Comparison of surface and subsurface vertical sequences in the Cretaceous Ferron Sandstone, Utah

Surface and subsurface vertical sequences of the Cretaceous Ferron Sandstone of east-central Utah were studied in order to refine the stratigraphic architecture and depositional history of this complex clastic wedge. Regional well log control documents an eastward-thinning prism of sediments derived from the Sevier orogenic belt in the west. Progradational, aggradational, and transgressive units are recognized.; The detailed study area is located near the towns of Ferron and Emery at the site of maximum eastward sediment progradation into the Cretaceous interior seaway. Gamma-ray well log curve motifs provide insight into the complex paleodepositional history of the Ferron Last Chance Delta system. Upper and lower delta plain, delta front, and stacked shoreface paleodepositional environments are examined.; Ferron deltaic exposures on the western flank of the San Rafael Swell were measured and profiled between the Ferron Gas Field and the Emery Coalfield. Gamma-ray profiles from measured sections were merged to form composite sequences over the entire Ferron interval. Cross sections integrating gamma-ray well log and surface profile data result in a more refined correlation than either data set yields independently.; Measured sections and profiles include examples from the delta front (distal and mouth bar), delta plain, and stacked shoreface units. Subenvironments of a transgressive barrier island sequence on an abandoned delta lobe (barrier spit, tidal inlet, ebb-tidal and flood-tidal deltas, and washover fans) are described and profiled. Field evidence indicates extensive storm damage to the barrier system.; Surface gamma-ray profiling is an experimental technique which provides a detailed record of a measured section. Measurements are taken with a scintillometer at one foot intervals and approximately 0-12 inches from the outcrop. Profiles can discriminate rock unit boundaries, marker beds, and subtle lithologic changes.; Gamma-ray profiles are described using curve shape characteristics, including marker-to-marker thickness, total magnitude of deflection, nature of upper and lower bed boundaries, rate of radioactive increase or decrease (convex, concave, or straight), general profile shape (cyclindrical, funnel, bell, symmetrical, or irregular), profile rugosity (serrations), and cyclicity. Shape characteristics can provide circumstantial evidence useful in the interpretation of depositional environments.