Date of Award

Spring 2-10-1978

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Geology and Geophysics

First Advisor

Lowe, Donald R.

Second Advisor

Hanor, Jeffrey S.

Third Advisor

Kupfer, Donald H.

Abstract

The upper member of the upper Precambrian Mount Rogers Formation of southwestern Virginia includes thick units of massive conglomeratic mudstone Interpreted as tillite (Rankin, 1970; Blondeau and Lowe, 1972; Blondeau, 1975; Schwab, 1976). The tillite is composed of unsorted angular plutonic, metamorphic, volcanic, and sedimentary rock fragments enclosed within a matrix of sandy hematitic mudstone. The tillite is interbedded with arkosic sandstone, argillite, and conglomerate. Sedimentary structures and textures of these units suggest deposition by glaciers which protruded from land into a standing body of water as floating ice. Glacial drift was deposited in a large body of water, probably a lake, by piedmont glaciers which flowed from highland areas on the east and west sides of the basin. Unstratified tillite was deposited beneath melting floating ice, while arkosic sandstone and conglomerate accumulated as subaqueous outwash deposits near the submerged glacial ice front. Argillite was deposited in quiet-water areas of the lake. Five tillite sheets are correlated between three outcrops in the western part of the study area, based on stratigraphic position and textural characteristics. Upper member sedimentary rocks were deposited during a single, large-scale cycle of subaqueous glacial sedimentation punctuated by nine periods of ice advance. Distal varves, turbidites, and stratified tillite were deposited in the lower portion of the upper member. These lithofacies are conformably overlain in the upper portion of the member by proximal massive argillite, structureless sandstone, and unstratified tillite. This stratigraphic succession and overall upward coarsening of the unit suggest increasing proximality during deposition of the upper member of the Mount Rogers Formation.

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