Abstract

The Good field is a Pennsylvanian Strawn to Missourian Canyon-B carbonate bio-herm located in southwestern Borden County. It was colonized by non-reef forming organisms including: phylloid-algae, binding-algae, bivalves, brachiopods, lacy-bryozoans, crinoids, echinoderms, foraminifers, fusulinids, gastropods, and solitary rugose corals. The field is entirely overlain by the Wolfcamp shale.

Initiated on a structural high of the underlying Ellenburger, and associated with the Horseshoe Atoll, the Good field bioherm amalgamated during a time of Midland Basin subsidence and eustatic sea level change. Normal bioherm growth was followed by repeated subaerial exposure. This is indicated by numerous karst surfaces, karst breccias, reworked bioclastic debris, and transported limestone clasts in fringing debris flows identified in cores.

Two cores were logged from the Good Field including the TJ Good No. 22 and TJ Good No. 24. Facies observed include the following: 1) crinoid-bivalve-bryozoan-bioclastic mud-stone, 2) crinoid-algal-foraminifer-bioclastic mudstone to wackestone, 3) crinoid-bivalve-fusulinid-foraminifer-bioclastic wackestone with rare mudstone-wackestone lithoclasts, 4) crinoid-bivalve-fusulinid-bryozoan wackestone to mud-dominated packstone, 5) crinoid-bivalve-fusulinid-bryozoan mud-dominated packstone with lithoclasts, 6) crinoid-ooid-bioclastic mud-dominated packstone, 7) crinoid-fusulinid-bivalve-foraminifer-bioclastic mud-to grain-dominated packstone, 8) crinoid-fusulinid-bivalve-ooid bioclastic grain-dominated packstone with rare mudstone-wackestone lithoclasts, 9) crinoid-fusulinid-echinoderm-ooid bioclastic grain-dominated packstone to grainstone, 10) crinoid-fusulinid-bivalve-echinoderm-ooid bioclastic grainstone with rare mud-dominated packstone lithoclasts, 11) algal boundstone, and 12) karst breccia.

Phylloid-algae is rare but visible as individual plates in facies 2, 3, 6, 7, and 8, as a binding-algae on mudstone-wackestone clasts in facies 6, in algal boundstone clasts in facies 10, and readily identifiable in facies 11.

The facies identified above from Good field cores are consistent with the general lithofacies of the Horseshoe Atoll described in Galloway et al. (1983) and Schatzinger (1988) which include sponge-algal-bryozoan and phylloid-algal-mound wackestones and bound-stones, crestal tidal-flat and peritidal wackestones, shoal and shoreface grainstones, shelf crinoidal wackestones, and debrisflow lithoclast packstones and wackestones.

The Good field has not been dolo-mitized but has been modified by fracturing, karsting, stylolitization, porosity development, and calcite cementation. Rare vertical and curved fault slickenlines have also been identified in the cores.

Fractures range from tight-hairline to fully open. The majority are horizontal to sub-horizontal and vertical to sub-vertical high-angle en echelon fractures that generally terminate at stylolite boundaries.

Karst erosional surfaces (epikarst) are typically marked by the termination of fractures and stylolites. The surfaces are often overlain by imbricated or non-imbricated brecciated zones exhibiting clasts up to 3 inches in diameter.

Breccia clasts range from oval-rounded to angular-blocky and are often sutured by low -amplitude radial serrated stylolites.

Non-breccia related pressure solution stylolites range from wispy, horsetail, low-to medium-amplitude serrated or blocky, to high-amplitude serrated. They are typically horizontal, sub-horizontal, to sub-vertical. Some reach 0.2 inches thick and are organic rich.

The most common porosity types documented include: fracture, vug, and moldic followed by intergrain, intragrain, intrafossil, and intercrystalline. Vugs range in diameter from 0.1 to 4.0 inches in diameter and are occasionally lined with clear to milky scalenohedron and rhombohedron calcite crystals.

Calcite cementation is apparent along fractures, between breccia clasts, in vugs, and pores.

Light tan oil staining is apparent in TJ Good No. 24.