Petrography and geochemistry of the Artesia Group, Palo Duro Basin, Texas Panhandle: Final report

The Artesia Group of the Texas Panhandle is an evaporite red-bed sequence which has been intensely altered by interaction of evaporites with ground water. Comparison of the upper, most altered part of the sequence with the lower, least altered part allows identification of the diagenetic sequence. The least altered lower part of the Artesia Group includes anhydrite beds, anhydritic halite, mudstone-halite mixtures, mudstone, claystone, siltstone, and sandstone. Diagenetic processes include cementation by halite, replacement of gypsum by anhydrite and minor polyhalite, and minor replacement of halite by dolomite and anhydrite. Halite is present throughout the lower part of the Artesia Group as bedded halite, as isolated halite crystals and veins, and as halite cement in clastic beds. The altered interval in the upper part of the Artesia Group is characterized by mudstone-anhydrite-dolomite breccias, thin, wavy laminae of anhydrite and dolomite, and abundant fractures filled with fibrous anhydrite and gypsum in mudstone, claystone, siltstone, and thin anhydrite beds. Halite is absent, and removal of halite is interpreted as the principal cause of the alteration, either directly, by dissolution and collapse, or indirectly, by increasing porosity and allowing increased ground-water penetration. At the top of the Artesia Group, anhydrite has been hydrated to gypsum, and minor amounts of gypsum have been replaced by calcite. The geochemistry of preserved halite in the lower part of the Artesia Group shows that meteoric waters have been included in halite and that halite has been recycled by dissolution and reprecipitation. The occurrence of this type of alteration might indicate that the halite of the Artesia Group was invaded by waters from the overlying aquifers. However, the stratigraphic and textural relationships in the halite indicate that the alteration reflects continental influences in the clastic-dominated depositional environment. 32 refs., 45 figs., 1 tab