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O¹⁸/O¹⁶ and D/H Ratios of Soils, Weathering Zones, and Clay Deposits


Lawrence, James Robert (1970) O¹⁸/O¹⁶ and D/H Ratios of Soils, Weathering Zones, and Clay Deposits. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Y4JD-S067.


NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. D/H and O18/O16 ratios have been determined for a large variety of bulk samples and mineral separates from: Quaternary soils and clay-rich weathering zones; Tertiary, Cretaceous and Pennsylvanian kaolinite deposits; a number of montmorillonite occurrences (from bentonites, fossil soils, alteration of pillow lavas, etc.); Precambrian, Paleozoic and Cretaceous shales; and Pleistocene glacial lake clays. Most samples are from the western and southern United States, but analyses have also been obtained from Hawaii and other parts of North America. Laboratory experiments indicate that kaolinites do not suffer any significant amount of hydrogen isotopic exchange at room temperature when in contact with D enriched waters. This also applied in general to montmorillonites, but in many instances partial hydrogen isotopic exchange occurs with interlayer water during the normal heating and outgassing that precedes extraction of OH water. The hydroxyl of halloysite, however, does undergo marked hydrogen isotopic exchange with its interlayer water in a few hours or days at room temperature, largely negating the usefulness of this mineral in isotopic studies. The D/H and O18/O16 ratios of clay minerals and hydroxides in Quaternary soils and weathering zones throughout the United States show a systematic correlation with the isotopic values of present-day meteoric waters. The [...] and [...], respectively, of these weathering products range as follows: Hawaii: -27 to -65 and +24 to +15; Southern United States: -55 to -75 and +22 to +17; coastal California: -55 to -80 and +23 to +16; Sierra Nevada, California: -75 to -95 and +19 to +14; Colorado: -95 to -110 and +16 to +8; Montana and Idaho: -105 to -165 and +12 to 0. The [...] values of the clay minerals are generally 0 to 40% lighter than local meteoric waters and the [...] values are generally 22 to 28% heavier than local meteoric waters. The isotopic values of the clay minerals plot in the vicinity of Savin and Epstein's (1970a) kaolinite line. The [...] and [...] values of the hydroxides (e.g., gibbsite) are generally 10 to 20% lighter and 15 to 20% heavier, respectively, than local meteoric waters. The isotopic values of the hydroxides plot in the vicinity of the line [...]. A kaolinite soil profile from Georgia and a montmorillonite profile from California, both formed on granitic rock types, were studied in detail. Other detailed sampling was done on a halloysite profile formed on basalt, on three poorly-developed profiles on Cretaceous shales, and a poorly-developed profile on a Precambrian shale. These studies indicate that igneous and sedimentary parent rock minerals do not undergo appreciable oxygen or hydrogen isotopic exchange with meteoric waters in the weathering environment. However, the clay minerals and hydroxides produced by the alteration of the parent rock are formed essentially in isotopic equilibrium with the local meteoric waters. The D/H and O18/O16 ratios of most Pre-Quaternary kaolinites, bentonites, and shales are significantly higher than those of clay-rich Quaternary soils in the same geographic areas. The D/H ratios of Lower Paleozoic and Precambrian shales from eastern United States to Montana and British Columbia show no correlation with the D/H ratios of present-day meteoric waters. The D/H ratios of glacial lake clays, which were exposed to glacial melt waters highly depleted in deuterium are identical to the D/H ratios of Lower Paleozoic shales of the eastern United States from which they were largely derived. All these data suggest that the isotopic ratios of the Pre-Quaternary clay minerals are largely preserved. Because the isotopic values of ancient clay minerals seem to be commonly preserved, the D/H ratios of ancient kaolinites formed by weathering processes can be used to estimate the D/H ratios of ancient meteoric waters. Using the [...] values of the Tertiary kaolinites and a [...] a tentative contour map of the [...] values of "mid-Tertiary" meteoric waters has been drawn. The distribution of the [...] values of Tertiary meteoric waters are similar to the present-day distribution except that the contrast in [...] values between coastal and high inland regions in the Tertiary was less extreme than the present contrast. The interpretation is that the distribution of land and the meteorological patterns in the Tertiary were somewhat similar to today but that the climate was generally warmer. Also it is possible that many present-day topographic barriers were absent or less important in the Tertiary. This is in agreement with climatic data suggested by paleobotanical evidence. The wide range of D/H and O18/O16 ratios determined for relatively pure (> 80%) kaolinites formed by the weathering process confirms that the kaolinite line derived by Savin and Epstein (1970a) is essentially correct. However, the D/H and O18/O16 ratios of montmorillonites formed as weathering products or in sedimentary environments display a much greater scatter than kaolinites, presumably as a result of (1) the greater range of chemical compositions of montmorillonites compared to kaolinites, (2) the greater range of the temperatures of formation of montmorillonites, and (3) the possibility that the D/H ratios determined for montmorillonite OH are contaminated during heating and outgassing procedures. Hence, the montmorillonite line derived by Savin and Epstein (1970a) apparently does not apply to most montmorillonites in nature.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:(Geochemistry)
Degree Grantor:California Institute of Technology
Division:Geological and Planetary Sciences
Major Option:Geochemistry
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Taylor, Hugh P.
Thesis Committee:
  • Unknown, Unknown
Defense Date:21 May 1970
Record Number:CaltechETD:etd-01132004-094857
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:149
Deposited By: Imported from ETD-db
Deposited On:14 Jan 2004
Last Modified:16 May 2024 23:12

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