Masters Theses

Date of Award

6-1985

Degree Type

Thesis

Degree Name

Master of Science

Major

Geology

Major Professor

Steven G. Driese

Committee Members

Nicholas Woodward, Thomas Broadhead

Abstract

The Lower Cambrian Chilhowee Group of northeastern Tennessee consists of the Unicoi, Hampton and Erwin Formations and is divided into four facies. Facies G occurs only within the lower 200 m of measured section (the Unicoi Formation) and consists of fine-grained to pebbly quartz wacke with rare thin beds of laminated siltstone. Subfacies Gh consist of low-angle to horizontally laminated, fine-grained sandstone with laminae and lenses of granules and pebbles. Subfacies Gh represents upper flow-regime, overbank deposition within a braided stream system that was proximal to a coastline. Subfacies Gmr consists of medium-scale, planar-tabular cross-stratified conglomerate in which megaripple bedforms are preserved. It is interpreted to represent deposition in interbar pools of braided channels, as flood stage waned and larger bedforms ceased to migrate. Subfacies Gp consists of large-scale, planar-tabular cross-stratified sandy conglomerate; the large sets represent migration of large transverse bars within a broad braided stream channel during high flood state.

Facies S occurs throughout the Chilhowee Group, and is therefore interbedded with the three other facies. Subfacies Sfl consists of thinly interbedded, laminated siltstone and sandstone that may exhibit wavy or lenticular bedding. It represents deposition during slack water periods between ebb and flood tides. Both subfacies Sls and Sms consist of medium- to very coarse-grained, subarkosic to arkosic arenite. Subfacies Sls is characterized by large-scale planar-tabular and trough cross-stratification, whereas Sms is characterized by medium-scale cross-stratification. Subfacies Sfl generally drapes the cross-stratified bed of both Subfacies Sms and Sls.

Subfacies Sls is interpreted to have been deposited within the deepest areas of a subtidal channel and Sms represents deposition in shallower water on shoals separating channels. Subfacies Sls and Sms are arranged in a thinning-upward sequence that most likely resulted from the longshore migration of channels and shoals.

Facies Shcs occurs only in the Erwin Formation and consists of horizontally laminated to hummocky, fine-grained arkosic to subarkosic arenite interbeded with equal amounts of bioturbated mudstone. It represents deposition between storm and fairweather wave base.

Facies QA is characterized by an absence of fine-grained units and lithologically consists of a supermature, medium- to coarse-grained quartz arenite. Subfacies QA-Unicoi is exhibits large-scale planar-tabular cross-stratification and abundant low-angle cross-stratification; symmetrical ripples are rare. Subfacies qA-Unicoi is interpreted to have been deposited within either a ridge-and-runnel system or a system of nearshore bars.

Subfaces QA-Erwin exhibits large-scale, planar-tabular cross-stratification and forms the top of two 40 m thick coarsening-upward sequences: Facies Schs → Facies S → Subfacies QA-Erwin. Subfacies QA-Erwin probably represents deposition on sand ridges that formed on a sand-starved shelf as transgression caused the detachment and reworking of shoreface channel-shoal couplets.

Paleocurrent data for the Chilhowee Group are unimodal but widely dispersed from 0° -180°, and exhibit a minor mode to the west. The data are interpreted to reflect the influence of longshore, tidal and storm currents. The ichnofossil assemblage changes upsection from one characterized only by Paleophycus to a Skolithos ichnofacies and finally to a Cruziana ichnofacies. The facies sequence, biogenic and paleocurrent data reflect the interaction through time of (1) nonmarine and marine processes; and (2) transgression coupled with shoreline progradation. The Chilhowee Group represents an overall deepening from terrestrial deposition to a marine shoreface that experienced both longshore and tidal currents, and finally to a storm shelf environment that periodically shoaled upward.

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