GEOCHEMICAL AND HYPERSPECTRAL ANALYSIS OF DIAGENETIC ALTERATION IN THE JURASSIC NAVAJO SANDSTONE, SOUTHERN UTAH

Chemical diagenesis within the Navajo Sandstone in southern Utah is the result of a complex history of groundwater flow and multiple episodes of cement precipitation and dissolution. Iron oxides, carbonates, and clays have been mobilized and re-precipitated several times within the interstitial system, indicating a multi-phase history of basin-wide fluid-rock interactions. Formation-wide relationships between mineralogy and geochemistry allow for identification of several diagenetic facies. These diagenetic facies have diagnostic geochemical signatures, as well as distinctive spectral signatures. Several types of diagenetic alteration can be identified with spectral data, including reduction of ferric iron, alteration of mixed-layer clays and feldspars to kaolinite, and changes in carbonate content. Remote sensing provides a non-destructive way of identifying mineralogy based on spectral characteristics of minerals. The arid climate and relative lack of vegetation in southern Utah provide ideal conditions for remote mineral identification. There are both diffuse (few %) and dense (>35%) zones of iron oxide mineralization related to the mixing of reducing iron-saturated waters with oxidizing meteoric groundwater. Landsat 7 ETM+ multispectral data are sufficient for regional mapping of diffuse alteration. However, analysis of dense iron mineralization requires a significantly higher spatial and spectral resolution sensor. Use of HyVista hyperspectral airborne imaging allows for detailed mapping of iron oxide mineralization, differentiation between goethite and hematite, and spatial associations between types of alteration. Alteration patterns are typically structurally influenced, which allows for constraints on timing of fluid flow, and implies a coupling between geochemical and structural systems. Spectral and geologic field verification facilitate interpretation of the airborne data. Spatial evaluation of alteration within the sandstone aids in evaluation of how flow effects sandstone characteristics, and can be diagnostic of certain economic mineral deposits (e.g. uranium, hydrocarbons). Furthermore, spectral characterization of diagenetic iron oxide deposits has implications for evaluating potentially similar digenetic systems in sediments on Mars.