STRATIGRAPHY AND SEDIMENTATION OF THE PRECAMBRIAN REVETT FORMATION, NORTHWEST MONTANA AND NORTHERN IDAHO

Author

David G. Alleman

Year of Award

1983

Document Type

Thesis

Degree Type

Master of Science (MS)

Other Degree Name/Area of Focus

Geology

Department or School/College

Department of Geology

Committee Chair

Don Winston

Publisher

University of Montana

Abstract

The Revett Formation of the Middle Proterozoic Belt Supergroup can be usefully divided into informal lower, middle, and upper members which can be correlated throughout the study area. The lower Revett is dominated by thick beds of clean, fine-grained quartzite which is most commonly flat-laminated or cross-stratified. The middle Revett is composed of thinly-laminated siltite and argillite with only occasional thin interbeds of clean quartzite. Laminae in the siltite are characteristically wavy and laterally discontinuous. The upper Revett comprises interstratified intervals tens of meters thick of both clean, fine-grained quartzite and thinly-laminated siltite-argillite.

Quartzite beds in the Revett Formation are tabular and laterally persistent, and lack channels or lateral accretion surfaces. Unchannelized, laterally unconfined sheet-floods are interpreted as the major depositional mechanism. Paleocurrent trends indicate dominantly north-northeastward sediment transport. Regional stratigraphic trends support this interpretation. Lateral and distal variation in sheet-flood deposits are represented in stratigraphic sections by changing ratios of clean quartzite to siltite. Vertical sequences of thickening, thinning, or thickening then thinning of quartzite beds represent abandonment, progradation, or shifting of depositional lobes.

Southward stratigraphic thickening in the upper Revett across the Jocko line, a proposed down-to-the-south syndepositional growth fault (Winston, 1982), is not abrupt enough to be clearly related to active faulting during deposition. A southward- thickening sediment wedge or structural displacement of thick next to thin stratigraphic sections may be better explanations of the observed thickness changes.

Recommended Citation

Alleman, David G., "STRATIGRAPHY AND SEDIMENTATION OF THE PRECAMBRIAN REVETT FORMATION, NORTHWEST MONTANA AND NORTHERN IDAHO" (1983). Graduate Student Theses, Dissertations, & Professional Papers. 10952.
https://scholarworks.umt.edu/etd/10952