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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 67 (1983)

Issue: 8. (August)

First Page: 1360

Last Page: 1360

Title: Paleotectonic Control of Depositional Facies, (Devonian), Southwest Montana: ABSTRACT

Author(s): John C. Webb, Chandler Wilhelm

Article Type: Meeting abstract


Deposition of the Jefferson Formation occurred on a shallow carbonate platform that extended westward to the Antler foreland basin. The distribution of facies and porosity trends was controlled by the structural trends imposed on the area during the late Precambrian and the relative movement of these paleostructural elements during Jefferson deposition. Isopach values (formation "thins") suggest the presence of paleohigh structural elements identified as the Alberta shelf, Tendoy high, and Beartooth shelf, separated by formation "thicks" in the paleolow structural elements (troughs), identified as the Central Montana trough and Ruby trough.

The Jefferson Formation is a moderately thick cyclical sequence of dolomitized carbonate rocks deposited in an extensive tidal flat-lagoonal environment similar to modern tidal flats of Andros Island and the sabkha-lagoonal regions of the Persian Gulf. Normal marine, restricted marine, and evaporite platform facies are recognizable in the Jeffereson, and occur in repetitious fining-upward cycles, which are generally capped by the evaporite facies. Evaporitic facies are predominant in the areas of paleohighs, whereas restricted and normal marine facies predominate in paleolows. Dolomitization was probably contemporaneous in areas of paleohighs, and resulted in microcrystalline dolomite associated with evaporites. Areas marginal to the paleohighs and in paleolows were originally the sit s of restricted and normal marine limestone deposition. Subsequent dolomitization has locally destroyed all primary structures.

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