Geology topics

L.C.S. Gundersen

Publications and source records attributed to L.C.S. Gundersen.

6 recordsLinked to original sources

USGS2004

Tectonics and metallogenesis of Proterozoic rocks of the Reading Prong

Detailed geologic mapping, petrography, and major and trace-element analyses of Proterozoic rocks from the Greenwood Lake Quadrangle, New York are compared with chemical analyses and stratigraphic information compiled for the entire Reading Prong. A persistent regional stratigraphy is evident in the mapped area whose geochemistry indicates protoliths consistent with a back-arc marginal basin sequence. The proposed marginal basin may have been floored by an older sialic basement and overlain by a basin-fill sequence consisting of a basal tholeiitic basalt, basic to intermediate volcanic or volcaniclastic rocks and carbonate sediments, a bimodal calc-alkaline volcanic sequence, and finally volcaniclastic, marine, and continental sediments. The presence of high-chlorine biotite and scapolite may indicate circulation of brine fluids or the presence of evaporite layers in the sequence. Abundant, stratabound magnetite deposits with a geologic setting very unlike that of cratonic, Proterozoic banded-iron formations are found throughout the proposed basin sequence. Associated with many of the magnetite deposits is unusual uranium and rare-earth element mineralization. It is proposed here that these deposits formed in an exhalative, volcanogenic, depositional environment within an extensional back-arc marginal basin. Such a tectonic setting is consistent with interpretations of protoliths in other portions of the Reading Prong, the Central Metasedimentary Belt of the Canadian Grenville Province, and recent interpretation of the origin of the Franklin lead-zinc deposits, suggesting a more cohesive evolving arc/back-arc tectonic model for the entire Proterozoic margin of the north-eastern portion of the North American craton. Published by Elsevier Ltd.

Journal of Geodynamics↗

USGS2000

Health risks due to radon in drinking water

Following more than a decade of scientific debate about the setting of a standard for 222Rn in drinking water, Congress established a timetable for the promulgation of a standard in the 1996 Amendments to the Safe Drinking Water Act. As a result of those Amendments, the EPA contracted with the National Academy of Sciences to undertake a risk assessment for exposure to radon in drinking water. In addition, the resulting committee was asked to address several other scientific issues including the national average ambient 222Rn concentration and the increment of 222Rn to the indoor- air concentration arising from the use of drinking water in a home. A new dosimetric analysis of the cancer risk to the stomach from ingestion was performed. The recently reported risk estimates developed by the BEIR VI Committee for inhalation of radon decay products were adopted. Because the 1996 Amendments permit states to develop programs in which mitigation of air- producing health-risk reductions equivalent to that which would be achieved by treating the drinking water, the scientific issues involved in such 'multimedia mitigation programs' were explored.

Environmental Science & Technology↗

USGS1997

Geologic and climatic controls on the radon emanation coefficient

Geologic, pedologic, and climatic factors, including radium content, grain size, siting of radon parents within soil grains or on grain coatings, and soil moisture conditions, determine a soil's emanating power and radon transport characteristics. Data from field studies indicate that soils derived from similar parent rocks in different regions have significantly different emanation coefficients due to the effects of climate on these soil characteristics. An important tool for measuring radon source strength (i.e., radium content) is ground-based and aerial gamma radioactivity measurements. Regional correlations between soil radium content, determined by gamma spectrometry, and soil-gas or indoor radon concentrations can be traced to the influence of climatic and geologic factors on intrinsic permeability and radon emanation coefficients. Data on soil radium content, permeability, and moisture content, when combined with data on emanation coefficients, can form a framework for development of quantitative predictive models for radon generation in rocks and soils.

Conference Paper↗

USGS1997

Mapping the radon potential of the united states: Examples from the Appalachians

The geologic radon potential of the United States was recently assessed by the U.S. Geological Survey. Results indicate that approximately 33% of the U.S. population lives within geologic provinces where the average indoor radon levels have the potential to be greater than 4 pCi/L (147 Bq/m3). Rock types most commonly associated with high indoor radon include: 1) Uraniferous metamorphosed sediments, volcanics, and granite intrusives, especially those that are highly deformed or sheared. 2) Glacial deposits derived from uranium-bearing rocks and sediments. 3) Carboniferous, black shales. 4) Soils derived from carbonate rock, especially in karstic terrain. 5) Uraniferous fluvial, deltaic, marine, and lacustrine deposits. Different geologic terrains of the eastern United States illustrate some of the problems inherent in correlating indoor radon with geology. The Central and Southern Appalachian Highlands of the eastern United States have not been glaciated and most soils there are saprolitic, derived directly from the underlying bedrock. Regression analyses of bedrock geologic and radon parameters yield positive correlations (R > 0.5 to 0.9) and indicate that bedrock geology can account for a significant portion of the indoor radon variation. In glaciated areas of the United States such as the northern Appalachian Highlands and Appalachian Plateau, the correlation of bedrock geology to indoor radon is obscured or is positive only in certain cases. In these glaciated areas of the country, it is the type, composition, thickness, and permeability of glacial deposits, rather than the bedrock geology, that controls the radon source.

Conference Paper↗

USGS1992

The effect of rock type, grain size, sorting, permeability, and moisture on measurements of radon in soil gas: A comparison of two measurement techniques

Soil surveys of radon conducted in the Coastal Plain of New Jersey, Alabama and Texas indicate that soil composition and grain size exert the strongest control on the concentration of radon measured. Soil-gas radon was measured in-situ using two techniques; one developed by G. Michael REIMER of the U.S. Geological Survey; the other developed by Rogers and Associates Engineering Corp. for use by the Environmental Protection Agency. The Reimer technique acquires a small-volume, grab sample of soil gas, whereas the Rogers and Associates technique acquires a large-volume, flow-through sample of soil gas. The two techniques yield similar radon concentrations in well-sorted sands, but do not correlate as well for poorly sorted soils and clays.

Conference Paper↗

USGS1989

A direct correlation among indoor Rn, soil gas Rn and geology in the Reading Prong near Boyertown, Pennsylvania

We feel that this study suggests a relationship among geology, soil gas Rn and the potential for indoor Rn accumulation in this portion of the Reading Prong. There are deviations from a perfect correlation but these are related to inhomogeneities in the geologic environment and perhaps variations in construction techniques of homes in the area. This study also demonstrates that several analyses in a small area may be necessary to adequately determine the Rn distribution for a particular geologic unit. That scale would be determined by the complexity of the local geology. Where no discrete source of elevated Rn supply is found for dwellings having a significant Rn accumulation, the implication is that overall gross permeability may be sufficient to supply Rn from a larger volume of soil and rock.

Health Physics↗