Late Proterozoic Rifting of Laurentia: Source and Deposition of Conglomerate Units of the Grandfather Mountain Formation, North Carolina Blue Ridge

Crustal extension and initiation of rifting of Laurentia during the Late Proterozoic resulted in formation of a northeast-trending system of discontinuous to continuous, half-graben basins situated cratonward of the Iapetus Ocean spreading ridge. Thick accumulations of sandstone, siltstone, bimodal volcanic rocks, conglomerate, diamictite, and minor limestone were deposited largely in response to rifting and relief formation on the basin margins. The Grandfather Mountain Formation contains five stratigraphically and compositionally distinct conglomerate/diamictite units and one pebbly sandstone unit which cap coarsening-upward, basin-fill sequences. The progradational sequences average 1300 m thick and are composed of a succession of volcanic flows (basalt/rhyolite) and/or siltstone, succeeded by fine- to coarse-grained feldspatholithic sandstone, succeeded by pebbly sandstone and conglomerate. Major rifting events (or clusters of events) occurred during deposition of volcanic rocks and fine-grained lacustrine or marine, and fluvial sediment near the basin margin fault After a time lag, alluvial fans and fan-deltas prograded basinward from the margin over the fine-grained sediment. Smaller-scale coarsening-upward sequences (few to 10\u27s m) are attributed to avulsion and lobe progradation due to inherent fan/fan-delta/subaqueous slope processes and to progradation following localized faulting events. Southwest-fining along strike of three of the five conglomerate units suggests: 1) derivation from the northeast, possibly from an accomodation zone and from the Mount Rogers Formation, or 2) more extensive, coarser-grained, southeastward progradation in the northern half of the basin. The Grandfather Mountain and Mount Rogers basins may have developed as an asymmetric, alternating, half-graben pair and at various times were joined or separated by an accommodation zone. The polymictic conglomerate of the Grandfather Mountain Formation is dominated by felsite and basalt clasts and contains lesser amounts of crystalline basement and sedimentary clasts. Two compositional sequences (upper and lower) are present within the conglomerate and are delineated by the presence or absence of perthite phenocrysts in felsite clasts. The lower sequence is dominated by porphyritic quartz-perthite felsite clasts and details an unroofing sequence: felsite -\u3e sandstone and siltstone -\u3e crystalline basement. In contrast, the upper sequence is dominated by felsite clasts containing only quartz phenocrysts (in the Banner Elk conglomerate) and basalt clasts (in the Broadstone Lodge diamictite). Certain conglomerate clasts are most reliably matched to nonconformably underlying Grenvillian Blowing Rock Gneiss and the intraformational Montezuma basalt Felsite clasts may be derived from either Grandfather Mountain Formation or Mount Rogers Formation rhyolite. Other clasts were derived from other, as yet unidentified, source terranes that have been eroded away or are not exposed. Four facies associations are composed of thirteen descriptive facies. Lateral and vertical changes in facies and facies associations of the conglomerate units of the Grandfather Mountain Formation indicate that coarse-grained alluvial fans, fan-deltas/subaqueous slopes, and braidplains prograded from the basin margins displacing finer-grained braidplain and marine or lake deposits back toward the basin center. Subaqueous (marine or lake?) slope and large-scale subaqueous channel deposits are more significant basin fill environments in the Grandfather Mountain Formation than previously thought. Their presence is particularly indicative of high relief due to basin-margin faulting. Differing clast composition and grain size between conglomerate units as well as interpreted hydrodynamics produce heterogeneous longitudinal bar sequences, braidplain and fan styles. The heterogeneous styles are due to heterogeneous fluvial processes and the complex interplay between proximal and distal environments such as at the alluvial fan-to-braidplain transition. Evidence in support of a glacial or proglacial origin for deposits in the upper part of the Grandfather Mountain Formation is either absent or ambiguous at best. Methods used in this study, if applied to other ancient rift sequences, especially those exposed in the Appalachian Blue Ridge, will further delineate rifting episodes, rift shoulder and basin paleogeography, and provide insight into subsurface stratigraphic patterns within rift basins along modem passive margins

Application of the electromagnetic borehole flowmeter and evaluation of previous pumping tests at Paducah Gaseous Diffusion Plant. Final report, June 15, 1992--August 31, 1992

Multi-well pumping tests have been concluded at wells MW79, MW108, and PW1 at the Paducah Gaseous Diffusion Plant (PGDP) to determine the hydraulic properties of the Regional Gravel Aquifer (RGA). Soil cores suggest that the RGA consists of a thin sandy facies (2 to 6 feet) at the top of a thicker (> 10 feet) gravelly facies. Previous analyses have not considered any permeability contrast between the two facies. To assess the accuracy of this assumption, TVA personnel conducted borehole flowmeter tests at wells MW108 and PW1. Well MW79 could not be tested. The high K sand unit is probably 10 times more permeable than comparable zone in the gravelly portion of the RGA. Previous analyses of the three multi-well aquifer tests do not use the same conceptual aquifer model. Data analysis for one pumping test assumed that leakance was significant. Data analysis for another pumping test assumed that a geologic boundary was significant. By collectively analyzing all three tests with the borehole flowmeter results, the inconsistency among the three pumping tests can be explained. Disparity exists because each pumping test had a different placement of observation wells relative to the high K zone delineating by flowmeter testing

Solubility of airborne uranium compounds at the Fernald Environmental Management Project

The in vitro volubility of airborne uranium dusts collected at a former uranium processing facility now undergoing safe shutdown, decontamination and dismantling was evaluated by immersing air filters from high volume samplers in simulated lung fluid and measuring the {sup 238}U in sequential dissolution fractions using specific radiochemical analysis for uranium. X rays and photons from the decay of uranium and thorium remaining on the filter after each dissolution period were also directly measured using a planar germanium detector as a means for rapidly evaluating the volubility of the uranium bearing dusts. Results of these analyses demonstrate that two -distinct types of uranium bearing dusts were collected on the filters depending upon the location of the air samplers. The first material exhibited a dissolution half-time much less than one day and was most likely UO{sub 3}. The dissolution rate of the second material, which was most likely U{sub 3}O{sub 8}, exhibited two components. Approximately one-third of this material dissolved with a halftime much less than one day. The remaining two-thirds of the material dissolved with half times between 230 {+-} 16 d and 1350 {+-} 202 d. The dissolution rates for uranium determined by radiochemical analysis and by gamma spectrometry were similar. However, gamma spectrometry analysis suggested a difference between the half times of {sup 238}U and its daughter {sup 234}Th which may have important implications for in vivo monitoring of uranium

Direct Determination of the Body Content of Radionuclides: Abstract

Previous ICRU reports have dealt with the formulation and properties of tissue substitutes and phantoms that are used to calibrate in vivo measurement systems. This report provides guidance on the overall process of the direct measurement of radionuclides in the human body for radiation protection and medical applications. It addresses the detectors and electronics used for the measurement; methods of background reduction and control; measurement geometries for whole body, partial body or organ counting; physical and mathematical calibration methods; data analysis; and quality assurance. It is directed to readers who need practical advice on the establishment and operation of direct measurement facilities. </jats:p