Date of Award

1990

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Geology and Geophysics

First Advisor

Clyde H. Moore

Abstract

The Smackover-Buckner sequence in the Jay-Big Escambia Creek area has three major lithostratigraphic units: lower Smackover, upper Smackover, and Buckner with an uppermost Smackover transitional sequence. The lower Smackover is regionally extensive, mostly low energy subtidal to intertidal, dolomitized packstones with abundant displacive anhydrite nodules. The upper Smackover is characterized by thick oolite-peloid high energy grainstone buildups generated over Louann salt induced bathymetric highs which were surrounded by areas of low energy, subtidal mudstones-wackestones. The Buckner is mostly nodular mosaic anhydrite with minor amounts of dolomite mudstones-packstones. Below the Smackover-Buckner contact in the grainstone areas is a transitional sequence (referred to here as uppermost Smackover) of high intertidal-low supratidal dolomitized mudstones-grainstones interbedded with nodular mosaic anhydrite layers. A combination of stratigraphic and geochemical evidence indicate dolomites of four separate origins, three of which are early diagenetic. The dolomites of the Buckner-uppermost Smackover have supratidal stratigraphy, heavy oxygen isotopic composition (mean $\delta\sp{18}0$ = +1.5$\perthous$PDB), high trace element composition (average Sr = 202 ppm, Na = 320 ppm) and are syndepositional. Immediately below and separated by a sharp chemical discontinuity within porous and permeable rock, are the upper Smackover oomoldic grainstone dolomites which are coarsely crystalline, well ordered, stoichiometric dolomites lower in $\delta\sp{18}0$ composition (average = $-$2.0$\perthous$PDB) and lower in trace element composition (average Sr = 73 ppm, Na = 228 ppm). Further delineation of the discontinuity by Powell (1984) shows definite flatness or horizontality across Jay Field. Combined with evidence of subaerial exposure (breccias) the chemical discontinuity is believed to be the reminants of a paleo-water table which existed in an island complex prior to uppermost Smackover and Buckner deposition. Moldic porosity development and subsequent dolomitization of the upper Smackover dolomite probably occurred in a mixed evaporated marine-meteoric water system (schizohaline) which existed during the subaerial exposure event.

Pages

414

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