pervasive dolomitization with subsequent hydrothermal alteration in the clarke lake gas field middle devonian slave point formation british columbia canada the clarke lake gas field in british columbia canada is hosted in pervasively dolomitized middle devonian carbonates of the slave point formation the clarke lake field consists mostly of pervasive matrix dolomite and some saddle dolomite the latter varying in volume from about zero in limestones to normally 20 40 locally up to 80 in dolostones over any given 10 m 33 ft core interval some of the saddle dolomite is replacive some is cement and both varieties are associated with dissolution porosity and recrystallized matrix dolomite the major objective of this study is to identify the causes and timing of matrix and saddle dolomite formation specifically whether these dolomites are hydrothermal a comprehensive petrographic and geochemical examination indicates that pervasive matrix dolomitization was accomplished by long distance migration of halite saturated brines during the late devonian to mississippian fluid inclusion homogenization temperatures suggest about 150 uncorrected to 190c corrected at the time of matrix dolomitization these temperatures differ markedly from most published work on the dolomitized devonian reefs in the alberta basin south of the peace river arch where pervasive matrix dolomitization was accomplished by advection of slightly modified seawater at temperatures of about 60 80c and where no hydrothermal influence was ever present the saddle dolomites at clarke lake are not cogenetic with matrix dolomite and are not the product of hydrothermal dolomitization sensu stricto instead they formed through the hydrothermal alteration of matrix dolomite by way of invasion of a gypsum saturated brine during periods of extremely high heat flow and regional plate margin tectonics in the late devonian to mississippian fluid inclusion homogenization temperatures suggest that hydrothermal alteration occurred between 230 uncorrected and 267c corrected which is significantly higher than the maximum temperature of about 190c attained by the slave point formation during burial the sources of the halite and gypsum saturated brines are middle devonian evaporite depositional environments roughly 200 km 124 mi south and or east of clarke lake near the peace river arch

oriented lake development in the context of late quaternary landscape evolution mckinley bay coastal plain western arctic canada abstract oriented lakes characterized by elongate forms central basins and shallow littoral shelves are common features of circum arctic coastal lowlands the environmental conditions geological processes and chronology associated with the development of oriented lakes however are little known but essential for understanding how such arctic lowlands evolve using combined techniques of field and drill log stratigraphy and sedimentology luminescence and radiocarbon dating methods and geomorphic mapping we reconstruct the landscape evolution leading toward oriented lake formation on the mckinley bay coastal plain of western arctic canada a region with over 900 oriented lakes most lakes with deep central basins are inherited from a preglacial braidplain ca 73 27 ka and alluvial braided channel network that extended beyond the glacial limit ca 18 6 14 3 ka eolian erosion active during the lateglacial and postglacial period ca 12 8 1 9 ka reworked fluvial deposits eolian processes modified existing basins and created other shallow deflationary basins as small barchanoid dunes migrated under cold dry paraglacial conditions between about 12 8 and 10 7 ka vegetation cover developed at the onset of the early holocene climatic optimum ca 10 7 ka and parabolic dunes were active between 9 6 and 4 6 ka thus oriented lakes developed in basins conditioned by fluvial and eolian processes in the absence of much near surface ground ice lateral expansion of deep basin lakes and shallow stabilized deflationary basins predominated during the late holocene through wind induced wave and current processes overall this sequence of oriented lake formation does not support a thaw lake cycle but rather small basin evolution of a periglacial landscape

classification of dolomite rock textures abstract dolomite rock textures can be classified according to crystal size distribution and crystal boundary shape the classification scheme presented here is largely descriptive but carries genetic implications because size distribution is controlled by both nucleation and growth kinetics and crystal boundary shape is controlled by growth kinetics size distributions are classified as unimodal or polymodal crystal boundary shapes are classified as planar or nonplanar if the evidence permits a complete classification includes a description of recognizable allochems matrix and void filling allochems and preexisting cements may be unreplaced partially replaced replaced mimically or replaced nonmimically allochems may be dissolved leaving molds matrix can be unreplace partially replaced or replaced by a unimodal or polymodal size dolomite unimodal size distributions generally indicated a single nucleation event on a unimodal substrate polymodal sizes can be formed by multiple nucleation events on a unimodal or polymodal substrate or differential nucleation on an originally polymodal substrate planar crystal boundaries develop when crystals undergo faceted growth and nonplanar boundaries develop when crystals undergo nonfaceted growth nonplanar boundaries are characteristic of growth at elevated temperature 50 c and or high supersaturation both planar and nonplanar dolomite can form as a cement replacement of caco3 or neomorphism of a precursor dolomite

sedimentation associated with antarctic peninsula ice shelves implications for palaeoenvironmental reconstructions of glacimarine sediments abstract recent disintegration of a number of antarctic peninsula ice shelves has given us a unique opportunity to investigate sub ice shelf sediments we characterize three sediment facies associations of two antarctic peninsula ice shelves larsen a and larsen inlet subglacial facies consist mainly of basal till diamicton with high shear strengths deposited under a grounded ice sheet progressive upward decrease in shear strength reflects a gradual decrease in the confining vertical effective pressure of grounded ice during till deposition proximal ice shelf glacimarine facies diamicton gravel rich and sand rich facies gravelly mud dropstone mud and sandy muds were deposited by sub ice shelf rain out bottom current activity and sediment gravity flows following decoupling of grounded ice from the sea floor distal ice shelf glacimarine and or open marine facies comprise terrigenous and diatom bearing bioturbated muds and gravelly muds that contain limited ice rafted debris these accumulated after recession of the grounding line to the coast with coarse grained surface sediments possibly documenting most recent ice shelf break up antarctic peninsula ice shelf sediments are more heterogeneous than ice shelf facies deposited elsewhere in antarctica cold polar antarctic ice shelves can be differentiated from temperate and sub polar marine terminated glacial sedimentary systems by the dominance of coarse grained proximal ice shelf glacimarine facies and an absence of subaqueous outwash meltwater sediment facies

the gas bearing devonian presqu ile dolomite of the cordova embayment region of british columbia canada dolomitization and the stratigraphic template white dolospar of the presqu ile dolomite forms the reservoir for many gas fields of northeastern british columbia within the keg river sulphur point and slave point formations along the shelf margin of the cordova embayment the embayment fill succession of the organic rich klua shale the otter park shale and marlstones equivalent to the sulphur point and slave point formations are aquicludes that blocked the upward and lateral flow of dolomitizing brines presqu ile dolomitization along the slave point shelf edge is interrupted in places where the klua shale extends shelfward underneath the slave point formation the watt mountain shale was also a regional aquiclude that prevented upward circulation of dolomitizing fluids in areas behind the slave point shelf edge flow of dolomitizing nacl cacl2 mgcl2 h2o brine solutions began in the shallow subsurface and precipitated dolomite cements type 1 at temperatures less than 50 degreesc possibly even during slave point deposition as northwestward directed shallow subsurface brine reflux from the elk point basin began this was followed by upward directed subsurface convective flow of nacl cacl2 mgcl2 h2o and nacl mgcl2 h2o brines and precipitation of dolomite cements at temperatures of about 130 degreesc during the late devonian carboniferous lower salinity brines that precipitated calcite cements and some dolomite type 2 may have interacted with connate fluids of marine origin or less likely with meteoric fluids modeling of organic maturation indicates that the muskwa shales above the slave point formation passed through the oil generation window in the permian and the onset of dry gas generation in the middle mesozoic postdolomitization calcite cements precipitated during these times contain abundant liquid hydrocarbon filled and methane filled inclusions high temperatures of close to 200 degreesc experienced by slave point strata in the mesozoic caused stretching but no leakage or refilling of fluid inclusions in all dolomite cements

paleohydrogeology of the canadian rockies and origins of brines pb zn deposits and dolomitization in the western canada sedimentary basin results of stable isotopic and fluid inclusion studies of cambrian carbonate units in the southern canadian rockies indicate that during the late devonian or early mississippian a warm brine migrated from miogeoclinal shales in the western part of the western canada sedimentary basin into the eastern carbonate sequences this fluid had a temperature of 150 25 c salinity values of 20 to 25 equivalent wt nacl and isotopic values of 18 o 7 to 0 13 c 1 2 d 70 19 and 87 sr 86 sr 0 710 the fluids formed large bodies of coarse sparry dolomite as well as pb zn magnesite and talc mineralizations in the cambrian units it is probable that this event was also responsible for the development of pb zn mineralization specifically pine point in the devonian units as well as a component of the present day basinal brines in the basin

multistage dolomitization in rainbow buildups middle devonian keg river formation alberta canada abstract more than 80 partially to completely dolomitized buildups of middle devonian keg river formation occur in the rainbow sub basin of northwestern alberta in six buildups a b e f g and tehze four petrographic types of dolomites are identified gray fine crystalline dolomite floating dolomite rhombs patches matrix dolomite and saddle dolomite the petrographic and geochemical data indicate that these dolomites probably formed in three principle stages of dolomitization during progressive burial gray fine crystalline dolomite less than 1 of total dolomite by volume is interpreted as penecontemporaneously dolomitized lime muds by either normal marine waters or evaporitic brines during early exposure the following evidence suggests that this dolomite probably formed early 1 it usually occurs in fractures and breccias presumably related to the early exposure of the buildups 2 it is absent in rugs and molds that formed in the subsurface environment and 3 locally clasts of gray fine crystalline dolomite are embedded in marine limestones rhomb patch dolomite is the major type of dolomite in dolomitic limestones and is widespread throughout the limestone buildups matrix dolomite is fabric destructive and is most abundant in the dolostone buildups both these dolomites probably formed during shallow to intermediate burial because they 1 postdate stylolites 2 are widespread throughout the buildups and crosscut various facies and 3 have light oxygen isotope compositions and low sr but high fe and mn concentrations dolomitizing fluids for dolomite rhombs patches and matrix dolomites were possibly derived from 1 mechanical compaction 2 dehydration of the adjacent muskeg gypsum at relatively shallow burial depths and 3 intermediate depth basinal fluids conducted updip along porous and permeable conduits during d vonian and carly carboniferous times compaction fluids were probably responsible for the early dolomite rhombs and patches however the main phase of matrix dolomitization took place later probably during late mississippian to jurassic time when the east side of the basin was intermittently tilted and uplifted causing updip flow of intermediate depth basinal brines saddle dolomite occurs as late stage vug and fracture fillings it is most depleted in 18o but most enriched in mn and fe suggesting precipitation during deeper burial from warm basinal fluids these fluids were expelled during upper cretaceous sedimentary and tectonic loading of the western side of the basin and then moved up the east side of the basin along existing platform fault and fracture conduits the source of the mg is uncertain some or most of the mg may have resulted from chemical compaction of the earlier matrix dolomite

dolomitization of the middle devonian winnipegosis carbonates in south central saskatchewan canada the middle devonian winnipegosis carbonate unit in south central saskatchewan is partially to completely dolomitized two major types of replacive dolomite are distinguished microcrystalline to finely crystalline dolomite type 1 displays nonplanar a to planar s textures mimetically replaces the precursor limestone accounts for about four fifths of dolomite phases volumetrically and mainly occurs in the winnipegosis mounds and the lower winnipegosis member directly underlying the mounds medium crystalline dolomite type 2 shows planar s to planar e textures commonly occurs in the lower winnipegosis and brightholme members and decreases upward in abundance the 87 sr 86 sr ratios of type 1 dolomite 0ae70795 to 0ae70807 fall within the estimated sr isotopic range for middle devonian marine carbonates stratigraphic petrographic and geochemical data constrain the formation of type 1 dolomite to hypersaline sea water in a near surface environment after marine cementation and sub aerial diagenesis and prior to precipitation of the middle devonian leofnard salts movement of dolomitizing fluids could be driven by density differences and elevation head the shift to lower d 18 o values of type 1 dolomite 7ae 4t o 5ae1 vienna pee dee belemnite vpdb is interpreted as the result of recrystallization at elevated temperatures during burial type 2 dolomite has higher 87 sr 86 sr ratios 0ae70809 0ae70928 suggesting that the dolomite probably formed from basinal fluids with an increased richness in the radiogenic sr isotope in type 2 dolomite sr 2 concentrations are lower and fe 2 and mn 2 concentrations are higher compared with the associated limestone and type 1 dolomite type 2 dolomite is interpreted as having been formed from upward migrating basinal fluids during latest devonian and carboniferous period

cryostratigraphy of late pleistocene syngenetic permafrost yedoma in northern alaska itkillik river exposure abstract extremely ice rich syngenetic permafrost or yedoma developed extensively under the cold climate of the pleistocene in unglaciated regions of eurasia and north america in alaska yedoma occurs in the arctic foothills the northern part of the seward peninsula and in interior alaska a remarkable 33 m high exposure along the lower itkillik river in northern alaska opened an opportunity to study the unmodified yedoma including stratigraphy particle size distribution soil carbon contents morphology and quantity of segregated wedge and thermokarst cave ice the exposed permafrost sequence comprised seven cryostratigraphic units which formed over a period from 48 000 to 5 000 14c yr bp including 1 active layer 2 intermediate layer of the upper permafrost 3 4 two yedoma silt units with different thicknesses of syngenetic ice wedges 5 buried peat layer 6 buried intermediate layer beneath the peat and 7 silt layer with short ice wedges this exposure is comparable to the well known mus khaya and duvanny yar yedoma exposures in russia based on our field observations literature sources and interpretation of satellite images and aerial photography we have developed a preliminary map of yedoma distribution in alaska

role of ground ice dynamics and ecological feedbacks in recent ice wedge degradation and stabilization ground ice is abundant in the upper permafrost throughout the arctic and fundamentally affects terrain responses to climate warming ice wedges which form near the surface and are the dominant type of massive ice in the arctic are particularly vulnerable to warming yet processes controlling ice wedge degradation and stabilization are poorly understood here we quantified ice wedge volume and degradation rates compared ground ice characteristics and thermal regimes across a sequence of five degradation and stabilization stages and evaluated biophysical feedbacks controlling permafrost stability near prudhoe bay alaska mean ice wedge volume in the top 3 m of permafrost was 21 imagery from 1949 to 2012 showed thermokarst extent area of water filled troughs was relatively small from 1949 0 9 to 1988 1 5 abruptly increased by 2004 6 3 and increased slightly by 2012 7 5 mean annual surface temperatures varied by 4 9 c among degradation and stabilization stages and by 9 9 c from polygon center to deep lake bottom mean thicknesses of the active layer ice poor transient layer ice rich intermediate layer thermokarst cave ice and wedge ice varied substantially among stages in early stages thaw settlement caused water to impound in thermokarst troughs creating positive feedbacks that increased net radiation soil heat flux and soil temperatures plant growth and organic matter accumulation in the degraded troughs provided negative feedbacks that allowed ground ice to aggrade and heave the surface thus reducing surface water depth and soil temperatures in later stages the ground ice dynamics and ecological feedbacks greatly complicate efforts to assess permafrost responses to climate change

enhanced carbonate petrography using fluorescence microscopy abstract fluorescence microscopy can recognize depositional facies and delineate diagenetic fabrics and porosity relationships in certain highly dolomitized or recrystallized limestones previously uninterpretable using standard petrographic techniques this tool has other valuable applications in the study of carbonate rocks these other applications include differentiating carbonate cements from neomorphic spar enhancing depositional and diagenetic fabrics rapidly evaluating mineralogical stabilization and recrystallization in holocene and pleistocene deposits and improving delineation of porosity and pore geometries in sedimentary rocks fluorescence microscopy is a rapid easily used and nondestructive technique that can be applied to unpolished thin sections or rock slabs by itself or in conjunction with other petrographic and geochemical tools it has the potential to expand our understanding of carbonate diagenetic processes and products in particular dolomitization and neomorphism and carbonate porosity evolution we strongly encourage routine usage of fluorescence microscopy in future carbonate petrographic studies

origin of cacl brines in devonian formations western canada sedimentary basin abstract the majority of waters in devonian formations of the western canada sedimentary basin are high salinity ca cl brines this relatively rare type of brine is of economic interest because of its association with both oil and hydrothermal ore deposits these brines are important sources of ca2 mg2 and ore metals in sedimentary basins it is possible to generate the ca cl brines by modification of residual evaporite brines the evaporation of devonian sea water produced large quantities of gypsum and halite such as the prairie formation residual brines were not retained in the evaporating system quantities of dense halite saturated brine sufficient to account for the high salinity formation waters in the basin were lost syndepositionally the cl and br content of waters within devonian formations in the basin can be explained by dilution of the residual evaporite brines brine composition was modified as a result of density driven reflux to depths of several kilometers this placed concentrated brines in contact with precambrian basement rocks at elevated temperatures 100 300 c the most important reactions between the brine and basement rocks appear to involve albitization of feldspars further modification of the brines occured as cements formed in devonian carbonates volumetrically the most important of these is dolomite in addition some devonian carbonates were dolomitized during ascent along faults mg2 was lost from hot brines as dolomite formed

hydrocarbon fluid inclusions in the argo salt offshore canadian atlantic margin1 fluid inclusions hosted in rock salt from the triassic argo formation in the canadian atlantic continental margin were studied to investigate the nature and origin of petroleum fluids in them incl

pan arctic ice wedge degradation in warming permafrost and its influence on tundra hydrology ice wedges are common features of the subsurface in permafrost regions they develop by repeated frost cracking and ice vein growth over hundreds to thousands of years ice wedge formation causes the archetypal polygonal patterns seen in tundra across the arctic landscape here we use field and remote sensing observations to document polygon succession due to ice wedge degradation and trough development in ten arctic localities over sub decadal timescales initial thaw drains polygon centres and forms disconnected troughs that hold isolated ponds continued ice wedge melting leads to increased trough connectivity and an overall draining of the landscape we find that melting at the tops of ice wedges over recent decades and subsequent decimetre scale ground subsidence is a widespread arctic phenomenon although permafrost temperatures have been increasing gradually we find that ice wedge degradation is occurring on sub decadal timescales our hydrological model simulations show that advanced ice wedge degradation can significantly alter the water balance of lowland tundra by reducing inundation and increasing runoff in particular due to changes in snow distribution as troughs form we predict that ice wedge degradation and the hydrological changes associated with the resulting differential ground subsidence will expand and amplify in rapidly warming permafrost regions the polygonal patterns in permafrost regions are caused by the formation of ice wedges observations of polygon evolution reveal that rapid ice wedge melting has occurred across the arctic since 1950 altering tundra hydrology

cryostratigraphy paleogeography and climate change during the early holocene warm interval western arctic coast canada botanical and cryostratigraphic records from northwest canada indicate that the climate of the early holocene was considerably warmer than today tree line was over 100 km farther north and a thaw unconformity dating from 8000 14c years bp formed at the base of an active layer 2 5 times thicker than at present numerous thermokarst lake basins formed in the preceding millennia both the botanical and cryostratigraphic indices described are products of summer conditions previous reconstructions of early holocene climate have not assessed the significance of paleocoastal location on the seasonality and extent of apparent climate warming at present there is a steep gradient in growing season conditions between cooler sites on the beaufort sea coast and warmer inland locations winter conditions are more uniform because both sea and land are snow covered coastal retreat in the region has been rapid due to sea level rising over a gently sloping shelf containing readily erodible sediments the coastlin

out of our depth on the impossibility of fathoming eustasy from the stratigraphic record the evolution of a sedimentary basin s gross morphology depends upon 1 basement movement 2 sediment accumulation and compaction and 3 variations of eustasy with time thus if an accurate history of eustasy could be derived it would aid in our understanding of basin stratigraphy and help in the prediction of sediment geometry from described areas techniques which attempt to determine the magnitude of eustatic sea level excursions include the measurement of 1 the amount of sedimentary onlap onto the continental margins with and without the use of hypsometric curves 2 the thickness of marine sedimentary cycles and the elevation and distance between indicators of old strandlines 3 the perturbations on individual thermo tectonic subsidence curves and stacked crustal subsidence curves 4 the variations in deep ocean oxygen isotopes found in sediments and 5 the size of variables used in graphical and numerical simulations of basin fill in terms of tectonic behavior rates of sediment accumulation and eustasy which invert the problem to date a combination of the use of relative sea level charts derived from sediment onlap of the continental margin with dimensioning by oxygen isotopes responding to glacial events offers the best potential for relative tectono eustatic sea level curves but even this method can not produce a unique solution for absolute eustatic variations mathematical modelling shows that at best it is possible to obtain only the sum of tectonic basement subsidence and sea level variations from the above methods and at worst not even that simple a combination thus every proposed scheme to measure eustatic sea level excursions assumes some behavior for two of the three underlying processes tectonic movement of the basement sedimentary accumulation and eustatic sea level each scheme then determines the third process relative to the assumed model behavior of the other two it would seem that like king canute we cannot command the sea though we can still use undifferentiated relative tectono eustatic sea level curves to generate a family of solutions which are the product of a variety of absolute sea level curves and tectonic models each solution has then to be assessed in terms of geologic setting and the hypotheses it generates

characterizing the shale gas resource potential of devonian mississippian strata in the western canada sedimentary basin application of an integrated formation evaluation devonian mississippian strata in the northwestern region of the western canada sedimentary basin wcsb were investigated for shale gas potential in the subsurface thermally mature strata of the besa river horn river muskwa and fort simpson formations attain thicknesses of more than 1 km 0 6 mi encompassing an area of approximately 125 000 km2 48 300 mi2 and represent an enormous potential gas resource total gas capacity estimates range between 60 and 600 bcf section of particular exploration interest are shales and mudrocks of the horn river formation including the laterally equivalent lower besa river mudrocks muskwa formation and upper besa river formation which yield total organic carbon toc contents of up to 5 7 wt fort simpson shales seldom have toc contents above 1 wt horn river and muskwa formations have excellent shale gas potential in a region between longitudes 122w and 123w and latitudes 59n and 60n national topographic system nts 94o08 to 94o15 in this area which covers an areal extent of 6250 km2 2404 mi2 average toc contents are higher 3 wt as determined by wire line log calibrations and have a stratal thickness of more than 200 m 656 ft gas capacities are estimated to be between 100 and 240 bcf section and possibly greater than 400 tcf gas in place a substantial percentage of the gas capacity is free gas caused by high reservoir temperatures and pressures muskwa shales have adsorbed gas capacities ranging between 0 3 and 0 5 cm3 g 9 6 16 scf t at reservoir temperatures of 60 80c 140 176f whereas besa river mudrocks and shales have low adsorbed gas capacities of less than 0 01 cm3 g 0 32 scf t liard basin region because reservoir temperatures exceed 130c 266f potential free gas capacities range from 1 2 to 9 5 cm3 g 38 4 to 304 scf t when total pore volumes 0 4 6 9 are saturated with gas the mineralogy has a major influence on total gas capacity carbonate rich samples indicative of adjacent carbonate platform and embayment successions commonly have lower organic carbon content and porosity and corresponding lower gas capacity 1 toc and 1 porosity seaward of the carbonate slave point edge muskwa and lower besa river mudrocks can be both silica and toc rich up to 92 quartz and 5 wt toc and most favorable for shale gas reservoir exploration because of possible fracture enhancement of the brittle organic and siliceous rich facies however an inverse relation between silica and porosity in some regions implies that zones with the best propensity for fracture completion may not provide optimal gas capacity and a balance between favorable reservoir characteristics needs to be sought

formation of coarsely crystalline hydrothermal dolomite reservoirs in the presqu ile barrier western canada sedimentary basin late stage coarsely crystalline replacement dolomite and associated saddle dolomite cement form a widespread diagenetic facies in the middle devonian presqu ile barrier that extends southwestward from pine point to the subsurface of the foothills in northeastern british columbia these dolomites create hydrocarbon reservoirs in otherwise tight limestones in the subsurface of the northwest territories and northeastern british columbia and host mississippi valley type deposits at pine point the coarsely crystalline replacement dolomite and saddle dolomite cement are interpreted to have formed during burial because they replace blocky sparry calcite cements occur continuously across the sub watt mountain unconformity postdate stylolites and earlier replacement dolomites and overlap sulfide mineralization the dgr18o values of both replacement and saddle dolomites increase eastward updip along the presqu ile barrier from 16 pmil pdb in the deeper subsurface of northeastern british columbia to 7 pmil pdb at pine point whereas the corresponding homogenization temperatures of saddle dolomite fluid inclusions decrease from 178 to 92 c the 87sr 86sr ratios of coarsely crystalline and saddle dolomites decrease eastward along the pres u ile barrier from about 0 7106 in the subsurface of northeastern british columbia to 0 7081 at pine point these geochemical trends suggest a possible basin scale migration of hot radiogenic dolomitizing fluids updip eastward along the presqu ile barrier such large scale fluid movements probably were related to western canada sedimentary basin tectonic compression and sedimentary loading which occurred at least twice during early burial between the late devonian and early carboniferous and during deep burial between the late jurassic and early tertiary

ice wedges on hillslopes and landform evolution in the late quaternary western arctic coast canada in rolling to hilly areas of the western arctic coast of canada anti syngenetic wedges which by definition are those that grow on denudational slopes are the most abundant type of ice wedge through prolonged slope denudation hilltop epigenetic wedges can evolve into hillslope anti syngenetic wedges and some bottom slope anti syngenetic wedges by means of deposition from upslope can evolve into bottom slope syngenetic wedges the axis of a hillslope wedge is oriented perpendicular to the slope so the wedge foliation varies according to the trend of the wedge with respect to the slope because the tops of hillslope wedges are truncated by slope recession the mean chronological age of anti syngenetic wedge ice decreases with time so the growth record for an old wedge is incomplete summer and winter measurements show that a thermally induced net movement of the active layer of hillslope polygons tends to transport material from their centres towards their troughs independent of the trends of the t

evolution of lakes and basins in northern alaska and discussion of the thaw lake cycle 1 we evaluated the development of lake basins on the central coastal plain of northern alaska on the basis of topographic profiles soil and ground ice surveys radiocarbon dating photogrammetric analysis and regional comparisons our analysis reveals that lake evolution is much more complex and less cyclic than theorized by previous investigations in the area we studied there was insufficient ground ice in the oldest terrain to form thaw lakes the aggradation of ice in the margins of drained lake basins was insufficient to heave the surface up to near original topographic conditions and the process occurs at too slow a rate for a thaw lake cycle to develop within the holocene accordingly we revised the conceptual model of lake and basin development to be consistent with the patterns and process we observed on the extensive sand sheets underlying most of the coastal plain developmental stages include 1 initial flooding of depressions to form primary lakes 2 lateral erosion with sorting and redistribution of sediments 3 lake drainage as the stream network expands 4 differential ice aggradation in silty centers and sandy margins 5 formation of secondary thaw lakes in the heaved centers of ice rich basins and infilling of ponds along the low margins and 6 basin stabilization

sedimentological and ichnological characterization of the middle to upper devonian horn river group british columbia canada insights into mudstone depositional conditions and processes below storm wave base abstract the middle and upper devonian horn river group in northeastern british columbia canada consists predominantly of organic rich mudstones that are typically described as black shales this stratigraphic unit has seen substantial exploration and development for natural gas during the last decade although black shales such as the horn river group have historically been interpreted as deposited in anoxic deep water basins detailed sedimentological and ichnological analyses of eleven horn river group cores indicate that the depositional conditions varied significantly with respect to paleoenvironments redox conditions and physical processes resulting in distinctive sedimentary facies this study integrates data on lithology and physical and biogenic sedimentary structures from detailed core descriptions combined with total organic carbon content to better understand depositional processes and conditions ten mudstone lithofacies and three lithofacies associations are identified massive mudstones and pyrite rich mudstones display very rare planar lamination and graded beds and scarce bioturbation bi 0 1 and are interpreted to represent anoxic waters below storm wave base swb with conditions of relatively low to moderate energy heterolithic laminated and more bioturbated lithofacies are interpreted to represent oxygenated waters below swb with relatively high energy conditions overall bioturbation intensity varies between moderate to intense bi 3 6 where these lithofacies are not intensely bioturbated oxygenated lithofacies show combinations of well preserved physical sedimentary structures including horizontal parallel lamination soft sediment deformation double mud drapes graded beds and current ripples a third lithofacies association represents conditions intermediate between anoxic and oxygenated lithofacies associations mainly based on local changes in the ichnological characteristics these lithofacies show either intense or sparse bioturbation bi 4 6 or bi 0 1 respectively depending on the core location possibly indicating local changes in the depositional conditions and processes e g variations in the oxygen content and or sedimentation rate they can also be found in thick anoxic and oxygenated deposits these lithofacies display intervals of faint lamination amalgamated current ripples and normally graded bedding the cores collectively display significant spatial and stratigraphic heterogeneity in lithology sedimentary structures and bioturbation that are related to relative water depth oxygen content sediment input and deep water currents we interpreted bioturbation intensity to vary mainly as a function of oxygen content related to proximity to the basin margin and sea level fluctuations although secondary stress conditions e g nutrient content and sedimentation rate may also be important unbioturbated and massive fabrics represent anoxic to dysoxic conditions current generated structures are present mainly in the central and distal parts of the basin and are interpreted to represent the presence of contour currents in the proximal parts of the basin laminated and heterolithic units are more common and more bioturbated than in the central and distal basin this study thus can provide significant insights into other shale basins that show similar lateral and vertical variations integration of multidisciplinary studies particularly sedimentology ichnology and total organic carbon aids in understanding and modeling the complexity of these systems

late cretaceous early tertiary remagnetization of the devonian swan hills formation recorded in carbonate cores from the caroline gas field alberta canada limestone and dolomite samples obtained from four unoriented swan hills formation cores from the caroline gas field were examined with the goal of dating both dolomitization and emplacement of solid hydrocarbon detailed analysis of 110 specimens showed no difference in the magnetic components in limestone dolomite and bitumen bearing rocks the first removed component a appears to have been acquired during sampling and is not considered further the second component b is interpreted as a record of the present day earth s magnetic field the third component c is a steeply dipping vector acquired during a period in the past when the earth s magnetic field was reversed and is recovered from almost all specimens declination values of component c were resolved by using component b as a fossil compass needle in cases where these two occurred together this yielded an in situ direction of declination inclination 155 7 73 3 k 26 4 a95 the cone of 95 confidence 7 1 for the c component the corresponding paleopole 74 7n 192 3e with 95 confidence limits of dp 11 4 dm 12 7 plots directly on the apparent polar wander path for apwp stable north america yielding a late cretaceous early tertiary age for the c component because the c component is not unique to the dolomite or bitumen bearing rocks but is shared by limestone far removed from the dolomite reservoir we are hesitant to assign this late cretaceous early tertiary age to the dolomitization or bitumen formation however this record does testify to a fluid pulse at the end of laramide orogeny such pulses currently are believed to be common events proximal to orogenic fronts and may participate in the migration of petroleum if we accept the flow of fluids through the reservoir at caroline as being responsible for the remagnetization then this suggests that the gas charge was not in place or completely in place until after this event this constrains the time of charging to during or after the late cretaceous early tertiary

isotropic thaw subsidence in undisturbed permafrost landscapes 1 observations in undisturbed terrain within some regions of the arctic reveal limited correlation between increasing air temperature and the thickness of the seasonally thawed layer above ice rich permafrost here we describe landscape scale thaw induced subsidence lacking the topographic contrasts associated with thermokarst terrain a high resolution 11 year record of temperature and vertical movement at the ground surface from contrasting physiographic regions of northern alaska obtained with differential global positioning systems technology indicates that thaw of an ice rich layer at the top of permafrost has produced decimeter scale subsidence extending over the entire landscapes without specialized observation techniques the subsidence is not apparent to observers at the surface this isotropic thaw subsidence explains the apparent stability of active layer thickness records from some landscapes of northern alaska despite warming near surface air temperatures integrated over extensive regions it may be responsible for thawing large volumes of carbon rich substrate and could have negative impacts on infrastructure

ice wedges growth thaw transformation and palaeoenvironmental significance frost cracking and ice wedge growth are fundamental processes within the permafrost environment extensive areas of contemporary permafrost terrain are characterised by frost fissure polygons formed by repeated thermal contraction cracking of the ground the incremental growth of ice veins and wedges along the axes of contraction cracks contributes significantly to the volume of ground ice in near surface permafrost in areas beyond the present limit of permafrost the recognition of ice wedge pseudomorphs provides one of the few unambiguous indications of the former existence of permafrost conditions an understanding of the processes of ice wedge growth and thaw transformation is essential if contemporary ice wedges are to be used as analogues for pleistocene frost fissure structures in palaeoenvironmental reconstructions

short term dynamics of a low centred ice wedge polygon near chokurdakh ne yakutia ne siberia and climate change during the last ca 1250 years abstract palaeoecological studies including analysis of pollen macrofossils geochemistry and ams radiocarbon dates of four peat sections from one low centred ice wedge polygon in ne yakutia ne siberia allow the three dimensional reconstruction of polygon development during the last ca 1250 years after drainage of a lake peat forming vegetation invaded rapidly comparison with palaeotemperature data shows that the initial formation of mature ridges coincided with a period of high summer temperatures around ad 1400 the ridges persisted and expanded during the subsequent colder ca 200 years partial collapse of various ridges at the end of the 18th century corresponded to a phase with low summer temperatures during the warm 20th century one collapsed ridge regenerated whereas another persisted in its collapsed state ice wedge polygons are thus complex and highly dynamic ecosystems in which changes in temperature and precipitation may induce rapid ecological changes by the complex interplay of water ice and vegetation our study indicates that global warming associated with a decrease in summer precipitation may initially result in enhanced polygon ridge formation the combination of longer summers and increased winter precipitation as predicted for high latitudes will however eventually result in larger meltwater input in the polygon mires which may cause the partial collapse of polygon ridges and underlying ice wedges

increased groundwater to stream discharge from permafrost thawing in the yukon river basin potential impacts on lateral export of carbon and nitrogen 1 arctic and subarctic watersheds are undergoing climate warming permafrost thawing and thermokarst formation resulting in quantitative shifts in surface water groundwater interaction at the basin scale groundwater currently comprises almost one fourth of yukon river water discharged to the bering sea and contributes 5 10 of the dissolved organic carbon doc and nitrogen don and 35 45 of the dissolved inorganic carbon dic and nitrogen din loads long term streamflow records 30 yrs of the yukon river basin indicate a general upward trend in groundwater contribution to streamflow of 0 7 0 9 yr and no pervasive change in annual flow we propose that the increases in groundwater contributions were caused predominately by climate warming and permafrost thawing that enhances infiltration and supports deeper flowpaths the increased groundwater fraction may result in decreased doc and don and increased dic and din export when annual flow remains unchanged

dolomite calcite equilibrium at 220 to 240 c at saturation vapour pressure experimental data abstract small amounts of dolomite and calcite were added as reactants to a series of cacl2 mgcl2 solutions with variable ca mg ratios at temperatures of 220 c and 240 c at vapour pressure in sixty experimental runs dolomitization of calcite and calcitization of dolomite in these runs indicates that the value of log aca 2 amg 2 in solutions at equilibrium with calcite and dolomite ranges from about 0 4 to 0 9 at these temperatures this is in agreement with previous experimental work at higher and lower temperatures these experimentally determined equilibrium log aca 2 amg 2 values are less than those calculated by thermodynamic based programs such as supcrt and pta for equilibrium with ordered dolomite and those which may be calculated from calorimetric data obtained from ordered ideal dolomite this may indicate that the experimentally observed calcite dolomite equilibrium is metastable and that the precipitated dolomites are imperfectly ordered precipitation of partially disordered metastable dolomite of stoichiometric composition may be favoured over that of ideal dolomite at these temperatures for kinetic reasons

orogenic remagnetizations in the front ranges and inner foothills of the southern canadian cordillera chemical harbinger and thermal handmaiden of cordilleran deformation abstract paleomagnetic studies of carbonate rocks in mountain belts have been helpful to the understanding of orogenic mational origin with only one exception the a component has normal polarity in the front ranges and reverse processes the timing of deformation and the nature of fluid flow in actively deforming foreland basins most studies on shallow water carbonates indicate that their remanence is not primary but rather they record remagnetization events contemporaneous with orogeny by considering the remanent directions fold test results and rock magnetic properties and tying these results to complementary structural geochronological and geochemical studies we are able to interpret deformation history hydrological environment and orogenic diagenesis we study the relationship between remagnetization and deformation of paleozoic carbonates of the front ranges and inner foothills of the southern canadian rockies the magnetic properties are remarkably constant along 500 km strike length as sampled at 124 sites through 4 transects primary paleozoic remanent directions which would have shallow inclination are never observed rather the paleomagnetic signal is dominated by geographically persistent remagnetizations characterized by steep inclination as well as a soft present field overprint we observed two distinctive secondary magnetizations named the a and b components carried by fine grained magnetite pervasive diagenesis induced the a component a total chemical remanent remagnetization poles for the a component are better concentrated after bedding correction indicating a pre or early syndefor polarity in the inner foothills pole positions polarity and geological and thermal constraints indicate that the a component was acquired diachronously in advance of the eastward migrating cordilleran tectonic wedge subsequently an intermediate temperature partial thermo remanent remagnetization the b component was superimposed on large regions of the front ranges and inner foothills b component directions are brought into optimal concentration by differential untilting of 0 to 50 indicating that the component was acquired after the rocks were incorporated into the orogenic wedge but before the end of contractional deformation the b component is strongest within a couple of kilometers of the frontal thrust of the front ranges the relative magnitude of the b to a components and the maximum unblocking temperature of the b component decrease away from the frontal thrust over about 30 km both to the west and to the east the b component thermal overprint was attained by 250 c heating in response to tectonic or possibly sedimentary loading it was preserved by a rapid cooling accompanying a differential uplift and erosion of up to 8 km in the vicinity of the frontal thrust late in or post dating its local tilting history the likely cause was uplift of the exposed structural panel by contraction of younger underlying thrust structures

the principles of cryostratigraphy abstract cryostratigraphy adopts concepts from both russian geocryology and modern sedimentology structures formed by the amount and distribution of ice within sediment and rock are termed cryostructures typically layered cryostructures are indicative of syngenetic permafrost while reticulate and irregular cryostructures are indicative of epigenetic permafrost cryofacies can be defined according to patterns of sediment characterized by distinct ice lenses and layers volumetric ice content and ice crystal size cryofacies can be subdivided according to cryostructure where a number of cryofacies form a distinctive cryostratigraphic unit these are termed a cryofacies assemblage the recognition if present of i thaw unconformities ii other ice bodies such as vein ice ice wedges aggradational ice and thermokarst cave pool ice and iii ice sand and gravelly pseudomorphs is also important in determining the nature of the freezing process the conditions under which frozen sediment accumulates and the history of permafrost

thermal maturity patterns in alaska implications for tectonic evolution and hydrocarbon potential nearly 10 000 vitrinite reflectance and conodont color alteration index determinations from sedimentary rocks in alaska were used to produce a thermal maturity map of rocks exposed at the surface and to evaluate subsurface thermal maturity relations in the colville and cook inlet basins rocks exposed at the surface of the tertiary interior basins and in the aleutian forearc and backarc basins uniformly are of very low thermal maturity indicating that these basins are at or near maximum burial have seen little uplift and exhumation and are probably thermally immature with respect to hydrocarbon generation in contrast many sedimentary basins show elevated levels of thermal maturity at the surface with the highest values at basin margins this geometry suggests a patt rn of greater uplift along basin margins possibly reflecting isostatic readjustments as crustal loads are removed by erosion we investigated thermal maturity relations in three sedimentary basins colville cook inlet and kandik in more detail thermal maturity patterns in the colville basin are broadly asymmetric indicating systematic differential uplift ranging from a minimum of no uplift in the north point thomson area to 9 13 km of uplift and exhumation in the central brooks range even greater uplift further to the south is indicated by the presence of greenschist facies and higher grade metamorphic rocks this pattern may reflect the deflexing of the lithosphere subsequent to the principal episode s of crustal convergence and thickening these patterns further suggest a similar thermal history for the proximal colville basin and the northern foothills belt suggesting the possibility of hydrocar on accumulations in the foothills thermal maturity isograds within the brooks range cut major thrust faults indicating that maximum burial postdated the principal phases of thrusting in contrast isograds in the foothills belt to the north are warped broadly by local structure indicating continued north south shortening subsequent to maximum burial such deformation could have remobilized hydrocarbons in early traps a broad southward extension of thermally immature rocks in the central portions of the foothills belt suggests relatively young east west shortening parallel to the strike of the orogene a feature that to date has not been included in regional tectonic syntheses alternatively the thermal maturity pattern could be explained by tectonically unrelated episodes of uplif in the eastern and western parts of the brooks range in the cook inlet basin vitrinite reflectance isograds also are indicative of relatively greater uplift at the basin margins than at the basin center which appears to be presently at its maximum burial depth uplift in the cook inlet basin may reflect compression along the faults bounding the basin relatively high thermal maturity along the western margin of the basin also may reflect magmatic heat sources from the alaska peninsula aleutian volcanic arc the seldovia arch a major structural feature of the end page 1874 basin does not appear to deform vitrinite reflectance isograds implying that deformation on that structure ceased prior to maximum burial in the kandik basin a thermal maturity anomaly thermally mature younger rocks in fault contact with thermally immature older rocks provides clues to the nature and timing of east west thrusting mesozoic foreland basin deposits associated with thrusting buried paleozoic rocks of the easternmost part of this fold and thrust belt to relatively shallow depths driving potential hydrocarbon source rocks into the oil generation window the western foreland basin deposits were overridden by advancing thrusts and tectonically buried to as deep as 10 km these disparate thermal domains are juxtaposed along the glenn creek fault which may represent a terrane boundary in east central alaska

zebra and boxwork fabrics in hydrothermal dolomites of northern canada indicators for dilational fracturing dissolution or in situ replacement zebra and boxwork fabrics in manetoe and presqu ile hydrothermal dolomites provide critical data for discrimination between hypotheses for their origin in a unique occurrence sets of weakly imbricated decimetre sized curvilinear lenticles of white dolospar are developed within sub metre sized tongues of greyish white dolomitized crinoidal packstone and grainstone this nascent zebra fabric has developed along wavy to nodular intra bed sedimentary partings primary bedding can be traced through dolomitized masses containing these fabrics into the surrounding undolomitized limestone all zebra and boxwork fabrics are confined within single beds consistent with an early burial time of origin no change in bed thickness occurs across zebra or boxwork fabrics within beds this indicates a dissolutional rather than a dilational origin for the creation of pore space partly cemented with white dolospar the dolomitized groundmass displays an abruptly gradational or sharp transition to centripetal saddle dolomite cement which partially to nearly completely occludes vugs circulation of geothermally heated hypersaline devonian elk point basinal sea water brines led to dissolution and replacive dolomitization of limestone adjacent to vugs and near contemporaneous precipitation of white dolospar within dissolutional vugs consistent with geochemical simulations the presence of downward extending galleries of white dolospar cemented solution collapse breccia provides further support for an interpretation of regional thermally driven convection of hydrothermal evaporative sea water brines across a broad area of northern canada the absence of gases under pressure in vacuoles within fluid inclusions from manetoe and presqu ile dolospars is also more consistent with a dissolutional and contemporaneous dolomitization origin for these fabrics rather than an origin involving dilational fracturing for space creation and dolospar precipitation the ubiquitous presence of zebra and boxwork fabrics in hydrothermal dolomite reservoirs indicates that they are not confined fault zones and instead occur wherever precursor limestones had relatively greater porosity and permeability prior to dolomitization