Iron and Mars
This episode of Science Moab continues the exploration of the Navajo sandstone with Marjorie Chan, Professor Emeritus at the University of Utah. The unique coloration of the sandstone is influenced by iron oxides that have analogies with the iron oxide ‘blueberries’ found on Mars and have implications for groundwater evidence on the planet. Margie elaborates on the concretions and weathering patterns within the Navajo sandstone and how these differ from the Wingate sandstone. We also discuss the challenges of geological research funding, the importance of fieldwork partnerships, and the significance of preserving natural geological features and educating the public on their value.
Meet the Scientist: Marjorie Chan
Dr. Marjorie Chan is Distinguished Professor Emeritus at the University of Utah, where she served on the geology faculty for 42 years. She has had a long career of sedimentary research in the Western U.S. with particular interest in the Jurassic Navajo Sandstone system of southern Utah, and red rock country analogs to the red planet Mars. She has received national awards for outstanding achievements in teaching, research, service, and outreach. Her leadership has included being past chair of the U.S. National Committee for Geological Sciences and many roles in the Geological Society of America plus numerous committees and boards.
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Interview Excerpt - A Modern Wonder from Ancient Dunes:
The Iconic Navajo Sandstone, Part 2
We continue our conversation on the Navajo sandstone with Marjorie Chan, retired professor from the University of Utah. In episode one, we discuss the origin of the formation and the many irregular features within it. Today we talk with Margie about her research. In particular, we discuss color variation within the sand and how it relates to iron and the planet Mars, as well as water distribution within the unit.
Chan: Early on in my studies of the Navajo sandstone, I was focused on the coloration, and that’s what we call diagenesis. Dia meaning secondary and genesis, meaning origin. These include the coloration are some of the things that happen after the sediments are deposited. Other things we find that are from the process of diagenesis are precipitation of the iron.
So the iron gets moved around from fluids, but it can also get moved from one place to another. I think that a lot of the iron that was originally making the sandstone red has been remobilized and then re-precipitated into these small marbles that are sometimes called mochi marbles. These features of cemented mineral masses are called concretions. I’ve been looking at concretions for a long time, and the ones in the Navajo sandstone are a little bit different because concretions are often cemented by calcium carbonate (CaCO3)
But a lot of the concretions in the Navajo are cemented by iron oxides, and that’s what makes them brown to reddish to yellowish colors. One of the exciting moments in my career was when we were looking at some of the concretions as possible analogs to the iron oxide on Mars. We started investigating it more and We thought this was a good explanation. shortly after that, the Mars Rover sent back some images showing some little round balls that they called blueberries. And those blueberries we felt were concretions and we felt that we had good evidence to make analog comparisons using the Navajo sandstone examples.
So the important contribution of that is if you could recognize these blueberries on Mars as being concretions, then you could say that there were past Groundwaters on Mars. And so that was significant because nobody else had really been able to explain that and have the evidence to say why you would make that inference.
Science Moab: the ones found on Mars are actually iron as well?
Chan: Yes, they are iron oxide, mostly the mineral hematite. A lot of the ones that we have in the Navajo sandstone are ide, which is another iron oxide, which is F-E-O-O-H. But they’re still iron oxides.
Science Moab: Very neat. In addition to the, the iron staining or coloring in the Navajo sandstone, you’ve also studied, uh, irregularities within the formation, whether from soft sediment deformation or various mineral deposits. So can you talk about some of the more interesting features that you’ve discovered in the Navajo?
Chan: Probably one of the things that also really struck me was some of the weathering patterns in the Navajo sandstone. the Navajo sandstone often makes very rounded smooth forms in contrast to the weathering of, say, the Wingate sandstone, which is another Eolian desert system that’s a rock unit that’s below the Navajo sandstone. When you see that unit, it’s much more splintery looking with steeper cliffs, and it’s not those rounded domes like the Navajo sandstone. That is a question that makes you wonder why are those things so different? And probably in that case it’s a difference of the grain size.
The Navajo is slightly coarser grain than the Wingate, and also the Navajo doesn’t have quite as much cement as the Wingate. The Wingate is more densely cemented. That’s why it’s more cliffy and splintery looking, and the Navajo tends to make more of those rounded kinds of shapes.
We’ve looked at some places where we can see different cracks and patterns, and some of those patterns are really a function of how the rock absorbs certain stresses.
For example, on Checkerboard Mesa in Zion, you’ve got these vertical cracks that kind of come down, that give it that checkered look, and the cracks are going perpendicular to the cross betting.
Then, if the cross betting angle changes, then the crack orientation also slightly changes. So that was an “aha” moment for me where I started looking at those cracks and started thinking that these cracks are forming in a lot of different places, and in some places the cracks don’t go straight down. They’re not vertical. They’re actually more polygonal types of patterns. Some of these polygonal types of patterns almost look like cauliflower weathering or something like that. The White Pocket in Northern Arizona is a classic place to see that expressed. These really old weathering surfaces that make it look puffy and the cracks are the areas that have helped give rise to some of the weathering around some of these areas.
Science Moab: These cracks, are they happening once the sand is exhumed or are they happening deep down or both?
Chan: I think most of the cracks are happening when the sandstone is exhumed or brought up to the surface. some of the old weathering surfaces will actually sometimes fall off and it’s almost like a crust gets taken away by erosion. Then underneath, sometimes you’ll see cracks that are starting to form a new pattern of the weathering. So it’s a surface phenomenon. Desert temperature changes, the slope aspect, and which way the outcrop facing can all make a difference in the cracking patterns.
