EXAMINING THE RELATIONSHIP BETWEEN WATER CHEMISTRY AND CARBONATE FACTORY TYPE, JURASSIC SMACKOVER, SOUTHWEST ALABAMA

The Jurassic Smackover formation along the northern rim of the Gulf of Mexico contains prolific carbonate ramp reservoir facies updip, and source rock facies downdip. Reservoir facies are characterized by dominantly thromobilitic, microbial facies in the eastern sector, in Alabama and Florida, and by oolitic grainstone facies to the west, in Texas, Louisiana, and Mississippi. In the eastern sector microbial facies were dominantly deposited during the initial transgression, while oolitic grainstone facies dominate the regressive systems tract. Lateral and temporal variations in paleotopography, ocean water chemistry and sediment supply could all have been responsible for changes in carbonate factory types.

In southwest Alabama, the Smackover formation displays changes in the carbonate factory type laterally across several embayments as well as vertically, through time. The study area is therefore an excellent natural laboratory for assessing the extent by which ocean water chemistry affects carbonate factory type, whereby anoxic, nutrient-rich waters favor microbial factories, while more oxygenated waters are associated with oolitic factories.

Handheld x-ray florescence and laser induced backscatter spectroscopy instruments were used on selected cores to assign quantitative values to redox (Mo, V and Cr), nutrient (Ba, Ni, Cu and Zn), and terrestrial (Al and Ti) sensitive elements on each facies in order to define the water chemistry controls. Preliminary data displays temporal changes in the elemental signatures suggesting that water chemistry may have exerted a significant control on determining the type of carbonate factories, the resultant depositional facies and ultimately the distribution of reservoir quality.