FIELD MAPPING AND MULTISPECTRAL ANALYSIS OF JURASSIC NAVAJO SANDSTONE COLOR AND IRON MINERALIZATION, GRAND STAIRCASE ESCALANTE NATIONAL MONUMENT, UTAH

Iron oxides within the Jurassic Navajo Sandstone produce dramatic crimson, orange, peach, pink, gold, yellow, and white landscapes unique to Southern Utah. Modern dune analogs and geochemical studies suggest that most of the eolian erg was red from hematite rims coating the grains soon after deposition or upon early burial. Color variations in the Navajo Sandstone occur on millimeter to formational scales, and are the result of reducing fluids that mobilize iron and bleach the sandstone white. Diagenetic fluid flow has redistributed the iron into oddly shaped concretions and colorful reaction fronts that can be used to evaluate how fluids migrate through this formation. Previous workers recognized a stratigraphically controlled color pattern in the Navajo Sandstone of (1) brown in the lower third, (2) unaltered pink/red in the middle third, and (3) bleached white in the upper third. This color transition correlates with a stratigraphic shift from a fine-grained sabkha facies in the lower part of the formation to a more permeable coarse-grained dune field facies in the upper part of the formation. However, there are many more complex color patterns, and in some cases the entire 400-meter section is bleached white, indicating other controls on fluid flow and sandstone color. Average iron content varies widely and systematically with color from .1% for white Navajo Sandstone, to .3% for red, 6% for yellow, and 30% for dark brown concretions. Use of a field reflectance spectrometer and whole rock analysis of different sandstone colors shows that reflectivity can be used as a proxy for iron content, making regional mapping possible using remote sensing. We mapped color differences and significant areas of iron mineralization in the Navajo Sandstone within Grand Staircase- Escalante National Monument using Landsat 7 ETM+ satellite imagery and detailed field mapping. Mapping the distribution of these various iron concentrations can help establish a mass balance for iron within the sandstone, and identify how paleo-fluid flow patterns are influenced by both stratigraphy and structure.