Sequence stratigraphy and comparative diagenesis of Middle Ordovician shelf to shelf-edge limestones, the Copper Creek Allochthon, East Tennessee

Author

David Mark Steinhauff

Date of Award

8-1993

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Geology

Major Professor

Kenneth R. Walker

Committee Members

S. D. Driese, M. L. McKinney, E.L. Wehry

Abstract

Surfaces of subaerial exposure in Middle Ordovician strata are correlated among seven stratigraphic sections, four on the shelf (+400 m thk) and three at or near the shelf-edge (300 m thk) near Thorn Hill, TN. These exposure surfaces define stratigraphic sequences within an apparently non-cyclic, largely subtidal, carbonate succession. Facies geometry is based on outcrop observation, analysis of thin-sections (+1,000) and consideration of water-depth curves based on multiple lines of evidence. In platform succession, most sequences are bounded by exposure surfaces, but in more continuously subtidal areas, periods of shallowing and drowning did not always occur. Apparently-non-cyclic carbonate strata have fourth-order subsequences that are grouped into third-order sequences based on the occurrence of pronounced and less pronounced exposure surfaces. Fifth-order parasequences occur within third- and fourth-order sequences. Parasequences are not correlative across the shelf nor from the shelf to the shelf-edge, and many are probably the result of lateral environmental migration. Surfaces of subaerial exposure are correlated from shelf to shelf-edge positions, showing that some sequences or "beats" are missing. Beats are missed in three ways: 1) sea-level remains below the shelf-edge even though sea- level is oscillating, 2) tectonic uplift exposes the shelf until subsidence allows submergence, and 3) during drowning.

Sequence stratigraphy provide a framework within which it is possible to interpret later diagenetic events. Cross-cutting relationships observed in polished slabs and thin-sections using conventional and cathodoluminescent petrography provide the basis for deciphering relative timing of different phases and for interpreting diagenetic origin. Isotopic (δ¹⁸O, δ¹³C, ⁸⁷Sr/⁸⁶Sr) and trace element (Mg, Mn, Fe, Sr) analyses of individual carbonate phases provides supporting evidence.

Cavities and vugs are developed below many third and fourth-order sequence boundaries. Early diagenetic phases filling these cavities represent a "second-cycle" or (?) "third-cycle" of early diagenesis. Fibrous calcite (δ18O = -6 to -4.1%, PDB; N = 89 ) is interpreted as marine. Bladed and clear blocky calcite are more depleted in δ¹⁸O than -6.0%, and are interpreted as meteoric. Bladed and blocky clear calcite do not show the large δ¹³C depletions reported for meteoric phases in younger rocks. Lack of δ¹³C depletion may be related to absence of land plants which might have provided ¹²C to the groundwater.

Intermediate through late burial phases at the shelf-edge have more depleted δ¹⁸O values, higher Fe and Mn contents, and are more enriched in ⁸⁷Sr than their counterparts on the shelf. If the source of fluids precipitating late burial phases was the Sevier basin to the southeast, then fluids at the shelf-edge would have encountered less carbonate rock than fluids traveling to shelf positions.

Analysis of temperatures assumed from burial curves, an assumed range of likely brine compositions, and known ;delta;¹⁸O values for late burial calcite and dolomite suggest that the Sevier basin is the most likely source of burial fluid that precipitated late burial phases. This analysis further suggests that burial fluids could have been generated in the Sevier basin before the end of the Middle Ordovician (ca. 450 Ma). "It was known that the bed rock of this valley is predominantly limestone of the Chickamauga group; and in the absence of definite information to the contrary it would be quite possible for this limestone to be traversed by solution channels, which could be independent of the surface drainage, and might run for miles underground, even conceivably passing beneath the Clinch River to emerge in springs which might be used by people for drinking purposes."

Paris B. Stockdale (1951) in reference to Bethel Valley.

Recommended Citation

Steinhauff, David Mark, "Sequence stratigraphy and comparative diagenesis of Middle Ordovician shelf to shelf-edge limestones, the Copper Creek Allochthon, East Tennessee. " PhD diss., University of Tennessee, 1993.
https://trace.tennessee.edu/utk_graddiss/10782