Facies and depositional environments of the Shattuck Sandstone on the northwestern shelf of the Permian Basin

Abstract

ABSTRACT The Artesia Group is a sequence of carbonates, evaporites, sandstones, siltstones, and shales that was deposited on the back-reef shelves of the Permian Basin of Texas and New Mexico during late Permian (Guadalupian) time. The facies and depositional environments of the shelf carbonates and evaporites in this group are fairly well established, but there is still debate about the origin of the shelf clastics and the role of sea-level fluctuations in their formation. This problem is not unique to the Artesia Group but is common to shelf clastics in stratigraphic sections around the world. This study examined cores and logs of one of the more prominent shelf clastics in the Artesia Group, the Shattuck Sandstone Member, from two oil fields on the Northwest Shelf of the Permian Basin in or er to address this problem. The Shattuck Sandstone is underlain and overlain by carbonates, evaporites, siltstones, and sandstones that were deposited in a shelf-interior lagoon and adjacent coastal sabkhas during relative highstands of sea level. However, the textures, colors, sedimentary structures, fabrics, and fossil content of the Shattuck, and the nature of its contacts with these bounding lagoonal and coastal sabkha deposits, indicate that it was deposited in semi-arid and poorly-vegetated desert coastal plain environments that prograded across the Northwest Shelf after exposure of the shelf by a sea-level fall. Three facies can be distinguished in the Shattuck Sandstone. Facies 1 consists largely of reddish-brown and non-fossiliferous cross-bedded and bedded sandstones, silty sandstones, and siltstones with silty mudstone drapes and infiltrated detrital clay; it is interpreted to be the deposits of a fluvial sandflat system. Facies 2 consists of non-fossiliferous well-sorted fine to very fine sandstone with dune cross-beds and wind-ripple, grainfall, and deflation-lag laminae; it is interpreted to be the deposits of an eolian sand sheet. Facies 3 is largely composed of reddish-brown and non-fossiliferous sandstones, silty sandstones and siltstones with haloturbation and dewatering structures, displacive anhydrite nodules, and thin nodular-mosaic anhydrite beds; it is interpreted to be the de osits of a clastic-dominated sabkha.