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NARROW
GeoRef Subject
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all geography including DSDP/ODP Sites and Legs
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Arctic Ocean
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Canada Basin (1)
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Canada (1)
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North America
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North American Craton (1)
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commodities
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mineral resources (1)
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water resources (1)
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Primary terms
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Arctic Ocean
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Canada Basin (1)
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Canada (1)
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deformation (1)
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geochemistry (1)
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mineral resources (1)
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North America
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North American Craton (1)
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orogeny (1)
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tectonics (1)
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water resources (1)
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Abstract The Interior Platform, underlain by Phanerozoic sedimentary rocks, is the northwestern part of the North American Craton, the stable interior region of the continent (Fig. 2A.1; see also Fig. 1.1). Essentially flat-lying rocks of the Interior Platform extend into the eastern Cordillera where they are thrust-faulted and folded (see Fig. 5.5, in pocket), but have undergone little or no metamorphism nor plutonism during the orogenic phases. This area of undeformed and deformed sedimentary rock commonly is called the Western Canada Basin. The Interior Platform is linked to Michigan Basin and St. Lawrence Platform of southeastern Canada through the central U.S.A. and merges with Arctic Platform in the north. It is separated from Hudson Platform by a broad expanse of the Canadian Shield. The area of nearly horizontal bedrock, forming the Interior Plains physiographic province, comprises plains and plateaux covered by a thick mantle of glacial drift. It is a region of grassland, forest, and tundra, some 2 000 000 km 2 in area, that embraces parts of the prairie provinces of Manitoba, Saskatchewan, and Alberta, the northeast corner of British Columbia, and much of the western District of Mackenzie, Northwest Territories. In the southern region, clastic, carbonate, and evaporite strata of Paleozoic age rest on a basement of Precambrian crystalline rocks. The Paleozoic sediments are overlain by a relatively thick blanket of Mesozoic and Tertiary clastic rocks. The southern part of Interior Platform is the main oil-producing region of western Canada; it has been extensively drilled and its geology is well
Abstract Geological exploration has greatly influenced the development of western Canada, particularly the growth of the petroleum and natural gas, coal, and mineral industries. During the late nineteenth century when railroads were being built across the plains, settlers were encouraged by geological reports on the favorable agricultural prospects and the availability of water and fuels. The prosperity of the prairie provinces, based on their rich natural resources, would not have been achieved without the determination, enterprise, and knowledge of dedicated explorers. This abbreviated account outlines the history of exploration and contributions of some of the notable individuals, particularly during the early years. The more recent history involves many more people, and it is not possible to acknowledge each and every one. Additional details on recent investigations may be found in the following chapters. This subchapter has been prepared from a variety of sources in addition to original reports. It draws on a history of the Geological Survey of Canada by Zaslow (1975) and accounts of the development of the petroleum industry in western Canada by Gray (1970), de Mille (1970), Gould (1976), and a group of authors whose papers appear in Hilborn (1968).
Abstract Physiographically and geologically, western Canada consists of three great parts: a core of crystalline rocks forming the Canadian (Precambrian) Shield; a surrounding band of younger, essentially flat-lying, stratified rocks; and on the western side, a rim of highly deformed sedimentary, volcanic, and igneous rocks (Fig. 2C.1, 2C.2, 2C.3). The Canadian Shield has a slightly depressed centre, presently the site of Hudson Bay and Hudson Bay Lowland. The surrounding band of undeformed Phanerozoic rocks forms the Interior Plains on the western margin and St. Lawrence Lowland on the southern margin. These areas are characterized by lowlands, plains, and plateaux, which were substantially modified by glacial action during Pleistocene time. The outer belt of deformed rock forms the magnificent mountainous terrain of the Canadian Cordillera. The classification of physiography in western Canada has evolved since the early writings of A.R.C. Selwyn and G.M. Dawson (1884) and a classic study by R.A. Daly (1912). The physiography of British Columbia was described by S.S. Holland (1964), and that of Canada by H.S. Bostock (1970a,b). These reports have been used extensively for the following summary. As part of the current syntheses of the Geology of Canada, W.H. Mathews (1986) has modified parts of the earlier classification of Cordilleran physiography, basing his study on landsat imagery and recent reports. The physiographic divisions set forth on Matthew’s geomorphic map are used in this section. A more detailed discussion of the geomorphology of the Cordillera may be found in the Cordilleran volume
Abstract This subchapter is concerned only with the tectonics affecting the Phanerozoic sedimentary cover of the Interior Platform, western basins, and eastern Cordillera and with those Upper Proterozoic deposits genetically related to them. Interpretation of the sedimentary and tectonic history of pre-Late Proterozoic time is subject to uncertainties much greater than those of Phanerozoic history, and Phanerozoic rocks are the principal focus of this volume. Precambrian tectonics as determined from stratified rocks is dealt with in Subchapter 4A, and the geology of the sparsely sampled and remotely sensed crystalline basement in Chapter 3. Furthermore, this subchapter is concerned only with those sedimentary successions that were deposited upon or in immediate connection with North America; the extremely complex history of the accreted terranes to the west is beyond the compass of this volume, and in any case is not recorded by the strata of the Western Canada Basin. The accreted terranes are fully treated by Gabrielse and Yorath (1991). In this subchapter only the most critical sources are cited; all significant literature is cited in Chapter 4. The region of concern here has generally been treated as the Western Canada Basin, a term useful only in designating a geographic area underlain entirely by sedimentary rocks. Most of the “basin”, as conventionally outlined, was a tectonic and sedimentary platform (“shelf” of some authors) during the divergent-margin phases of sedimentation, a part of it was a platform during the convergent-margin phases, and it has been a tectonic platform for most of Tertiary time. where
Abstract Over vast areas of the undeformed platform of southwestern Canada, the sedimentary cover of the ancient North American Craton is entirely of Phanerozoic age. In northwestern Canada, on the other hand, thick Proterozoic strata intervene between Phanerozoic deposits and crystalline basement (Fig. 4A.1). Even there, the preserved sediments contain only a fraction of the record of geological events that is preserved in the Foreland Belt of the Cordillera. Precambrian crystalline rocks beneath the sedimentary cover of the Interior Platform are dealt with in a separate chapter (Burwash et al., Chapter 3 in this volume). This brief treatment is largely a condensation of two chapters (“Middle Proterozoic”, and “Upper Proterozoic”) of the companion volume, “Geology of the Cordilleran Orogen in Canada” (Gabrielse and Yorath, 1991); it considers not only the Proterozoic sedimentary record of the undeformed basins and platforms, but also the more complete record preserved in the Eastern Cordillera. H. Gabrielse and M.E. McMechan have provided welcome assistance with fact and interpretation.
Abstract The Western Canada Basin provides exceptional opportunities for the study of Cambrian and Lower Ordovician rocks. In the southwest, these rocks are part of the Cordilleran Miogeocline, the wedge of sedimentary and minor volcanic rocks deposited on a passive margin of western North America that came into being at about the beginning of the Cambrian (Fig. 4B.1). In the northeast, they form the purely sedimentary and much thinner cover of the Interior Platform. Although it is clear that a hinge line marked the transition from platform to miogeocline, the position of the hinge is difficult to locate precisely, even for small chronostratigraphic units, because of the vagaries of preservation and the uneven distribution of thickness data. In any event, the position of the hinge line was not fixed. The best approximation of its long-term average position is the eastern limit of Mesozoic deformation. The unit chosen for analysis here is the Sauk Sequence of L.L. Sloss (1963, 1976), the record of a long period of almost continuous sedimentation on the cratons, limited below by a widespread unconformity near the base of the Cambrian and above by a widespread unconformity near the base of the Middle Ordovician. Sub-sequences I, II, and III are demarcated by relatively subtle breaks at the base of the Middle Cambrian and the base of the Franconian. The present synthesis provides a descriptive summary, and emphasizes the striking differences seen between cross-sections from platform to miogeocline drawn through the southern Rocky Mountains, the northern Rocky Mountains, the
Abstract Most Ordovician and Silurian rocks in western and northwestern Canada were deposited on the North American craton and its western continental margin. Strata of these ages have also been recognized in three allochthonous terranes in the Cordillera, described in the companion volume on the Cordilleran Orogen (Gabrielse and Yorath, 1991). The continental margin is equated with the Cordilleran Miogeocline of western Canada. The miogeocline/craton boundary is along a hinge line west of which the rate of thickening of Paleozoic strata increases significantly. On the basis of initial 87 Sr/ 86 Sr ratios for Mesozoic and younger plutonic rocks (Armstrong, 1979) that intrude them, all autochthonous Ordovician and Silurian strata, of both platformal and basinal facies, are inferred to be underlain by attenuated continental crust, and are thus in the miogeocline. Oceanic rocks are virtually unknown, and if present are either buried beneath younger strata, masked by metamorphism, and/or transported northwestward by Mesozoic and Cenozoic strike-slip faults. The only strata of this age that may be oceanic are rocks of the Kootenay Terrane in southernmost British Columbia. The Cordilleran Miogeocline formed in Late Proterozoic to Early Cambrian time (see Bond and Kominz, 1984). It is considered to be a continental margin of Atlantic type that was affected by several periods of renewed extensional tectonism, one of which occurred during late Early Ordovician and Middle Ordovician time. The eastern part of this ancient continental margin and adjacent craton were characterized by shallow-water, carbonate platforms and/or land areas composed mostly of exposed older Paleozoic and Precambrian
Abstract The region described in this subchapter lies between the craton and the western edge of the carbonate platform built upon the Devonian continental shelf within one or two hundred kilometres of the continental margin. Sediments deposited west of the platform edge are described in the companion volume, “Geology of the Cordilleran Orogen in Canada” (Gabrielse and Yorath,1991). The depositional record described here starts with rocks deposited in Late Silurian time following a widespread regression accompanied by epeirogenic uplift, warping, and erosion. These rocks are the first of Kaskaskia sequence (Sloss, 1963). The record ends at the base of dark radioactive shales spanning the Devonian-Mississippian boundary and marking a major transgression. In the far north, this transgression is masked by a clastic wedge originating in the Ellesmerian Orogen of the Arctic Islands and northern Alaska. Within the region, Devonian sediments cover an area of 2 500 000 km2. Thickness varies greatly from place to place. The thickest carbonate packets occur at the margin of the platform; close to Selwyn Basin, for example, the “Bear Rock sequence”, one of the five divisions of the Devonian analyzed here, alone constitutes over 2000 m of carbonate strata. In contrast, some bathymetric basins, such as the one occupying the Mackenzie Valley region during the Givetian, were starved of sediment.
Abstract The Carboniferous System in Western Canada Basin (Fig. 4E.1-4E.3) is a thick succesion of strata deposited on the downwarped and downfaulted western margin of the ancestral North American plate, the central to western cratonic platform, and southern Yukon Fold Belt. This succession, representing the upper Kaskaskia sequenceand lower Absaroka sequence of Sloss (1963), comprises two main lithofacies assemblages. The lower assemblage is basinal shale and generally thickens southwestward or basinward (see Fig. 4 E . 9 - 4 E . 1 3) . Upward and northeastward, it passe into an upper assemblage of platform and ramp carbonates (Fig. 4E.4, 4E.5, 4E.9-4E.13) and sandstone-dominated siliciclastic facies, deposited in deep-water slope to continental settings. Both assemblages consist of numerous formations, some separated by regional disconformities. Subaerial erosion during the Late Carboniferous, Permian, and subsequent periods removed large parts of the succession, particularly in the Interior Plains, the region west of the Rocky Mountain Front Ranges, and the Cordillera between southwestern District of Mackenzie and northern Yukon Territory. Where the Carboniferous remains, it is generally unconformably overlain byeither Permian or Mesozoic strata. Carboniferous formations are preserved in twomain regions. The southern one, which includes much of the eastern Cordillera andsouthern to western Interior Plains, extends from southwestern Manitoba to southwestern District of Mackenzie. The northern area includes the eastern Cordillera ofnorthern Yukon Territory and northwestern District of Mackenzie (Fig. 4E.1). Betweenthese regions, erosional remnants are present in the Mackenzie and Selwyn Mountains of east-central Yukon and west-central District of Mackenzie.
Abstract Permian rocks are preserved throughout most of the eastern Cordillera and locally, in the Peace River-Liard River area, on the Interior Platform (Fig. 4F.1, 4F.2, 4F.3). They are absent from the remainder of the Interior Platform and from most of the Mackenzie Mountains through truncation at several disconformities beneath Mesozoic strata. Permian sediments were deposited mainly along the margin of the North American plate in a Permian depositional basin, here named Ishbel Trough, extending from the 49th parallel to the Ancestral Aklavik Arch in northern Yukon Territory. The trough occupies approximately the same position as the Carboniferous Prophet Trough (Richards et al., Subchapter 4E in this volume). In the Peace River-Liard River area, Permian sediments were also deposited on the western cratonic platform. The western margin of Ishbel Trough has not been identified. It (Fig. 4F.2, 4F.3) may have been in the area presently occupied by Cariboo Terrane (Struik and Orchard, 1985; Struik, 1986), which lacks Permian strata and may have been partly subaerially exposed during the Permian Period. A marginal basin to the west of Cariboo Terrane (Barkerville Subterrane of Kootenay Terrane; Monger and Price, 1979) contains a remnant of Permian strata (Sugar Limestone). The eastern margin of Ishbel Trough was a broad hinge-line along the western margin of the cratonic platform. In northeastern British Columbia and southwestern District of Mackenzie the hinge coincided with a zone of normal faulting, but generally the position of the eastern trough margin is unclear, because of eastward truncation of Permian strata (Fig. 4F.2, 4F.3).
Abstract Triassic rocks of the Interior Platform and eastern Cordillera of Canada have long been recognized as an interesting and variable sequence of marine strata occupying an elongate belt that extends from the United States border on the south to 69°N latitude and Beaufort Sea on the north (Fig. 4G.1, 4G.2). Triassic deposits are best developed in Western Canada Basin of British Columbia and Alberta, where they occupy three main physiographic provinces, Rocky Mountains on the west, Rocky Mountain Foothills, and Interior Plains to the east. Triassic rocks also occur in Liard River area of southern Yukon Territory and within northern Yukon Territory and District of Mackenzie in the British, Barn, Richardson, Selwyn, Wernecke, and northwestern Ogilvie Mountains. However, because much more published information on Triassic rocks in Western Canada Basin is available, and because of the greater development and economic importance of the system there, most of this report will be directed toward the region south of latitude 60°N. Triassic rocks of the Rocky Mountains, Foothills, and Interior Plains comprise over 1200 m (Fig. 4G.1) of westward-thickening, siliciclastic and carbonate rocks and lesser amounts of evaporites. Contained marine faunas range in age from Griesbachian to Norian. The Triassic rocks of northern Yukon Territory display similar lithofacies but lack evaporites. The strata form a marine wedge deposited along a topographically low, tectonically stable continental shelf and shoreline, a continuation of Permian conditions at the passive western margin of the North American Craton. They form part of what is referred to as
Abstract The Jurassic System in western Canada is of interest particularly for the evidence it brings to bear on the early history of the mid-Jurassic to mid-Cretaceous Columbian orogeny, and for its economic significance. Its sediments contain the record of eustatic and epeirogenic events related partly to the early stages of the opening of the North Atlantic Ocean in the east, and the history of collision of allochthonous terranes in the west with the westerly drifting continent. Superimposition of the effects of the early phases of the Columbian Orogeny and the related foredeep on the older pre-orogenic sediments of Western Canada Basin, and the demise of Williston Basin as a depocentre are seen in the Jurassic succession of the western Plains and Rocky Mountains. Late events of the Ellesmerian tectonic phase in Brooks-Mackenzie Basin are recorded in northern Yukon Territory and adjacent Northwest Territories. Jurassic sedimentary rocks form significant hydrocarbon reservoirs and source rocks in western Canada. The immense coal reserves of the southern Canadian Rocky Mountains occur in an Upper Jurassic-Lower Cretaceous succession; the Jurassic of southern Manitoba hosts two of Canada’s major gypsum mines; and some of the phosphate deposits, currently subeconomic, in southeastern British Columbia are Jurassic in age.
Cretaceous
Abstract Cretaceous rocks extend through the mid-continent from northern Yukon Territory and District of Mackenzie southward along Mackenzie and Rocky Mountains and eastward across the Plains of Alberta, Saskatchewan, and Manitoba to the Canadian Shield. They underlie Mackenzie Delta and Plains in the District of Mackenzie. Exposures of Cretaceous rocks are found in the southern Plains along many of the major river systems. One of the celebrated localities is at Dinosaur Park, southeastern Alberta, designated a World Heritage Site. Elsewhere in the Plains, Cretaceous rocks are mainly covered by Pleistocene drift, except in the Cypress Hills and along the Manitoba Escarpment on the eastern side of the basin. Many investigations of Cretaceous rocks have been carried out over a period of more than 125 years. Studies of oil sands, heavy oil areas, and coal-bearing areas, regional and economic studies, and detailed surface and subsurface studies have contributed to understanding the history of these rocks. More than 100 000 boreholes have been drilled in the southern part of the Western Canada Basin. Well control is relatively sparse in the District of Mackenzie where, too, outcrops are lacking in large areas. Drilling in the Eagle Plains, Mackenzie Delta, and along the Mackenzie Valley has provided much needed data. Recent coal exploration in the foothills and mountains of British Columbia and in the Plains of Alberta and Saskatchewan has contributed greatly to the overall knowledge of the Cretaceous rocks.
Tertiary
Abstract The depositional environments existing at the end of the Cretaceous Period continued into the Paleocene Epoch as the Laramide Orogeny continued to affect the western margin of the basin. Thick sequences of sediments derived from the Cordilleran Orogen were deposited in the Beaufort Sea in the north, while continental Paleocene beds were widely distributed in the south, spreading eastward from the rising Rocky Mountains across the Interior Platform. The thickest Tertiary sediments in the southern part of Western Canada Basin are preserved along the eastern side of the Rocky Mountain Foothills and within the adjacent Alberta Syncline (Fig. 4J.1). These strata originally extended much more widely across the Interior Plains, but occur now only as erosional remnants, the largest being the Cypress Hills of southern Alberta and Saskatchewan (Fig. 4J.2) and their eastern extension along the Saskatchewan-United States border from Wood Mountain to Turtle Mountain in Manitoba. Tertiary sediments of the eastern Canadian Cordillera and Interior Plains are almost wholly continental, contrasting with the thick marine and nonmarine section encountered in the region of Mackenzie Delta and Beaufort Sea. Tertiary sediments are extensively developed in Mackenzie Delta, Arctic Coastal Plain, and on the Arctic Continental Shelf. Limited exposures are found in the Caribou Hills on the eastern side of Mackenzie Delta (Fig. 4J.3), along the western margin of the delta, in the Richardson Mountains, and in a small area near Babbage River on Yukon Coastal Plain. Other occurrences are found in Bonnet Plume Basin, Brackett Basin near Norman Wells, and
Abstract The Quaternary spans approximately the last two million years (Fig. 4K.1). In Canada, it is associated with glaciation, and the Interior Plains display a glacial record that may be unrivalled for detail and completeness. This review gives a synopsis of the period; a fuller account is found in Chapter 2 (Klassen, 1989; Vincent, 1989) of the Quaternary volume of this series (Fulton, 1989). That account also includes additional references, figures, and tables. The Quaternary record of the Interior Plains is relatively rich, but still very incomplete. First, although much is known about the glaciations and some of the interglaciations, most of nonglacial time is probably unrecorded. Second, much of the region, and especially parts of northern Alberta, northeast British Columbia, and southern parts of the Northwest Territories, have not been mapped. This lack of information renders correlation between the better known southern Plains and the region near the Arctic coast extremely difficult. Third, the available information indicates little about climate and environment during most of the Quaternary Period.
Abstract Petroleum has been discovered in commercial quantities in two major sedimentary basins of the Western Interior: Western Canada Basin and Beaufort-Mackenzie Basin. Western Canada Basin comprises the Phanerozoic sedimentary wedge lying between the Canadian Shield and the Cordillera; it includes the thrust-faulted rocks of the Foothills Belt but not the Rocky, Mackenzie, and Ogilvie mountains. This vast basin extends from the 49th parallel northward beyond the Arctic Circle (Fig. 6 A.1). Western Canada Basin is divided into the following regions: Alberta Basin, Williston Basin, Foothills Belt, and Northern Basins. Beaufort-Mackenzie Basin straddles the Arctic coastline north of Western Canada Basin; a summary description is given in this subchapter but its geology and economic potential are described more fully in the companion volume on the Arctic Region (Grantz et al., 1990). The distribution of oil and natural gas in western Canada south of latitude 60°N is shown on two pocket figures (Maps 1558A, 1559A), which may be used to locate fields referred to in the text. The maps are coloured to show the geological age of the reservoirs. Marginal notes contain statistical data on the largest pools, including Initial Volume In Place (IVIP), initial recoverable oil (Initial Established Reserves (IER)), pool area, net pay, porosity, and discovery year. Pie diagrams show the initial volume and the initial reserves, and the initial reserves by age of reservoir (see also Fig. 6 A.2, 6A.3). For current statistical data on reserves and production for individual fields, the annual summaries published by the provincial regulatory
Abstract Over 95% of Canada’s known coal resources are found in the sedimentary basins of the Interior Platform and eastern Cordillera (Fig. 6B.1); a minor amount is found in the Moose River Basin of the Hudson Platform. This distribution is shown in Table 6B.1, which summarizes coal resources for all of Canada. Coal also occurs in the platforms and basins of western Northwest Territories, eastern and northern Yukon Territory and the Arctic Islands, but low exploration activity has limited calculation of regional resources. The coals range in rank from lignite to anthracite and in age from Early Carboniferous to Tertiary. An interesting pattern of resource distribution by rank is shown by Table 6B.1. A large proportion is subbit-uminous and lignite - valuable as fuels for power generation and possible future feedstocks for gasification and liquefaction. High-volatile bituminous coals constitute a relatively small percentage of total resources. On the other hand, Canada is well endowed with medium- and low-volatile bituminous coals, and these are of special interest to the metallurgical market. Of Canada’s total resources of immediate interest probably 25% are in the medium/low-volatile bituminous category, virtually all of which are in Alberta and British Columbia. Coal in western Canada has gone through periods of fluctuating fortunes paralleling the experience of the industry elsewhere in North America. During the late 1950s and early 1960s, production decreased markedly and many mines closed. In the late 1960s and the decade of the 70s, a resurgence in mining took place due to increased exports of
Abstract Geothermal sources in sedimentary basins are of moderate to low temperature, are associated with flat-lying or gently dipping sediments, extend over long distances, and take the shape of the layered host rocks. They contrast with geothermal fields on continental margins associated with subduction zones or of rift zones associated with crustal extension; these are the result of vigorous hydrothermal systems feeding on volcanic heat sources, are relatively localized, generally small, irregular in shape, and of diverse character. Geothermal heat may be recoverable from almost any part of the sedimentary section because mobile water is present to some extent in all sediments with the exception of halite and other evaporite beds. However, the amount of water, its temperature, chemical character, pressure, and potential production rate may vary considerably from place to place, even in the same aquifer. Porosity and permeability of the rock are factors that affect the pressure drawdown and the lifetime of any production well. Thus, the economic geothermal potential must be individually evaluated at any proposed location. Temperatures in sedimentary aquifers range from near zero to 150°C and possibly higher in very deep basins. The lower limit of utility is about 40°C, which corresponds to a depth of about 500 to 1500 m, depending on surface temperature and geothermal gradient. Geothermal gradient in sediments is often distorted by hydrological effects, and conductive heat is disturbed by convective heat transfer. Areas of relatively high surface elevation act as recharge zones, depressing subsurface temperature, and low areas act as discharge
Abstract The Western Canada Basin is a storehouse of vast industrial mineral wealth. All of the Phanerozoic systems are represented in the basin and most of them have contributed or have the potential of contributing useful industrial mineral commodities. Producing deposits and significant occurrences are scattered throughout the more populous southern region of the basin (Fig. 6D.1, 6D.2). Commodities of low value such as sand and gravel, brick clay, and expandable clays tend to be relatively common and widespread. Development of these therefore tends to be concentrated around urban centres close to markets. Others, such as refractory clays, gypsum, cement raw materials, and lime are processed or used in manufacturing end products, whose added value permits transportation over relatively long distances. Some commodities, potash and sulphur for example, have gained global significance. Production of industrial minerals in the Western Canada Basin accounts for about 65% of the total value of Canadian production, of which about 75% is contributed by sulphur and potash (Table 6D.1). Reviews of industrial minerals have been published recently for Manitoba (Bannatyne, 1984a; Davies et al., 1962; Fogwill, 1983), for Saskatchewan (Guliov, 1984; Saskatchewan Energy and Mines, 1983) and for Alberta (Hamilton, 1976, 1984). An earlier summary of the industrial minerals of the western provinces was published by Douglas (1970).
Abstract The main metallic mineral deposits, with the important exception of Pine Point, lie within the eastern Cordillera and most are not being produced currently. Ferrous deposits of sedimentary origin and placer gold, both of low commercial interest at present, occur within the Plains. The metallic mineral deposits are outlined only briefly; additional detail may be found in the companion volumes on “Geology of the Cordilleran Orogen in Canada” (Gabrielse and Yorath, 1991) and “Mineral Deposits of Canada” (Geology of Canada, no. 8, Thorpe and Eckstrand, in prep.).