Quantitative approach in the spectral reflectance-lithostratigraphy of the Wind River and southern Bighorn basins, Wyoming

A procedure developed for quantifying spectral variability was applied to visible and near-infrared spectra from a database of the Wind River and Bighorn basins. Principal Components Analysis (PCA) of 94 sedimentary rock spectra distinguished shales, sandstones, limestones, dolostones, bedded gypsum and bentonites from 25 stratigraphic units. However, only twelve spectrally distinct groups were delineated because of lithological homogeneity. Albedo and slope characteristics of the spectra were found to be related to the first and second PC, respectively, and absorption bands related to the remaining components. A second PCA phase, using vertically scaled spectra to minimize the albedo variability, indicated space distributions that enhanced major absorption features in the ncar-infrared region. Parameters describing absorption bands were also calculated from spectral continuum. The best parameters for spectra discrimination were band depths at 1900, 2200 and 2300 nm, in agreement with the PCA results using scaled spectra. Finally, the stratigraphic column was characterized by correlated log sections composed by PC scores of the original data and of scaled spectra, in lieu of band, band-ratios, area and depths of absorption bands. Reflectance-lithostratigraphic markers were identified in the log sections and indicated the potential of reflectance-lithostratigraphy in correlation studies. We concluded that PCA using a small number of narrow bands to represent the spectrum was an adequate mathematical approach for spectral analysis. PCA of scaled spectra was found to be a useful tool to enhance differentiations due to absorption features.