University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Earth and Atmospheric Sciences, Department Papers in the Earth and Atmospheric Sciences of 2019 Rinded, Iron-Oxide Concretions in Navajo Sandstone Along the Trail to Upper Calf Creek Falls, Garfield County David Loope Richard Kettler Follow this and additional works at: https://digitalcommons.unl.edu/geosciencefacpub Part of the Earth Sciences Commons This Article is brought to you for free and open access by the Earth and Atmospheric Sciences, Department of at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Papers in the Earth and Atmospheric Sciences by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. M. Milligan, R.F. Biek, P. Inkenbrandt, and P. Nielsen, editors 2019 Utah Geological Association Publication 48 Rinded, Iron-Oxide Concretions in Navajo Sandstone Along the Trail to Upper Calf Creek Falls, Garfield County David B. Loope and Richard M. Kettler Earth & Atmospheric Sciences, University of Nebraska Lincoln, NE 68588-0340 [email protected] Utah Geosites 2019 Utah Geological Association Publication 48 M. Milligan, R.F. Biek, P. Inkenbrandt, and P. Nielsen, editors Cover Image: View of a concretion along a trail in Upper Calf Creek Falls. M. Milligan, R.F. Biek, P. Inkenbrandt, and P. Nielsen, editors 2019 Utah Geological Association Publication 48 Presidents Message I have had the pleasure of working with many diff erent geologists from all around the world. As I have traveled around Utah for work and pleasure, many times I have observed vehicles parked alongside the road with many people climbing around an outcrop or walking up a trail in a canyon. Whether these people are from Utah or from another state or country, they all are quick to mention to me how wonderful our geology is here in Utah. Utah Geosites 2019 Utah is at the junction of several diff erent geological provinces. We have the Basin and Range to the west and the Central Utah Utah Geological Association Publication 48 Hingeline and Th rust Belt down the middle. Th e Uinta Mountains M. Milligan, R.F. Biek, P. Inkenbrandt, and P. Nielsen, editors have outcrops of some of the oldest sedimentary rock in Utah. Utah also has its share of young cinder cones and basaltic lava Utah Geosites showcases some of Utah’s spectacular geology, both fl ows, and ancient laccoliths, stratovolcanoes, and plutonic rocks. little-known localities and sites seen by visitors to Utah’s many Th e general public comes to Utah to experience our wonderful national and state parks and monuments. Th e geosites refl ect the scenic geology throughout our state and national parks. Driving interests of the many volunteers who wrote to share some of their between our national and state parks is a breathtaking experience. favorite geologic sites. Th e list is eclectic and far from complete, and we hope that additional geosites will be added in the coming Th e “Utah Geosites” has been a great undertaking by many people. years. Th e Utah Geological Survey also maintains a list of geosites I wanted to involve as many people as we could in preparing this https://geology.utah.gov/apps/geosights/index.htm. guidebook. We have had great response from authors that visit or work here in the state. Several authors have more than one site that We thank the many authors for their geosite contributions, they consider unique and want to share with the rest of us. I wanted Utah Geological Association members who make annual UGA to make the guidebook usable by geologists wanting to see outcrops publications possible, and the American Association of Petroleum and to the informed general public. Th e articles are well written Geologists—Rocky Mountain Section Foundation for a generous and the editorial work on this guidebook has been top quality. grant for desktop publishing of these geosite papers. I would like to personally thank Mark Milligan, Bob Biek, and Design and desktop publishing by Jenny Erickson, Graphic Paul Inkenbrandt for their editorial work on this guidebook. Designer, dutchiedesign.com, Salt Lake City, Utah. Th is guidebook could not have happened without their support. I would like to thank Jenny Erickson for doing the great desktop Th is is an open-access article in which the Utah Geological publishing and the many authors and reviewers that helped Association permits unrestricted use, distribution, and reproduction prepare the articles. Your work has been outstanding and will of text and fi gures that are not noted as copyrighted, provided the certainly showcase the many great places and geology of Utah. original author and source are credited. See the Utah Geological Last, but not least, Th ank you to the American Association of Association website, www.utahgeology.org, and Creative Commons Petroleum Geologists, Rocky Mountain Section Foundation for https://creativecommons.org/licenses/by/4.0/ for details. their fi nancial support for this publication. Suggested citation for this geosite: Guidebook 48 will hopefully be a dynamic document with the potential to add additional “geosites” in the future. I hope more Loope, D.B., and Kettler, R.M., 2019, Rinded iron-oxide authors will volunteer articles on their favorite sites. I would like concretions in Navajo Sandstone along the trail to Upper to fi ll the map with locations so that a person or family looking at Calf Creek Falls, Garfi eld County, in Milligan, M., Biek, the map or articles will see a great location to read about and visit. R.F., Inkenbrandt, P., and Nielsen, P., editors, Utah Geosites: Enjoy Guidebook 48 and enjoy the geology of Utah. Utah Geological Association Publication 48, 7 p., https://doi. org/10.31711/geosites.v1i1.59. Peter J. Nielsen 2019 UGA President 2 D.B. Loope and R.M. Kettler Giant Concretions of Upper Calf Creek Falls INTRODUCTION All the research cited above was stimulated by the discovery, on Concretions are hard rock masses, usually spheroidal, but com- Mars, of small, iron-rich, spheroidal concretions (the aforemen- monly oblate or discoidal, that are formed by strongly localized tioned blueberries), but the concretions exposed at this GeoSite precipitation of minerals in the pores of an otherwise weaker are neither small nor spheroidal. They are, however, iron-rich, sedimentary rock (see Bates and Jackson, 1980, for a more extensive calcite-free, rinded, and very interesting. We think that the spatial definition). The iron-oxide-rich concretions in the Jurassic Navajo arrangement of their internal features aid interpretation of the Sandstone in southern Utah are unusual in two fundamental ways. small, rinded spheroids. In this article, we briefly present our First, they are cemented by iron oxide (Fe O , or Fe(OH) ); most 2 3 3 interpretation (Loope and others, 2010; Loope and others, 2011; other concretions are cemented by silica (SiO ), calcite (CaCO ), 2 3 i.e., the second interpretation above) of the very large, non-sphe- dolomite (CaMg(CO ) ), or siderite (FeCO ). Second, unlike 3 2 3 roidal, rinded concretions that are common on the beautiful trail other concretions, they are not strongly cemented throughout, but to Upper Calf Creek Falls. instead, the iron oxide is concentrated in a very strongly cemented, sharply defined, exterior rind or shell. In the smaller concretions, to Boulder the entire interior lacks iron-oxide cement, and is similar to the rock outside the concretion; in the larger concretions, there is a cen- tral zone that is strongly cemented by iron oxide, but the sandstone between the central core and the rind has no iron-oxide cement. The processes involved in the formation of the Navajo concretions have been extensively studied by geologists ever since the Martian rover Opportunity imaged small, spheroidal, iron-rich concretions on the surface of Mars (Moore, 2004). The Navajo concretions were quickly recognized as possible terrestrial analogs to the Martian “blueberries” (Chan and others, 2004). At present there are three Parking main explanations for how these concretions formed. The first inter- pretation of the Navajo concretions (Chan and others, 2004; Beitler and others, 2005) views the iron-oxide cement and the “rinded” as- pect of today’s concretions as primary features—just a thin, three-di- mensional band of sandstone (circular when viewed in two dimen- sions) that had been cemented by iron oxide (Chan and others, 2004). A complication of this interpretation is that, because iron is not transported by water containing oxygen, mixing of an iron-bear- ing water (devoid of oxygen) with a second, oxygenated water mass is required (Chan and others, 2004). Mixing is typically not required for growth of silica, calcite, dolomite, or siderite concretions. to Escalante The second interpretation (Loope and others, 2010; Weber and Figure 1. Topographic map showing location of parking area and trail head for Upper others, 2012) is that solid, spheroidal concretions were originally Calf Creek Falls. well-cemented throughout by siderite (FeCO ). The rinds formed 3 Driving Instructions and Hiking Suggestions secondarily, during much later alteration of the older, primary siderite. A weakness of this interpretation is that unaltered siderite The trailhead is 7.4 miles (11.8 km) southwest of Boulder, UT has not been found in any Navajo concretions. and 20.5 miles (32.8 km) northeast of Escalante along a portion of Utah Highway 12 that follows the narrow, flat surface of New The third interpretation (Yoshida and others, 2018) holds that the Home Bench, above the canyons of Calf Creek (to the west) and original spheroidal concretions were solid spheres cemented by Dry Hollow (to the east; figure 1). The turnoff for the trailhead is calcite (CaCO3). The rinds formed later when acidic, iron-bearing on the west side of the highway, between mile 80 and mile 81.