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1983 | Buch

Terrigenous Clastic Depositional Systems

Applications to Petroleum, Coal, and Uranium Exploration

verfasst von: W. E. Galloway, D. K. Hobday

Verlag: Springer US

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Über dieses Buch

The reserves, or extractable fraction, of the fuel-mineral endowment are sufficient to supply the bulk of the world's energy requirements for the immediately forseeable future-well into the next century according to even the most pessimistic predictions. But increasingly sophisticated exploration concepts and technology must be employed to maintain and, if possible, add to the reserve base. Most of the world's fuel-mineral resources are in sedimentary rocks. Any procedure or concept that helps describe, under­ stand, and predict the external geometry and internal attributes of major sedimentary units can therefore contribute to discovery and recovery of coal, uranium, and petroleum. While conceding the desirability of renewable and nonpolluting energy supply from gravitational, wind, or solar sources, the widespread deployment of these systems lies far in the future-thus the continued commercial emphasis on conventional nonrenewable fuel mineral resources, even though their relative significance will fluctuate with time. For example, a decade ago the progilostications for uranium were uniformly optimistic. But in the early 1980s the uranium picture is quite sombre, although unlikely to remain permanently depressed. Whether uranium soars to the heights of early expectations remains to be seen. Problems of waste disposal and public acceptance persist. Fusion reactors may ultimately eliminate the need for uranium in power generation, but for the next few decades there will be continued demand for uranium to fuel existing power plants and those that come on stream. This book is, to some extent, a hybrid.

Inhaltsverzeichnis

Frontmatter
Chapter 1. The Fuel-Mineral Resource Base
Abstract
Nonrenewable energy resources available in very large quantities are limited to heavy hydrogen and dry geothermal energy. Large-scale renewable resources are solar and atmospheric electricity (Moody, 1978). These four may be regarded as the ultimate energy sources, but they are unlikely to contribute significantly to the total energy budget for at least the next few decades. Synthetic fuels are already in production, but widespread conversion is being held back by economic and environmental considerations. Wind, water, and biomass conversion will play an enlarged, but still relatively minor, role. This leaves coal, uranium, and petroleum to provide the bulk of the immediately foreseeable energy requirements.
W. E. Galloway, D. K. Hobday
Chapter 2. Approaches to Genetic Stratigraphic Analysis
Abstract
One of the most difficult tasks in the application of genetic facies interpretation in resourc exploration, appraisal, and development is the delineation of depositional units of sufficient extent and appropriate scale for analysis. The depositional basin defines the boundaries and general conditions of the accumulation of a sediment pile. Depositional systems, as described in subsequent chapters, provide “meaningful sections” of the basin fill. Their recognition and delineation establish a framework for facies differentiation and mapping, using appropriate process-response models. It is commonly at the facies level that source units, fluid-migration pathways (the basin plumbing), potential hosts or reservoirs, and trapping configurations are sought and dissected.
W. E. Galloway, D. K. Hobday
Chapter 3. Alluvial-Fan Systems
Abstract
Alluvial fans are conical, lobate, or arcuate accumulations of predominantly coarse-grained clastics extending from a mountain front or escarpment across an adjacent lowland. They represent the coarsest, most poorly sorted, proximal unit in the range of subaerial depositional systems, and commonly merge downdip into finer grained, lower gradient fluvial systems. Some fans, however, terminate directly in lakes or ocean basins as fan deltas, which generally show some degree of distal modification by currents or waves (Fig. 3-1).
W. E. Galloway, D. K. Hobday
Chapter 4. Fluvial Systems
Abstract
Fluvial systems serve primarily to collect and transport sediment into major lacustrine or marine basins. However, in certain settings favoring subaerial accumulation of sediment, such as subsiding coastal plains, intermontane basins, and tectonic forelands, fluvial depositional systems may become a major, or even dominant component of the basin’s fill. Even where their volumes are minor, fluvial facies are often disproportionately important as hosts for mineral fuel deposits, particularly petroleum and uranium.
W. E. Galloway, D. K. Hobday
Chapter 5. Delta Systems
Abstract
A delta forms where a river transporting significant quantities of sediment enters a receiving basin. In one sense, few processes or environments are unique to the deltaic setting. However, the interaction of subaerial fluvial processes and subaqueous processes of marine or lake basins produces distinctive facies assemblages. In the following discussion, a delta is considered to be a river-fed depositional system that produces an irregular progradation of the shoreline into a body of water (Fisher et al., 1969). As suggested by Moore and Asquith (1971), and consistent with the concept of a depositional system, the entire subaerial and subaqueous, contiguous sediment mass is included in a delta system.
W. E. Galloway, D. K. Hobday
Chapter 6. Clastic Shore-Zone Systems
Abstract
The shore zone (Fig. 6-1), excluding deltas, comprises the narrow, high-energy transitional environment that extends from wave base at a highly variable depth averaging 35 ft (10 m) to the seaward edge of the alluvial coastal plain, raised terrace, or cliffs. Although restricted in area, migration of shorelines through time has resulted in widespread shore-zone deposits in the rock record, with considerable bearing on the distribution of hydrocarbon, coal, and uranium resources.
W. E. Galloway, D. K. Hobday
Chapter 7. Terrigenous Shelf Systems
Abstract
Terrigenous shelves include both epeiric (epicontinental) platforms and continental shelves, with a mantle of land-derived sediments, as opposed to biogenic and chemical precipitates. Epeiric platforms are broad, shallowly inundated continental areas. Modem examples such as the North Sea, Hudson Bay, and Gulf of Carpentaria are small by comparison with many of their ancient counterparts. Continental shelves are submerged continental margins, dipping very gently from the outer edge of the shore zone to a depth, generally between 300 and 800 ft (100 and 250 m), at which there is an abrupt increase in slope. If the shelf break is not well defined, the shelf is arbitrarily confined to depths shallower than 200 m (650 ft) (Bates and Jackson, 1980). Present-day shelves have a complex depositional and erosional evolution which commenced in the Mesozoic (Swift, 1969).
W. E. Galloway, D. K. Hobday
Chapter 8. Terrigenous Slope and Basin Systems
Abstract
Slope and basin systems originate in relatively deep water beyond the shelf break. Although this environment encompasses a bathymetric range from upper slope at depths of several hundred feet to the abyssal plain at several thousand feet, many economically important ancient slope systems originated at more modest depths along the margins of shallow intracratonic seas (Galloway and Brown, 1972); others originated ahead of prograding oceanic delta systems and were carried to substantially greater depths by ongoing subsidence and growth faulting (Caughey, 1981; Galloway et al., 1982).
W. E. Galloway, D. K. Hobday
Chapter 9. Lacustrine Systems
Abstract
Terrigenous lacustrine systems are assuming new importance with the recognition of their role as hosts for a variety of minerals, including hydrocarbons, coal, and uranium. Some lake deposits are among the best known petroleum source rocks (Demaison and Moore, 1980), and locally contain good reservoirs. The energy resources of lacustrine oil shales are creating considerable interest, which is likely to increase in the coming decades. Commercial coal seams are widely developed in lacustrine and associated systems, and the permeability and geochemical gradients in fluvial-lacustrine transitions are ideal for epigenetic uranium mineralization. The association of bedded metalliferous deposits with ancient lake sediments has spurred additional economic interest, and lacustrine evaporites such as trona are fetching high prices on world markets.
W. E. Galloway, D. K. Hobday
Chapter 10. Eolian Systems
Abstract
Modem environments in which wind is the dominant agent of deposition range from tropical to polar, the sole requirements being the availability of uncohesive sediment and an incomplete cover of vegetation. Hot, arid regions, the most favored locale for eolian accumulation, are typical of tropical to subtropical high-pressure regions, of mid-latitude rain shadows and landlocked continental interiors, and of the western margins of continents swept by cold ocean currents or subject to upwelling. Humid regions dominated by eolian deposition generally involve copious sand supply, as along beaches and broad fluvial tracts, or very cold, unstable conditions that inhibit plant growth. High-latitude deserts result from the aridity associated with divergent air flow. Pleistocene circulation of this type redistributed glacial sand into substantial dune systems in North America and northern Europe (Glennie, 1970, p. 6).
W. E. Galloway, D. K. Hobday
Chapter 11. Depositional Systems and Basin Hydrology
Abstract
Although a discussion of hydrogeologic processes and basinal flow systems may seem to be a departure from this examination of genetic stratigraphic analysis and energy mineral occurrence, it is included for several compelling reasons.
W. E. Galloway, D. K. Hobday
Chapter 12. Coal
Abstract
Coal-forming environments have existed since mid-Paleozoic time in areas where substantial quantities of vegetal matter are accumulating and being preserved. Widespread peat accumulation only became possible with the appearance of psilophyte vegetation during the Silurian, which accounts for the first Devonian coals and then the extensive Carboniferous seams. Evolving Mesozoic and Tertiary vegetation occupied an ever expanding range of environments. Today tropical swamps and marshes are undergoing the most rapid accumulation of peat, with rates in Borneo of 17 m (55 ft) in 4000 years (Stach et al., 1975, p. 15); but peats are also forming in temperate and even polar regions, and at high altitudes. The same geographic diversity is apparent in the origin of coal (Fig. 12-1). The majority of early seams were laid down in humid tropical regions, but in Permian and later times coal formation shifted to temperate and polar regions (Diessel, 1970).
W. E. Galloway, D. K. Hobday
Chapter 13. Sedimentary Uranium
Abstract
Though not a fossil fuel, uranium shares with petroleum and coal many similarities in both geologic occurrence and utilization. The uranium fuel cycle includes a series of extraction and enrichment processes beginning with discovery and mining of a uranium deposit and including: (1) milling and enrichment of the uranium ore, which has a typical initial concentration (ore grade) of only a few hundredths to a few tenths of a percent of U3O8, to produce nearly pure U3O8 (yellowcake); (2) concentration of the U235 isotope in gaseous UF6 (uranium hexafluoride); (3) fabrication of solid fuel pellets; and (4) fission of the uranium in a reactor, generating heat to drive turbine generators. Existing fission reactors “bum” U235 in that they consume it, producing waste by-products of the induced fission process. It is noteworthy that less than one percent of naturally occurring uranium is the desired U235 isotope.
W. E. Galloway, D. K. Hobday
Chapter 14. Petroleum
Abstract
For the industrial nations of the world, it may be reasonably stated that petroleum has fueled the twentieth century. Despite accelerating depletion of the resource, oil and gas will remain major contributors to the world energy supply into the next century. Because the discovery of hydrocarbon reserves is an extremely geology-intensive process, the petroleum industry has directly and indirectly initiated, supported, and incorporated much of the accumulated research on sedimentary basins and their contained deposits. Similarly, the industry has been the single largest world-wide employer of earth scientists. This tremendous expenditure of manpower and research on a particular energy resource and its geologic environs has led to considerable understanding of its origins and distribution patterns. Still, answers to many questions remain elusive, and petroleum liquids are described in legal terminology as “fugacious,” a term which most petroleum geologists can readily support.
W. E. Galloway, D. K. Hobday
Backmatter
Metadaten
Titel
Terrigenous Clastic Depositional Systems
verfasst von
W. E. Galloway
D. K. Hobday
Copyright-Jahr
1983
Verlag
Springer US
Electronic ISBN
978-1-4684-0170-7
Print ISBN
978-1-4684-0172-1
DOI
https://doi.org/10.1007/978-1-4684-0170-7