Date of Award

Summer 8-1975

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Geology and Geophysics

First Advisor

Lowe, Donald R.

Second Advisor

Hanor, J.S.

Third Advisor

Ferrell, Ray E.

Abstract

The Mount Rogers Formation of southwestern Virginia is a thick, upper Precambrian sequence of interbedded conglomeratic mudstones, rhythmically layered argillites, arkosic sandstones and conglomerates, polymict conglomerates, and associated rhyolitic and latitic flows and pyroclastics. The conglomeratic mudstone consists of unsorted, angular to sub rounded grains, ranging in size from silt up to boulders one meter in diameter, enclosed within a fine-grained hematitic matrix or cement. The rhythmically layered argillite is made up of thin, alternating couplets of light, very fine-grained sandstone or siltstone grading upward into dark red argillite. Many of the couplets contain "outsized" exotic clasts which penetrate and deform underlying laminae and are overlain by undeformed laminae. Irregularly interbedded within the rhythmically layered argillite is a second population of thicker graded units composed of fine-grained sandstone containing shale rip-up clasts and exhibiting massive, flat laminated and small-scale cross-bedded zones which resemble Bouma intervals. The polymict conglomerate consists of rounded cobbles and pebbles of plutonic, metamorphic, volcanic and sedimentary rock embedded in a matrix of poorly-sorted coarse-grained arkose. The conglomerate is characterized by large-scale festoon cross-bedding, lateral impersistence of individual beds, and poor sorting. The sedimentary units of the Mount Rogers Formation are interpreted as a sequence of glacial and periglacial deposits including tillite (conglomeratic mudstone), glacio-lacustrine or glacio-marine varves (rhythmically layered argillite), interbedded turbidites, and glacio-fluvial debris (arkosic sandstone and conglomerate and polymict conglomerate). The sediment source included an older plutonic, metamorphic terrain and a penecontemporaneous rhyolitic volcanic complex.

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