Multi-Scale Mapping of Diagenetic Processes in Sandstones Using Imaging Spectroscopy: A Case Study of the Frontier Formation (Wyoming, U.S.A.) and the Utrillas Formation (Burgos, Spain)

Imaging spectroscopy is applied to two sandstone formations to study diagenetic processes in sedimentary deposits. Spectral data from hand specimens and cores were acquired and compared with close-range hyperspectral imaging to analyze lateral and vertical geochemical variations and quantify facies and diagenetic mineral abundances. The study was carried out on the delta front deposits of Wall Creek Member of the Cretaceous Frontier Formation, Wyoming and on the upper member of the Utrillas Formation, Spain. Visible Near-Infrared (VNIR) and Shortwave-Infrared (SWIR) Specim® hyperspectral cameras were used to scan near vertical and well exposed outcrop walls. Reflectance spectra was analyzed and compared with high resolution laboratory spectral and hyperspectral imagining data, thin sections, and results of previous sedimentological studies. Spectral Angle Mapper (SAM) and Mixture Tuned Matched Filtering (MTMF) classification algorithms were applied to quantify facies and mineral abundances in the Frontier Formation. MTMF is the most effective and reliable technique when studying spectrally similar materials. Classification results show that Parasequence #6 of the Wall Creek Member in the Frontier Formation is composed of 87 m2 of bar facies, 150 m2 of channel facies, 11 m2 of distal facies, and 27 m2 of carbonate concretions. Calcite cement in channel facies concretions is homogeneously distributed, whereas the bar facies was shown to be interbedded with layers of non-calcite-cemented sandstone. Distinctive characteristics of the absorption features of clay minerals (well-ordered kaolinite, poorly-ordered kaolinite, and mica (illite + muscovite)) were used to identify authigenic kaolinite and detrital kaolinite in the Utrillas Formation. Results show that poorly-ordered kaolinite is only present in floodplain deposits, while well-ordered authigenic kaolinite is related to paleochannel deposits and organic rich irregular patches. Meteoric water flux probably induced feldspar and mica alteration, and authigenic clays precipitation. Contemporary bacterial degradation of organic matter might be the cause of authigenic clay formation. The exposures of Utrillas Formation at Basconcillos del Tozo quarry are composed of 214 m2 of paleochannel facies, 235 m2 of floodplain facies, and 36 m2 of altered areas.