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C. A. Bush

Publications and source records attributed to C. A. Bush.

At least 19 recordsLinked to original sources
USGS2017

Uranium-series dating of carbonate (tufa) deposits associated with quaternary fluctuations of Pyramid Lake, Nevada

Uranium-series dating of dense tufa deposited in a small cave, at former lake margins, and in large tufa mounds clarifies the timing of lake-level variation during the past 400,000 yr in the Pyramid Lake basin. A moderate-sized lake occasionally overflowed the Emerson Pass sill at elevation of ???1207 m between ca. 400,000 and 170,000 and from ca. 60,000 to 20,000 yr B.P., as shown by 230Th/234U ages of the cave samples, 230Th-excess ages of tubular tufas, and average isochron-plot ages of shoreline-deposited tufas. (By comparison, modern Pyramid Lake is ???50 m below this sill). There is a lack of tufa record during the intervening period from ca. 170,000 to 60,000 yr B.P. After ca. 20,000 yr, Pyramid Lake underwent abrupt changes in level and, based on previous 14C ages, reached its highest elevation (ca 1335 m) at ca. 14,000 yr B.P. The youngest uranium-series ages are comparable with previously reported 14C ages. ?? 1996 University of Washington.

Quaternary Research↗
USGS2006

Genesis of marine terrace soils, Barbados, West Indies: evidence from mineralogy and geochemistry

Well-developed, clay-rich soils dominated by interstratified kaolinite-smectite are found on the uplifted coral reef terraces on the island of Barbados. The reef limestone is unlikely to have been the soil parent material however, because it is 98% CaCO 3 and geomorphic evidence argues against the 20 m of reef solution required to produce the soils by this process. The mineralogy of the sand, silt, and clay fractions of the soils, and trace element geochemistry, suggest that aeolian materials carried on the trade winds from Africa, volcanic ash from the island of St. Vincent, and quartz from Tertiary bedrock on the island itself are the parent materials for the soils. -Authors

Earth Surface Processes and Landforms↗
USGS2004

Limits of mountain and continental glaciations east of the Continental Divide in northern Montana and north-western North Dakota, U.S.A.

This chapter provides an overview of the limits of glaciations and glacial history in, and east and south-east of, Glacier National Park, Montana, and on the Northern Plains further east in Montana and north-western North Dakota. The term “Laurentide glacier” was applied to a continental ice sheet east of the Rocky Mountains in North America. It describes Laurentide Ice Sheet as any Quaternary continental ice sheet east of the Rocky Mountains in the United States and Canada. Laurentide till refers to till deposited by a Laurentide Ice Sheet. A Laurentide continental ice sheet is distinguished from a Cordilleran continental ice sheet in the Cordilleran region in parts of Washington, Idaho, and Montana in the United States and in adjacent Canada. Clague indicated that Cordilleran Ice Sheets formed several times during the Pleistocene. The chapter also reviews that the base for the digital map is simplified. Selected hydrographic features, selected towns and cities, selected physiographic features, and a grid of 1° × 2° topographic quadrangles are included to aid the reader in location of the glacial limits and other features depicted here on other maps at different scales.

Montana, North Dakota↗
USGS1996

Origin of the late quaternary dune fields of northeastern Colorado

Stabilized eolian deposits, mostly parabolic dunes and sand sheets, cover much of the landscape of northeastern Colorado and adjacent parts of southwestern Nebraska in four geographically distinct dune fields. Stratigraphic and soil-geomorphic relations and accelerator radiocarbon dating indicate that at least three episodes of eolian sand movement occurred between 27 ka and 11 ka, possibly between 11 ka and 4 ka, and within the past 1.5 ka. Thus, eolian sand deposition took place under both glacial and interglacial climatic conditions. In the youngest episodes of eolian sand movement, Holocene parabolic dunes partially buried Pleistocene sand sheet deposits. Late Holocene sands in the Fort Morgan and Wray dune fields, to the south of the South Platte River, have trace element ratios that are indistinguishable from modern South Platte River sands, but different from Ogallala Formation bedrock, which has previously been cited as the main source of dune sand on the Great Plains. Sands in the Greeley dune field, to the north of the South Platte River, have trace element concentrations that indicate a probable Laramie Formation source. Measurements of parabolic dunes indicate paleowinds from the northwest in all dune fields, in good agreement with resultant drift directions calculated for nearby weather stations. Thus, paleowinds were probably not significantly different from present-day winds, and are consistent with a South Platte River source for the Fort Morgan and Wray dune fields, and a Laramie Formation source for the Greeley dune field. Sand accumulated downwind of the South Platte River to form the Fort Morgan duen field. In addition, sand was also transported farther downwind over the upland formed by the calcrete caprock of the Ogallala Formation, and deposited in the lee of the upland on the southeast side. Because of high wind energy, the upland itself served as a zone of sand transport, but little or no sand accumulation took place on this surface. These studies, which demonstrate the importance of fluvial-source sediments for dune fields in Colorado, may be applicable to other dune fields in North America. Because modern drift potentials in northeastern Colorado are among the highest in the world, the present stability of dunes in the region may be in part a function of the dunes being supply-limited rather than solely transport-limited. Extensive (∼ 7700 km 2 ) late Holocene dunes document that eolian sand in northeastern Colorado is very sensitive to small changes in climate or fluvial source conditions.

Geomorphology↗
USGS1990

Uranium-series dating of secondary carbonates near Yucca Mountain, Nevada. Applications to tectonic, paleoclimatic, and paleohydrologic problems

Near-surface accumulations of secondary carbonates are common in the soils and sediments of the Yucca Mountain area. These carbonates contain small amounts of uranium that allow dating by the uranium-series disequilibrium method. Preliminary results from the Yucca Mountain area indicate that the U-series methods can (1) identify multiple episodes of tectonic fracturing, (2) provide a chronologic framework for paleoclimatically significant eolian deposits, and (3) place constraints on the probable source of waters from which the carbonates precipitated.

Conference Paper↗
USGS1989

The Uranium-trend dating method: Principles and application for southern California marine terrace deposits

Uranium-trend dating is an open-system method for age estimation of Quaternary sediments, using disequilibrium in the 238U234U230Th decay series. The technique has been applied to alluvium, colluvium, loess, till, and marine sediments. In this study we tested the U-trend dating method on calcareous marine terrace deposits from the Palos Verdes Hills and San Nicolas Island, California. Independent age estimates indicate that terraces in these areas range from ???80 ka to greater than 1.0 Ma. Two low terraces on San Nicolas Island yielded U-trend plots that have a clustered array of points and the ages of these deposits are indeterminate or highly suspect. Middle Pleistocene terraces and one early Pleistocene terrace on San Nicolas Island and all terraces on the Palos Verdes Hills gave reasonably linear U-trend plots and estimated ages that are stratigraphically consistent and in agreement with independent age estimates. We conclude that many marine terrace deposits are suitable for U-trend dating, but U-trend plots must be carefully evaluated and U-trend ages should be consistent with independent geologic control. ?? 1989.

Quaternary International↗
USGS1987

Geochemistry and preliminary assessment of resource potential for postorogenic granites of the southwestern Arabian Shield, Kingdom of Saudi Arabia

Geochemical data for samples from 55 postorogenic plutons of the southwestern Arabian Shield show that these granitoids are generally less evolved than similar granitoids of the eastern Arabian Shield. Radioelement contents are low to normal relative to typical granitic rocks and uranium contents are distinctly low relative to rocks of the eastern Arabian Shield. The data indicate low favorability for ore deposits of elements that are typically enriched in granites at the end stages of magmatism such as tin, tungsten, niobium, tantalum, molybdenum, rare-earth elements, and radioactive elements. Regional geochemical patterns are not consistent with the north-south trending microplate boundary that has been proposed by other workers. Correlation coefficients for trace-element data obtained during the current study also argue against sharp compositional breaks in the protolith for the postorogenic granites. Consideration of the data presented here and similar data for granitoids of the eastern Arabian Shield, suggest the existence of a compositionally gradational protolith of continental affinity to the east and oceanic affinity to the west.

Open-File Report↗
USGS1986

Uranium series disequilibrium in a young surficial uranium deposit, northeastern Washington, U.S.A.

A recently discovered ore-grade accumulation of U in organic-rich sediments of late Quaternary age provides an opportunity for studying the early association of U, U-daughters, and organic matter in a natural setting. The U occurs in valley-fill sediments of peat, peaty clay, silt, and sand along the north fork of Flodelle Creek, Stevens County, Washington. Radiometric techniques (delayed neutron, high-resolution gamma-ray spectrometry, thin-source alpha spectrometry) were employed to determine the abundance and distribution of U-series nuclides, the extent of secular equilibrium within the U decay series, and the apparent U-series ages of U incorporation. Sixteen lithologically distinct intervals were sampled from a 292 cm core. Uranium contents range from 140 to 2790 ppm and are positively correlated with organic contents. Measured alpha activity ratios of 234 U/ 238 U (1.31–1.38) are very similar to those reported in coexisting waters, suggesting a rather constant isotopic composition of introduced U. Much lower Th contents of <10–40 ppm are controlled by the type and abundance of silicate detritus. The youth of the host sediments (<15 000 a) and the paucity of associated radioactivity suggested large excesses of U relative to radioactive daughters and such excesses were observed, particularly in the shallowest intervals. Apparent ages of U emplacement determined by the (alpha) activity ratio of 230 Th daughter to 234 U parent show a general increase with depth and fair agreement with estimated depositional ages. This observation suggests dominantly syndepositional or early post depositional emplacement of U followed by decay-generated buildup of 230 Th daughter with time. However, interval by interval comparisons of the relative abundances of other daughters, particularly 226 Ra and 210 Pb, indicate variability caused by processes other than closed-system growth and decay, probably because chemically diverse daughters that are decay-generated in situ have differing mobilities and because upwelling ground water continuously adds more U and minor amounts of daughters. If 230 Th is considered the least susceptible to these modifications, the data suggest some addition of 234 U in the deepest intervals and some loss of 226 Ra and/or gain of 222 Rn throughout the studied core.

Washington↗
USGS1983

Preliminary assessment of the geochemistry and mineral favorability of the postorogenic granites of the southeastern Arabian Shield, Kingdom of Saudi Arabia

Chemical analyses of samples for 19 postorogenic plutons from the southeastern Arabian Shield show that these rocks have average potassium/rubidium ratios (162) and average rubidium/strontium ratios (11.8) characteristic of highly evolved granites. Most of the analyzed samples are peraluminous. Three plutons are physically similar in terms of shape and megascopic textural zonation to peralkaline complexes in the northeastern part of the Shield, but none of the samples from these plutons is peralkaline. However, these plutons do contain the least-evolved samples. Zinc, yttrium, uranium, thorium, and possibly copper, each occur in anomalously high concentrations in at least one pluton relative to contents typically cited for granite. The average regional concentrations of copper and zinc are anomalously high. These facts suggest at least a moderate potential for mineralization in the southeastern part of the Shield. Good correlations (r of 0.5 to 0.8) between uranium, thorium, yttrium, and rubidium and an excellent correlation (r=0.98) between uranium and radium-equivalent uranium suggest that secondary deposits of these elements are unlikely and that magmatic deposits, especially of a pegmatitic nature, are more likely. Concentrations of some major elements and several trace elements covary with sample location as measured by latitude and longitude. This fact is interpreted to reflect regional variations in the protolith that have been proposed on the basis of lead isotopic data. The chemical variations suggest a largely oceanic crustal component for granites in the southwestern part of the southeastern Shield and a largely continental crustal component to the northeast. Further quantitative analysis is recommended to verify and accurately delineate anomalous concentrations of trace elements. Trend surface analysis of all available data for postorogenic granites from the eastern Arabian Shield is suggested as a method for testing regional variations in the protolith that might control locations of highly favorable areas of ore deposition.

Open-File Report↗
USGS1977

Geochemical and petrological studies of a uraniferous granite from the Granite Mountains, Wyoming

Granite rocks from the Granite Mountains, Wyo. have been proposed as the source of uranium deposits in the Crooks Gap, Gas Hills and Shirley Basin uranium districts, Wyoming. We have divided these granitic rocks into four units: (1) a biotitic phase which forms the dominant unit at the western end of the Granite Mountains, (2) a leucocratic phase which was found from 215 to 405 metres in drill hole GM-1, (3) silicified zones which crosscut the granitic rocks and form topographic highs, and (4) fractured zones, in drill hole GM-1, which seem to have been hydrothermally altered. The biotitic phase is hypidiomorphic-granular to xenomorphic-granular alkali granite with anomalously high contents of U (10 parts per million), Th (50 ppm), and Pb (50 ppm). Fission-track studies show that uranium is located in zircon, sphene, apatite, monzite, xenotime, biotite, chlorite, epidote, and magnetite; no intergranular uranium was found. The leucocratic phase is mineralogically similar to the biotitic phase, but contains less than half as much iron. It is xenomorphic granular and commonly contains rounded and retrograded garnets, which suggests that this phase is either metamorphic or contaminated with metamorphic materials. The leucocratic phase has anomalously high contents of U (8 ppm) and Pb (55 ppm), but has a low Th content (10 ppm). The silicified phase and fracture zones exhibit cataclastic and crystalloblastic textures and are highly variable in mineralogy. Potassium-bearing minerals are generally absent. Microcline is replaced by albite and (or) quartz, and biotite is replaced by clinozoisite. Uranium values may be anomalously high in the fracture zones. One sample contains 1100 ppm radium-equivalent uranium. In this and other uranium-rich samples from the fracture zones, the uranium is associated with iron oxides which commonly fill microfractures. According to our model and currently available data, an alkali granite is the best crystalline source rock for uranium, especially if it is unmetamorphosed and rapidly exposed to near-surface conditions for the first time when a favorable basin existed nearby.

Wyoming↗