Sandstone bleaching and iron concretions: An index to fluid pathways and diagenetic history of the Jurassic Navajo Sandstone, southern Utah

An explanation of spectacular color variations in the Navajo Sandstone has remained one of the long-standing mysteries of southern Utah's world-famous redrock geology. This research seeks to explain the causes of the crimson, orange, pink, gold, yellow, and white colored landscapes, and what they reveal about the early Jurassic Navajo Sandstone's 190 million-year history. The Navajo Sandstone is the remnant of one of the largest accumulations of windblown sand in the geologic record and creates many of the cliffs and canyons of southern Utah's parks and monuments. Relatively high porosity and permeability has resulted in a complex history of interstitial fluid flow that has progressively altered the texture and color of the sandstone. By examining the spatial patterns and geochemistry of color variations in the sandstone, this research evaluates fluid flow pathways and characteristics of the fluids that have passed through. Micro- to regional-scale manifestations of fluid-related diagenesis in the Navajo Sandstone indicate where diverse chemistries of groundwater have flowed through this important reservoir. Spatial variations in sedimentary and diagenetic fades in the Jurassic Navajo Sandstone are investigated, incorporating field observations, interpretation of multi- and hyper-spectral remote sensing datasets, microscopy, and a variety of analytical geochemical tools including X-ray diffraction, stable isotopes, major oxide and trace element geochemistry, and visible and near-infrared spectroscopy. Combining these tools on a range of scales allows for an increased understanding of how fluid flow in this sedimentary system is closely coupled to structural evolution.; This research has several diverse applications. For example, the timing and magnitude of diagenesis, tectonic uplift, and exhumation of paleo-hydrocarbon traps on the Colorado Plateau suggests that greenhouse gases released from rapidly eroding reservoirs may have influenced climate change on geologic time scales. Another unique extension of this work has involved studying this system as an analog to hematite-rich regions of Mars. Bridging geologic communities, this work has elicited interest from the petroleum industry, allowed for public outreach and education through National Park and Monument agencies, and contributed to interpreting some of the latest discoveries in the planetary community.