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Smackover carbonates were deposited on a regional ramp which was locally affected by salt-generated paleotopography and basement structures. The paleobathymetry at North Haynesville field was a salt-generated high on which oolite grainstones accumulated. These shoals consisted of tide-dominated sand waves that were flanked by algal-rich grainstones and packstones which, in turn, were surrounded by open marine, peloidal wackestones.
The sand shoals were lithified primarily in the marine phreatic environment, but as they had accumulated significant depositional relief, they became exposed during minor regressions. Consequently, the shoals were affected by early meteoric phreatic diagenesis. Blocky calcite cements and inversion of metastable allochems marked this diagenetic episode.
Subsequent burial diagenetic history can be charted from early to late by the sequential appearance (in order) of the following characteristics: microstylolites, dolomitization, macrostylolites, poikilotopic calcite cements, baroque dolomite cements, and late leaching.
Whole-rock trace element analyses indicate that magnesium, iron, and manganese correlate strongly with dolomitized horizons; strontium correlates with algal-encrusted grains; and aluminum correlates with tight, argillaceous micrites. To an extent, the algal-encrusted grains are also correlated with late, dissolution-enhanced intergranular porosity.
The North Haynesville reservoir is both selective and nonselective for certain depositional microfacies. Selection is for those sand shoals that had the highest primary porosity and permeability and that were affected by dissolution enhancement in the subsurface. However, the same late dissolution processes affected both micrite and allochems in the nonfacies-selective sectors of the reservoir.
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