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Depositional Environments and Hydrocarbon Potential of Copper Ridge Dolomite in Union County, Tennessee

Michael W. Conklin

The Upper Cambrian Copper Ridge Dolomite in Union County, Tennessee, consists of subtidal, intertidal, and supratidal facies that formed in a hypersaline setting. Subtidal facies are dark and thrombolitic; intertidal facies contain thick, planar to wavy laminations, and may be cross-stratified. Supratidal facies are light colored, mud cracked, and thinly laminated. Algal stromatolites, thought to comprise up to 60% of the unit, were not found to be a major rock type in the area studied.

Facies in the unit occur as cyclic, shallowing-upward sequences. The lower member consists of complete cycles, whereas the upper member consists of partial cycles. Cycles are a result of low-amplitude sea level oscillations with long oscillation periods and slow rates of subsidence. Partial cycles lack subtidal facies and were probably caused by tidal flat progradation.

Nearly all cement in the unit consists of white sparry (saddle) dolomite, and occurs in vugs, fractures, and interparticle voids. White sparry dolomite displays cathodoluminescence that consists of dark to bright to dull zones. This sequence suggests that cementation occurred during deep burial of the unit.

Total organic carbon content of carbonate rocks in the unit indicates that the rocks are not a potential hydrocarbon source. Porous zones with up to 12% porosity occur in thrombolitic rocks and packstones to grainstones.

AAPG Search and Discovery Article #91031©1988 AAPG Eastern Section, Charleston, West Virginia, 13-16 September 1988.