Subsurface Glen Rose Reef Trend in East Texas and West-Central Louisiana: ABSTRACT

Abstract

The subsurface Glen Rose trend in east Texas and west central Louisiana (Lower Cretaceous Comanchean) is a regressive carbonate complex deposited on a broad shallow water shelf. The major structural influences on deposition were the East Texas basin and the northwest Louisiana basin, separated by the Sabine uplift. The Glen Rose trend can be differentiated into two separate reef tracts that prograded seaward over a slowly subsiding shelf. The Upper and Middle tracts overlap within the East Texas embayment and diverge over the southern flank of the Sabine uplift eastward into Louisiana. The trend appears to be located midway between the shoreline and shelf edge. It remains to be seen whether the Glen Rose are actual framework reefs or mounds of transported material. Cores through the massive limestones reveal porous buildups of varying compositions. Reef facies include poorly sorted caprinid-coral grainstones, moderately sorted peloid and oncolite packstones and grainstones, and well-sorted, very fine grained skeletal grainstones. Coated grains, abraded skeletal fragments, scoured bedding surfaces, and minor cross-beds are evidence for deposition of the facies in a high-energy shoal setting. The reefal buildups grade laterally into low-energy shallow water wackestones and mudstones containing toucasids, orbitolinids, and serpulid burrows. Porosities associated with the reefal buildups appear facies controlled. Caprinid-coral packstones and grainstones exhibit intraparticle, moldic, and vuggy porosities of 10 to 15%. Pinpoint End_Page 410------------------------------ microporosity of 5 to 10% are found within the finegrained skeletal grainstones. Fracture porosity enhances permeability in several facies. Moldic and vuggy porosity types are generally secondary whereas intraparticle porosity may be preserved primary. Pinpoint microporosity is probably matrix related secondary porosity. Coarse equant calcite commonly occludes intraparticle, moldic, vuggy, and fracture porosities. Dolomitization within the reef limestones may have acted to create or preserve porosities. Poor production from the Glen Rose trend has been attributed to the lack of structural closure. Use of all available electric logs and sample logs in conjunction with extensive core and thin section analysis should provide new insight on carbonate diagenesis and the relationship to porosity-permeability trends within the Glen Rose trend. End_of_Article - Last_Page 411------------