Belly River Research Articles

Possible controls of hydrogeological and stress regimes on the producibility of coalbed methane in Upper Cretaceous–Tertiary strata of the Alberta basin, Canada

The coalbed methane potential and producibility of any coal-bearing strata are strongly affected by the hydrogeological regime of formation waters and by coal permeability, which in turn depends on the effective stress regime of the coals. Peat that accumulated in the Alberta basin during the Late Cretaceous and early Tertiary led to the formation of coal deposits that may contain significant coalbed methane resources. The flow of formation waters plays an important role in the maintenance and producibility of this resource. The present-day flow is driven by gravity (topography) and erosional rebound and is controlled by rock permeability and the presence of gas-saturated sandstones. The estimated gas in place in the Tertiary–Upper Cretaceous coals decreases significantly with stratigraphic age, ranging between less than 2 bcf/mi2 in the lower coal zones and 12 bcf/mi2 in the uppermost coals. The gas content, especially of the deeper coals, is lower than would be expected for the corresponding coal rank and burial depth, most likely because the underpressuring has caused the release of gas from the coals and accumulation in adjacent sands. The shallow coals, although of low rank, may contain important amounts of late-stage biogenic methane. The salinity of formation water in shallow coal seams, where the flow is driven by topography, is low, generally less than 1500 mg/L, although in places, it reaches 3000–5000 mg/L. The salinity of formation water in the deeper, underpressured strata in the west-central part of the basin is significantly higher, reaching 18,000 mg/L. This affects treatment and/or disposal strategies with regard to the water produced concurrent to coalbed methane.The producibility of this resource depends on coal permeability, which decreases west-southwestward with increasing burial depth, from the order of several darcys in the shallow zones to millidarcys in the deep zones. The minimum effective stress, which affects coal permeability by closing fractures, increases west-southwestward from zero at the erosional edge of these strata to approximately 20 MPa near the Rocky Mountain deformation front. Fractures, including those in coal seams, will generally be vertical and will propagate on a southwest-northeast axis along the direction of the maximum horizontal stress, in a direction generally perpendicular to the Rocky Mountain deformation front.Considering the hydrogeological and stress regimes in conjunction with estimations of the gas content in coals, the region with probably good coalbed methane potential and producibility are the Ardley coal zone in the Scollard Formation and maybe, to a lesser extent, the coal zones of the stratigraphically deeper Edmonton and Belly River groups along their respective subcrop in central and southern Alberta. The deep Edmonton and Belly River strata in western and central Alberta have most likely a reduced coalbed methane potential as a result of lower gas content and of low permeability. These regional considerations need to be applied against local studies of coal thickness, rank, permeability, and gas content to identify the best targets for coalbed methane exploration and production.

ABSTRACT: Evidence Of First Order Tectonic Control and Point Load Migration in the Upper Cretaceous Milk River - Basal Belly River Interval in the Alberta Foreland Basin

ABSTRACT: Evidence Of First Order Tectonic Control and Point Load Migration in the Upper Cretaceous Milk River - Basal Belly River Interval in the Alberta Foreland Basin

Stratigraphic Architecture of the Oldman Formation, Belly River Group, Surface and Subsurface of Southern Alberta

ABSTRACT Regional surface and subsurface correlation of the middle Belly River Group clastic wedge confirms that the Oldman Formation is present throughout southern and central Alberta. The Oldman generally thins to the north and northeast due to depositional thinning and to truncation by the overlying Dinosaur Park Formation. The Oldman Formation, primarily a transgressive fourth-order subunit, can be informally divided into two mappable units, referred to here as the lower Comrey Member sandstone and the upper siltstone member. The Comrey Member is dominated by light grey, fine to coarse sandstone with a sheet-like geometry over much of the map area. However, variations in thickness suggest that it is arranged in sharp-based linear WSW/ENE-oriented incised valley fill trends, up to 33 m thick, composed of stacked lenticular fining-upward channel units. Based on limited outcrop data from the southern part of the study area, paleoflow within these valleys was likely toward the eastern hemisphere. Corresponding clean sandstone trends (potential reservoir rock) are up to 25 m thick. The overlying upper siltstone member is dominated by pale-coloured, thinly interbedded noncalcareous mudstone and fine sandstone, with abundant rooting, convolute lamination and pedogenic horizons. The sediments of the Oldman Formation were derived from the west and southwest. The regionally consistent upward sequence of facies from erosional base to sandstone-dominated to mudstone-dominated can be interpreted to represent a fundamental reorientation of paleogeography related to an increasing rate of basin subsidence and consequent transgressive pressure in southern Alberta. A rapid and extensive base level fall, interpreted as the result of tectonic quiescence, basinwide rebound and erosion, was followed by deposition of an overall transgressive succession during increasing base level rise related to widespread subsidence during a phase of renewed tectonic thrust loading. The formation encloses known gas pools, but the presence of large areas of thick clean sandstone with no designated pools suggests further exploration possibilities. Included maps are intended as guides; for practical application, more detailed mapping of individual sandstone bodies is necessary. RESUME La correlation de la surface et de la subsurface regionales du coin clastique du Groupe Belly River intermediaire confirme la presence de la Formation Oldman dans les regions sud et centre de l'Alberta. La Formation Oldman s'amincit vers le nord et le nord-est a cause d'amincissement des sediments et de la troncature par la Formation Dinosaur Park susjacente. La Formation Oldman, une sous-unite de quatrieme ordre principalement transgressive, peut etre informellement divisee en deux unites cartographiables, adressees dans le present document comme du gres du Membre Comrey inferieur et du membre de l'aleuronite superieure. Le Membre Comrey est domine principalement par la couleur grispale, le gres s'echelonne de fin a epais avec une geometrie stratiforme couvrant une grande partie de la region cartographiee. Toutefois, les variations d'epaisseurs suggerent les directions OSO/ENE des vallees encaisses, jusqu'a 33 m d'epaisseur, composes d'unites avec des depots de particules lenticulaires fines vers le haut entasses. Selon les donnees limitees sur les affleurements de la partie sud de la region etudiee, le paleocourant dans ces vallees ce dirigeait fort probablement vers l'hemisphere est. Les directions nettes des gres (roches reservoir possibles) correspondant mesurent jusqu'a 25 m d'epaisseur. Le membre sus-jacent de l'aleuronite superieure est domine de minces couches de pelites, couleur pale, non-calcaire et de gres fins, avec une abondance d'enracinements, de laminations contournees et d'horizons pedologiques. Les sediments de la Formation Oldman proviennent de l'ouest et du nord-ouest. 1 Geological Survey of Canada Contribution No. 1996254 End_Page 155------------------------ La sequence de facies ascendante regionalement uniforme du socle d'erosion, a principalement de gres, a principalement de pelites, peut etre interpretee de facon a representer une nouvelle orientation de la paleogeographie connexe a l'augmentation du taux croissant d'effondrement du bassin et de la pression transgressive qui en resulte dans le sud de l'Alberta. Une chute rapide importante du niveau du socle, interpretee comme etant le resultat d'un repos tectonique, le rebond et l'erosion a l'echelle du bassin, suivi du depot d'une succession en general transgressive pendant une augmentation du socle reliee a l'effondrement etendu pendant une phase de chargement renouvele de poussee tectonique. La formation englobe les gisements de gaz, mais la presence de regions importantes de gres net epais sans gisement designe, suggere des possibilites d'exploration avenir. Les cartes incluses ont pour but d'etre des guides; pour application pratique, des cartes plus detaillees des masses de gres sont necessaires. Traduit par Marie-Louise Tomas

Allostratigraphy of the Upper Cretaceous Lea Park - Belly River Transition in Central Alberta, Canada

Allostratigraphy of the Upper Cretaceous Lea Park - Belly River Transition in Central Alberta, Canada

Numerical Modelling of the Hydrodynamically Trapped Milk River Gas Field, Western Canada

Abstract The Milk River Gas Field, located in southeastern Alberta, is the largest single gas accumulation in the Western. Canadian Sedimentary Basin, with recoverable reserves estimated at 140 000 X 106m3. This hydrodynamically trapped gas field, positioned over the-Sweetgrass Arch, covers an area greater than 200 townships and has no identifiable up-dip structural closure. A steady-state, finite difference, single-phase, numerical fluid flow model was constructed for a 24 X 24 township area (Townships 1 – 24, Ranges 25W3-19\V4M). The water migration from the Belly River to the Bow Island was modelled in three dimensions. The primary input data included aquifer structure thickness and permeability. The permeability of the aquitards was varied until a good match was obtained with observed water potentials. The structural top and the modelled potentiometric surface for the Milk River aquifer were combined using the method described by Hubbert in 1953 (UVZ). The resulting gas isopotential map illustrates 'the migration paths and accumulation sites of gas within a hydrodynamic system. Since the gas pool interferes with the water migration, the model was sensitized to account for the effective aquifer and aquitard permeabilities with the presence of the gas. This altered the position and gross pay distribution of the gas pool. The model was used to estimate the significance of cross formational flow. When the aquitards were made impermeable, the resulting water potentials showed no resemblance to field data. A minimum of three layers are required to represent flow within the aquifer. The middle layer represents the aquifer and the adjacent layers account for vertical, cross-formational flow into and out of the aquifer- The model demonstrates that aquitard permeability is a controlling factor, and that hydrocarbon pools will alter water migration in their vicinity and therefore need to be taken into account. Introduction This paper illustrates the utility of hydrogeological modelling in explaining the trapping of the Milk River Gas Field. An understanding of the nature of this hydrodynamic trap will greatly assist future exploration efforts in similar environments. The project area illustrated in Figure 1 extends from the U.S. border up to Township 24, and from Range 24W3M in Saskatchewan to Range 19W4M in Albena. The first well drilled to produce gas from the Milk River formation was spudded in 1904(1). The Medicine Hen #2, located at JO-31-012-05W-t-M the centre of the city of Medicine Hat supplied the city with natural gas. In 1911, three additional Milk River gas wells were put on production within the dry of Medicine Hat and ten more in 1913. It wasn't until 1914 that the first well was drilled outside of the city limits. Some of the wells drilled within the city limits were owned by local businesses (e.g., Alberta Clay and Maple Leaf). Development of the field around the Suffield Military Reserve was controlled by gas prices and drilling areas offsetting existing production. Today, the Milk River Gas Field has grown to cover over 200 townships, and has 30,000 gas wells and total proven recoverable reserves exceeding 140.000 × 106m3.

Instream flows and the decline of riparian cottonwoods along the St. Mary River, Alberta

Completed in 1951, the St. Mary Dam enables water storage and diversion for irrigation; river flows downstream are consequently dramatically reduced during summer months. To assess historical changes in the abundance of riparian cottonwoods (Populus balsamifera, Populus angustifolia, and a few Populus deltoides), airphoto analyses were conducted for 40-km river reaches upstream and downstream from the dam and along adjacent dammed and undammed rivers. Cottonwoods along the lower St. Mary River are confined by steep-walled canyons to narrow bands and consequently analyses of the lineal river distance associated with cottonwoods were conducted. These revealed a 68% decline from 1951 to 1985. The decline was progressive, with 28.9, 27.6, 15.1, and 7.6% of the reach associated with cottonwoods in 1951, 1961, 1981, and 1985, respectively. Ground surveys from 1985 to 1994 indicated further decline after 1985 and an absence of cottonwood seedlings and saplings. Cottonwood stands upstream from the St. Mary Dam and along adjacent rivers are more extensive and analyses of the areal extent of stands were consequently appropriate. These indicated minor change along the upper St. Mary (−0.5%), the upper (+1.9%) and lower Waterton (+3.5%), and the upper Belly (−9.1%) rivers, and an increase in forest abundance along the lower Belly River (+52.2%), between 1951 and 1985. Thus, the decline of cottonwoods along the lower St. Mary River was not symptomatic of a general pattern of decline in the region. Analyses of historical stream flows indicated that the cottonwood mortality was drought induced as a result of insufficient flows during the hot, dry summer periods and abrupt flow reductions following the high-flow period in the late spring. The riparian water table was determined to be closely coordinated with river stage, as changes in river elevation were followed by quantitatively similar changes in water table depth. Along the St. Mary River, reduced sedimentation downstream from the dam was not considered to be responsible for the cottonwood decline. The historically sparse cottonwood abundance along the lower St. Mary River may have reflected environmental conditions that were naturally only marginally suitable, and those groves may have been particularly vulnerable to the impacts of river flow regulation. Key words: Populus, cottonwoods, instream flows, mortality, riparian vegetation.

Stratigraphy, structure and syntectonic sedimentation of the Campanian 'Belly River' clastic wedge in the southern Canadian Cordillera

The parautochthonous, subproximal segment of the 'Belly River' clastic wedge is subdivided into five new formations, listed here from oldest to youngest: Lees Lake, Burmis, Connelly Creek, Lundbreck and Drywood Creek. The Pakowki Formation divides the 'Belly River' clastic wedge into a lower succession consisting of predominantly marine sediments (the Lees Lake and Burmis Formations) and an upper succession (the Connelly Creek, Lundbreck and Drywood Creek Formations). The lower succession including the Pakowki Formation belongs to the Alberta Group and the upper succession represents the Belly River Group. The formations have been mapped in the Foreland Thrust and Fold Belt west of Lundbreck, Alberta, and correlated with the subsurface distal, autochthonous formations of the Interior Platform. Early indications of Laramide tectonic activity in the source area are recorded by the turbidites of the Lees Lake Formation. An increase in the supply of sand during deposition of the Lees Lake Formation produced thick sandstone layers which were syndepositionally deformed and partly eroded by sediment-laden density currents. The contact between the Lees Lake Formation and the overlying Burmis Formation is unconformable because of submarine erosion. The Burmis Formation is recognized as a deltaic sequence containing a lateral transition from fluviatile through distributary channel-fill to distributary mouth-bar facies. The next phase of the Laramide Orogeny is recorded by the upper delta plain facies of the Connelly Creek Formation and the alluvial fan facies of the Lundbreck Formation. The fan-shape geometry and sedimentological features of the Lundbreck Formation, especially the ephemeral, high-energy channels, semi-arid paleosols and playa deposits indicate sedimentation on a semi-arid alluvial fan bordering the upper delta plain environment. Flash-flood deposition within the ephemeral channels and deep erosion of the alluvial plain during sedimentation of the Lundbreck Formation suggest significant syndepositional topography. The semi-arid alluvial fan environment suggested for the Lundbreck Formation implies an uplifted mountain front during its formation. Basinward progradation of the Connelly Creek/Lundbreck delta was caused by easterly propagation of the tectonic deformation that forced the Pakowki Sea to retreat from the Crowsnest Embayment.

Coal deposits in the front ranges and foothills of the Canadian Rocky Mountains, southern Canadian Cordillera

Canada has the fifth largest inventory of coal resources in the World. More than one-third of Canada's resources currently favourable for exploitation occur in the southern Canadian Rocky Mountains, with major deposits in the Front Ranges, Inner Foothills and Outer Foothills physiographic provinces. In the Front Ranges, major deposits of metallurgical and thermal, high-volatile bituminous to semi-anthracite coal occur in the Late Jurassic-Early Cretaceous Mist Mountain Formation. In the Inner Foothills of northeastern British Columbia and west-central Alberta, significant resources of metallurgical and thermal, medium- and low-volatile bituminous coal occur in Early Cretaceous strata of the Gething (Aptian) and Gates (Albian) Formations. In the Outer Foothills resources of thermal, high-volatile bituminous coal occur in Late Cretaceous and Paleocene strata of the Belly River (Campanian), Coalspur (Maastrichtian-Paleocene) and Paskapoo (Paleocene) Formations. The major coal deposits of the Front Ranges and Inner Foothills accumulated within the coastal plains of the Fernie and Moosebar-Clearwater seas, respectively. Shorelines prograded to the north and northeast into a foreland basin that evolved in advance of, and in response to, the evolving Columbian Orogen. In the Outer Foothills, coal deposits of the Belly River Formation originated within prograding coastal plains during the withdrawal of the Pakowki Sea. The major coal deposits of the Coalspur and Paskapoo Formations accumulated in the alluvial plain environments of the foreland basin during the Laramide orogeny. Coal measures of the southern Canadian Rocky Mountains were variably folded and faulted during the Laramide orogeny (Late Cretaceous-Eocene). Structural deformation has significantly affected the mineability and quality of the coals. Many of the coal seams are sheared, structurally thickened or thinned and repeated by thrust faults or truncated by normal faults. Shearing of the seams in adjacent hanging and footwall strata has led locally to pronounced oxidation, resulting in weak coal pillars and roofs in underground mines. Faulting and folding has partitioned many coal deposits into discrete structural domains of varying style and complexity, each of which can present a unique challenge in designing optimum coal extraction methods. The variation in coal rank in the southern Canadian Rocky Mountains mainly reflects the preorogenic (pre-Laramide) depth of burial. In some areas, however, there is evidence for syn- and post-orogenic coalification, resulting from the emplacement of thick overthrust sheets and/or deposition of thick Tertiary molasse, most of which has been subsequently eroded. With few exceptions, coals of the southern Canadian Rocky Mountains are characterized by low sulphur contents (< 1%) and ash yields that range from 10% to 30%. The maceral composition of the coals is highly variable; Late Jurassic and Early Cretaceous coals are known for high percentages of semi-fusinite (ca. 30%) and Late Cretaceous and Paleocene coals for high vitrinite contents compared to most coals. All of the coal-bearing stratigraphic successions include multiple, thick seams and all existing mining operations are designed to extract and, where necessary, blend multiple seams.

Tectonic, stratigraphic, and sedimentologic significance of a regional discontinuity in the upper Judith River Group (Belly River wedge) of southern Alberta, Saskatchewan, and northern Montana

The lithostratigraphic interval between the Taber and Lethbridge coal zones in the upper portion of the nonmarine Judith River Group of southeastern Alberta is divisible into two lithostratigraphic units separated by a regionally extensive and diachronous discontinuity. The lower unit, referred to here as the Oldman Formation, is characterized by very fine grained to fine-grained sandstones that contain fewer than 2% volcanic rock fragments; sandstone bodies with numerous sets of horizontally stratified sandstone, showing little or no evidence of lateral accretion; siliceous paleosols (ganisters); and a relatively high gamma-ray signal in the upper half of the formation. The Oldman Formation comprises deposits of a low-sinuosity, perhaps ephemeral fluvial system that originated in the southern Cordillera of Canada and northern Montana and flowed northeastward, perpendicular to the axis of the Alberta Basin.The upper unit is assigned to a new formation, the Dinosaur Park Formation, and is characterized by fine- to medium-grained sandstones with up to 10% volcanic rock fragments; sandstone bodies that exhibit lateral-accretion surfaces in the form of inclined heterolithic stratification; numerous articulated dinosaurs and dinosaur bone beds; and a relatively low gamma-ray signal in the lower half of the formation. The Dinosaur Park Formation comprises deposits of a high-sinuosity, fluvial-to-estuarine system that originated in the north and central Cordillera and flowed southeastward, subparallel to the axis of the Alberta Basin.40Ar/39Ar and K–Ar dating of Judith River Group bentonites shows that the contact between the Oldman and Dinosaur Park formations becomes younger toward the south and southeast. These data also demonstrate that the Dinosaur Park Formation clastics migrated southeastward at a rate of approximately 130–140 km/Ma, gradually overstepping the Oldman Formation elastics.The widely recognized north-to-south increase in intensity of overthrust loading along the western margin of the Alberta Basin during the Late Cretaceous is thought to be responsible for (i) differences in accommodation space for the proximal portions of the Oldman and Dinosaur Park formations, and (ii) the establishment of a southerly tilt in the Alberta Basin leading to the southeastward migration of the Dinosaur Park Formation elastics. In the northern portion of the basin, relatively lower rates of subsidence, combined with periods of isostatic rebound in the foredeep, resulted in the southeastward migration of Dinosaur Park Formation elastics as sediment input exceeded accommodation space. In the southern portion of the basin, relatively higher rates of subsidence and little isostatic rebound acted to trap coarse-grained Oldman Formation elastics in the foredeep and may have led to periods of sediment starvation in more distal portions of the basin. An inferred lower depositional slope associated with the Dinosaur Park Formation (relative to the Oldman Formation) is thought to have resulted from gradual loading of the basin as Dinosaur Park Formation elastics migrated southeastward or some form of tectonically induced subsidence.

Allostratigraphy and Depositional Environments of the Basal Belly River Formation (Campanian) in Central Alberta

Allostratigraphy and Depositional Environments of the Basal Belly River Formation (Campanian) in Central Alberta

Palinspastically Restored Belly River Delta in the Crowsnest Embayment of the Wapiabi (Colorado) Sea: Southern Foothills of the Canadian Cordillera

Palinspastically Restored Belly River Delta in the Crowsnest Embayment of the Wapiabi (Colorado) Sea: Southern Foothills of the Canadian Cordillera

Compaction and Porosity Prediction in Chert-Rich Sandstones and Conglomerates

Chert-rich sandstones and conglomerates are volumetrically important oil and gas reservoir units in western and northern Canada and in Alaska. Unlike quartzofeldspathic sandstones, chert-rich sandstones are highly susceptible to intergranular pressure solution resulting in dramatic loss of intergranular volume (IGV) and porosity with burial. Thin-section petrographic data were used to develop a suite of IGV-decline curves for chert-rich sandstones and conglomerates as the basis for porosity prediction algorithms. The samples studied range in composition from chert-quartz litharenites (Viking Formation, Paddy-Cadotte and Falher members, western Canada basin) to chert-rich litharenites containing appreciable feldspars and volcanic grains (Clearwater and Belly River formations, western Canada basin, and Reindeer Sequence, Mackenzie Delta). Physical characteristics of chert, such as the degree of microcrystallinity or the presence of impurities and micropores, in part, determine chert's susceptibility to dissolution. Where chert and quartz grains are compacted together, chert is typically penetrated by quartz. Pressure-solution features of chert, such as pocked or dimpled clasts and microstylolitic textures, can be observed in core and cuttings, thin sections, and SEM samples. Early cementation in chert-rich sandstones can limit the effects of compaction. For example, quartz overgrowths in the Viking Formation inhibit later intergranular pressure solution. Formation inhibit later intergranular pressuremore » solution. In chert-rich sandstones and conglomerates, porosity and permeability prediction is complicated by cement timing, cement type and distribution, degree of leaching, and grain textural variety.« less

Minerological and O-isotope studies of diagenesis and porewater evolution in continental sandstones, Cretaceous Belly River Group, Alberta, Canada

The mineralogy and O-isotope geochemistry of diagenetic phases from continental sandstones of the Upper Cretaceous Belly River Group, west-central and south-western Alberta, have been determined. Diagenesis of the continental sandstones is dominated by crystallization of clay minerals, including Fe-rich chlorite (δ 18O = +3.3 to +9.3‰), I/S, C/S and illite (δ 18O= +9.5 to + 10.7‰), kaolinite (δ 18O = +5.9 to +12.7‰), S/I and smectite (δ 18O = +11.0 to 14.0‰). Other diagenetic phases include quartz overgrowths (δ 18O = +12.0 to +21.0‰) and calcite (δ 18O = +8.5 to +12.9‰; δ 13C = #x02212;14.3 to −2.0‰). Chlorite generally crystallized first in the paragenetic sequence, followed by quartz, I/S, calcite and kaolinite, and then S/I and smectite. Interpretation of these data suggests that early diagenesis occurred in the presence of low- 18O meteoric water whose δ 18O value rose moderately during subsequent burial. Highest burial temperatures (≈110°C) were probably achieved in the south-western portion of the study area, and are reflected by the appearance of R1-ordered I/S in this locality. Post-Laramide influx of meteoric water subsequently resulted in a substantially lower porewater δ 18O value. Values of δ 18O for diagenetic minerals from the continental sandstones and immediately underlying deltaic and shoreline, basal sandstones are systematically lower (by +1 to +6‰) than equivalent phases from the Lower Cretaceous marine sandstones of the Viking Formation. Relative differences in the oxygen isotopic compositions of connate waters (freshwater vs sea water) have been preserved, surviving δ 18O-enrichment during burial and δ 18O-depletion during post-Laramide influx of meteoric water. While substantial meteoric dilution of the porewater has occurred, flushing of (evolved) connate waters has not been complete.

Hydrogen-isotope geochemistry of diagenetic clay minerals from Cretaceous sandstones, Alberta, Canada: evidence for exchange

The δD and δ 18O values of diagenetic kaolinite and 10Åclay minerals (illite, illite/smectite) have been determined for Lower Cretaceous Viking Formation marine sandstones and conglomerates, Upper Cretaceous basal Belly River Group shoreline and deltaic sandstones, and overlying Belly River/Brazeau Groups continental sandstones from the western Canada sedimentary basin. Early and late diagenetic kaolinites have a remarkably small range of δD values (−132 to − 112%, Viking Formation; −137 to−128%, Belly River/Brazeau Groups) relative to their δD 18O compositions (+13.8 to +26.9%, Viking Formation; +5.9 to +12.7%, Belly River/Brazeau Groups). The δD values are also much lower than commonly reported for kaolinite. Calculations indicate that the diagenetic kaolinite from all units is in, or close to, hydrogen-isotopic equilibrium with present formation waters at present subsurface temperatures. Within the limits of available fractionation data, similar observations can be made for diagenetic 10Åclay minerals from these units (δD = −132 to −107 %, Viking Formation; −138 to −123%, Belly River/Brazeau Groups). By comparison, a general state of oxygen-isotope equilibrium does not exist between diagenetic kaolinite and present formation waters. Kaolinite has retained oxygen-isotope compositions characteristic of neoformation during earlier stages of diagenesis. Some diagenetic 10Åclay minerals (e.g. Belly River/Brazeau Groups) may be in oxygen-isotope equilibrium with present formation waters because of neoformation from these waters (in sandstones), or oxygen-isotopic exchange during the smectite to illite transformation (in shales). The results of this study suggest that hydrogen-isotope re-equilibration between diagenetic kaolinite and formation water in sandstones can occur independent of oxygen-isotope exchange at temperatures as low as ≈40°C. Interpretation of hydrogen- and oxygen-isotope compositions for clay minerals from such systems (i.e. high water/rock ratio, low temperatures) should therefore be decoupled.

Thomas Chesmer Weston and the Red Deer River Fossil Fields

Thomas Chesmer Weston was an English lapidary, who was employed by the Geological Survey of Canada from 1858. He enjoyed field work and made important collections of minerals and fossils in various parts of Canada. In 1889 he made a boat trip down the Red Deer River of Alberta, assisted by Roderick McKenzie of Red Deer. Weston made important fossil finds on this trip, but his most notable discovery was the "Belly River" fossil field, now the Dinosaur Provincial Park. He recognized that this field was older than that of the "Edmonton Series" of Tyrrell, and predicted that it would be one of the world's great fossil fields, a prediction that his successors have fully confirmed.

Hydrocarbon generation and migration in the Western Canada sedimentary basin

Abstract A total of ten marine, petroleum source rocks ranging in age from Middle Devonian to Late Cretaceous exist within the Western Canada Basin. Principal hydrocarbon reserves occur in the Lower Cretaceous Mannville Group and subcropping Paleozoic carbonates, where 270 × 10 9 m 3 (1.7 trillion barrels) of heavy oil form one of the largest deposits of oil on Earth. Biomarker analyses of these heavy oils, many conventional oils and most source rocks in the basin have been combined with basic geology to establish the source and migration history of the Western Canada Basin. Several pre-Cretaceous source rocks (principally the Lower Jurassic Nordegg Formation, the Mississippian Exshaw/Bakken Formation, the Triassic Doig/Phosphate Formation and the Upper Devonian Duvernay Formation) have contributed to the Mannville accumulations. The Joli Fou shale, overlying the Mannville, is a regional seal for the Mannville and older section. Oils present in the overlying Viking, Cardium, and Belly River sands are all of a single family, sourced from the Colorado Shale section and are quite distinct from the oils in the Mannville and older section. Meteoric water incursion at the eastern limb of the basin permitted biodegradation, which converted the conventional Mannville crude oil to heavy oil. The Western Canada Basin also contains an estimated 5 × 10 12 m 3 (180 TCF) of gas. Gas sources are the marine, oil-prone source rocks where overmature, as well as Lower Cretaceous Mannville coals and coaly shales. Hydrogen sulphide is contributed from overmature Paleozoic evaporites/carbonates with an estimated 36% of the total in-place gas reserves being classified as sour.

The Alberta foreland basin: relationship between stratigraphy and Cordilleran terrane-accretion events

A foreland-basin sequence resulting from accretion of a terrane to a continental passive margin ideally should be unconformity bounded, with a shallowing-upward pattern, like the classic Flysch to Molasse sequence of Alpine foreland basins. The basal unconformity is cut as the peripheral bulge associated with lithospheric flexure migrates cratonward ahead of the basin and the advancing overthrusts. The shallowing occurs because sediment supply at first is low – early stages of accretion near the continental slope generate little or no topography above sea level; later stages result in significant tectonic uplift, and much sediment is shed into the foreland, filling the basin. The upper unconformity is cut as lithospheric bending stresses are relaxed following overthrusting, and reduction of the flexural load on the lithosphere through erosion and (or) tectonic denudation of the overthrusts causes regional uplift or basin "rebound". Actual sequences show differences from this idealized version in that (i) basal unconformities may not develop under conditions of high eustatic sea level; and (ii) they may not shallow upward in all cases. These differences can occur because later terranes that accrete onto the seaward side of a previously accreted terrane may simply push it farther onboard, thus initiating sediment supply as rapidly as the load-induced subsidence. Also, in this way, a small terrane can influence the filling of a foreland basin that is more than one "lithospheric flexural half-wavelength" away from the site of accretion.The stratigraphy of the Alberta basin has been divided after comparison with the idealized sequence resulting from an individual accretion event. The six clastic wedges recognized (Fernie–Kootenay, Mannville, Dun vegan, Belly River, Edmonton, and Paskapoo) show a temporal correlation with the times of accretion of terranes (Intermontane superterrane, Bridge River, Cascadia, Insular superterrane, Pacific Rim – Chugach, and Olympic, respectively) in the Cordillera. Therefore, the stratigraphy of the foreland basin may be best interpreted in terms of Cordilleran tectonics rather than sea-level fluctuations. Eustatic sea-level variations are believed to affect the internal stratigraphy and sedimentology of some clastic wedges and are responsible for the deposition of some thin units, but they appear to operate on time scales that differ from those of the clastic wedges identified here.

Abrupt downstream forest decline following river damming in southern Alberta

The influence of river damming on the abundance of riparian poplar forests was investigated by comparing forest abundances on the dammed St. Mary and Waterton rivers of southern Alberta with the neighbouring undammed Belly River. Forest distributions were determined by estimating the linear river distance of forests from airphotos taken in 1961 and 1981, both upstream and downstream from the dams. During the 20-year interval, a 48% reduction occurred downstream from the St. Mary Dam, which was completed in 1951. Downstream from the Waterton Dam, completed in 1964, riparian forests declined 23 %. Poplar abundance along the downstream region of the undammed Belly River was relatively unchanged over the study period, showing less than a 1 % reduction. The upstream (undammed) portions of all three rivers underwent a slight forest decline during the 20-year interval; declines of 4.7, 4.6, and 6.1 % occurred along the St. Mary, Belly, and Waterton rivers, respectively. Thus, the damming of two rivers in southern Alberta has been followed by a rapid and dramatic downstream decline in riparian forests. Further, the close association between the location and extent of the forest decline supports a causal relationship between the river damming and the forest decline. Possible causes of the decline are discussed, including drought-induced mortality, particularly of seedlings.

Belly River Formation of Western Alberta, Canada: Anatomy of an Emerging Deep Basin Oil Play: ABSTRACT

The Campanian Belly River Formation of western Alberta appears to form a largely bypassed deep basin type of oil play. In this setting hydrocarbons are found in lenticular fluvial reservoirs located upon folds or intersected by northwest-striking thrust faults and northeast-striking fractures. In the western fold and thrust belt, primary porosity is preserved within relatively thick and widespread grain-supported conglomerates. To the east, secondary porosity predominates in sandy lithofacies, and the best developed porosity is found proximal to fractures which enhanced fluid migration and grain dissolution. To the west, the unit exhibits progressive underpressuring, which reflects postorogenic sediment stripping combined with westward ground-water flow. A manifestation of the hydrodynamic regime is that many wells appear to have damaged Belly River zones because historically most exploration has been focused on deeper targets which require heavier mud weights. This style of hydrocarbon accumulation in the Belly River zone appears to cover several thousand square kilometers. The prior emphasis on deeper targets has also inhibited seismic delineation of Belly River reservoirs. Seismic acquisition must be designed to account for the relatively shallow depth and complex geometry of potential targets. Shear wave data appear to be a promising source of information in locating themore » distribution of reservoirs relative to fractures. The structural, depositional, diagenetic, and hydrodynamic development of the Belly River in western Alberta is similar to other clastic wedges formed during Laramide orogenic events. Thus, hydrocarbon accumulations may be anticipated in these other areas as well.« less

Sedimentological and palynological evidence of regional climatic changes in the Campanian to Paleocene sediments of the Rocky Mountain Foothills, Canada

Evidence of paleoclimatic variations in the upper Campanian to lower Paleocene post-Wapiabi sequence of strata is visible both laterally between the central and southern Foothills, and vertically in the stratigraphic record. These differences are expressed by the distribution of climatically sensitive sediments, i.e. coal and caliche, and associated palynological assemblages within floodplain facies, as well as by changes in the style of fluvial channels. The interpretation of a semi-arid environment for mature caliche paleosols is supported by the impoverished character of the associated palynological assemblages, both in terms of diversity and the number of specimens recovered, and by the conspicuous presence of Classopollis. The lateral extent of the semiarid floodplain facies and associated broad and mobile channel deposits is limited to the southern part of the basin. No signs of a caliche facies have been found in the post-Wapiabi strata of the central Foothills. Instead, some of the floodplain deposits associated with meandering streams in this part of the basin contain numerous, thick, coal-bearing intervals. The relative climatic differences between the more humid central part and the drier southern part of the basin prevailed throughout the entire post-Wapiabi interval. As this cannot be satisfactorily explained by the position of the sea shore or by orographic influences alone, there was probably another external factor. This could have been the pattern of atmospheric circulation, such as that responsible for the present-day climatic differences existing between the southern and central Foothills. Semiarid floodplain facies occur at two levels in the stratigraphic column of the southern Foothills (in the late Campanian, Belly River Formation and in the upper Maastrichtian to lower Paleocene, Willow Creek Formation). They correspond to regressive episodes of the epicontinental seaway. Intervening between these semiarid floodplain facies are the marine shales of the Bearpaw Formation and, both overlying and underlying them, thin coal beds. These represent recurrent periods of swamp growth and peat accumulation in back-barrier environments (lagoon-fill and supratidal marsh respectively). Because of the proximity of these swamps to the sea shore it is difficult to assess the influence of climate on the relative humidity of these settings on strictly sedimentological grounds. However, the terrestrial components of the palynological assemblages recovered from these marginal-marine settings and correlative lacustrine sediments (containing fresh-water stromatolites but no coal) in the central Foothills are in sharp contrast with the impoverished assemblages known from the caliche facies. The former are prolific, diverse, and contain a number of triprojectate pollen species, which indicate a relatively humid climate during the latest Campanian time.