Abstract Early Guadalupian Grayburg dolostones and siltstones accumulated on shallow-water to exposed platforms that encircled the Midland Basin, West Texas. The Grayburg Formation is the uppermost of several upward-shoaling sequences of the lower Guadalupian and is transitional between the dolostone strata of the underlying San Andres Formation and the siltstone and anhydrite of the overlying Queen Formation. The siltstone and silty dolostone units within the Grayburg mark the base of a number of thinner, upward-shoaling cycles. In Dune Field, Central Basin Platform, siltstones and silty dolostones are associated with subtidal fusulinid wackestones to supratidal pisolite wackestone to grainstone; in some areas a single marker is associated with this entire range of depositional environments. Most of the siltstone cores exhibit structures interpreted to have developed under subaqueous conditions. In Farmer Field, Ozona Arch, siltstones mark the base of many thin cycles within the reservoir section.