Purpose

Aasaa~tAc-r: Reflectance spectroscopy, a useful analytical tool available to geologists for over 100 years, has not been widely used in petrologic or stratigraphic studies of sedimentary ocks. We are routinely using laboratory spectral reflectance data covering the 0.4 to 12.0 ~m wavelength interval in an investigation ofthe stratigraphic and structural evolution of the Wind River and Bighorn basin areas, Wyoming. Two types of laboratory spectral reflectance measurements were made on 192 weathered outcrop, bedrock, and core samples: 1) hemispherical reflectance, from 0.4 to 2.5 um (229 spectra) and 2) biconicai reflectance, from 8.0 to 12.0 um (84 spectra). Results show stratigraphic variations in the spectral properties of sedimentary ocks as encountered in the field. Sample mineralogy was determined using X-ray diffraction and interpretation fspectra. The mineralogy, iithology and stratigraphic distribution of samples are diverse and representative of Phanerozoic silicielastic and carbonate strata encountered in foreland sedimentary basins. Spectra were sorted into 36 distinct groups, according to the presence or absence of 68 visible and infrared reflectance f atures. Many spectral features can be assigned to specific molecular phenomena and allow rapid determination fspecific minerals. Minerals detectable spectrally include: gypsum, kaolinite, smectite, analcime, goethite, jarosite, calcite, dolomite, and feldspar. Results are contributing to our understanding of the depositional history of the Wind River and Bighorn basin areas; more importantly, results uggest that laboratory, field and remote reflectance spectroscopy have more general geologic applicability in studies of sedimentary ocks. Reflectance spectroscopy can augment conventional l boratory and field methods for petrologic analysis