multiple fluid flow events and the formation of saddle dolomite case studies from the middle devonian of the western canada sedimentary basin abstract in western canada sedimentary basin wcsb large scale and focused fluid flow that caused hydrothermal dolomitization have been suggested with different timing and intensity in this study we conducted a petrographic and geochemical comparison between the middle devonian sulphur point and slave point carbonates from northwestern alberta the results demonstrate the presence of both an early fluid flow event associated with the late devonian to mississippian antler orogeny as well as a later event coincident with the late cretaceous to early tertiary laramide orogeny early fluid flow event is characterized by high salinity fluids and high temperatures and oxygen isotopic values of marine or slightly enriched values as demonstrated in saddle dolomite from the slave point formation in contrast later fluids that caused the precipitation of saddle dolomite in the sulphur point formation are characterized by having slightly saline values comparable homogenization temperatures but more enriched 18 o values and slightly depleted 13 c signatures geochemical data indicate that this later hydrothermal fluid was mixture of middle devonian brines and radiogenic basement fluids

apatite fission track thermochronometry from central alberta implications for the thermal history of the western canada sedimentary basin apatite separated from 47 cretaceous and tertiary drill core and surface samples from the foreland basin strata of the western canada sedimentary basin wcsb have been analyzed for their apatite fission track aft age and confined track length distribution thermal histories of the fission track data were then estimated using a constrained random search inversion technique based on the durango apatite annealing model most importantly this technique provides an estimate of the peak postdepositional temperature experienced by each sample with error bounds determined by the precision of the fission track data most apatite samples retain at least some tracks that formed prior to the time of maximum cenozoic burial assumed to be coincident with maximum temperature seven apatite samples were fully annealed during burial during or following the laramide orogeny and provide a minimum age of 42 ma for heating lower cretaceous samples from near the deformation front were fully annealed and attained temperatures of at least 119 138 c during maximum burial in contrast stratigraphically equivalent samples at the northeastern end of the transect near the cold lake heavy oil and tar sand deposits did not exceed 80 c paleogeothermal gradients calculated using bounded estimates of the peak temperatures experienced by the samples together with maximum burial estimates from coal moisture studies range from 20 c km near the deformation front to as high as 60 c km near the cratonic edge of the basin this variation has the same trend as present geothermal gradients which range from 30 c km to 45 c km but indicates a greater contrast at the end of the laramide the results are consistent with the concept of heat transport by basinal scale fluid flow

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

constraints on the lithospheric structure of venus from mechanical models and tectonic surface features radar images of the surface of venus show numerous structures that are interpreted as having formed due to horizontal compression and extension of the lithosphere many of these features exhibit characteristic scales widths or spacings of deformation one of 10 20 km and another of 100 300 km for a range of simple models we test the hypothesis that these length scales are controlled by dominant wavelengths arising from unstable compression or extension of the venus lithosphere results show that the existence of tectonic features that exhibit both length scales can be explained if at the time of deformation the lithosphere consisted of a crust that was relatively strong near the surface and weak at its base and an upper mantle that was stronger than or of nearly comparable strength to the upper crust the spacings of these features imply crustal thicknesses in the approximate range 5 30 km and a thermal gradient not greater than 25 k km 1 features that exhibit only the smaller scale of deformation can be explained by either a lithosphere with a thick crust that overlies a weak mantle or a lithosphere with a strong mantle but with small internal strength contrasts for a broad range of parameters the models require not only that smaller scale compressional and extensional features have similar spacings but also that the widths and spacings of larger scale compressional features be greater than those formed in extension this is consistent with observed differences in the characteristic length scales of larger scale surface features as well as the similarities in spacings of observed smaller scale features

relationship between thermal maturation gradients geothermal gradients and estimates of the thickness of the eroded foreland section southern alberta plains canada abstract analysis of post laramide tertiary uplift and erosion in the southern alberta plains indicates that the greatest erosion occurred in regions where the youngest stratigraphic units are preserved this is consistent with geological structure and the few preserved stratigraphic constraints on erosional history throughout this region erosion is pervasive and the uplift history is commonly constrained by coalification data the analysis of coalification erosion and paleogeothermics are interrelated and knowledge of them is important to understand hydrocarbon generation and tectonic history several independent attempts to analyse coalification erosion and paleogeothermics in this area have given different results the most striking differences are those between estimates derived from the analysis of well profile coalification gradient and those determined using a commonly accepted relationship between the amount of eroded section and the equilibrium moisture content of near surface coals the match between present and paleogeothermal gradient fields is better when the latter technique is used correlation is expected between the late orogenic and present geothermal gradient fields because the hydrodynamically controlled advective heat flow pattern that now dominates geothermal gradients in the mesozoic and tertiary foreland succession was initiated by the growth of topography in the west throughout cordilleran orogeny well profile coalification gradients have significant though commonly unacknowledged uncertainties these uncertainties are propagated in erosion and paleogeothermal gradient calculations ideally the relationship between erosion estimates using well profile coalification gradients and near surface coal properties can be compared unfortunately the uncertainties in well profile coalification gradients prevent this

physical and chemical properties of the sulphur mountain thermal springs banff national park and implications for endangered snails nine thermal springs in three groups occur along the flank of sulphur mountain in banff national park the principal recharge zone is suggested to be above 2000 m elevation on mount rundle circulation depths are estimated to be 3 2 0 6 km and discharge is focused along the sulphur mountain thrust springs show constant temperature and total dissolved solids load throughout the winter whereas both drop in association with spring snowmelt the degree and timing of temperature drops are a function of elevation with the highest springs showing the earliest and most significant temperature drop the highest elevation springs also show the greatest seasonal variability in water chemistry unusual seasonal flow stoppages of these springs are related to extreme low precipitation years the biogeochemistry of the thermal springs and population fluctuations of the endemic and endangered banff springs snail physella johnsoni are strongly related to seasonal variability in flow rates changes in redox condi

timing and petroleum sources for the lower cretaceous mannville group oil sands of northern alberta based on 4 d modeling the lower cretaceous mannville group oil sands of northern alberta have an estimated 270 3 billion m3 bcm 1700 billion bbl of in place heavy oil and tar our study area includes oil sand accumulations and downdip areas that partially extend into the deformation zone in western alberta the oil sands are composed of highly biodegraded oil and tar collectively referred to as bitumen whose source remains controversial this is addressed in our study with a four dimensional 4 d petroleum system model the modeled primary trap for generated and migrated oil is subtle structures a probable seal for the oil sands was a gradual updip removal of the lighter hydrocarbon fractions as migrated oil was progressively biodegraded this is hypothetical because the modeling software did not include seals resulting from the biodegradation of oil although the 4 d model shows that source rocks ranging from the devonian mississippian exshaw formation to the lower cretaceous mannville group coals and ostracode zone contributed oil to mannville group reservoirs source rocks in the jurassic fernie group gordondale member and poker chip a shale were the initial and major contributors kinetics associated with the type iis kerogen in fernie group source rocks resulted in the early generation and expulsion of oil as early as 85 ma and prior to the generation from the type ii kerogen of deeper and older source rocks the modeled 50 peak transformation to oil was reached about 75 ma for the gordondale member and poker chip a shale near the west margin of the study area and prior to onset about 65 ma from other source rocks this early petroleum generation from the fernie group source rocks resulted in large volumes of generated oil and prior to the laramide uplift and onset of erosion 58 ma which curtailed oil generation from all source rocks oil generation from all source rocks ended by 40 ma although the modeled study area did not include possible western contributions of generated oil to the oil sands the amount generated by the jurassic source rocks within the study area was 475 bcm 2990 billion bbl

flow system controls of the chemical evolution of groundwater abstract isotopic and major ion analyses of 130 fresh and brackish groundwater samples reveal a strikingly consistent pattern of variation over 28 000 km 2 of the western canada sedimentary basin hydrodynamic interpretations based on drill stem tests and piezometric data reveal a pattern of broad regional flow from south to north however there is some evidence to suggest that patterns of groundwater flow have been influenced in the past by wisconsin glaciation all the permeable units appear to be recharged by meteoric water in the south where they outcrop or come close to the surface samples of groundwater collected down dip in each of six major sandstone units are progressively enriched in d 18 o na and cl for example the deepest waters of the artesian milk river aquifer are enriched by up to 70 and 15 with respect to the d and 18 o of the modern recharge waters the pattern of chemical evolution is strongly related to the hydraulic characteristics of individual units the isotopic composition is determined by the extent to which hydraulic conductivity has facilitated meteoric water flushing of connate water thus more permeable units and permeable zones within a unit tend to be isotopically lighter because of a more complete and more rapid invasion of meteoric water interestingly the largest conductivity values are found in some of the deepest units 1500 m consequently water in these deeper units have d and 18 o values which approach that of the recharge the major ion chemistry is controlled both by this process and a complex set of rock water interactions in addition to providing information about the chemical evolution of groundwater this study can begin to quantify the complex pattern of flushing in a large sedimentary basin

rapid evaluation of the hydrochemistry of a sedimentary basin using only standard formation water analyses example from the canadian portion of the williston basin abstract the canadian portion of the williston basin is used as an example of how 15 000 standard formation water analyses in about 15 aquifers can be evaluated rapidly using easily available culling and data distribution display software techniques and software used include a program for culling erroneous and missing data in standard formation water analyses electronic grids of stratigraphic surfaces and unit boundaries from the new geological atlas of the western canada sedimentary basin grid manipulation software and a geochemical modelling program solmineq 88 intra and inter basinal hydrochemical continuity at the regional scale was matched visually by comparing salinity maps on the canadian side of the basin with salinity maps from the american side and with the adjacent alberta basin inter aquifer continuity to identify aquifer systems and the relative strength of aquitards was determined using a combination of 1 salinity distribution maps 2 maps showing salinity differences between aquifers and across intervening aquitards and 3 the relation among so 4 in formation waters the distribution of anhydrite and the saturation of the formation waters with respect to anhydrite evaporites strongly influence the composition of adjacent formation waters even to the extent that in one aquifer the normal increase of salinity with depth is reversed the process of freshwater influx into the western part of the basin is demonstrated by a series of salinity maps they suggest that the process is current and has included removal of halite from the major basinal aquitard this regional scale evaluation required an elapsed time of only about 10 working days hence a fairly rapid study

serpentinites from winklarn northeastern bavaria f r g and from brezovica and radusa yugoslavia relics of sub oceanic mantle abstract subordinate serpentinites in moldanubian gneisses in northeastern bavaria were formerly harzburgites to dunites they contain relics of apparently primary chromite which are similar in composition to chromites in ophiolitic alpine type tectonites as described in the literature and as studied at brezovica and radusa yugoslavia the northeastern bavarian serpentinites are relics of uppermost mantle ultramafitites formed beneath former oceanic crust and thus indicate the presence of a former although probably narrow ocean some northeastern bavarian serpentinites are accompanied by amphibolites and eclogite amphibolites a genetic relationship in the form of parts of dismembered ophiolites is highly probable in this case the emplacement of oceanic crust mantle took place before the high pressure metamorphism recognized in the moldanubian as the serpentinized peridotites carry neither garnet nor indications of its former presence pressure during this metamorphism apparently has not exceeded that of the cr rich spinel peridotite stability field

the relation between stratigraphic elements pressure regime and hydrocarbons in the alberta deep basin with emphasis on select mesozoic units we have very little to state by way of a response to bachu et al 2002 except to make the following brief observations and comments 1 the reader will note that the title specifically deals with the relation between stratigraphic elements pressures and hydrocarbons with an emphasis on mesozoic units this emphasis is clearly stated in putnam and ward 2001 p 692 the major aim of this article is to document and interpret the significance of overpressured mesozoic sandstones in western alberta bachu et al s 2002 p 525 comments however are focused on pressure and flow systems particularly in the devonian in fact our results have been reviewed with reference to the complete geological column in west central alberta and the units discussed were provided both as examples of the two hydrodynamic regimes present and the

manetoe facies a gas bearing megacrystalline devonian dolomite yukon and northwest territories canada the manetoe facies is a broadly stratiform and regionally developed 38 000 km2 or 15 000 mi2 body of white sparry dolomite hosted in lower and middle devonian strata and is the northwestward continuation of the similar but better known presqu ile facies dolomite several large gas fields have been discovered within anomalously thick developments of the manetoe dolomite close to the northwest limit of the devonian elk point basin of alberta the external geometry of the manetoe facies indicates that it may have been a cavern or karst system excavated in the late middle devonian by a large vertically confined coastal aquifer the local regions of anomalously thick manetoe facies may have developed where the aquifer stoped upward into strata above the confining aquiclude of the headless formation shale dolomite cementation may have occurred during any of three possible episodes of large scale fluid movement fluid inclusion and strontium isotope data favor the hypothesis that manetoe dolomites precipitated from heated 150 210 c or 300 410 f hypersaline evaporitic brines that have interacted with the underlying precambrian crust probably in the late devonian lead isotope data support the general concept of pre mesozoic dolomite cementation and largely preclude a late early tertiary deep burial setting spectacular zones of detrital dolomite cement within the manetoe are most readily accommodated by a near surface very early middle devonian aquifer mixing model origin but the presence of these zones does not preclude the other possible origins carbon and xygen isotope data from the manetoe facies support the concept that the presqu ile and manetoe facies are physically continuous and had a common origin

quantitative evaluation of lower cretaceous mannville group as source rock for alberta s oil sands the western canada sedimentary basin hosts about 12 billion bbl of conventional oil in devonian to cretaceous reservoirs lower cretaceous oil sands contain an additional 1 3 trillion bbl in place the oil sands represent the biodegraded remnants of supergiant conventional oil deposits the source for which has been thought to be mature rocks of the equivalent age mannville group this work shows however that the known mannville rocks alone are incapable of generating the required volume of hydrocarbons the volume of hydrocarbons generated in the mannville beneath central alberta was calculated by combining measured geochemical and geologic data with lopatin s method for thermal maturation original hydrocarbon generative capacity of the mannville rocks was calculated from geochemical analyses of immature samples using average values for total organic carbon toc 1 3 and rock eval hydrogen index 100 mg hc g toc maximum hydrocarbon generation per unit volume of source rock was calculated the maturation model was then employed to estimate the extent to which maximum yield has actually been achieved total volume of source rock in the basin was obtained from isopach maps of mannville shale multiplication of actual oil generation per unit volume by source rock volume gave a generated volume of 450 billion bbl these calculated values are exceedingly optimistic however because they ignore inefficiencies in expulsion and migration inclusion of oil generated in mannville equivalent source rock in the foothills belt would less than double this quantity assuming that source potential there is similar to that of the central alberta rocks it is clear that the mannville group of the western canada sedimentary basin cannot be the major source of alberta s oil sand hydrocarbons either the hydrocarbons were generated in as yet undocumented very organic rich mannville equivalent rocks in the foothills or they are derived from multiple sources throughout the basin

thermal history of alberta deep basin comparative study of fluid inclusion and vitrinite reflectance data the thermal history of the alberta deep basin the gas saturated westernmost part of the western canadian sedimentary basin has been studied by analyzing aqueous and hydrocarbon fluid inclusions in diagenetic cements and comparing the results with coal maturity data results indicate that most of the diagenetic quartz druse precipitated from low salinity fluids 2 3 wt at a temperature of 170 195 c calcite cement precipitated after quartz druse during uplift and cooling at temperatures of 108 169 c inclusions rich in larger hydrocarbon molecules occur in cements that precipitated at 150 c whereas methane rich inclusions occur in cements that precipitated at 165 c or at lower temperatures after significant uplift and cooling of the b sin maximum burial temperatures tmb calculated from vitrinite reflectance data using the lopatin waples tti ro calibration are significantly lower 150 c than the temperature at which quartz druse precipitated in the same area 190 c an equation directly relating tmb and ro proposed by barker and pawlewicz in 1986 yields maximum burial temperatures 200 210 c only slightly higher than the fluid temperatures the results from this study suggest that hot fluids migrated updip along permeable conglomerates and bedding plane fractures to produce unexpectedly high geothermal gradients 38 c km in the western part of the study area the apparent restriction of hot fluids to the western part of the study area sugge ts that convective heat transfer by fluids may have operated on a scale of only tens of kilometers in lower cretaceous rocks of the alberta deep basin

coalification shale diagenesis and thermal modelling in the alpine foreland basin the western molasse basin switzerland france abstract the analysis of coalification and shale diagenesis in oligocene and lower miocene sediments in the western part of the molasse basin western switzerland and haute savoie france shows a close relationship between the very low temperature metamorphism in the foreland and the tectonic history in the orogenic belt the degree of thermal maturation generally increases towards the alpine front isomaturity lines however run slightly oblique to today s alpine front this is probably due to the tectonic burying under the alpine nappes in early miocene time second order variations of the coalification pattern are explained as resulting from a regional discharge of warm fluids controlled by tectonic structures

origin chemistry and flow of formation waters in the mississippian jurassic sedimentary succession in the west central part of the alberta basin canada abstract the flow and chemistry of formation waters was analyzed in the mississippian jurassic succession in the west central part of the alberta basin using publicly available standard chemical analyses of formation waters and drillstem test data collected by the petroleum industry in alberta the interpretation of the thoroughly culled hydrogeological data show that a transition between a southern and a northern basin scale flow system takes place in the study area in the southeastern half of the study area the mississippian jurassic hydrostratigraphic group represents a single continuous carbonate sandstone aquifer system consisting of the lower jurassic nordegg member the triassic montney formation the permian belloy formation and the mississippian stoddart and rundle groups the confining units are the competent fernie and exshaw banff aquitards at the top and base respectively the salinity of formation waters increases northwestwards from 50 to 150 g l while the bicarbonate content decreases in similar fashion from 3 to 0 5 g l the flow pattern based on hydraulic heads and chemical composition of formation waters indicate decreasing mixing of meteoric water carried northward in the southern basin scale long range system with heavier connate water present in the northern part of the study area in the center and in the northeast the permian and mississippian carbonates and the triassic montney and charlie lake halfway sandstones form individual aquifers separated by the intervening doig montney aquitard the flow in the charlie lake halfway and the permo mississippian aquifers is directed east northeastward from the deformation front into the overlying aquitards or discharging into the southern basin scale flow system respectively only in the montney aquifer the flow is directed inward south southwestward drawn into a local hydrocarbon saturated sink which is created by a higher rate of gas escape than of gas generation through a low permeability and capillary seal region the high salinity in the 130 150 g l range and low bicarbonate content 0 5 g l of formation waters in the northern part of the study area indicate a connate origin the relation of na ca cl br concentrations in the formation waters suggest that these waters initially originated as seawater that was altered to some degree by subaerial evaporation and dolomitization but halite dissolution probably is the main source of salinity the driving mechanism for the flow of these waters could be either tectonic expulsion from deep strata in the deformed part of the basin as suggested by the high salinity of these waters or topography driven meteoric recharge in the rocky mountains through a tortuous path unidentified as yet the integrated interpretation of flow and chemistry of formation water shows that mississippian jurassic formation waters in the deep west central parts of the alberta basin have been influenced less by mixing with meteoric water than was identified previously in the central southern and northern parts of the basin the main reasons for the isolation of relict mississippian jurassic formation waters in the deep alberta basin are effective confining aquitards and the fact that this area is influenced only marginally by mixing with meteoric water carried by a gravity driven flow system

basement heat flow in the western canada sedimentary basin abstract the effective thermal conductivity of the entire sedimentary succession is calculated at 487 locations in the western canada sedimentary basin based on net rock analyses and thermal conductivity values corrected for temperature and porosity effects an easterly trend of increasing values is caused by shallower burial depth and by a reduced proportion of low conductivity shales geothermal gradients calculated previously and corrected for pleistocene glaciations are used in estimating the basement heat flow after subtracting the heat generated by radioactive decay in the sedimentary strata the distribution of basement heat flow with values between 30 and 80 mw m 2 is linked with the complex structure of the basement which is comprised of archean blocks accreted terranes orogenic belts and magmatic arcs heat flow heat generation relations in alberta show that the reduced heat flow and the characteristic length scale for the uppercrust thermal layer are of the order of 35 mw m 2 and 6 km respectively

mechanisms of coal metamorphism case studies from paleozoic coalfields controls on coal metamorphism can be complex in this paper we examine four paleozoic coalfields the western kentucky portion of the illinois basin the pennsylvania anthracite fields the south wales coalfield and the bowen basin an increase in temperature with depth of burial is certainly a factor in coal metamorphism in many coalfields however including the coalfields reviewed here it has become apparent that such a simple mechanism does not explain the coal rank patterns observed the flow of hydrothermal fluids through the coals has been proposed as a cause of coal metamorphism evidence includes inverted rank gradients elevated cfl as an indicator of brine fluids isotopic evidence for hydrothermal fluids and vein and cleat mineral assemblages in any case multiple hypotheses must often be evaluated in the examination of any coalfield since the simple paradigm of coal rank increases with a simple increase in temperature with increasing depth does not fit the evidence observed in many cases

temperature pressure conditions in coalbed methane reservoirs of the black warrior basin implications for carbon sequestration and enhanced coalbed methane recovery abstract sorption of gas onto coal is sensitive to pressure and temperature and carbon dioxide can be a potentially volatile supercritical fluid in coalbed methane reservoirs more than 5000 wells have been drilled in the coalbed methane fields of the black warrior basin in west central alabama and the hydrologic and geothermic information from geophysical well logs provides a robust database that can be used to assess the potential for carbon sequestration in coal bearing strata reservoir temperature within the coalbed methane target zone generally ranges from 80 to 125 f 27 52 c and geothermal gradient ranges from 6 0 to 19 9 f 1000 ft 10 9 36 2 c km geothermal gradient data have a strong central tendency about a mean of 9 0 f 1000 ft 16 4 c km hydrostatic pressure gradients in the coalbed methane fields range from normal 0 43 psi ft to extremely underpressured geothermal gradients within the coalbed methane fields are high enough that reservoirs never cross the gas liquid condensation line for carbon dioxide however reservoirs have potential for supercritical fluid conditions beyond a depth of 2480 ft 756 m under normally pressured conditions all target coal beds are subcritically pressured in the northeastern half of the coalbed methane exploration fairway whereas those same beds were in the supercritical phase window prior to gas production in the southwestern half of the fairway although mature reservoirs are dewatered and thus are in the carbon dioxide gas window supercritical conditions may develop as reservoirs equilibrate toward a normal hydrostatic pressure gradient after abandonment coal can hold large quantities of carbon dioxide under supercritical conditions and supercritical isotherms indicate non langmiur conditions under which some carbon dioxide may remain mobile in coal or may react with formation fluids or minerals hence carbon sequestration and enhanced coalbed methane recovery show great promise in subcritical reservoirs and additional research is required to assess the behavior of carbon dioxide in coal under supercritical conditions where additional sequestration capacity may exist

geothermal gradients hydrodynamics and hydrocarbon occurrences alberta canada using coal rank data and the demonstrated genetic link between the present hydrodynamic regime and geothermal gradient pattern it is possible to reconstruct the geothermal history of alberta over the past 60 m y palinspastic adjustment for tectonic compression caused by the major laramide thrusting shows that the predeformation isoreflectance lines increased logarithmically with depth in the late paleocene the geothermal gradient was about 23 c km 1 25 f 100 ft in the eastern alberta plains compared to about 30 c km 1 65 f 100 ft in the western alberta plains a regional trend opposite to the post laramide trends reconstruction of the early eocene surface indicates western uplands with geothermal gradients as low as 21 c km 1 15 f 00 ft and eastern lowlands with geothermal gradients of 27 c km 1 5 f 100 ft compared to the present situation this represents an enhanced topographic surface and a subdued geothermal gradient pattern the genetic relations of topography water table elevation hydrodynamic regime and geothermal gradient pattern in both the early eocene and the present conform to a model developed for any compacted sedimentary basin with subaerial relief in this model on a regional scale high topographic areas have high water table elevations with correspondingly high potentiometric surfaces these areas control the regional recharge of cold meteoric water and hence have low geothermal gradients areas of medium elevation exhibit regional lateral flow and intermediate geothermal gradients regional topographic lows correspond with low potentiometric surfaces and the regional discharge of warm formation waters from deep in the basin results in high geothermal gradients local topographic featur s cause perturbations in this picture study of both the regional pattern and fine detail of the early eocene and present topographic surfaces and geothermal gradient patterns shows the validity of the model the result of the second laramide orogenic pulse was therefore to reverse the geothermal gradient pattern resulting mainly from compaction flow and to impose a topographically controlled hydrodynamic regime with flow in the same direction but with a 9 c km 0 5 f 100 ft decreased geothermal gradient in western alberta and a 4 c km 0 2 f 100 ft increased geothermal gradient in eastern alberta as erosion proceeded during the tertiary the entire alberta basin warmed up until the present temperature regime was attained study of some major hydrocarbon occurrences shows a genetic link between the hydrocarbon occurrence and the present fluid regime which itself is controlled by the present topography for at least the significant upper cretaceous shallow gas reserves in southeastern alberta however their position may already have been determined as early as the beginning of the eocene by the topographic surface at that time therefore the extent to which the present topographic surface is responsible for hydrocarbon accumulation through gravity induced cross formational flow remains unknown because this process was operative as long ago as the early eocene what does not ap ear to be in doubt is the fact that gravity induced cross formational flow does control the hydrodynamic regime which in turn influences the geothermal gradient pattern and the accumulation of hydrocarbons

stable isotope and major element compositions of fluid inclusions in devonian and cambrian dolomite cements western canada abstract homogenization and melting temperatures major element and hydrogen and oxygen isotope data for fluid inclusions and carbon and oxygen isotope data for dolomite from the manetoe facies devonian and cathedral formation cambrian of western canada indicate that the dolomite cements formed from alteration of the host limestone by heated mixtures of evaporated seawater or residual evaporite brines and meteoric water the measured 18o values for fluid inclusion waters are much more negative about 8 than those calculated for waters in isotope equilibrium with dolomite at the moderately high temperatures of formation fluid inclusion waters appear to have exchanged oxygen isotopes reequilibrated with the host dolomite as they cooled the data may provide low temperature isotope exchange equilibrium fractionation factors between dolomite and water since no hydrogen bearing compounds other than water were found in these samples using quadrupole mass spectrometry the inclusion fluids likely retained their initial hydrogen isotope compositions therefore their 8d values 81 to 42 o are more useful for determining the origin of the dolomitizing fluids

coupled fluid flow heat and mass transport and erosion in the alberta basin implications for the origin of the athabasca oil sands regional topography driven flow systems related to laramide tectonic rebound were simulated using two dimensional coupled fluid flow heat transport and solute transport numerical models to replicate present formation water salinity and temperature distributions and investigate the accumulation of the athabasca oil sands previous modelling of this system was replicated and it predicted repeated replacement of all basin formation water with freshwater during deposition of the oil sands due to high permeabilities to match present alberta basin temperature and salinity distributions model hydrostratigraphy permeabilities and heat fluxes were adjusted this revised model conducts fluids along the mannville aquifer rather than the upper devonian aquifer and replicates present salinity distributions assuming instantaneous uplift around 60 ma fluid fluxes in principal aquifers decrease by two orders of magnitude using new permeabilities resulting in primarily conductive heat transport thus genesis

generation accumulation and resource potential of biogenic gas biogenic gas is generated at low temperatures by decomposition of organic matter by anaerobic microorganisms more than 20 of the world s discovered gas reserves are of biogenic origin a higher percentage of gases of predominantly biogenic origin will be discovered in the future biogenic gas is an important target for exploration because it occurs in geologically predictable circumstances and in areally widespread large quantities at shallow depths in rapidly accumulating marine sediments a succession of microbial ecosystems leads to the generation of biogenic gas after oxygen is consumed by aerobic respiration sulfate reduction becomes the dominant form of respiration methane generation and accumulation become dominant only after sulfate in sediment pore water is depleted the most important mechanism of methane generation in marine sediments is the reduction of co2 by hydrogen electrons produced by the anaerobic oxidation of organic matter co2 is the product of either metabolic decarboxylation or chemical decarboxylation at slightly higher temperatures the factors that control the level of methane production after sediment burial are anoxic environment sulfate deficient environment low temperatu e availability of organic matter and sufficient space the timing of these factors is such that most biogenic gas is generated prior to burial depths of 1 000 m in marine sediments most of the biogenic gas formed can be retained in solution in the interstitial pore waters because of higher methane solubility at the higher hydrostatic pressures due to the weight of the overlying water column under certain conditions of high pressures and or low temperatures biogenic methane combines with water to form gas hydrates biogenic gas usually can be distinguished from thermogenic gas by chemical and isotopic analyses the hydrocarbon fraction of biogenic gas consists predominantly of methane the presence of as much as 2 of heavier hydrocarbons can be attributed to admixture of minor thermogenic gas due to low temperature degradation of organic matter the amounts of hydrocarbon components other than methane generally are proportional to temperature age and organic matter content of the sediments biogenic methane is enriched in the light isotope 12c dgr13c1 lighter than 55 ppt owing to kinetic isotope fractionation by methanogens the variations in isotopic composition of biogenic methane are controlled primarily by dgr13c of the original co2 substrate which reflects the net isotopic effect of both addition and removal of co2 the methane isotopic composition also can be affected by mixing of isotopically heavier thermogenic gas the possible complicating factors require that geologic chemical and isotopic evidence be considered in attempts to interpret the origin of gas accumulations accumulations of biogenic gas have been discovered in canada germany italy japan trinidad the united states and ussr in cretaceous and younger rocks at less than 3 350 m of burial and in marine and nonmarine rocks other gas accumulations of biogenic origin have undoubtedly been discovered however data that permit their recognition are not available

cleat mineralization of upper permian baralaba rangal coal measures bowen basin australia coals from the permo triassic bowen basin have been investigated using a variety of complementary analytical techniques face cleat minerals in the studied samples are dominated by authigenic clays notably pure illite or illite chlorite mixtures butt cleats and joints are dominated by carbonates mostly calcite with less abundant ferroan calcite ankerite and siderite k ar ages of cleat fill illites and one fracture illite smectite fill indicate three phases of illite formation during the triassic 1 an early phase with ages clustered around 244 ma ago 2 a second phase about 232 ma ago and 3 the latest phase about 219 ma ago thermal modelling of selected boreholes from the study area and other geological data indicate that the first phase of illitization occurred when the coal seams were about 1000m below the surface and at a temperature of between 70 and 80 c at a time when the basin was rapidly subsiding these early illites were stable and retained their 1m polytype even after being exposed to temperatures of 150 190 c during maximum burial in the southeastern bowen basin the second phase of illitization at 232 3 occurred at about the time of maximum burial the latest phase took place between 223 3 and 212 3 ma ago and occurred in a wider temperature range between 170 and 100 c during a rapid uplift in the late triassic the bowen basin area experienced a second cycle of subsidence that commenced in the early jurassic with the formation of the surat basin which overlies the bowen basin and forms part of the great artesian basin system regional uplift and erosion in middle cretaceous times terminated sediment accumulation in the surat basin during the second cycle of burial widespread carbonate mineralization in butt cleats and joints took place calcite fluid inclusions indicate that calcite was precipitated from meteoric water at about 80 c the widespread carbonate mineralization in butt cleats and the near absence of carbonates in the face cleats is here attributed to permeability anisotropy caused by a change in the direction of lateral compressive stress during jurassic cretaceous times relative to that during the triassic hunter bowen orogeny

source rock contributions to the lower cretaceous heavy oil accumulations in alberta a basin modeling study the origin of the immense oil sand deposits in lower cretaceous reservoirs of the western canada sedimentary basin is still a matter of debate specifically with respect to the original in place volumes and contributing source rocks in this study the contributions from the main source rocks were addressed using a three dimensional petroleum system model calibrated to well data a sensitivity analysis of source rock definition was performed in the case of the two main contributors which are the lower jurassic gordondale member of the fernie group and the upper devonian lower mississippian exshaw formation this sensitivity analysis included variations of assigned total organic carbon and hydrogen index for both source intervals and in the case of the exshaw formation variations of thickness in areas beneath the rocky mountains were also considered all of the modeled source rocks reached the early or main oil generation stages by 60 ma before the onset of the laramide orogeny reconstructed oil accumulations were initially modest because of limited trapping efficiency this was improved by defining lateral stratigraphic seals within the carrier system an additional sealing effect by biodegraded oil may have hindered the migration of petroleum in the northern areas but not to the east of athabasca in the latter case the main trapping controls are dominantly stratigraphic and structural our model based on available data identifies the gordondale source rock as the contributor of more than 54 of the oil in the athabasca and peace river accumulations followed by minor amounts from exshaw 15 and other devonian to lower jurassic source rocks the proposed strong contribution of petroleum from the exshaw formation source rock to the athabasca oil sands is only reproduced by assuming 25 m 82 ft of mature exshaw in the kitchen areas with original total organic carbon of 9 or more