| dc.description.abstract | Morrowan sandstones of the Oklahoma Panhandle commonly are divided into informal stratigraphic units. The "Upper" Morrowan sandstone generally is considered to have been deposited in a fluvial setting; "Lower" Morrowan sandstones generally are interpreted as having been deposited during a shallow-marine transgression. Interpretation of Upper Morrowan sandstones is based on evidence such as (1) quartz, feldspars, and rock fragments that range widely in, grain size, (2) carbonized plant remains that are common, (3) overall fining-upward sequences, (4) strata that are finer grained upward, from granules and coarse grained sands to medium sized grains, (5) abundant medium scale crossbeds (6) lateral discontinuity of strata, and (7) absence of fossils andjor glauconite. Interpretation of Lower Morrowan sandstones is based on (1) fairly consistent grain size, (2) abundant glauconite and fossil fragments, (3) sparse detrital clay, (4) some small scale to medium scale crossbeds, and (5) overall blanket-type geometry. 1 2 The Morrowan interval thickens to more than 600 ft. in the western half of the study area, from slightly more than 500 ft. in the southeast part of the study area. Thickness of Upper Morrowan strata varies approximately 70-80 ft. across the study area, whereas Lower Morrowan strata vary as much a9 150 ft. in thickness. The top of the Morrowan interval dips gently southeastward at about 0.5 degrees. Dip is interrupted by three syndepositional faults that trend northeastward and by four small domes. Porosity in Upper and Lower Morrowan sandstones is mostly secondary, due to enlarged pores and partly dissolved grains; minor types of porosity include intergranular porosity and microporosity within authigenic clays. Petroleum from Upper Morrowan rocks is produced mostly from stratigraphic'traps. The sandstones are encased in nonmarine shales and siltstones. Lower Morrowan reservoirs mostly are in structural traps. | |
