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Geology topics

F. J. Pearson

Publications and source records attributed to F. J. Pearson.

9 recordsLinked to original sources
USGS1978

Mass transfer and carbon isotope evolution in natural water systems

This paper presents a theoretical treatment of the evolution of the carbon isotopes C13 and C14 in natural waters and in precipitates which derive from such waters. The effects of an arbitrary number of sources (such as dissolution of carbonate minerals and oxidation of organic material) and sinks (such as mineral precipitation, CO2 degassing and production of methane), and of equilibrium fractionation between solid, gas and aqueous phases are considered. The results are expressed as equations relating changes in isotopic composition to changes in conventional carbonate chemistry. One implication of the equations is that the isotopic composition of an aqueous phase may approach a limiting value whenever there are simultaneous inputs and outputs of carbonate. In order to unambiguously interpret isotopic data from carbonate precipitates and identify reactants and products in reacting natural waters, it is essential that isotopic changes are determined chiefly by reactant and product stoichiometry, independent of reaction path. We demonstrate that this is so by means of quantitative examples. The evolution equations are applied to: 1. (1) carbon-14 dating of groundwaters; 2. (2) interpretation of the isotopic composition of carbonate precipitates, carbonate cements and diagenetically altered carbonates; and 3. (3) the identification of chemical reaction stoichiometry. These applications are illustrated by examples which show the variation of ??C13 in solutions and in precipitates formed under a variety of conditions involving incongruent dissolution, CO2 degassing, methane production and mineral precipitation. ?? 1978.

Geochimica et Cosmochimica Acta↗
USGS1978

Correction of ground-water chemistry and carbon isotopic composition for effects of CO2 outgassing

Direct P co 2 "> P co2 measurements on water samples from several CO 2 -charged warm springs are significantly higher than P co 2 "> P co2 values calculated from field pH and alkalinity (and other constituents). In addition, calcite saturation indices calculated from field pH and solution composition indicated supersaturation in samples which, on the basis of hydrogeologic concepts, should be near saturation or undersaturated. We attribute these discrepancies to uncertainties in field pH, resulting from CO 2 outgassing during pH measurement. Because samples for direct P co 2 "> P co2 measurement can be taken with minimal disturbance to the water chemistry, we have used the measured P co 2 "> P co2 to back calculate an estimate of the field pH and the carbon isotopic composition of the water before outgassing. By reconstructing water chemistry in this way, we find generally consistent grouping of δ 13 C "> δ 13 C , pH, and degree of calcite saturation in samples taken from the same source at different times, an observation which we expect based on our understanding of the hydrogeology and geochemistry of the ground-water systems. This suggests that for very careful geochemical work, particularly on ground-waters much above ambient temperature, P co 2 "> P co2 measurements may provide more information on the system and a better estimate of its state of saturation with respect to carbonate minerals than can field measurements of pH.

Geochimica et Cosmochimica Acta↗
USGS1977

Geochemical and hydrologic data for wells and springs in thermal-spring areas of the Appalachians

Current interest in geothermal potential of thermal-spring areas in the Appalachians enhances the value of data on thermal springs and wells in these areas. This report presents maps showing locations of selected springs and wells and tables of physical and chemical data pertaining to these wells and springs. The chemical tables show compositions of gases (oxygen, nitrogen, argon, methane, carbon dioxide, and helium), isotope contents (tritium, carbon-13, and oxygen-18), trace and minor element chemical data, and concentrations of the major chemical constituents.

Water-Resources Investigations Report↗
USGS1976

Geochemical and hydrologic data for wells and springs in thermal-spring areas of the Appalachians

Current interest in geothermal potential of thermal-spring areas in the Appalachians makes all data on thermal springs and wells in these areas valuable. Presented here without interpretive comment are maps showing selected springs and wells and tables of physical and chemical data pertaining to these wells and springs. The chemical tables show compositions of gases (oxygen, nitrogen, argon, methane, carbon dioxide, and helium), isotope contents (tritium, carbon (13), and oxygen (18)), trace and minor element Chemical data, and the usual complete chemical data.

Open-File Report↗