Episodic potassic diagenesis of Ordovician tuffs in the Mississippi Valley area
Cambrian-Ordovician strata of the Mississippi Valley have been extensively modified by potassic diagenesis. Ordovician vitric tuffs are altered to K-feldspar and illite-rich, mixed-layer illite-smectite (I/S), both of which have been dated by K/Ar. Rb/Sr dates for K-feldspar support its reliability as a K/Ar clock, despite a dislocation density of 10/sup 9/-10/sup 10/ cm/sup -2/. Age data document three Paleozoic episodes of potassic diagenesis, which have mean ages of 396 Ma (Early Devonian) for K-feldspar of the upper Mississippi Valley (UMV), 362 Ma (Late Devonian) for I/S of the UMV, and 265 Ma (Permian) for I/S of Missouri. Devonian dates from the UMV correspond to times of wide-spread epeirogeny in the US midcontinent, and diagenetic episodes are attributed to regional flow of basinal brines caused by ground-water recharge on uplifted arches. Potassium for K-feldspar may have come from the Michigan basin, and K for illite may have come from the east-central Iowa basin. K-feldspar and I/S of the UMV are in oxygen-isotopic disequilibrium, indicating that the K-feldspar crystallized from fluid that was either warmer or had lower ..delta../sup 18/O values than that of the I/S. Permian illitization apparently records northward movement of warm saline fluid as a result of the Ouachita orogeny.
- Research Organization:
- Univ. of Illinois, Urbana (USA)
- OSTI ID:
- 6860789
- Journal Information:
- Geology; (United States), Vol. 16:8
- Country of Publication:
- United States
- Language:
- English
Similar Records
Diagenesis of Ordovician tuffs in the Upper Mississippi Valley: Evidence from authigenic I/S and K-feldspar
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Related Subjects
MISSISSIPPI RIVER BASIN
GEOLOGIC HISTORY
TUFF
DIAGENESIS
AGE ESTIMATION
ARGON
FELDSPARS
ILLITE
ISOTOPE DATING
MINERALIZATION
POTASSIUM
RUBIDIUM
SMECTITE
STRATIGRAPHY
STRONTIUM
ALKALI METALS
ALKALINE EARTH METALS
ALUMINIUM COMPOUNDS
ALUMINIUM SILICATES
CLAYS
ELEMENTS
FLUIDS
GASES
GEOLOGY
METALS
MINERALS
NONMETALS
OXYGEN COMPOUNDS
RARE GASES
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
WATERSHEDS
580100* - Geology & Hydrology- (-1989)