Masters Theses

Date of Award

8-1982

Degree Type

Thesis

Degree Name

Master of Science

Major

Geology

Major Professor

Thomas W. Broadhead

Committee Members

Kenneth R. Walker, Robert E. McLaughlin

Abstract

Approximately 425 meters of Middle Ordovician predominantly carbonate rocks are exposed at Stanley Farm, Union County, Tennessee. The stratigraphic section begins at the Post-Knox unconformity and consists in ascending order of seven formations; Five Oaks Formation, Lincolnshire Formation (Eidson, Fleanor, and Hogskin members), Rockdell Formation, Benbolt Formation, Wardell Formation, Bowen Formation, and Witten Formation. Detailed field observations and petrographic analysis of 132 thin sections allowed inferences of the paleodepositional environment of each formation and member.

The Five Oaks Formation represents tidal flat deposition on the Knox karst surface. Lower and middle intervals of the formation represent supratidal to high intertidal deposition while upper intervals represent low intertidal to subtidal deposition. The Lincolnshire Formation (Eidson, Fleanor, and Hogskin members) represents an inter tidal to subtidal-restricted carbonate shelf punctuated by episodes of terrigenous clastic sedimentation. The Eidson Member represents a stable, subtidal (restricted shelf) facies. The Fleanor Member represents very shallow (wave-active), current-influenced terrigenous clastic deposition. The Hogskin Member represents deposition in a Fleanor-like environment, however, the percentage of terrigenous clastic material gradually decreases stratigraphically upward. The Rockdell Formation represents stable, shallow subtidal deposition. The Benbolt Formation reflects water shallowing and an associated influx of terrigenous clastic material. The lower intervals of the Benbolt represent non-agitated, stable deposition, while the middle intervals reflect shoaling carbonate and sporadic terrigenous clastic sedimenta tion. The upper intervals reflect deeper, non-agitated depositional regimes. The Wardell Formation represents a storm influenced, shallow (wave-active) facies. The Bowen Formation represents intertidal, terrigenous clastic-influenced deposition, indicative of an encroaching southeastern sediment source. The Witten Formation represents a return to stable, subtidal deposition in the lower intervals, while the upper intervals reflect shallow subtidal to intertidal regimes.

The members of the Lincolnshire Formation (Eidson, Fleanor, and Hogskin) were examined along strike for the purpose of resolving their strati graphic relationships and mode of formation. The Fleanor, originally designated as a formation (Cooper and Cooper, 1946), lies between the Eidson and Hogskin Members and grades into the Hogskin at the Stanley Farm Section; consequently, all three units are considered members of the Lincolnshire Formation. The lens shaped configuration, rapid strati graphic appearance, and lack of lateral interfingering suggest a deltaic paleoenvironmental setting for the Fleanor Member.

Ten bedding planes within the Benbolt Formation were chosen for the purpose of paleoecological analysis; point counts of 52 slab surfaces and microscopic analysis of 20 acetate peels allowed biovolume computations and environmental interpretations, respectively. Biovolume percentages exhibit a dominance (>99% total biovolume) of suspension feeding organisms. Furthermore, biotic diversity is highest in the lower third of the Formation. The co-occurrence of echinoderms and bryozoans and virtual mutual exclusion of echinoderms and brachiopods may be explained either by niche stratification (tiering) resulting from food partitioning in the water column, or by physical environmental constraints. Low stress environments exhibit high diversity; assemblage composition was probably governed by tiering. Conversely, high stress environments exhibit low diversity; assemblage composition was most likely governed by organism adaptability to environmental constraints rather than food availability.

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