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The Stuart City member of the Edwards Limestone (Lower Cretaceous) was cored in 2 wells in Washburn Ranch field, LaSalle County, Texas. Depositional sequences encountered in the cored intervals represent an alternating sequence of reef-derived grainstone, pellet-rich grainstone, near-reef wackestone, and lagoonal mud-rich facies, with a general trend toward more shallow marine conditions. Deposition of the Stuart City member ended abruptly with deepening water conditions and deposition of a pelagic foraminiferal facies.
Porosity in the cored intervals can be related to incomplete cementation of the reef-derived grainstone facies. Four separate and unevenly developed generations of cementation have occurred as determined by standard petrography and cathodoluminescence. Thin, isopachous, syntaxial marine cement is present at some grain contacts. An influx of meteoric waters precipitated a nonluminescent, blocky calcite spar. Following a period of partial dissolution, a brightly luminescent cement lined cavities and indicates deeper burial. The bright cement is followed in optical continuity by an unzoned, faintly luminescent cement forming blocky spar that terminates in rhombic euhedra extending into the remaining pore spaces. It appears that invasion by hydrocarbons expelled meteoric waters and abrupt y ended cementation.
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