Masters Theses

Date of Award

12-1995

Degree Type

Thesis

Degree Name

Master of Science

Major

Geology

Major Professor

Michael L. McKinney

Committee Members

Thomas W. Broadhead, Hazel R. Delcourt

Abstract

The Florala Limestone Member of the Bridgeboro Limestone (Lower Oligocene, Vicksburg Stage) comprises a sequence of richly fossiliferous coralgal wackestones and packstones that outcrop in southeastern Alabama and are present in the subsurface of the western Florida Panhandle. Previous research suggests the Florala reflects a quiescent, middle-shelf environment existing at depths between 70 and 80 meters and may represent, in part, a progressive bathymetric shoaling; however, strong empirical data supporting these conclusions are lacking. The current study represents a paleoecological analysis of this unit using its inherently abundant and diverse cheilostome and cyclostome bryozoan assemblages as a principal means of interpretation. This investigation was conducted at two study localities: the type section, located in Covington County, Alabama, and a core from Walton County, Florida. The principal methods of analysis used in this study include the application of zoarial morphology to infer the nature of substrate, turbulence, and relative rates of sedimentation between study sites and among stratigraphic samples, as well as the robust techniques of Detrended Correspondence Analysis (DCA) and rarefaction to quantitatively examine the ecological structure and respective stratigraphic changes in taxonomic associations. The results of this study indicate that considerable paleoenvironmental variation exists than has been previously determined. The inferred paleoecological conditions at the Walton County site denote a higher incidence of particulate substrates, a relatively higher degree of water energy, and possibly greater sedimentation influx than determined for the type locality. Stratigraphic changes in the taxonomic composition of faunal assemblages suggests a pattern of allogenic replacement at both study localities possibly accompanied by a progressive decline in ecological stability and equability. The underlying factor of the allogenic replacement may have been related to a shallowing in bathymetry, which, on the basis of stratigraphic changes in the abundance of zoarial morphology and taxonomic associations, is a plausible interpretation. The application of known bathymetric ranges of modern congeners to extant taxa found in the Florala suggest an average depth of 60 meters which is close to results from previous studies.

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