Evaluating Structural Diagenesis with Imaging Spectroscopy: Examples from the Jurassic ‎Navajo Sandstone

Knowledge of the history of structurally-influenced fluid flow and diagenetic processes ‎within sandstone deposits can provide important information on the deposits' function as ‎reservoirs for hydrocarbons, their potential for economic minerals, and overall ‎understanding of basin evolution and burial history. Imaging spectroscopy provides a ‎valuable tool for mapping surface patterns of authigenic mineralogy in exposed ‎sedimentary rocks. The early Jurassic Navajo Sandstone is a thick, porous, and ‎permeable eolian unit prominently exposed throughout southern Utah. Typical Navajo ‎Sandstone is ~90% quartz, a mineral which lacks any significant absorption features in ‎the VNIR/SWIR wavelength region. This detrital composition, with spectrally bland ‎background as well as extensive surface exposure, allows for spectral identification and ‎regional mapping of minor secondary cements such as carbonate, clays, iron oxides, and ‎sulfates. Kavaicuwac (aka “Mollies Nipple”) is an anomalous jarosite-cemented butte of ‎Navajo Sandstone in Grand Staircase Escalante National Monument. This site is of ‎particular interest for understanding the history of fluid flow and chemical diagenesis in ‎this area, due to its unique mineralogical and geomorphic characteristics. One hypothesis ‎for the unusual nature of this site is that Kavaicuwac experienced alteration related to ‎fluid flow at the intersection of multiple faults. Field observations, classification of data ‎acquired from two aerial hyperspectral sensors (HyMap covering the VNIR/SWIR, and ‎SEBASS covering the LWIR), evaluation of in situ spectral data, combined with ‎petrographic, mineralogical, and geochemical analyses are being used to examine the ‎diagenetic history of this site. This site is compared to other structurally-influenced ‎diagenetic features elsewhere in the Navajo Sandstone to address the range of ‎geochemical conditions that have existed in this reservoir over time and the benefit of ‎investigating structural diagenesis with imaging spectroscopy. ‎