Glen Rose is a small town on the northern edge of the Texas Hill Country known to fossil hunters far and wide. But what most miss when visiting the area’s fossilized dinosaur tracks is the number of buildings in town that feature petrified wood in their construction. Stone masons used petrified wood that is more than 100 million years old and found all over the area of Glen Rose, to build walls, fountains, garden walls, gas stations, and houses for local residents. There are still around 40 remaining 1920's vintage structures built from this time period to be discovered and appreciated by geologists, fossil hunters, history lovers, and Texans (see https://wisemommies.com/the-stunning-petrified-wood-of-glen-rose-tx/). Perhaps the most impressive is the surprisingly beautiful and photogenic ruin of a gas station constructed from petrified wood, the site in front of you. This abandoned building, which acted as a speakeasy during Prohibition, is composed almost entirely of petrified wood, white quartz, and other stones mixed in for decoration. After Prohibition, the station was briefly a small grocery store, which closed in the 1950s. It’s striking that the structure is still standing, as there is no roof and one side of the building is split through the middle. The structure has not been maintained for at least 50 years.
Wood Fossilization
The most important cause of wood fossilization is the rapid burial of wood plant matter. This quick burial process creates an environment poor in oxygen and seals off bacteria and fungus that would cause decomposition. After this, two different processes can occur:
- The more recognizable process called "Permineralization" occurs when groundwater, full of minerals, flows through the overlying sediments and into the buried wood. As the water flows through the material, it deposits minerals picked up from the sediments. These mineral particles replace the organic matter but preserve all the textures and structures the wood had when it was still above ground. Some of these pieces will even show bark or tree rings!
- Another way wood can be fossilized is through the "Cast and Mold" process. After the wood is submerged, water flows through the sediment into the material, but instead of slowly replacing the internal structures of the wood, the wood is essentially dissolved away leaving a cavity called a mold. This cavity is then filled with minerals, like quartz, that preserve the exterior texture of the wood. This replacement is called a cast.
The fossilization process, called petrification occurs underground, when wood becomes buried in water or volcanic ash. The presence of water reduces the availability of oxygen which inhibits aerobic decomposition by bacteria and fungi. Mineral-laden water flowing through the sediments may lead to permineralization, which occurs when minerals precipitate out of solution filling the interiors of cells and other empty spaces. During replacement, the plant's cell walls act as a template for mineralization.
Petrified wood is found in a rainbow of colors.
Like many gemstones, the colors of petrified wood are caused by different compounds or elements within the mineral. For example, the red, brown and yellow coloration can be caused by iron oxides. Pinks and oranges can be produced by trace amounts of manganese. Purple and blue coloration in petrified wood is caused by manganese dioxide. Shades of green found in petrified wood can be attributed to iron, copper, cobalt or chromium.
Age of the Stone
Most petrified wood on earth can be from 50 to 500 million years old spanning from the Paleozoic Era (570-240 million years ago), the Mesozoic Era (240-64 million years ago) and even some in the Cenozoic Era (65 million-present). Despite many samples being older than dinosaurs, petrified wood can form in as little as 5,000 to 10,000 years compared to older specimens. In this case the samples found at this site are thought to be 100-120 million years old (Middle Cretaceous in age) and were discovered on private land only a few miles of where you are standing.
Where Found
Petrified wood is found worldwide in sedimentary beds ranging in age from the Devonial (about 390 million years ago), when woody plants first appeared on dry land, to nearly the present. Petrified "forests" tend to be either entire ecosystems buried by volcanic eruptions, in which trunks often remain in their growth positions, or accumulations of drift wood in fluvial environments. Amethyst Ridge at Yellowstone National Park shows 27 successive forest ecosystems buried by eruptions (see earthcache GC14YVK), while Petrified Forest National Park is a particularly fine example of fluvial accumulations of driftwood (see earthcache GC50C8N). The Florissant Fossil Beds is another excellent example of vocanic deposits (see earthcache GC99QJB). Volcanic ash is particularly suitable for preservation of wood, because large quantities of silica are released as the ash weathers. The presence of petrified wood in a sedimentary bed is often an indication of the presence of weathered volcanic ash. Petrified wood has been found on every continent, including Antartica.
To log your discovery: Please send an email to the Cache Owner with the following:
1) A photo of you (or a personal identifier in lieu of your photo) at the site
2) Look at the logs on the building and answer the following: a) What colors do you see on the logs, b) What chemical elements yield these colorations and, c) Describe the texture of the logs.
3. What type of rock does petrified wood belong (Google may be your friend): Sedimentary, Igneous, or Metamorphic?
4. Of the two process of fosssilization mentioned above (Permineralization or Cast-and-Mold); which petrification process resulted in the formation of this stone (and why you believe this to be the case)?
5. Look closely at the texture of the wood used to construct the building and propose if: a) it likely came from a forest of widely varied trees or 2) it likely came from a forest primarily composed of a single species (and tell why you think that).
6. Look at the colors of wood and describe if the source of wood for the entire building: a) likely came from a single site or b) from multiple and widely seperated locations (and why you believe either to be the case).