About This Item
Share This Item
Middle Permian Artesia Group sandstones of the Northwestern shelf and Central Basin platform of the Permian basin contain some interesting authigenic minerals (cements) which include clays, sulfates, dolomite, halite, quartz, and orthoclase. To a large degree, diagenetic minerals reflect environments of deposition, although the relation is not always one of cause and effect.
Red-brown and red sandstones were deposited in continental depositional environments which include coastal and continental sabkhas and brine pans, eolian plains, and wadis. Deposition of illuviated clay on grain surfaces formed optically oriented cutans (ferriargillans). The red and red-brown coloration reflects iron oxide pigmentation of clay cutans. Formation of ferriargillans was followed by precipitation of sulfates (anhydrite, gypsum, and hemihydrate), dolomite, and halite. The predominant cements are anhydrite and halite which form large crystals that poikilotopically enclose many sand grains. These poikilotopic cements form a very dense matrix which precludes any accumulation of hydrocarbons.
Most tan, gray, and white sandstones were deposited in peritidal marine environments. In these sands the following succession of diagenetic minerals was precipitated: (1) quartz overgrowths on quartz grains and orthoclase overgrowths on orthoclase grains, (2) dolomite, and (3) sulfates (anhydrite, gypsum, hemihydrate, celestite, and barite). All effective porosity and permeability are in dolomite cements which consist of tiny rhombic crystals. Anhydrite is the predominant sulfate cement and, as in continental sandstones, occurs in large crystals and very dense poikilotopic fabrics which preclude migration of hydrocarbons. The critical factor which controls the economic potential of these sands is the relative proportion of porous, permeable dolomite cements to nonporous anhydrite ceme t.
End_of_Article - Last_Page 474------------