Variations in [sup 18]O/[sup 16]O ratios of kaolinites within a lateritic profile: Their significance for laterite genesis and isotope paleoclimatology

Conference · Wed Jan 01 04:00:00 EST 1992 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5878658

Giral, S; Girard, J P; Savin, S M ^[1]; Nahon, D B ^[2]

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1. Case Western Reserve Univ., Cleveland, OH (United States). Dept. of Geological Sciences
2. Univ. d'Aix-Marseille III, Marseille (France)

The authors have made an integrated study of the field occurrence, petrology, mineralogy and crystallography, and oxygen isotope geochemistry of an active lateritic profile from about 60 km north of Manaus (Amazonia, Brazil). The parent rock is an arkosic sandstone. The delta O-18 values of kaolinites from the profile are far from uniform. The total range is about 2.4 per mil (18.7 to 21.1 per mil). The calculated delta O-18 value of kaolinite in isotopic equilibrium with local average precipitation and mean annual temperature is 19.6 per mil, within the range of the measured values. Kaolinite of each of several textural occurrences also shows significant isotopic variation both vertically and within a given horizon. Different size fractions of kaolinite of a single textural occurrence within a single horizon also exhibit differences in delta O-18 values. At depths below a few meters, they expect the temperature and the delta O-18 values of the soil water profile to be relatively uniform at any time. If this is so, the variations in delta O-18 values of the kaolinites would suggest that the formation of different populations occurred at different times. They cannot yet distinguish between variations of conditions that were seasonal and variations that occurred on scales of many years. However, it is most important to resolve the causes of these variations before using the delta O-18 values of soil clays for purposes of paleoclimatic reconstruction.

• OSTI ID: 5878658
• Report Number(s): CONF-921058--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 24:7
• Country of Publication: United States
• Language: English

Related Subjects

15 GEOTHERMAL ENERGY
152004 -- Geothermal Data & Theory-- Isotope & Trace Element Studies
58 GEOSCIENCES
580000* -- Geosciences
ALUMINIUM COMPOUNDS
ALUMINIUM SILICATES
BRAZIL
CHEMISTRY
DEVELOPING COUNTRIES
EVEN-EVEN NUCLEI
GEOCHEMISTRY
GEOLOGY
ISOTOPE RATIO
ISOTOPES
KAOLINITE
LATIN AMERICA
LIGHT NUCLEI
MINERALOGY
MINERALS
NUCLEI
OXYGEN 16
OXYGEN 18
OXYGEN COMPOUNDS
OXYGEN ISOTOPES
PALEOCLIMATOLOGY
PALEONTOLOGY
PETROLOGY
RESERVOIR TEMPERATURE
ROCKS
SANDSTONES
SEDIMENTARY ROCKS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
SOILS
SOUTH AMERICA
STABLE ISOTOPES
VARIATIONS