Abstract: Spectral Reflectance Response of Big Sagebrush to Hydrocarbon-Induced Stress in the Bighorn Basin, WY

B. H. Bammel, R. W. Birnie

A geobotanical reflectance study was conducted at five areas in the Bighorn Basin of Wyoming. Three of the areas are active hydrocarbon producing fields, including Little Buffalo Basin, Bonanza, and Enigma oil fields. One area was specifically chosen not to contain surface or subsurface hydrocarbons, and was termed the Cody Base area. The fifth area, Trapper Canyon, is a surface tar sand deposit on the west flank of the Bighorn Mountains. In each area numerous reflectance spectra were measured from sagebrush plants (Artemisia tridentata) in on-field (Productive), off-field (Barren), and marginal-field (Edge) locations. At two areas, Bonanza and Trapper Canyon, sagebrush plants were also found growing directly in oil and/or tar impregnated formations. Over 1400 individual spectral meas rements were made and later analyzed for this work.

Spectral measurements were collected in the visible and near infrared regions (0.4 to 1.1 microns). Reflectance intensity values across the full spectrum; wavelength positions of specific reflectance minima (blue and red), maxima (green), and inflection points (red edge); and general features of absorption troughs (height, width, asymmetry) were analyzed using multivariate statistical methods. A correlation analysis of the spectral data was designed to show the relationships of these values to the individual areas' boundaries and production trends.

The results of this investigation show that a consistent and significant blue shift (shift to shorter wavelength) of the green peak (0.56 micron area) and red trough (0.67 micron area) positional data are the most reliable indicator of hydrocarbon-induced stress in sagebrush plants. This shift can only be detected where the sage is actually growing in large amounts of surface visible or very near-surface hydrocarbons. Spectral reflectance intensity data were found to have no significant correlation with the presence or absence of underlying near-surface or deeper subsurface hydrocarbons.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994