FINE-SCALE LITHOFACIES DISCRIMINATION OF JURASSIC SEDIMENTARY ROCKS USING ASTER DATA, BIGHORN BASIN, NORTH-CENTRAL WYOMING

The Jurassic section of the Bighorn Basin in north-central Wyoming consists of many discreet carbonate and siliciclastic lithofacies. Lithofacies identification and spatial orientation are crucial to the interpretation of Jurassic depositional environments and paleogeography, but are difficult to map in practice due to the large, remote nature of the study area. In order to further the concept of lithofacies mapping from remote sensing data, ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) datasets were used that provided coverage of the exposed Jurassic section in the Bighorn Basin. Using ENVI software, atmospheric and topographic corrections were applied. Principal component analysis, band ratios, minimum noise fraction, and spectral sharpening techniques were performed on the visible and near infrared (VNIR), and shortwave infrared (SWIR) ASTER data to determine if useful lithologic information could be discriminated. In addition, thermal infrared (TIR) data from ASTER were corrected for radiance and atmospheric effects, reference channel emissivity and emissivity normalization techniques were applied, and alpha residuals were extracted. Although the TIR data have low spatial resolution compared with the shorter wavelength ASTER bands, it confirmed spectral diversity apparent in the VNIR and SWIR data. Calibration of the data was furthered by acquiring field spectral data of a wide variety of lithofacies of known UTM coordinates with a portable spectroradiometer.

Results of the analyses exhibit subtle and dramatic spectral variations that correlate to known lithologic changes in the field, though not evident on high-resolution digital air photos. These variations were enhanced with the field-acquired lithofacies’ spectra. Extrapolating ASTER data from known lithofacies to areas of no field data was a primary goal of this research. Promising outcrops were located by using UTM coordinates extracted from the ASTER data, then locating these coordinates in the field using GPS. One of the first benefits of the ASTER analyses was the location of oolitic limestone facies in the field not detected by other methods. These encouraging results have demonstrated the utility of high spatial resolution, multispectral ASTER data as an important tool in geologic mapping.