A FRESH LOOK AT OLD PROBLEMS: UNLOCKING THE RELATIONSHIP BETWEEN CARBONATE FACTORY TYPE AND WATER CHEMISTRY ON CARBONATE RAMPS, JURASSIC SMACKOVER, GULF OF MEXICO

The Smackover Formation was deposited in the early Late Jurassic along the periphery of the Gulf of Mexico and is an example of a mixed microbial, oolitic, evaporite and clastic ramp system. Carbonate factory types vary both temporally, and laterally across the depositional profile and along strike at the regional scale. The regressive and western portion of the Gulf Coast, in Texas, Arkansas and Louisiana is dominated by oolite grainstone facies, while the transgressive and eastern portion, in Alabama and Florida is dominated by microbial mound facies.

The controls on carbonate factory type and facies architecture on ramps are poorly understood. Oceanographic setting, bathymetry, clastic sediment supply, and water chemistry all have an influence on factory type and facies distribution. Previous models have adopted a qualitative approach focused on physical parameters in an attempt to understand their controls on carbonate factory type in ramp settings. However, carbonate ramps display complex facies architectures that cannot be fully explained by physical parameters alone. We propose that water chemistry may hold the key to unlocking our understanding of carbonate ramp factory types and we further hypothesize that transgressive, microbial-rich facies correspond to anoxic conditions, whereas regressive, oolitic-rich facies correspond to more oxygenated conditions.

In order to investigate the relationship between water chemistry and carbonate factory type, handheld X-ray fluorescence and laser induced backscatter spectrometer instruments were used to determine the presence and concentration of redox-sensitive elements within each facies of the Smackover and analogue systems. Wepresent preliminary data on the lateral distribution of geochemical proxies in a sequence-stratigraphic frame in order to discuss the relationship between water chemistry and corresponding carbonate factory type.