Isotopic composition of Silurian seawater
Direct isotopic analyses of 21 samples of the Silurian hydrosphere preserved as fluid inclusions in Silurian halite deposits in the Michigan Basin Salina Group yield delta/sup 18/O, deltaD ranging from 0.2 to +5.9 and -26 to -73, respectively. delta/sup 18/O has the same range as observed for modern halite facies evaporite waters and is a few per thousand higher than 100 analyses of fluid inclusions in Permian halite. deltaD is about 20 to 30 per thousand lower than modern and Permian examples. The trajectory of evaporating seawater on a deltaD-delta/sup 18/O diagram initially has a positive slope of 3-6, but hooks strongly downward to negative values, the shape of the hook depending upon humidity. Halite begins to precipitate at delta values similar to those observed for the most /sup 18/O rich fluid inclusions. Subsequent evaporation yields progressively more negative delta values as observed for the fluid inclusions. The fluid inclusion data can be readily explained in terms of evaporating seawater and are consistent with the degree of evaporation deduced from measured bromide profiles. These data are strongly inconsistent with arguments that Silurian seawater was 5.5 per thousand depleted in /sup 18/O. delta/sup 18/O for evaporite waters is systematically related to that of seawater, and does not show a -5.5 per thousand shift in the Silurian, even allowing for variables which affect the isotope evaporation trajectory. The lower deltaD may indicate a component of gypsum dehydration waters or may suggest a D-depleted Silurian hydrosphere.
- Research Organization:
- Arizona State Univ., Tempe (USA)
- OSTI ID:
- 6194806
- Report Number(s):
- CONF-8510489-
- Journal Information:
- Geol. Soc. Am., Abstr. Programs; (United States), Vol. 17; Conference: 98. annual meeting of the Geological Society of America, Orlando, FL, USA, 28 Oct 1985
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
INCLUSIONS
GEOCHEMISTRY
MICHIGAN
SALT DEPOSITS
CHEMICAL COMPOSITION
GYPSUM
HALITE
ISOTOPE RATIO
QUANTITATIVE CHEMICAL ANALYSIS
SEAWATER
SEDIMENTARY BASINS
SILURIAN PERIOD
WATER CHEMISTRY
ALKALINE EARTH METAL COMPOUNDS
CALCIUM COMPOUNDS
CALCIUM SULFATES
CHEMICAL ANALYSIS
CHEMISTRY
FEDERAL REGION V
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC STRUCTURES
HALIDE MINERALS
HYDROGEN COMPOUNDS
MINERALS
NORTH AMERICA
OXYGEN COMPOUNDS
PALEOZOIC ERA
SULFATE MINERALS
SULFATES
SULFUR COMPOUNDS
USA
WATER
580400* - Geochemistry- (-1989)