Masters Theses

Date of Award

3-1987

Degree Type

Thesis

Degree Name

Master of Science

Major

Geology

Major Professor

Steven G. Driese

Committee Members

Thomas Broadhead, Kenneth Walker

Abstract

A detailed sedimentologic study was made of the Clinch Sandstone (Lower Silurian) in northeastern Tennessee. The Clinch is divided into two distinct members, each of which represents a unique depositional environment. The Hagan Shale Member consists of very fine-grained sandstone and siltstone sequences, whereas the overlying Poor Valley Ridge Sandstone Member is comprised of mostly medium-grained, quartz-rich sandstone beds. The Hagan Shale comprises three recognizable fades: (1) a clayey siltstone with extensive burrowing and rare horizontal laminations, (2) a thin- to medium-bedded, very fine-grained sandstone with horizontal laminations, ripple cross-laminations, and bioturbation, and (3) a thinly interbedded, very fine-grained sandstone and siltstone sequence. The Poor Valley Ridge Sandstone is divided into four facies: (1) a mostly medium-grained sandstone with medium- to large-scale planar-tabular cross-stratification, (2) a fine- to medium-grained sandstone with medium- to large-scale trough cross-stratification, (3) a fine- to medium-grained, extensively bioturbated sandstone with trace fossils that include Skolithos, Diplocraterion, and Arthrophycus, and (4) a thinly interbedded, fine-grained sandstone and clayey siltstone sequence.

Hagan Shale strata were deposited within a back-barrier lagoonal setting that developed in response to eustatic transgression during latest Late Ordovician and Early Silurian time. Siltstone beds represent suspension fallout within the deepest portion of the lagoon, whereas sandstone beds formed as a result of storm-washover from an inferred barrier into the lagoon.

Strata of the Poor Valley Ridge Sandstone are not only coarser-grained than those of the Hagan Shale, but are also more quartz-rich (virtually no detrital feldspar). Two hypotheses are presented in order to explain the change in both texture and to a lesser degree, mineralogy, which defines the contact between the two members of the Clinch Sandstone. (1) A similar source terrain provided detrital material for each member, and the relative enrichment of feldspar within sandstone units of the Hagan Shale resulted from preferential sorting in high-energy paleoenvironments. (2) A lobe of medium- to coarse-grained, quartz-rich sand prograded south (alongshelf) from northern Virginia (major depocenter) into northeastern Tennessee. Storm- and tidally induced currents (in the shoreface and inner shelf) kept the southward advancing sand lobe in motion. With the introduction of coarser-grained sand and the rise in sea-level (due to transgression), deposition of Hagan sediment was terminated, and Poor Valley Ridge deposition was initiated.

Poor Valley Ridge Sandstone strata were deposited in a combined storm- and tide-dominated, shallow-marine shelf setting, characterized by sand ridge fields. The modern North Sea and North American Atlantic Shelf are possible analogs. Sand ridges were oriented and shaped by a predominant current directed to the west and northwest (ebb-tidal flow, storm-surge-ebb flow, and/or a combination of the two) and a subordinate current directed to the southwest (geostrophic flow).

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