Edward J. Zeller

Solar cosmic ray events for the period 1561–1994: 1. Identification in polar ice, 1561–1950

The geophysical significance of the thin nitrate-rich layers that have been found in both Arctic and Antarctic firn and ice cores, dating from the period 1561–1991, is examined in detail. It is shown that variations of meteorological origin dominate the record until the snow has consolidated to high-density firn some 30 years after deposition. The thin nitrate layers have a characteristic short timescale ( 30 MeV solar proton fluence. The proton fluences (omnidirectional fluence cm−2) derived from the 70 largest impulsive nitrate events between 1561 and 1950 are tabulated. The proton fluence probability distribution derived from these large impulsive nitrate events are in good agreement with earlier studies of the cumulative probabilities of solar proton events and with the observation of cosmogenic isotopes in moon rocks. The cumulative probability curve derived from the impulsive nitrate events indicates a rapidly decreasing probability of occurrence of >30 MeV solar proton events having an omnidirectional fluence exceeding 6 × 109 cm−2. It is concluded that the impulsive nitrate events are reliable indicators of the occurrence of large fluence solar proton events and that they provide a quantitative measure of these events. It is further concluded that the impulsive nitrate events will permit the study of solar activity for many thousands of years into the past.

Serpentinization and the Origin of Hydrogen Gas in Kansas

Hydrogen gas occurs in ten Kansas wells near the Mid-Continent rift system. Since 1982, two wells have yielded small amounts of gases containing an average of 29-37 mole % H2, the remainder being chiefly N2 with only traces of hydrocarbons. Isotopic compositions for hydrogen (^dgrD = -740 to -836 ^pmil) imply near-ambient (about 10°C) equilibration temperatures for the gases, which are among the most deuterium-depleted in nature and resemble the H2-rich gases described from ophiolites in Oman. Isotopic values for the Kansas N2 differ slightly from those of the atmosphere, but not enough to rule out an atmospheric origin. Because they are low in CH4 and CO2, expected byproducts of biogenic activity, the gases are probably abiogenic in origin. The existence of such gases near a major rift system, containing mafic rocks, and not far from known kimberlites is consistent with an origin from reactions involving Fe+2 oxidation, for example during serpentinization. Because the gases may be associated with kimberlites and deep-seated rifting, mantle outgassing is possible, but such an origin would be difficult to reconcile with the low isotopic temperatures. The H2 gases from Kansas (and elsewhere) seem to be too low in pressure to have commercial value. However, neither the Kansas gases nor those from other H2 occurrences have been adequately examined to assess their importance as potential resources.

Factors Influencing Precipitation of Calcium Carbonate

Aragonite, calcite, and vaterite have been precipitated under conditions of controlled temperature, pH, and impurity ion concentration. Results from X-ray diffraction studies, spectrographic analyses, microscopic examination, and thermoluminescence studies have provided information regarding the factors affecting the formation of the various crystalline forms. The immediate factor influencing the form of calcium carbonate precipitates is the impurity content of the crystals. The impurity content has been found to be greatly affected by the pH, temperature, impurity ion concentration in the original solution, the solubility of the polymorphs, crystal size, and the time the precipitate remains in contact with the solution. All of these factors are closely interrelated. The actors influencing the artificial precipitation of calcium carbonate are believed to be applicable to studies concerning the origin of carbonate sediments.

The distribution of nitrate content in the surface snow of the Antarctic Ice Sheet along the route of the 1990 International Trans‐Antarctica Expedition

Previous work showed that nitrate measured at very high resolution (1.5 cm) in snow depositional sequences in Antarctica could be correlated with short-term phenomena such as solar proton events (Dreschhoff and Zeller, 1990). It was clear that deposition of the ionization products in the snow is strongly dependent upon precipitation and atmospheric conditions during and immediately after the event. Information about the geographic distribution of the nitrate fallout over Antarctica was limited to only a few sites, however. A unique opportunity to examine this aspect of the nitrate distribution and to test more fully the hypothesis that atmospheric ionization from solar-charged particles is responsible for a significant portion of nitrate was presented to us by a set of surface snow samples collected by the International Trans-Antarctica Expedition foot traverse. The set of 95 samples of the upper 25 cm was collected by one of us (Qin) at roughly equal distances along the 5736-km route from July 27, 1989, to March 3, 1990. Samples are distributed along a track from 65°05′S, 59°35′W, through 90°S, to 66°33′S, 95°39′E, which represents geomagnetic latitudes 50°S, west longitude, to 77°S, east longitude. The profiles of nitrate concentration and flux along the route were plotted and indicate that (especially at the higher elevation of the polar plateau) the distribution may be affected by electron precipitation.

Factors in Age Determination of Carbonate Sediments by Thermoluminescence

New data obtained from pressure experiments have shown that at least two genetic types of thermoluminescence exist and have furnished an objective means for the selection of limestone samples for age determination tests. The quantity of gamma radiation necessary to reproduce the natural thermoluminescence of a sample can be determined experimentally. When this value is divided by the natural radiation rate, an index is obtained which bears a linear relationship to geologic age. Possible sources of error have been recognized and their effects are discussed.

Uranium Resource Evaluation in Antarctica: ABSTRACT

The continent of Antarctica is the only large land area on earth that has been left almost totally unexplored for uranium resources. In 1976 the first systematic uranium resource evaluation was started as part of the Antarctic International Radiometric Survey. Two areas in the Transantarctic Mountains and one area in Marie Byrd Land have been examined by airborne gamma-ray spectrometric methods. Most flight operations are conducted using Bell 212 helicopters. The equipment in use is a GeoMetrics GR-800 gamma-ray spectrometer with a GAX 512 detector and a GAR 6 analog-recorder. The equipment has proved to be satisfactory, and no plans have been made to increase detector size or to alter data acquisition systems owing to the extremely rigorous nature of the Antarctic field perations. End_Page 441------------------------------ The crystalline igneous and metamorphic rocks of the Precambrian basement, the Paleozoic and Mesozoic sediments of the Beacon Group, and the Cenozoic and recent volcanic rocks have been examined. Localized concentrations of radioactive minerals have been detected in Precambrian rocks, but only small concentrations have been found associated with pegmatites. Thus far, the area covered by the radiometric survey has been too limited to provide any detailed assessment of the uranium resource potential of Antarctica. In general, however, it appears that the potential for uranium resources in the ice-free areas is essentially the same as that of the surface area of any other continental landmass. End_of_Article - Last_Page 442------------