Selected fractionation factors for D, O18, C13, and S34 have been compiled from the literature and plotted on a convenient linear temperature coordinate system. Elementary discussions of terminology and the problems of isotope standards are presented, together with equations relating the various standards used for reporting O18 values. Where data are available at only a few temperatures, the fractionations are given in tabular form. For each fractionation factor, a reference to the original work is given. 'Some authors have used the symbol OL' to refer to a measured fractionation factor, even though it may not be an equilibrium fractionation. 'Corrected from the published value of 1.0407 using revised mass spectrometer correction factors.
The content of total dissolved solids and δD and δO18 values are given for 95 oil‐field brines from the Illinois, Michigan, and Alberta basins and the Gulf Coast. The variation in deuterium content among basins is found to be much greater than that within each basin. Oxygen isotopic composition, on the other hand, shows a large range in each basin, strongly correlated with salinity. The relationships between isotopic and chemical compositions of the brines lead to the following conclusions: (a) the water is predominantly of local meteoric origin; (b) the deuterium content has not been greatly altered by exchange or fractionation processes; (c) extensive oxygen exchange has taken place between water and reservoir rocks. Several samples contain water which appears to have originated as precipitation during Pleistocene glacial periods.
Over a 7‐year period from April 1982 to April 1989, integrated samples of rain and snow were collected at 32 sites by oil‐sealed storage gage stations in (and adjoining) the southeast California desert; station elevations ranged from −65 m to 2280 m, and the collection network covered an area measuring about 400 km in each dimension. Deuterium (δD) analysis of 406 samples shows that the average δD of summer precipitation was −56 per mil (‰) whereas winter values averaged −78‰, averaged annual values were close to −69‰ because most of the area is in a winter‐dominated precipitation regime. We found no correlation between wetness or dryness of a season and the δD of its precipitation. The δ18O versus δD plots show that rain samples define a line of slope 6.5, less than the 8 of the Meteoric Water Line, whereas snow samples define a line of slope 9.2. These differences in slope are the result of isotopic fractionation which occurred during evaporation of raindrops but not during sublimation of snow. Trajectory plots of 68 of the major storm events show that all of the winter storms originated in the Pacific, and passed over high mountains before reaching our collection stations. However, 21 of the 30 summer storms had trajectories that originated either over the Gulf of Mexico or the subtropical Pacific and traveled either west or north to reach our stations, without traversing high mountains. The difference in δD between winter and summer precipitation is due to different air flow patterns during those seasons.
The hydration rates of 12 obsidian samples of different chemical compositions were measured at temperatures from 95 degrees to 245 degrees C. An expression relating hydration rate to temperature was derived for each sample. The SiO(2) content and refractive index are related to the hydration rate, as are the CaO, MgO, and original water contents. With this information it is possible to calculate the hydration rate of a sample from its silica content, refractive index, or chemical index and a knowledge of the effective temperature at which the hydration occurred. The effective hydration temperature can be either measured or approximated from weather records. Rates have been calculated by both methods, and the results show that weather records can give a good approximation to the true EHT, particularly in tropical and subtropical climates. If one determines the EHT by any of the methods suggested, and also measures or knows the rate of hydration of the particular obsidian used, it should be possible to carry out absolute dating to +/- 10 percent of the true age over periods as short as several years and as long as millions of years.
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