Masters Theses

Date of Award

12-1986

Degree Type

Thesis

Degree Name

Master of Science

Major

Geology

Major Professor

Kenneth R. Walker

Committee Members

Steven G. Driese, Thomas W. Broadhead

Abstract

The Maryville Limestone (Middle Cambrian) is part of the nearly 600 meter thick Conasauga Group, which crops out along a series of northeasterly trending strike belts in the Valley and Ridge Province of the southern Appalachians. The interlayered limestone, shale, and dolostone comprising the Conasauga result from the interfingering of the Conasauga Shale to the west and northwest and the Honaker Dolomite to the east and southeast. Apart from detailed lithologic and paleoenvironmental work concerning Conasauga strata in southwestern Virginia and northeasternmost Tennessee, few studies have examined the Maryville in detail in east Tennessee.

In the study area, a total of 330 m of section were measured and described at three localities (Clinton Highway, Joy 2,and GW 129). Although the base of the Maryville is unexposed at Clinton Highway (77.24 m), both the Joy 2 (142.48 m) and the GW 129 (107.23 m) localities record a complete Maryville sequence. These sections were analyzed in order to establish a paleoenvironmental model for the Maryville near the transition of this interval into the Conasauga Shale. The 12 lithologies recognized within the stratigraphic sections reflect the interaction between contemporaneous shallow-water carbonate ramp environments and a siliciclastic-dominated intrashelf basin. Deposition on the carbonate ramp was in the form of lime mudstone and wackestone and oolitic and oncolitic packstone and grainstone. In these shallow-water areas, wave and storm influence were at a maximum as evidenced by the abundance of wave-rippled, planar, and microhummocky cross-laminated calcareous siltstone. To the west and southwest, deeper-water conditions were more common. Sedimentation on the deeper- water margin of the ramp and within the intrashelf basin occurred near or below mean storm wave-base. Deposition was mainly in the form of discontinuous, wave-rippled (linsen-bedded), quartz-rich peloidal packstone; very thin-bedded, planar and low-angle cross-laminated peloidal packstone/grainstone; carbonate-streaked mudstone; and shale. There, sedimentation was governed by fairweather waves and storms that winnowed fine-grained carbonate in shallow- water and transported it off-ramp. In some instances, bottom-hugging geostrophic (?) currents were capable of redistributing sediment, thereby modifying the earlier hemipelagically deposited carbonate. Where they were not winnowed by currents, rhythmic interbeds of lime mud and shale were preserved.

Throughout these sections limestone-clast conglomerate beds also were deposited. Evidence from clast fabrics, matrix type, bed geometries, and associated lithologies indicate that conglomerate deposits owe their origin to two related end-member processes, storms and mass-sediment-gravity movement. Storm-derived conglomerate beds occur more commonly in shallower-water ramp areas. Debris-flow derived conglomerate deposits underwent a more complex history and occur in more basinward areas.

A modified Markov-chain analysis was applied to the nearly 1100 lithologic transitions recorded at the three localities to objectively test for cyclicity. Although statistical analysis supports the presence of rare and subtle cycles, longer-term 10,000-100,000 year Milankovitch cycles, similar to those proposed for coeval deposits in southwestern Virginia, are not recognized within the Maryville sequence. The near absence of statistically verifiable cycles is believed to be related to the heterogenous nature of the ramp depositional system, as well as the prevalence of storm related processes. Storms were sporadic in time and space and capable of reworking the sediment, thus modifying the stratigraphic record.

Analysis of the three Maryville sections reveals a sequential alternation of lithologies which collectively indicate progradational events. Progradational patterns are asymmetric and record the increasing influence of shallow-water carbonate environments which extended southwestward into the intrashelf basin. These sequences are common elsewhere in the Maryville along structural strike. Progradational events were superimposed on an overall transgressive sequence and may have been by stillstands in regional sea-level and/or a lull in subsidence.

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