Post by: Macaira Smith, Rachel Schones, and Justin Nelson

Coordinates: 44.04614, -123.07386
Google Earth (Group 2)

Location/Description: This feature is of petrified wood found inside Cascade Hall. This wood is from the remains of a conifer tree from the Late Triassic (~220 million years ago) in northeastern Arizona (Dept. of Earth Science, 2002). This log originated from a tree that was washed downstream and accumulated in an area of dead trees, where it later collected ash from a volcano along with other debris before it could rot or decompose (Dept. of Earth Science, 2002). 

Geological Observations: The petrified wood sample is mottled in appearance, or in other words, marked with spots and smears in a variety of colors. These colors are the result of chemical impurities in the quartz (Dept. of Earth Science, 2002). The shades represent different metallic compositions, with red, brown, and yellow resulting from traces of iron Figure 1). The green and blue result from traces of copper and cobalt, while manganese results in a pink hue (Dept. of Earth Science, 2002). These colors are most clearly visible on the polished top of the wood sample. Cracks along the sides of the outer bark range in size longer than 20 cm.

What caused the lines/cracks in the outer bark? 

Contributed by: Macaira Smith

Geologic question: When deciding what site I wanted to dive further into, I was interested in the petrified wood largely because I didn’t understand it. How could something look like a tree stump and feel like a rock? When my group went to collect observations, however, the first thing that drew my attention was the long lines of crevices or cracks, kind of resembling scratch marks or insect tunnels, scattered along the outer bark. There were far too many for it to have been done by humans, so I began to wonder what really caused these lines? This question is related to geology because the things that are preserved in wood through petrification can tell us a great deal about the environment in which the tree lived.

Description of scientific article: To answer my question, I read two articles from Genise and Hazeldine (1955) and Fisk and Fritz (1984) which described different processes that might create perforations, or holes, in the wood that are preserved through petrification, a process that turns living matter into a hard stony substance. I will compare the characteristics of holes or tunnels created by the different processes provided to the lines on the outer bark of our petrified wood feature, which will possibly allow me to figure out how these lines got here or, at the very least, rule out what didn’t cause it.

Intersection between peer-reviewed research and observations on campus: The traces described by Genise and Hazeldine (1955) are borings, or tunnels made by insects inside wood, in this case, beetles found in conifers from the Jurassic. Although there is no evidence of the lines on the outside of our feature leading to tunnels in the internal wood, which would be visible in the cross-section if the lines near the top traveled inward (Figure 4), they do have a similarity to tunnels in shape and semi-uniformity. Of the three directions beetle tunnels might go in: longitudinal or up and down, tangential, or parallel to the growth rings, and radial, or from the center of the tree to the outer bark (Genise and Hazeldine, 1955), our feature only contains tangential “tunnels” (Figure 2). All of the traces described by Genise and Hazeldine (1955) contain small circular exit holes in the outer bark. There are a couple of holes like this in our feature that could possibly indicate ancient insect activity. Still, they do not contribute to the lines exclusively on the outer bark and are therefore not the focus. In the second article I read, Fisk and Fritz (1984) described a process that created pseudoborings, holes that only look like they were caused by beetles, but preserve cell structure through channels. These fake borings are made through selective weathering, breaking down materials through acid rain or groundwater, of exposed calcified tissue in trees that are silicified. Silicification replaces living cells with silica that hardens and preserves the cell structure. While we know our feature is silicified due to its wide range in color, there are only a couple of small ashy areas noticeable in the cross-section that could possibly be calcified, crystallized through a similar process as silicification, but with calcite, however, I don’t think that’s what they are.

Answer to the question? Based on my findings from Genise and Hazeldine (1955) and Fisk and Fritz (1984) I did not find an answer to my question, but I do feel closer. My first thought was that these lines could be from insects, but now I have learned that most insect traces are circular holes and are primarily found inside the tree. I’m also certain the lines are not pseudoborings caused by weathering, due to the fact that these are also circular holes, which is not what we’re looking for. Learning about that process has led me to believe that the lines on our feature were most likely caused by natural processes, perhaps just being cracks from events before petrification that were preserved, but I’m really not sure.

Something additional I learned and future questions: While searching for an answer to my question, I learned that calcite comes from acidic groundwater primarily in humid areas, whereas silica comes from basic groundwater and thrives in dry areas (Fisk and Fritz, 1984). This made me wonder how things that can be petrified outside of wood might be affected by quick changes in climate.

Sources cited:
Genise, J. F., & Hazeldine, P. L. (1995). A new insect trace fossil in Jurassic wood from Patagonia, Argentina. Ichnos, 4(1), 1–5. https://doi.org/10.1080/10420949509380109

Fisk, L.H., & Fritz, W.J. (1984). Pseudoborings in petrified wood from Yellowstone “Fossil Forests”. Journal of Paleontology, 58(1), 58-62. https://doi.org/1304733

What geological and environmental conditions determine whether wood becomes petrified rather than decaying?

Contributed by: Rachel Schones

Geological Question: One of the first questions that I had when me and my group went to this site is what exactly is petrified wood? I knew basic information about it, but I was really curious about what scientific details could explain the occurrence. The concept of wood “turning into stone” was so fascinating to me and I wanted to explore that question on a deeper level. Reading the context behind this site specifically made me interested in the type of geological and environmental conditions that causes wood to become petrified instead of rotting. The question that I chose relates to geology because petrified wood undergoes geological processes, not just biological ones, and has a lot to do with minerals and sediments.

Description of Scientific Article: When researching to answer my question, I chose an article by Mustoe (2017), because it specifically touches on the topic of petrified wood and the types of processes it can go through. Another reason why I chose this was because it’s peer-reviewed, and goes into detail about the investigations they did on those specific processes. This article is relatively new, so it offers fresh material on the topic, and it explains how minerals and groundwater preserve wood overtime, which answers the question I’m investigating.

Intersection Between Peer-Reviewed Research and Observations on Campus: Looking at Figure 3, the wood has notably red, yellow, green, and blue shades that are caused by different materials. Petrified wood forms when mineral-water infiltrates the wood’s original material and determines the color of the petrified wood (Mustoe, 2017). To become petrified, wood goes through one of two processes, or a combination of both, called permineralization or replacement (Mustoe, 2017). During permineralization, minerals from mineral-water, such as silica, seep in the cracks inside the wood and into the cells but keep the organic material intact (Mustoe, 2017). Replacement on the other hand, the wood becomes decayed and rotten, and minerals infiltrate the wood and use it as a template while it completely replaces the material but still keeps its external properties (Mustoe, 2017). Certain mineral-like materials that are dissolved, like silica, iron and manganese, can control the type of petrification that occurs and the color of the wood (Mustoe, 2017). The petrified wood seen in Figure 3 is most likely a combination of (Figure 3: Close up of an angle showing the both permineralization and replacement, as it’s most common. Petrification happens top and side of petrified wood with 20cm scale) in steps, starting with the dissolved silica settling in the cracks of the wood, filling in the
space but keeping the original material, then eventually overtime more minerals form until the original wood has decayed completely (Mustoe, 2017). Looking at Figure 3 again, the cracks and lines on the side of the wood are the result from minerals can shrink and crack the external part of the wood (Mustoe, 2017). From the context behind this site, it’s likely the volcanic ash, and mud from the river settled on top of the wood and preserved it’s material, causing it to have all these colors (Dept. of Earth Sciences, 2002). It’s also very likely that overtime more materials took place of the woods organic material and changed the chemistry of it to become fully petrified and replaced.

Answer to the Question: This article by Mustoe (2017) confidently answered my question, as it explained the geological conditions that causes wood to become petrified instead of rotting. It even helped give an explanation for the specific petrified wood my group was looking at. The volcanic ash that fell on top of the wood is one of the minerals that caused it to become petrified instead of decayed, as it infiltrated between the cracks in the wood and eventually replaced all its biological material. The cracks in Figure 3 are physical evidence of what Mustoe (2017) explains about the silica and other minerals causing the cracks to appear.

Something Additional I learned and Future Questions: One of the coolest things to me reading this article is that the vibrant colors in the petrified wood are a result of it becoming petrified and all the different minerals inside of it. The fact that each mineral caused each color was so fascinating. This opens up even more questions to me revolving around the colors, such as in this cite what kind of material caused each color to appear in the petrified wood? I also have other questions similar, like does the type of wood determine how it looks when petrified?

Sources Cited:

Department of Earth Sciences.(n,d). Petrified Log. Department of Earth Sciences.

G. Mustoe. (2017) Wood Petrifaction: A New View of Permineralization and Replacement. Geosciences MDPI
https://www.mdpi.com/2076-3263/7/4/119

 

How can the location of petrified wood samples teach us about its past climates and environment?

Contributed by: Justin Nelson

Geological Question: Petrified wood samples can be found all throughout the world. These geological features can date back from millions of years in the past. There are many different types of petrified wood samples, and each tells us a different story on how it was formed. I found it interesting how these preserved relics of the past could be examined to explain how the past looked like. This led me to question: How can the location of petrified wood samples teach us about its past climates and environment?

Scientific Article Chosen: In order to answer my question, I read an article by Elliot and Foster (2014) about petrified wood in southwestern Oregon. I chose this article because one of the main focuses of the paper is to research past climates and environments using petrified wood samples. Elliot and Foster examined petrified wood samples from different time periods in the same area in southwestern Oregon to see how climate and environment in the region developed. I thought it would be useful to see how petrified wood is used to describe past environments in context through this article.

Intersection between research and observations on campus: Elliot and Foster (2014) use a number of different measurements to determine past climates. The main one used throughout the article is by comparing growth rings. Growth rings are the layers of wood you can see when viewing stumps or cut wood from the top, as can be seen in Figure 4. Along these growth rings are a series of vessel elements varying in size and distribution based on the type of wood. Vessel elements are cells resembling pores along growth rings which transports water between roots and leaves. The type of wood that Elliot and Foster (2014) examine are ring porous and semi-ring porous petrified wood samples. This type of wood has very distinct growth rings, with vessel elements that range in size based on the season the growth ring grew. As Elliot and Foster (2014) demonstrate, you can tell how cold or temperate the environment is based on how many ring porous or semi-ring porous wood samples are found from that time period. Ring porous and semi-ring porous wood are associated with colder climates, leading Elliot and Foster (2014) to map out a timeline of climatic change within southwestern Oregon. Unfortunately, during the research for this field post I discovered that Conifer trees, the type of wood in Figure 4, does not behave the same way as the tree samples used in the article. Conifer trees are gymnosperms, whereas the type of trees described above are angiosperms. The vessel elements described above only work in that way in angiosperms, whereas gymnosperms use other methods. As such, without more information or samples from the area where this sample was found, no conclusions can be drawn about past climates from this location.

An answer to the question? My original question was: How can the location of petrified wood samples teach us about its past climates and environment? Elliot and Foster (2014) mostly answered my question about how petrified wood samples can teach us about past climates. They demonstrated how to use growth rings on petrified wood samples to interpret past climates. However, due to the method they used, I was unable to replicate their example on the petrified wood sample on campus. Despite this, they demonstrated fully how to use a collection of wood samples to interpret the past.

Something additional I learned and future questions: I had to learn a lot about different wood structures for this blog post as the article didn’t define any of the terms they used. Elliot and Foster (2014) looked at a lot of different petrified wood samples over the course of their article. The volume of samples collected made me wonder about the processes by which scientific journals obtain samples. Do researchers have to obtain these samples from museums or organizations, or do they collect samples themselves from the site? In other words: How do geologists obtain samples for use in research articles?

Sources Cited:

Elliott, W. S., & Foster, J. D. (2014). Petrified wood of southwestern Oregon: Implications for Cenozoic climate change. Palaeogeography Palaeoclimatology Palaeoecology, 402, 1–11. https://doi.org/10.1016/j.palaeo.2014.03.004