Rb-Sr, K-Ar, and /sup 40/Ar//sup 39/Ar systematics in Paleozoic glauconite from Mississippi Valley-type localities, and the dating of events during sediment diagenesis

Thesis/Dissertation · Fri Jan 01 04:00:00 EST 1982

OSTI ID:5926724

Laskowski, T E

Rb-Sr, conventional K-Ar, and /sup 40/Ar//sup 39/Ar systematics of Paleozoic glauconite in the Cincinnati arch area of Ohio-Indiana (Brassfield Formation), S.E. Missouri Lead District (Bonneterre and Davis Formations), and from glauconite subject to cation-exchange experiments were investigated in an attempt to understand the circumstances which lead to the anomalously young Rb-Sr and K-Ar ages from these glauconite occurrences. Rb-Sr systematics in Lower Silurian Brassfield Formation glauconite samples from the Cincinnati arch area (depositional age about 430 Myr.) have been completely reset by an event about 370 +/- 11 Myr. ago. The similarity between the glauconite isochron initial /sup 87/Sr//sup 86/Sr ratio (0.7096 +/- 3) and the /sup 87/Sr//sup 86/Sr ratio of gangue vug-filling calcite (0.7098 +/- 3) directly associated with glauconitic horizons, suggests that the fluids which precipitated the calcite were also responsible for resetting the Rb-Sr glauconite age. The mechanism involved was probably cation-exchange involving Sr in the fluid and in the glauconite. These fluids may have been Mississippi Valley-type ore fluids. Rb-Sr ages of Upper Cambrian glauconite pellets from the Viburnum Trend area (Davis Formation) in S.E. Missouri also may have been reset by Mississippi Valley-type ore fluids about 387 +/- 21 Myr. ago. All glauconite samples measured by the /sup 40/Ar//sup 39/Ar method have sustained /sup 39/Ar loss due to recoil during neutron irradiation.

• OSTI ID: 5926724
• Country of Publication: United States
• Language: English

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58 GEOSCIENCES
580100* -- Geology & Hydrology-- (-1989)
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BETA DECAY RADIOISOTOPES
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