Are Those Stromatolite Fossils in Arches National Park?

– by Mary Ecsedy, 7/14/2010

Abstract

Stromatolite Fossils
Concretions in Arches

This article describes some of the mysterious objects that we've found over the years while hiking across the Navajo Sandstone in Arches National Park. Based on comparisons with examples from Google image searches, we thought that our field observations might be stromatolite fossils. However, we're not at all sure. Stromatolites are very specific objects, and we are not professional geologists.

Still, even if these are not stromatolite fossils, we think we've found something interesting that we'd like to share; we want to know more about it ourselves!

This article briefly describes stromatolites, and why the possibility of finding their fossils – or indeed ANY fossils – in an ancient dune desert is significant. Stromatolite fossils were first identified in Navajo Sandstone in southeastern Utah by Fran Barnes. (1) They were discovered by other researchers (Loope, Eisenberg, Wais) in Capital Reef National Park in 2004, and in other locations near Moab, Utah over the past few years (2). We don't know if that's what we've found in Arches, but we'd like to find out.

Introduction

Several weeks ago I was looking for photographs of fossil stromatolites, and came across an excellent article, Stromatolite Fossils in the Hakatai Shale, by Bob Keller of Bob's Rock Shop, about backpacking in the Grand Canyon from a rockhound's perspective.

While reading the article and looking at the photographs of the fossil stromatolites Bob found deep in the Grand Canyon, I suddenly realized that the fossils looked really familiar. They reminded me of some of the objects Don and I have found over the years while hiking across the Navajo Sandstone deposit in the "Petrified Dunes" area of Arches National Park.

I was so excited! I started looking through my hiking photographs for examples of our field observations. Within just a few minutes I found pictures of some of the odd shapes and color anomalies we've observed eroding out of the Navajo sandstone. I don't have a trained eye, but I thought they looked a lot like Bob's photos. I'm assuming that Bob's identification is correct, but I don't know if his find has been verified as stromatolites.

Fossil Identification

Don and I are not geologists. We're just tourists who like to hike across the slickrock desert of the Colorado Plateau, especially in Arches. But we are fairly observant, and we've taken thousands of photographs on our hikes over the years. The following sections compare photos taken by rockhounds with some of my own hiking photographs, and there is enough similarity to at least take a closer look and see if some of these objects are the fossils of stromatolites or the result of some other life process of an unknown organism.

These objects may simply be the result of iron in suspension in water precipitating out and forming wierd shapes. But even that's pretty interesting when you think about it.

Image Comparisons

More research is needed, however. Image comparisons are a good start, but no substitution for scientific identification. (If you know of good example photographs of positively identified fossil stromatolites, please send me the link.)

The following images compare Bob Keller's photos from the Stromatolite Fossils in the Hakatai Shale article, with photographs that I've shot in and around Arches National Park since 2004.

Fig. 1 – Possible Fossil Stromatolites in the Grand Canyon – Photo by Bob Keller

Fig. 2 – Possible Fossil Stromatolites in the Grand Canyon – Photo by Bob Keller

Fossil Stromatolites
Fig. 3 – Possible Fossil Stromatolite in the Grand Canyon – Photo by Bob Keller

What caught my attention in Bob's photos were the concentric rings and the rounded edges on the tops of the fossils. To see the similarities between the fossils in Bob's photos and mine, look at the fossil directly above his lens cap in Fig. 1, and the one directly below the lens cap in Fig. 2. Those are the fossils that really caught my eye. Compare them with the next set of images, which are from my own collection.

Fig. 4 – Hematite coloration and objects in the Navajo Sandstone located in the Sand Flats Recreation Area near Moab Utah – Photo by Mary Ecsedy. Click on the image to view larger. (Note the handle of my walking stick for scale.)

Fig. 5 – Hematite coloration and objects in Navajo Sandstone, located in Arches National Park – Photo by Mary Ecsedy. Click on the image to view larger.

Don and I have been finding these objects in the Navajo for years. And for years we've puzzled over their round shapes and concentric rings. They're harder than the surrounding sandstone, and many of them have a profile several centimeters higher than the rest of the surface.

These circles appear in groups, and the effect is that of standing in a grove of tree stumps that have been cut close to the ground. But when you look closely, they are made of sand grains that appear to be identical to those in the surrounding matrix, they're just a different color and hardness. So the rings are tree-like, but their texture is completely different from the actual pieces of fossilized wood we've found nearby in the same layer.

Fig. 6 – Hematite in Navajo Sandstone, located in Arches National Park. These appear to be objects embedded within the sandstone, not coloration after deposition. – Photo by Mary Ecsedy. Click on the image to view larger.

Our understanding from Marjorie Chan's work is that the red and maroon coloration is from hematite, which is a form of iron.

More comparison photographs below.

More Fossil Stromatolite Images

Fig 7 – Fossil Stromatolites in India

This image shows possible stromatolite fossils in India that also look similar to the objects in our photos, but I'm not very confident about the quality of the science on the page I found it on. Just because it's on the Web doesn't make it true!

Fig. 8 – Hematite coloration and shapes in Navajo Sandstone, located in Arches National Park – Photo by Mary Ecsedy. Click the image to view full-size.

Fig. 9 – Close-up of hematite coloration and shapes in Navajo Sandstone in situ, located in Arches National Park – Photo by Mary Ecsedy. Click on the image to view larger.

The next 4 photographs were all shot at the same location in Arches, in a place we call The Broad Wash. The Broad Wash is located in the top layers of Navajo Sandstone. Note the dark patches on the surface – that's desert varnish. It forms very slowly, and its presence indicates that the rock surface it's on is harder than the other stone, because it's been there longer. It may be harder from being exposed to weathering when it was originally deposited. Desert varnish can be a marker that indicates expossures of petrified original surface.

Fig. 10 – Hematite in Navajo Sandstone, located in Arches National Park – Photo by Mary Ecsedy. Click on the image to view larger.

Fig. 11 – Close-up of hematite in Navajo Sandstone, located in Arches National Park – Photo by Mary Ecsedy. Click on the image to view larger.

Fig. 12 – Hematite in Navajo Sandstone, located in Arches National Park – Photo by Mary Ecsedy. Click on the image to view larger.

Fig. 13 – Hematite in Navajo Sandstone, located in Arches National Park – Photo by Mary Ecsedy. Note how thick the stromatolite deposits are! Click on the image to view larger.

This is another photograph I came across in my searches for images of fossil stromatolites. Again, this is from a rockhound.

Fig. 14 – Moroccan Fossil Stromatolite from the Science eStore.

The following figures show the same kind of small, rounded objects with concentric rings as the one from the Science eStore in Figure 14 above. Figures 15 and 16 show two objects from the sloping Navajo hillside in Figure 17, which is located just below playa deposits.

Fig. 15 – Objects eroding from Navajo Sandstone, located in Arches National Park – Photo by Mary Ecsedy. Click on the image to view larger.

Possible Stromatolite fossils in
Arches
Fig. 16 – Objects Flipped Over – Photo by Mary Ecsedy.

Fig. 17 – A cluster of round objects eroding out of Navajo Sandstone, located in Arches National Park – Photo by Mary Ecsedy. Click on the image to view larger.

Here is another image I found while searching for pictures of fossil stromatolites in Utah. This is is by a professional.

Fossil stromatolite limestone
balls from Utah
Fig. 18 – Fossil Stromatolites on the NOVA Geoblog

The following two images show similar small ball shapes that we've found. These pictures were taken in bleached, white Navajo Sandstone near playa deposits. They are separated by several miles, so it's hard to tell, but I think they're from different layers.

Fig. 19 – Small round objects colored with hematite in Navajo Sandstone, located in Arches National Park – Photo by Mary Ecsedy. Click on the image to view larger.

Fig. 20 – Hematite balls in Navajo Sandstone, located in Arches National Park – Photo by Mary Ecsedy. (The one in the upper-center is about the size of a marble.) Click on the image to view larger.

What Are Stromatolites?

At this point it would probably be useful to describe what stromatolites are, in order to understand the significance of finding their fossils in the Navajo Sandstone. This is a high-level description. See the References at the end of this article for more information.

Stromatolites in Shark
Bay
Fig. 21 – Stromatolites in Shark Bay, Australia
(courtesy Wikimedia Commons)

Stromatolites are the oldest fossils on Earth, dating back over 3 billion years. They are created by the life processes of organisms called cyanobacteria and others. Cyanobacteria are very primitive, making their living through photosynthesis, similar to plants, but Stromatolites are prokaryotes. They lack the DNA cellular nucleus that characterizes eucaryotes, i.e., single- and multi-cellular organisms such as plants, insects, and animals. They used to be considered a form of blue-green algae, but they predate algae by a couple of billion years. They were the dominant life form on our planet for over 2 billion years, thriving in the ancient oceans. They were the builders of the first reefs, and they are responsible for the oxygen in Earth's atmosphere. They are now almost extinct, but can still be found living in abundance in Shark Bay, Australia.

Formed in Thin Concentric Layers

One of the main characteristics of stromatolites is that they form mats and reefs in thin micro layers. Photosynthesis depletes carbon dioxide from the surrounding water, causing calcium carbonate to precipate out. As the cyanobacteria grows, it forms a sticky layer on the exposed surface. The calcium carbonate grains and grains of quartz sand become trapped in this "mucus". As the bacteria continue to grow upwards towards the light, it forms a new layer. (3)

"A stromatolite is produced by cyanobacteria. The distinctive layers are produced as calcium carbonate is precipitated over the growing mat of bacterial filaments. Photosynthesis in the bacteria depletes carbon dioxide in the surrounding water and makes it less acidic thus initiating the precipitation of the calcium carbonate. The minerals, along with grains of sediment precipitating from the water become trapped within the sticky layer of mucilage that surrounds the bacterial colonies. As the colony continues to grow upwards through the sediment a new layer is formed. As this process occurs over and over again, the layers of sediment are created. (2)

Apparently, this distinctive layering is the key to identifying these fossils. However, in the objects we've found, the layering is much bigger than "micro" layers.

Navajo Sandstone

The Navajo Sandstone is a very mysterious layer in the Canyon Country stratigraphy column. We know that it was deposited primarily as wind-blown sand, on the western shore of Pangaea. The Navajo desert stretched from present-day Arizona through southern Utah, western Colorado, and southern Wyoming. It is only a few feet thick on its eastern perimeter, but 2,500 feet thick to the west, in Zion National Park. During its deposition, the Navajo was a vast sand erg, or sea of sand. The immense dune desert existed for millions years during the early Jurassic, from approximately 200 - 180 million years ago. Dates are largely unknown because of the dearth of datable fossils found in it.

Navajo Sandstone contains relatively high concentrations of soluble marine salts and minerals, including nitrates, borates, carbonates, gypsum, etc.

In fact, very little is known for certain about this deposit, including its origin, age, and termination. Until recently, it has been assumed that the Navajo paleoenvironment was like the Sahara desert: dry and lifeless. (3)

Evidence of Life in the Navajo Sandstone

Fran Barnes, of Canyon Country Publications, was the first person to really notice that there was much more to the Navajo Sandstone than the professional geologists had recognized. For years he struggled with little success to attract their attention to his field observations. His book, Navajo Sandstone; a Canyon Country Enigma, Canyon Country Publications Series No. 55, written in 1998, is a must-read for anyone interested in this beautiful deposit.

We've read Fran Barnes' books describing the life that once thrived in the peoleoenvironment of the ancient Navajo Sandstone desert, which was located on the western coast of Pangea near the equator, approximately 190 - 150 million years ago. Like Barnes, we've also discovered burrow colonies, fossil wood, and all kinds of odd shapes in a rainbos of colors eroding from the surrounding sandstone matrix. We've spent a lot of time exploring the petrified playas and the bleached sandstone beneath them. And Barnes was absolutely right: It is quickly obvious to anyone who hikes across the surface of Navajo Sandstone that although it was definitely a desert, the Navajo also hosted a robust food chain, at least in southeastern Utah.

Stromatolites Discovered in Navajo Sandstone

Barnes was the first person to recognize fossil stromatolites in Navajo Sandstone, in the last couple of years preceding his death in October of 2003. It was one of his last discoveries. He lists "Miles of horizons that exhibit a unique phenomenon – algal-based stromatolites" among his field discoveries in the Sequel that is pasted into the back cover of Navajo Sandstone. The Sequel is dated August 30, 2003. He died just a few weeks later, but his work is being carried on by several enlightened geologists.

I was intrigued by Fran's mention of the stromatolites, and wondered what his finds looked like because there were no photographs in his book. In fact, I found the Grand Canyon hiking article mentioned at the top of this page while searching on Google for stromatolite fossil images. I never suspected that we'd been looking at them all along!

Several months before Fran's death, Len Eisenburg, one of the geologists whom he'd inspired, discovered a giant stromatolite in the backcountry of Capital Reef National Park. (2) Since then, Eisenburg and some of the other geologists who were inspired by Fran have discovered stromatolites in the Navajo near Canyonlands National Park.

There's no doubt about it: somehow these organisms were able to live and thrive in a hostile desert environment.

How?!!!

Why Stromatolites in Navajo Sandstone are Significant

The Navajo Sandstone was deposited as a vast, arid desert of endlessly shifting sand dunes – the largest dunes ever to form on Earth. The only living stromatolites on Earth today are located in Shark Bay on the west coast of Australia. The fact that stromatolite fossils are being found in the Navajo Sandstone requires us to change our basic assumptions about the Navajo desert, stromatolites, or both.

Accommodating the presence of stromatolites in that ancient desert environment will require extensive field research and creative thinking. Our own discovery of these fossils in Arches National Park adds another chapter to a growing body of knowledge that is creatin an astonishing picture of the ancient desert. Since we're not academic scientists, merely observant tourists, our hope is that our photographs and descriptions will inspire some professionals to take a closer look.

This is a big topic and this article is just a start. I've learned more while doing research as I write, and I'll be updating this article and writing more as time allows.

Field Locations in Arches

All of the objects we've found are located in and around the "bleached" Navajo sandstone that lies underneath many of playas. Navajo playas are flat lenses of limestone and other hard minerals that were deposited at the bottom of the broad, shallow "drylakes" that formed in the areas between the sand dunes. "Playa" is Spanish for "beach", which is something of a misnomer, but that's what these mineral deposits are called. They apparently formed after heavy rains, or even possibly from tsunami or storm surges. The western shoreline of Pangaea was located in present-day central Utah, so the sea was very close. The fossils and tracks that were left behind in the playa muds contribute abundant evidence that there was a very robust food chain in the paleoenvironment of the Navajo Sandstone. At the top of the chain were 3-toed Theropods - the ancestors of dinosaurs.

If you are seriously interested and would like more precise location information, please contact me at 412.422.1611.

References

I'll be updating this section and the next with more links to references as time allows. Enjoy!

(1) Navajo Sandstone; a Canyon Country Enigma, by Fran Barnes, Canyon Country Publications Series No. 55, 1998.

(2) Stromatolite Fossils, an Unlikely Giant in Capital Reef National Park

(3) Wikipedia entry for Stromatolite

(4) Stromatolite Fossils in the Hakatai Shale in the Grand Canyon

(5) Enigmas on Mars – Includes a brief overview of the Mars–Navajo Sandstone connection, with lots of images of Utah "Moki Marbles" and hematite "concretions" found on Mars.

Additional Reading

Rainbow of Rocks – Mysteries of Sandstone Colors and Concretions in Colorado Plateau Canyon Country, by Marjorie Chan and William Parry, Public Information Series 77, Utah Geological Survey.

Earth to Mars: NLCS Lands in Utah Contribute to Search for Life on Mars, BLM Publication, 2010.

Navajo sand sea of near-equatorial Pangea: Tropical westerlies, slumps, and giant stromatolites, by David Loope, Len Eisenberg, Erik Waiss, Geological Society of America Field Guide 5, 2004.

Stromatolite Blog – Includes a ton of information about these mysterious objects.

Stratigraphy of Arches National Park.

Paleo Maps.

Fig. 23 –Possible fossil stromatolites in Navajo Sandstone, located in Arches National Park – Photo by Mary Ecsedy. We've always called these deposits "purple lace" because that's what it looks like; purple and white and maroon and cream colors in very precise circles and rings. This is a thick shelf lying below a playa, located on the canyon rim high above Courthouse Wash. Click on the image to view larger.