetries exist in the freezing and thawing rates and the thickness response paleotemperature models based on ice cores predict current permafrost thicknesses that are too large models with the long term mean surface temperature of permafrost within a few degrees of the current value of 11 c and with the last glacial period temperatures no more than 6 8 c lower are compatible with current prudhoe bay conditions these include models developed for east siberia from isotopic profiles in deep sea sediments and for barrow alaska modified for prudhoe bay these models predict that the permafrost thickness at prudhoe bay varied by about 10 or less 60 m over the last glacial cycle freezing and thawing rates were less than 6 mm yr 1 at present this permafrost should be near its long term equilibrium thickness and thawing at 1 mm yr 1

late cenozoic arctic ocean sea ice and terrestrial paleoclimate sea otter remains found in deposits of two marine transgressions bigbendian and fishcreekian of the alaskan arctic coastal plain which occurred between 2 4 and 3 ma suggest that during these two events the southern limit of seasonal sea ice was at least 1600 km farther north than at present in alaskan waters perennial sea ice must have been severely restricted or absent and winters were warmer than at present during these two sea level highstands paleomagnetic faunal and palynological data indicate that the later transgression fishcreekian occurred during the early part of the matuyama reversed polarity chron amino acid diagenesis in fossil mollusks suggests that since the later transgression the effective diagenetic temperature edt in the deposits has been about 16 c which is about 7 c colder than modern values and slightly colder than the edt calculated for the past 125 ka such a low edt suggests that permafrost and perennial sea ice have been present nearly continuously since this transgression permafrost probably was absent however during the earlier bigbendian transgression permafrost and extensive perennial sea ice may have been initiated during the late stages of climatic cooling that spanned the gauss normal matuyama reversed polarity chron boundary and led into the first major late cenozoic glaciation of the northern hemisphere

orbital forcing in a stochastic resonance model of the late pleistocene climatic variations applying a number of simplifying assumptions we have used a zero dimensional energy balance climate model ebm of the budyko sellers type to investigate the degree to which the climatic variability of the late pleistocene can be explained by the mechanism of stochastic resonance as a logical extension of an earlier version of this model we have included a more complete representation for the orbital forcings to show that a reasonably good agreement with the paleoclimatic record can be obtained this zerodimensional ebm is appealing because of its simplicity and its ability to reproduce some of the most striking qualitative features of the observed climatic variability with a very limited number of parameters several of which can be derived from either the observations or general circulation model gcm simulations of ice age conditions

thermal structure of the anadarko basin the anadarko basin of oklahoma is a two stage paleozoic cratonic basin with as much as 12 km 7 5 mi or more of sedimentary fill we present a present day thermal model of the basin based on lithologic analysis at 3 m 10 ft intervals in 63 wells heat flow measurements at seven sites and in situ thermal conductivity calibration of the sediment section at two sites we do not use bht bottom hole temperature information in the process but we do at the end of the process compare the independently predicted temperatures to bht information the in situ calibration of thermal conductivity was accomplished using detailed temperature logs and represents a new practical application for evaluating basin thermal characteristics shale exerts the most control on the temperature distribution because it is the most abundant lithology and has the lowest thermal conductivity shale comprises 47 by volume of rock in the basin and represents 75 of total thermal resistance directly related to temperature gradient therefore shale dominates the thermal structure of the basin thus the problems in sampling and in characterizing the in situ thermal conductivity of shale from laboratory measurements represent a major limitation in basin thermal analysis we use the in situ calibration approach as a way to address the difficulty the temperatures calculated do not mimic the structure of the sediments i e the hottest area on a given age horizon in the lower paleozoic is not in the most deeply buried part of the anadarko basin the combination of decreasing heat flow toward the wichita mountains and the facies changes in the pennsylvanian units from marine shale low thermal conductivity in the basin to the granite wash high thermal conductivity toward the uplift results in the highest temperatures being displaced about 50 km 31 mi northward into the basin the pattern of vitrinite reflectance in the woodford shale is virtually identical to the present day reconstructed temperature pattern therefore we conclude that the thermal pattern is and has been dominated by conductive heat transport

the use of fourier descriptors in the classification of particle shape a new quantitative method for characterizing quartz grain shape is presented the method employs a harmonic analysis based upon fourier descriptors which is a distinct variation of the traditional and widely used fourier series quartz grain images from a scanning electron microscope were frame grabbed and converted to a digitized grey level image the image processing techniques of enhancement segmentation and boundary tracking were applied to remove all features except the image boundary this boundary was sampled at uniform intervals of are length and represented mathematically on the complex plane in this way problems associated with the location of particle centroid and re entrant values were avoided the resulting data was standardized relative to scale rotation and starting position hence the discrete fourier transform was applied using modern fast fourier transform techniques and the modulus of the resulting harmonic amplitude used to characterize the grain shape the technique was applied to a sample of 0 5 m quartz grains from three distinct populations desert quartz beach grains fire island new york and brazilian crushed quartz whilst plots of average amplitude vs harmonic number for each population appeared similar discriminant analysis applied to each grain sample distinguished characteristic grain shape with an excellent degree of success the problems of location of the centroid and re entrant values were eliminated this allowed the technique to be applied to a much wider group of irregularly shaped sedimentary particles such as loess

coupling of vampers within iloveclim experiments during the lgm and last deglaciation the vampers vrije universiteit amsterdam permafrost snow model has been coupled within iloveclim an earth system model this advancement allows the thermal coupling between permafrost and climate to be examined from a millennial timescale using equilibrium experiments during the last glacial maximum 21 ka and transient experiments for the subsequent deglaciation period 21 11 ka it appears that the role of permafrost during both stable and transitional glacial interglacial climate periods is seasonal resulting in cooler summers and warmer winters by approximately 2 c maximum this conclusion reinforces the importance of including the active layer within climate models in addition the coupling of vampers also yields a simulation of transient permafrost conditions not only for estimating areal changes in extent but also total permafrost gain loss

characteristics of the active layer and shallow subsea permafrost a seasonal active layer associated with subsea permafrost was found in the sediments near the seabed of the beaufort sea near prudhoe bay alaska the active layer existed where sea ice was frozen to the seabed and also in shallow water where the under ice seawater salinities exceeded open water values initial freezing of the active layer was about coincident with the formation of new sea ice within 400 m of shore it appeared to freeze to an underlying ice bonded permafrost table ibpt farther offshore where this table is deeper the active layer thickness decreased with distance offshore and the layer was underlain by a talik relative ice contents in the active layer generally decreased with distance offshore were a few hundred parts per thousand ppt in the fall and ranged to more than 800 ppt in the spring seasonal changes in the bulk soil solution salinity showed that the partially frozen active layer redistributed salts during freezing was infiltrated by concentrated brines derived from the growth of sea ice and affected the timing of brine drainage to lower depths in the sediments these brines provide the salts required for thawing the underlying subsea permafrost in the presence of negative sediment temperatures the region near shore had a partially frozen transition layer just above the ibpt where the ice content increased and the brine content decreased with depth temperature at the ibpt is nearly constant beyond about 412 m to at least 3 5 km offshore at about 2 41 c implying relatively constant soil solution salinities there

a full scale field experiment 1978 1995 on the growth of permafrost by means of lake drainage western arctic coast a discussion of the method and some results on 13 august 1978 a lake on the western arctic coast was artificially drained in a multidisciplinary experiment on the growth of permafrost on the unfrozen bottom of the drained lake a bowl shaped talik unfrozen basin with a maximum depth of about 32 m underlay the lake bottom prior to drainage in the first winter after drainage downward freezing started on the exposed lake bottom and upward freezing from permafrost beneath the talik after drainage the soft lake bottom sediments hardened from water loss and freeze thaw consolidation gradual thinning of the active layer at many sites was accompanied by ground uplift and the growth of aggradational ice downward and upward freezing has resulted in solute rejection freezing point depressions pore water expulsion from the freezing of the saturated lake bottom sands and convective heat transfer from groundwater flow in an open hydrologie system the increasingly saline intrapermafrost groundwater flowing at an increasingly negative temperature be

the evaluation of macroscopic and microscopic textures of sand grains using elliptic fourier and principal component analysis implications for the discrimination of sedimentary environments a method that integrates elliptic fourier and principal component analysis is a new development in the analysis of the shapes of sand grains however conventional elliptic fourier and principal component analysis based on the variance covariance matrix of the elliptic fourier results can determine only the form of sand grains and fails to quantify fine scale boundary smoothness of grains in this study sand grains from glacial fluvial foreshore and aeolian environments were analysed using both elliptic fourier and principal component analysis and an extension of elliptic fourier and principal component analysis based on the correlation matrix to extract information on grain form macroscopic and grain boundary smoothness microscopic separately conventional elliptic fourier and principal component analysis based on the variance covariance matrix produces macroscopic particle shape descriptors such as the elongation index and bump indices these indices indicate that sand grains exposed to subaqueous transportation fluvial and foreshore have forms that are more elongated than those exposed to subaerial transportation aeolian dunes however elliptic fourier and principal component analysis based on the correlation matrix is in addition able to extract microscopic particle features which can be interpreted in terms of a boundary smoothness index the boundary smoothness index indicates that the surfaces of glacial grains are the most rugged whereas the surfaces of aeolian grains are the smoothest on bivariate plots of the boundary smoothness and elongation indices samples from fluvial foreshore aeolian and glacial environments cluster in discrete regions in addition the analysis reveals that glacial grains are exposed to different morphological maturation pathways than those from fluvial foreshore and aeolian environments

evaluation of image analysis methods used for quantification of particle angularity angularity is an important parameter in the characterization of particle morphology that is used to interpret the transport history of particles in sedimentary deposits in the past visual classification using silhouette charts was widely used to determine particle angularity but this approach is subjective and time consuming with advances in modern image analysis techniques and low cost software packages it is possible to rapidly quantify particle angularity more objectively than using visual classification methods this study re examines the performance of three existing image analysis methods and one new image analysis procedure applied to six rock and sediment samples that were visually different in angularity to facilitate comparison between the angularity results measurements were reduced to rankings for each aggregate sample these results show that the four image analysis methods rank the angularity of the samples differently and that none rank the mean angularity index in the same order as the angularity ranking using visual classification therefore further research is needed to develop an image analysis method that can quantify the angularity of sedimentary particles more precisely

massive ice of the tuktoyaktuk area western arctic coast canada the extensive coastal exposure of massive underground ice at peninsula point southwest of tuktoyaktuk northwest territories is believed to be intrasedimental ice the ice grew beneath a frozen d

estimating 3d variation in active layer thickness beneath arctic streams using ground penetrating radar we acquired three dimensional 3d ground penetrating radar gpr data across three stream sites on the north slope ak in august 2005 to investigate the dependence of thaw depth on channel morphology data were migrated with mean velocities derived from multi offset gpr profiles collected across a stream section within each of the 3d survey areas gpr data interpretations from the alluvial lined stream site illustrate greater thaw depths beneath riffle and gravel bar features relative to neighboring pool features the peat lined stream sites indicate the opposite greater thaw depths beneath pools and shallower thaw beneath the connecting runs results provide detailed 3d geometry of active layer thaw depths that can support hydrological studies seeking to quantify transport and biogeochemical processes that occur within the hyporheic zone

equivalence of abrupt grain size transitions in alluvial rivers and eolian sand seas a hypothesis gravel bed rivers organize to a threshold state in which the fluid stress during dominant flow conditions slightly exceeds the critical value these channels change fairly abruptly to sand dominated beds facilitated by a paucity of sediment in the range of 1 10 mm eolian sediments are also bimodal sand seas often transition rapidly downwind to silty loess deposits in this paper we hypothesize that both transitions result from the same processes 1 production of fine sediment by spallation from saltation abrasion of coarse grains and 2 segregation of fine and coarse modes by suspension and saltation transport respectively we demonstrate that gravel rivers and eolian dune fields are dynamically equivalent in terms of threshold transport shields stress and collision dynamics stokes number while abrasion may not be the dominant cause of downstream fining of fluvial gravels the reduction of collision efficiency with grain diameter sets a lower limit on gravel size leading to a grain size gap the collision efficiency hypothesis potentially reconciles conflicting studies on the importance of sorting and lithology in downstream fining shields and stokes similitude in rivers and deserts may be used to design appropriately scaled experiments to test and refine our hypothesis

aeolian silt transport processes as fingerprinted by dynamic image analysis of the grain size and shape characteristics of chinese loess and red clay deposits abstract this study applied dynamic image analysis dia sympatec qicpic to characterize the grain size and shape of chinese aeolian sediments in order to fingerprint their transportation processes this is the first time this technique has been applied to late neogene and quaternary silt particles 2 63 m from the chinese loess plateau clp we selected four well studied quaternary loess palaeosol sequences along a north south transect across the clp and compared their grain size distribution obtained by dia with that yielded by laser diffraction particle size analysis ld fritsch analysette 22 and sympatec helos kr this comparison demonstrated that dia is successfully able to differentiate loess units from palaeosols and to characterize clearly spatiotemporal variations in the grain size records of loess palaeosol sequences formed during the last two glacial and interglacial periods this is consistent with grain size results obtained using ld dia is also able to characterize spatial variations in the more fine grained aeolian red clay deposits underlying the quaternary loess and allows the quantification of the fluvial contribution to red clay sequences dia of the characteristics of grain shapes in loess palaeosol sequences and red clay deposits revealed a systematic pattern whereby the aspect ratio decreased with increasing grain size indicating that systematic shape sorting occurred during the aeolian transportation of these dust particles it could be inferred from our study that particles in a certain grain size range correspond to a specific aspect ratio range and may in turn be aerodynamically distinguishable from each other and further correlated with the wind velocity strength also evident from analysis of our dia data was a subtle but systematic downwind decrease in the aspect ratio of the particles in the loess units this observation suggests that elongated and or flat particles with a low aspect ratio were transported further downwind than more symmetrically shaped particles with a high aspect ratio this study indicates that dia of grain size and shape characteristics can be an additional powerful tool for identifying grain size and shape sorting trends determining the dominant mode of transport and reconstructing transport pathways of silt sized aeolian sediments

hydrothermics in the wyoming overthrust belt a thermal study was made across a 25 km 15 5 mi traverse of the overthrust belt in southwestern wyoming estimates of relative heat flow from temperature measurements made in shallow 30 m or 98 ft boreholes reveal a systematic variation of at least 400 mw m2 10 cal cm2 sec magnitude across the study area the cause of this variation is believed to be forced convection of heat by moving ground water two relative heat flow highs coincide with zones where structurally related faults possibly providing avenues for vertical water flow project to the surface between those two zones in a topographically elevated area low and predominately negative temperature gradients were observed in opposite seasons these shallow negative gradients are believed to exist seasonally in quasisteady state and could be indicative of a broad zone of ground water recharge the association of two relative heat flow highs with the two major deep geologic structures implies either a direct vertical communication of deep and shallow ground water or a coupling of deeper and shallower ground water systems the two structures studied are hydrocarbon bearing and associated with whitney canyon and ryckman creek fields the thermal measurements support the possibility that ascending waters have influenced the hydrocarbon migration and accumulation in these structures such measurements may be useful in delineating and understanding similar features in other areas

thermal analysis of the southern powder river basin wyoming temperature and geologic data from over 3000 oil and gas wells within a 180 km 30 km area that transect across the southern powder river basin in wyoming u s a were used to determine the present thermal regime of the basin three dimensional temperature fields within the transect based on corrected bottomhole temperatures bhts and other geologic information were assessed using 1 a laterally constant temperature gradient model in conjunction with an l1 norm inversion method and 2 a laterally variable temperature gradient model in conjunction with a stochastic inversion technique the mean geothermal gradient in the transect is 29 c km but important lateral variations in the geothermal gradient exist the average heat flow for the southern powder river basin is 52mw m2 with systematic variations between 40mw m2 and 60mw m2 along the transect extremely high local heat flow values up to 225mw m2 in the vicinity of the teapot dome and the salt creek anticline and low heat flow of 25mw m2 occ

fourier grain shape analysis of antarctic marine core the relative influence of provenance and glacial activity on grain shape abstract grain shape is useful as a depositional environmental diagenetic and provenance proxy here we conduct the first study of down core grain shape variation in antarctica this study further examines the utility of grain shape as a depositional proxy namely of glacial influence in the james ross basin and joinville plateau of the antarctic peninsula from the eocene to the present fourier grain shape analysis was used to quantify the grain shape of 31 samples spanning the glacial history of the antarctic peninsula ice sheet a total of 6 442 quartz grain peripheries were digitized and described through the twenty first fourier harmonic sediment provenance has a greater influence on grain roughness than glacial activity in the study area however provided a similar sedimentary source secondary changes in roughness correlate with changes in the extent of the antarctic peninsula ice sheet since the late oligocene grain roughness increased with increased glacial influence during the middle miocene after an early pliocene warm period and just above a pliocene regional glacial unconformity conversely grain roughness decreased with less glacial influence during the late oligocene and during an early pliocene warm period this study further illustrates the usefulness of grain shape in distinguishing sediment provenance and environmental conditions in antarctic settings

numerical simulation of permafrost thermal regime and talik development under shallow thaw lakes on the alaskan arctic coastal plain 1 thaw lakes are one of the most obvious manifestations of the hydrological system at work in the tundra regions of the alaskan arctic coastal plain but the extent of the role of thaw lakes in arctic land atmosphere interactions and feedback has yet to be fully understood this study uses a two dimensional heat transfer model with phase change under a cylindrical coordinate system to simulate the long term influence of shallow thaw lakes on the thermal regime of permafrost and talik development on the alaskan arctic coastal plain on the basis of previous studies of permafrost and thaw lakes at barrow alaska a series of simulation cases was conducted using different combinations of long term mean lake bottom temperature and lake depth the simulated results indicate that shallow thaw lakes are a significant heat source to permafrost and talik for a thaw lake with a long term mean lake bottom temperature of greater than 0 0 c a talik forms under the thaw lake the maximum talik thicknesses vertical distance from the ground surface to the permafrost surface are 28 0 43 0 and 53 2 m 3000 years after the formation of a shallow thaw lake with long term mean lake bottom temperatures of 1 0 2 0 and 3 0 c respectively talik development rate is very high in the first several years after a thaw lake formation and decreases gradually with time no talik forms below a thaw lake with a long term mean lake bottom temperature equal to or lower than 0 0 c but the temperature of permafrost below the thaw lake increases with time three thousand years after the formation of a thaw lake with a long term mean lake bottom temperature of greater than or equal to 2 0 c ground temperature increases of more than 0 5 c occur as far as 300 m from the lake shore and as deep as about 400 m below the ground surface it is concluded that variation of long term mean lake bottom temperature has a significant influence on permafrost thermal regime and talik development continued monitoring for thaw lake bottom temperature and ground temperature under shallow thaw lakes is needed to further improve the simulation

erosion profiles due to particles entrained by wind application of an eolian sediment transport model erosion by impacts of particles entrained in the wind scales with the kinetic energy of impacting grains a recent model of eolian sediment transport permits calculation of expected erosion patterns in objects of simple geometry the modeling of vertical erosion profiles in turn provides an exacting test of the transport model realistic distributions of liftoff velocities for saltating grains give rise to kinetic energy flux profiles characterized by a strong maximum as much as 1 4 m above the bed during strong winds kinetic energy flux due to suspended grains also peaks above the bed the height and strength of the maxima depend very strongly on the grain size distribution as grain size diminishes increased particle deflection by the air flow around an obstacle reduces delivery of kinetic energy to the surface for both saltating and suspended grains kinetic energy flux scales with the fifth power of the wind shear velocity erosion profiles in man made obstacles are well modeled with only slight modification of the saltation model to account for the relatively high elasticity of actual deflationary surfaces lending considerable support for the model the modeling also elucidates several aspects of ventifaction as small ventifacts 1 2 m in diameter and the lower portions of larger ones are predominantly eroded by saltating grains upwind surface irregularities are quickly damped leading to facets that dip upwind and sharply truncate lee surfaces sandblasting by suspended grains dominates along the upper portions of large ventifacts where grain paths are partially deflected by the obstacle and may lead to radially symmetrical flutes and grooves

the last pluvial climatic episodes in the deserts of southwestern north america long term variations in the effective moisture of deserts are linked both to glacial interglacial climatic cycles and through the milankovitch theory to orbitally induced changes in solar radiation intensity1 4 for southwestern north america comparison of palaeobotanical data with model predictions of palaeoclimate reveals two distinct pluvial regimes during the late wisconsin and early holocene 23 8 kyr bp southward displacement of the aleutian low pressure centre and strengthened westerlies from 40 to 30 n were important features of the full glacial 18 kyr bp pluvial maximum increased cyclonic storms and weakened monsoons led to a winter precipitation regime a feature seen both in the fossil record5 6 and climate models7 8 dominantly zonal flow during this period contrasts with the latest wisconsin and early holocene 12 8 kyr bp when meridional circulation transported maritime tropical air into the desert interior we now show that plant macrofossil assemblages from packrat neotoma spp middens9 in the mojave desert provide evidence for increased temperatures and summer rainfall during this period10 12 the anomalously late persistence to 8 kyr bp of woodland in low latitude low elevation deserts of the south west13 is attributed to enhanced monsoonal circulation3

assessing automated image analysis of sand grain shape to identify sedimentary facies gran dolina archaeological site burgos spain abstract gran dolina is a cave sierra de atapuerca spain infilled by a 25 m thick sedimentary record divided into 12 lithostratigraphic units that have been separated into 19 sedimentary facies containing early and middle pleistocene hominin remains in this paper an automated image analysis method has been used to study the shape of the sedimentary particles since particle shape is interpreted as the result of sedimentary transport and sediment source this study can provide valuable data about the sedimentological mechanism of sequence formation the shape of the sand fraction in 73 samples from gran dolina site and sierra de atapuerca was analyzed using the malvern morphologi g3 an advanced particle characterization tool in this first complete test we used this method to the published sequence of gran dolina defined previously through field work observations and geochemical and textural analysis the results indicate that this image analysis method allows differentiation of the sedimentary facies providing objective tools to identify weathered layers and measure the textural maturity of the sediments channel facies have the highest values of circularity and convexity showing the highest textural maturity of particles on the other hand terra rossa and debris flow samples show similar values with the lowest particle maturity

on the shapes of natural sand grains 1 digitized outlines of sand grains from a dozen locations including deserts beaches and seabeds have been acquired using an optical microscope linked to a desktop computer fourier analysis of the outlines returns the normalized power spectrum of each sample averaged over several hundred grains regardless of the origin of the samples these power spectra all exhibit essentially the same inverse power law dependence on the harmonic number n varying as n 10 3 for 2 n 20 this universal spectrum provides the basis of a numerical technique for synthesizing the irregular outline of a sand grain the outline is represented as a random pulse train in which identically shaped microasperities with normally distributed amplitudes are randomly superimposed on the perimeter of a circle by identifying the spectrum of the microasperities with the observed inverse power law dependence derived from the optical images the synthetic outlines are constrained to show the same statistical properties as the outlines of the real grains the synthesized and real outlines are qualitatively similar in that visually it is difficult to distinguish between them the new numerical technique for synthesizing irregular outlines of sand grains has potential for investigating the random packing of realistically rough particles through computer simulation

deriving geothermal parameters from bottom hole temperatures in wyoming this article describes a method to determine geothermal gradients and formation temperatures using bottom hole temperatures bhts from wireline log headers and then tests the method by applying it to analyses from more traditional sources bottom hole temperatures depths and times since circulation ended were collected from at least one well in every township that had been drilled for petroleum exploration in the state of wyoming using approximately 3500 bhts collected from almost 2000 wells equations were developed for average formation temperatures and geothermal gradients across the state a method of correcting the average data to true formation temperatures in each individual well was also developed the geothermal temperatures so derived very closely match temperatures from production bhts that are the normal industry standard for formation temperatures and suggest that bht information is much more accurate than commonly thought the use of bht measurements to compute temperature gradients was also developed the effects upon formation temperatures of common data recording errors of vertical circulation of groundwater especially above 1700 m 5577 ft depth and of lateral groundwater circulation through deep aquifers are documented the methods developed offer promising avenues for research in the areas of hydrogeology geothermal exploration determining formation temperatures and heat flow

numerical simulation of permafrost growth and decay a series of numerical models on permafrost growth and decay are presented with special emphasis on the climatic conditions in western europe during the last glacial stage numerical modelling of growth and decay of the active layer suggests penetration depths in the range between 0 6 to 1 4 m permafrost is estimated to have grown depending on the sediment type to a thickness of 90 m to 140 m in northern germany and the netherlands within 10 000 y during the peak period of the last glacial stage permafrost continued to exist at depth for about 2000 y after the climatic improvement following the younger dryas permafrost growth under rivers and lakes is shown to be unlikely under the climatic conditions of the last glacial stage in northern germany a time period of 10 000 to 42 000 years and a massive climatic excursion of the order of 11 c is required to remove the thick permafrost layers in siberia and alaska of today 1998 john wiley sons ltd

thermal simulation of subsea saline permafrost thermal analyses of the response of offshore permafrost to emergence and submergence have traditionally employed simple closed form solutions where phase change is confined to a discrete freezing temperature these have led to rather rapid rates of return to thermal equilibrium which have proved difficult to explain in the light of recent deep temperature measurements in offshore permafrost profiles this paper reviews the need for an appropriate unfrozen water content relationship for a saline frozen soil and describes some simulations of long term thermal response in offshore permafrost using the author s geothermal simulator simulations of submergence assumed an initial permafrost thickness of 600 m and a mean soil surface temperature of 9 0 c the salinity was assumed constant at 30 the initial temperature profile was linear varying between 9 0 c and a freezing point of 1 8 c at the bottom of ice bonded permafrost the temperature of the ground surface was assumed to have changed to 0 8

subsea ice bearing permafrost on the u s beaufort margin 1 minimum seaward extent defined from multichannel seismic reflection data subsea ice bearing permafrost ibpf and associated gas hydrate in the arctic have been subject to a warming climate and saline intrusion since the last transgression at the end of the pleistocene the consequent degradation of ibpf is potentially associated with significant degassing of dissociating gas hydrate deposits previous studies interpreted the distribution of subsea permafrost on the us beaufort continental shelf based on geographically sparse datasets and modeling of expected thermal history the most cited work projects subsea permafrost to the shelf edge 100 m isobath this study uses a compilation of stacking velocity analyses from 100 000 line km of industry collected multichannel seismic reflection data acquired over 57 000 km2 of the us beaufort shelf to delineate continuous subsea ibpf gridded average velocities of the uppermost 750 ms two way travel time range from 1475 to 3110 m s 1 the monotonic cross shore pattern in velocity distribution suggests that the seaward extent of continuous ibpf is within 37 km of the modern shoreline at water depths 25 m these interpretations corroborate recent beaufort seismic refraction studies and provide the best margin scale evidence that continuous subsea ibpf does not currently extend to the northern limits of the continental shelf this article is protected by copyright all rights reserved

vostok ice core a continuous isotope temperature record over the last climatic cycle 160 000 years a continuous deuterium profile along the 160 000 year vostok ice core antarctica is interpreted in terms of atmospheric temperature changes this climatic record is the awaited terrestrial complement of the deep sea records supporting the existence of a relation between the pleistocene climate and orbital forcing

how round is round a new approach to the topic roundness by fourier grain shape analysis numerous methods for roundness measurement have been developed none however has been generally accepted because of conceptual and practical deficiencies modern image processing and fourier grain shape analysis have eliminated the practical shortcomings but the conceptual ones remained single higher harmonics of the fourier series for example fail to serve as reliable equivalents for roundness evaluation the concept outlined in this paper recognizes three criteria for the evaluation of roundness 1 all curvatures convex as well as concave or plane elements must be considered 2 the positions of morphological elements are significant because salient parts of a particle are more easily abraded than protected ones consequently the curvatures have to be weighted by their relative position on the particle 3 positions and curvatures of morphological elements have to be compared with the particle s ultimate abraded shape which is assumed to be an ellipsoid the ellipsoid reflects the aspect of form or sphericity the distinction between sphericity and roundness is retained because there is no evidence that sphericity changes significantly during transport the measurement is based on the outline of a particle s maximum projection plane which is transformed to a fourier series roundness data are derived from the complete amplitude spectrum the aspect of sphericity is eliminated by subtracting the amplitude spectrum of the best approximating ellipse from the spectrum of the empirical shape the residual amplitudes are normalized and summed in a final step the resulting values are rescaled this guarantees reasonable boundaries and a normal distribution of roundness values the procedure is automated and its efficiency permits the calculation of large samples tests on fluvial and coastal gravel populations demonstrate that the method is sensitive to abrasional wear during all stages of roundness

formation history and physical properties of sediments from the mount elbert gas hydrate stratigraphic test well alaska north slope abstract the synthesis of available geological information and surface temperature evolution in the alaska north slope region suggests that biogenic and deeper thermogenic gases migrated through fault networks and preferentially invaded coarse grained layers that have relatively high hydraulic conductivity and low gas entry pressures hydrate started forming before the beginning of the permafrost eventually the permafrost deepened and any remaining free water froze so that ice and hydrate may coexist at some elevations the single tested specimen depth 620 47 620 62 m from the d unit consists of uncemented quartzitic fine sand with a high fraction of fines 56 by mass finer than sieve 200 the as received specimen shows no evidence of gas present the surface texture of sediment grains is compatible with a fluvial deltaic sedimentation environment and shows no signs of glacial entrainment tests conducted on sediments with and without thf hydrates show that effective stress porosity and hydrate saturation are the major controls on the mechanical and geophysical properties previously derived relationships between these variables and mechanical geophysical parameters properly fit the measurements gathered with mount elbert specimens at different hydrate saturations and effective stress levels we show that these measurements can be combined with index properties and empirical geomechanical relationships to estimate engineering design parameters volumetric strains measured during hydrate dissociation vanish at 2 4 mpa therefore minimal volumetric strains are anticipated during gas production at the mount elbert well however volume changes could increase if extensive grain crushing takes place during depressurization driven production strategies if the sediment has unexpectedly high in situ porosity associated to the formation history or if fines migration and clogging cause a situation of sustained sand production

modeling study of talik freeze up and permafrost response under drained thaw lakes on the alaskan arctic coastal plain 1 numerical simulations were conducted to investigate the long term impact of thaw lake drainage on the thermal regime of ground under and around drained thaw lakes on the alaskan arctic coastal plain the numerical model used in this study is a two dimensional unsteady finite element model for heat transfer with phase change under a cylindrical coordinate system the initial conditions are the simulated ground thermal regime and talik thickness data at year 3000 under a thaw lake with long term mean lake bottom temperatures of 1 0 2 0 and 3 0 c near barrow alaska the simulated results indicate that lake drainage leads to a rapid freeze up of talik and a substantial decrease in permafrost temperatures under the former lake bottom the initial ground temperature conditions have significant influence not only on the talik freeze up time but also on the permafrost temperature decrease processes after thaw lake drainage taliks with thicknesses of 28 43 and 53 m under the lake will freeze up completely by 40 106 and 157 years and the corresponding ratios of upward and downward freeze up depths for the three simulation cases are 1 8 0 1 7 6 and 1 6 1 respectively after completion of talik freeze up permafrost temperatures still decreased with time and gradually reached a relatively stable value depending on the initial ground temperature and the distance to the former lake bottom

pollen studies in the junin area central peruvian andes laguna junin is a large lake 675 km long but only 4 m deep located in the grass covered altiplano at an altitude of 4 100 m northeast of lima pollen analysis of a 30 m core indicates that from about 12 000 yr ago until some time after 3 000 yr ago about 30 of the pollen was carried in by easterly winds from the east andean forests which today are at least 600 m lower in elevation contemporaneous pollen deposition in lakes on moraines of the last glaciation west of the junin plain was dominated by local grassland types and had little contribution from this easterly source at some time after 3 000 yr ago perhaps about 1 200 yr ago the pollen influx to laguna junin from this distant forest source greatly diminished perhaps because of deforestation by increased human populations between about 12 000 and 24 000 yr ago in the junin core the sparse pollen concentration was dominated by grassland types supplemented by polylepis acaena alnus and compositae blown in from the sub puna shrublands that may have occupied much of the east andean slopes in place of the humid forest that occurs there today the silty sediment in this section of the core is interpreted as outwash from piedmont glaciers that invaded the plain especially from the cordillera to the west these glaciers left a distinctive pattern of moraines and outwash fans which served to dam tine lake basin an unconformity in the sediment covers the time from about 24 000 to 39 000 yr ago when the lake was probably dry before this time the silty sediment and the dominance of grassland and shrubland pollen types indicates an earlier interval of glaciation recorded on the landscape by an older set of moraines and outwash fans which initially dammed the lake basin

significance of past and recent heat flow and radioactivity studies in the southern rocky mountains region as reported in the geological society of america bulletin of 1950 francis birch s innovative heat flow research in the colorado front range introduced frequently used terrain correction and thermal conductivity measurement methods that report also presented the first empirical evidence for a positive correlation between above normal flux and radioactive roots in an isostatically compensated mountain area with a thick crust an observation that strongly influenced continental heat flow studies for the next 18 years birch s front range study clearly showed that reliable continental heat flow research requires knowledge of bedrock radioactivity this concept reached an unprecedented level of acceptance in 1968 when linear relations between heat flow and radiogenic heat production were discovered for three contrasting provinces in the united states subsequently such lines have been central to virtually all heat flow and radioactivity research on land heat flow q data for 139 boreholes provide new detail on thermal regimes in the southern rocky mountains and bordering areas as do radiogenic heat production a data for 60 locales interpretations also emphasize reduced and residual heat flow values reduced values correspond to the intercepts of regional q a lines whereas a residual value is the flux at a locale after the probable effect of near surface heat production has been subtracted the observed q a lines demonstrate that the front range and other easterly frontal ranges of the southern rocky mountains in colorado and northern new mexico are characterized by a reduced flux 54 58 mwm 2 that is dramatically higher than that 27 mwm 2 in the wyoming basin southern rocky mountains area in southeastern wyoming because the transitions between these provinces are narrow 50 60 km sources in the upper crust must explain some of the contrasting reduced heat flow values in southeastern wyoming normal heat flow in archean and early proterozoic basement terranes probably reflects deep erosion that produced a thin 7 km near surface granitic layer that overlies a low radioactivity lower crust in the colorado front range proterozoic mesozoic and cenozoic silicic rocks with relatively enriched radiogenic heat could comprise a 20 to 25 km thick granitic layer in the upper crust that produces a large part of the above normal reduced and residual flux here partial melting of deep protolithic rocks in late mesozoic and cenozoic times could have produced a lower crust with low radiogenic heat production by these views birch s high heat flow radioactive mountain root model of the colorado front range is confirmed if a large part of the topography is isostatically compensated by low density pre miocene crystal line masses in the upper crust background reduced heat flow in colorado parts of the southern rocky mountains and the eastern colorado plateau is high 54 68 mwm 2 zones of unusually high residual flux 88 118 mwm 2 occur in the rio grande rift zone in the environs of the colorado mineral belt in the leadville northern sawatch range region eastern parts of the san juan mountains in southern colorado and in the park range mountain parks area near the colorado wyoming border the flux in these areas implies unrealistically high equilibrium temperatures near the crustmantle boundary and the 50 to 60 km wide borders of the leadville northern sawatch range residual heat flow anomaly must be caused by sources in the upper crust there fore young 10 to 1 m y old intrusions in a late cenozoic rhyolitic complex in the upper crust are preferred to explain gravity lows late cenozoic uplift and igneous activity and the high residual flux in the leadville northern sawatch range area similar models may apply elsewhere in the northern rift zone if this interpretation is correct magmatic thickening of the crust not extensional subsidence mechanisms probably explains late cenozoic uplift and extension of the northern rio grande rift southern rocky mountains system because very high regional flux in the northern rift zone and the san juan mountains areas implies above liquidus equilibrium temperatures in the lower crust and upper mantle serious inconsistencies arise when steady state thermal models are examined relative to volumes of late tertiary volcanism uniform crustal thickness and the absence of unusually low p wave velocities in the mantle in the southern rocky mountains

paleoclimatic estimates from water and energy budgets of east african lakes abstract the turkana nakuru elmenteita and naivasha basins in the rift valley of east africa experienced high water levels during the period of 10 000 7000 yr b p analyses of the modern hydrologic and energy budgets for these basins along with that of lake victoria were used to infer the amount of precipitation that would have been required to maintain the enlarged paleolakes of the early holocene precipitation must have been at least 150 300 mm yr 15 to 35 above the modern average the precipitation estimates were fairly consistent among the various basins but no quantitative estimate was made for the additional precipitation required to account for overflow from the rift valley lake basins discharge from the lake victoria basin around 1880 a d was considerably above the more recent average and the increased discharge into the white nile for that period might have been similar to that of the early holocene a sensitivity analysis showed that temperature changes were probably not too important for changing the hydrologic energy budget changes of albedo bowen ratio and cloudiness were likely to have been of greater importance

permafrost heat flow and the geothermal regime at prudhoe bay alaska temperature measurements through permafrost in the oil field at prudhoe bay alaska combined with laboratory measurements of the thermal conductivity of drill cuttings permit an evaluation of in situ thermal properties and an understanding of the general factors that control the geothermal regime a sharp contrast in temperature gradient at approx 600 m represents a contrast in thermal conductivity caused by the downward change from interstitial ice to interstitial water at the base of permafrost under near steady state conditions interpretation of the gradient contrast in terms of a simple mode for the conductivity of an aggregate yields the mean ice content approx 39 and thermal conductivities for the frozen and thawed section 8 1 and 4 7 mcal cm s sup 0 c respectively these results yield a heat flow of approx 1 3 hfu which is similar to other values on the alaskan arctic coast the anomalously deep permafrost is a result of the anomalously high conductivity of the siliceous ice rich sediments curvature in the upper 160 m of the temperature profiles represents a warming of approx 1 8 sup 0 c of the mean surface temperature and a net accumulation of 5 6 kcal cm sup 2 by the solid earth surface during the last 100 years or so rising sea levelmore and thawing of ice rich sea cliffs probably caused the shoreline to advance tens of kilometers in the last 20 000 years inundating a portion of the continental shelf that is presently the target of intensive oil exploration a simple conduction model suggests that this recently inundated region is underlain by near melting ice rich permafrost to depths of 300 500 m its presence is important to seismic interpretations in oil exploration and to engineering considerations in oil production with confirmation of the permafrost configuration by offshore drilling heat conduction models can yield reliable new information on the chronology of arctic shorelines less

ice core sample measurements give atmospheric co 2 content during the past 40 000 yr recent measurements1 2 on ice samples from camp century greenland 77 10 n 61 08 w byrd station antarctica 80 01 s 110 31 w and dome c 74 40 s 125 10 e suggest that during the late part of the last glaciation the atmospheric co2 concentration was significantly lower than during the holocene further investigation of this natural increase of the atmospheric co2 concentration in the past should aid our understanding of the climatic implications of the man made co2 increase since the beginning of industrialization3 here we report new and precise measurements of the co2 concentration of the air occluded in bubbles of ice samples from camp century and byrd station using a new dry extraction technique the extracted gases were analysed with an ir laser spectrometer irls samples from 22 different depths were analysed from each core the samples are distributed over a depth interval corresponding approximately to the past 40 000 yr in addition results for ice samples from selected depth horizons from a colder region north central greenland 74 37 n 39 36 w and from a warmer region dye 3 greenland 65 11 n 43 50 w are given based on these results we estimate the trend of the atmospheric co2 concentration during the past 40 000 yr

coherent response of arabian sea upwelling and pollen transport to late quaternary monsoonal winds the indian summer monsoon causes large seasonal changes in the environments of both eastern africa and the arabian sea here we compare time series 140 kyr long of selected pollen types and foraminiferal upwelling faunas preserved in marine sediments to identify the frequencies of their variability and the coherence and phase of the terrestrial and marine responses to monsoonal circulation during interglacial intervals the pollen and upwelling records of the western arabian sea indicate stronger monsoons and are both coherent and in phase at periodicities near the precession of the earth s rotational axis 23 kyr we conclude that the strength of the monsoonal southwesterlies accounts for this high coherence of marine and terrestrial records during interglacial intervals low correlation during glacial phases indicates weaker monsoons and some decoupling of these two records these data indicate that two distinct modes of monsoon variability may exist an interglacial mode with strong monsoons and effective coupling of terrestrial and marine records and a glacial mode with both weaker monsoons and decreased linkage between arabian sea pollen and upwelling records

simulating the decadal to millennial scale dynamics of morphology and sequestered carbon mobilization of two thermokarst lakes in nw alaska 1 thermokarst lakes alter landscape topography and hydrology in widespread permafrost regions and mobilize significant permafrost carbon pools including releasing methane ch4 to the atmosphere despite this the dynamics of lake evolution permafrost thawing and carbon mobilization are not well known we present a 3 d numerical model of thermokarst lakes on organic rich yedoma permafrost terrains with surface water flow and pooling naturally defining lakes that deepen expand laterally and drain due to talik formation bank retreat and both gradual and catastrophic drainage we predict the 3 d pattern of microbial methane production within the talik over time as a first model test and calibration beginning with small protolakes we simulated 10 000 years of evolution of pear and claudi lakes two neighboring thermokarst features on the northern seward peninsula alaska simulated lakes approximated observed bathymetry but results are sensitive to initial topography and soil ice content local topography caused markedly different dynamics for the two lakes pear expanded rapidly across low relief topography fully drained multiple times and released little methane in later stages due to pleistocene carbon depletion by the first and largest lake generation claudi grew slowly and continuously across high relief topography forming high subaerial banks partial drainages left remnant horseshoe lakes that continued to expand into virgin yedoma mobilizing carbon at roughly the same rate irrespective of lake drainage the 2 discrepancy between simulated ch4 production and observed emission rates in claudi likely results from misestimation of hot spot ebullition labile carbon content ch4 co2 production ratio or microbial ch4 oxidation