Geohydrology of the Piceance Creek structural basin between the White and Colorado Rivers, northwestern Colorado
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Certain areas of the Piceance Creek Basin are important, not only for their beauty and other amenities but also for their unusual ecosystems. Stoecker (1974) has suggested maintaining one of the larger boxcanyons in the southern portion as a nature reserve. Knutson & Boardman (1973) have suggested preserving a ‘green belt’ to involve the magnificient bluffs adjacent to the Colorado River. Preservation of the Cathedral Bluffs running north and south in the western portion has also been suggested. It is clear that a movement is growing to provide a system of natural areas throughout the Basin. Such a system would maintain important examples of representative vegetation types, wildlife habitat, geological and archaeological features, and other areas of particular ecological interest. This preserve system would maintain natural (or semi-natural) areas both as ecological baselines and as nuclei for obtaining biological ‘seed’ for rehabilitation of disturbed areas. A study to delineate suitable areas that could be included in such a system is surely needed.Man is viewing vast resources in the Piceance Creek Basin, which probably has the world's largest known hydrocarbon deposit, and his use thereof seems inevitable. The magnitude of the deposit certainly demands a major planning effort. One can even speculate into the future, as Knutson & Boardman (1973) have done, to visualize a concerted or systems approach to obtaining and processing this resource.Nevertheless, until commercial activity begins and monitoring procures actual data, predictions will remain speculative. Operation of a few commercial plants, mines, and rehabilitation activities, is needed in order that precise predictions can be made for better delineation and quantification of the environmental impacts of a major shale-oil industry.
Certain areas of the Piceance Creek Basin are important, not only for their beauty and other amenities but also for their unusual ecosystems. Stoecker (1974) has suggested maintaining one of the larger boxcanyons in the southern portion as a nature reserve. Knutson & Boardman (1973) have suggested preserving a ‘green belt’ to involve the magnificient bluffs adjacent to the Colorado River. Preservation of the Cathedral Bluffs running north and south in the western portion has also been suggested. It is clear that a movement is growing to provide a system of natural areas throughout the Basin. Such a system would maintain important examples of representative vegetation types, wildlife habitat, geological and archaeological features, and other areas of particular ecological interest. This preserve system would maintain natural (or semi-natural) areas both as ecological baselines and as nuclei for obtaining biological ‘seed’ for rehabilitation of disturbed areas. A study to delineate suitable areas that could be included in such a system is surely needed.Man is viewing vast resources in the Piceance Creek Basin, which probably has the world's largest known hydrocarbon deposit, and his use thereof seems inevitable. The magnitude of the deposit certainly demands a major planning effort. One can even speculate into the future, as Knutson & Boardman (1973) have done, to visualize a concerted or systems approach to obtaining and processing this resource.Nevertheless, until commercial activity begins and monitoring procures actual data, predictions will remain speculative. Operation of a few commercial plants, mines, and rehabilitation activities, is needed in order that precise predictions can be made for better delineation and quantification of the environmental impacts of a major shale-oil industry.
Stratigraphy and nahcolite resources of the saline facies of the Green River Formation, Rio Blanco County, Colorado
Based on a study of 10 drill cores, a sequence of oil shale and associated nahcolite, nearly 2,000 feet thick, in the lacustrine Green River Formation (Eocene) in the Piceance Creek basin, Rio Blanco County, Colo., was divided in ascending order into zones 1 to 13, B-groove, Mahogany zone (with lower, middle, and upper parts), and A-groove at the top. The odd-numbered zones and the Mahogany zone are mappable subsurface units of relatively thick oil shale and are distinguished from the even-numbered zones and A-and B-grooves which are thinner units of oil shale of lower grade.Large amounts of nahcolite found in zones 5 to 12 occur in (1) coarsegrained crystalline aggregates scattered through oil shale, (2) laterally continuous units of fine-grained crystals disseminated in oil shale, (3) brown microcrystalline beds, and (4) white coarse-grained beds that grade laterally into halitic rocks toward basin center. The original upper limit of the nahcolite and halitic rocks is not yet completely known, but the present top is marked by a dissolution surface. Above this surface the rocks, extending from zones 11 or 12 upward into the Mahogany zone, form a water-saturated "leached zone," a geohydrologic unit in which large amounts of water-soluble minerals probably mostly nahcolite and halite, were removed by ground-water dissolution. Rocks' in the leached zone, mostly oil shale, are commonly broken and fractured and contain crystal cavities and solution breccias. Several solution breccias can be traced laterally into unleached beds of nahcolite and halite. Although evidence of salines is found in rocks above A-groove, the original saline facies that includes most of the bedded deposits extends from zone 5 upward into A-groove.Potentially minable beds of white nahcolite as much as 12 feet thick are found at depths of 1,560 or more feet below the surface. Some thicker beds of high-grade nahcolite are believed to be too close to the dissolution surface for safe room-and-pillar mining. Probably the most economical method of mining nahcolite would be as a coproduct of a shale-oil industry. Removal of nahcolite prior to retorting increases significantly the grade of oil shale by as much as 1.6 times. Several zones are more than 300 feet thick and average 30 or more weight percent nahcolite. Resources of nahcolite per square mile range as high as 489 million short tons. The total nahcolite resource in the basin is conservatively estimated at 32 billion short tons, which makes it the second , largest deposit of sodium carbonate known in the world.
Digital model of ground-water flow in the Piceance Basin, Rio Blanco and Garfield Counties, Colorado
The digital model used to simulate ground-water flow in the aquifer system in the basin drained by Piceance and Yellow Creeks in northwestern Colorado is described in detail. The model is quasi three-dimensional in that it simulates ground-water flow in a multiaquifer system by assuming horizontal flow in the aquifers and vertical flow through the confining layers separating the aquifers. The model uses the iterative alternating-direction implicit procedure to solve the finite-difference flow equations.The digital model is documented by a program listing and flow charts. Data used in the model and sample output are presented to document the simulation of steady-state flow in the aquifer system. The variables used in the computer program and program options are discussed in detail. ABSTRACTThe digital model used to simulate ground-water flow in the aquifer system in the basin drained by Piceance and Yellow Creeks in northwestern Colorado is described in detail. The model is quasi three-dimensional in that it simulates ground-water flow in a multiaquifer system by assuming horizontal flow in the aquifers and vertical flow through the confining layers separating the aquifers. The model uses the iterative alternating-direction implicit procedure to solve the finite-difference flow equations.The digital model is documented by a program listing and flow charts. Data used in the model and sample output are presented to document the simulation of steady-state flow in the aquifer system. The variables used in the computer program and program options are discussed in detail.
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