Abstract
Airborne spectroradiometer data reveal an unusual pattern of near-infrared reflectance at the exposed center of Table Rock anticline, Sweetwater County, Wyoming. The feature is represented by a reflectance minimum near 2200 nm, characteristic of areas with abundant clay minerals. Smectite and mixed-layer illite-smectite were found associated with the anomalous spectral feature. Concentrations of iron and sulfate minerals in the soils at the center of the clay-rich zone correspond roughly to an area of red coloring in the Wasatch formation exposed at the highest structural elevation in the center of the anticline.A photogeologic interpretation of Thematic Mapper Simulator (TMS) image data was made for the Table Rock area. Stratigraphic and structural details of the interpretation are excellent and provide greater detail than do available maps of the area. Structural analysis suggests that at least two episodes of stress affected the area. The greatest concentration of fractures occurs at the crest of the anticline and is coincident with the spectrally anomalous region. The investigation indicates that the mineralogic pattern at the surface of Table Rock anticline could result from a geochemical transformation process. Groundwaters, with ionic concentrations in the stability field of smectite, are being drawn through fractures to the surface in the anomalous region. Evaporation and fluid replacement in the near-surface are accelerated. Illites apparently become unstable in the near-surface and transform into a more stable phase of smectite. Gypsum, jarosite, and carbonate cement concentrations at the surface further support this assumption and suggest a possible influence of escaping hydrocarbon reservoir gases. This process is consistent with models proposed for the formation of petroleum-related surface anomalies. However, a cause-and-effect relationship between the petroleum accumulation and the surface anomaly could not be established.
