What is a fossil?
The Americam Museum of Natural History defines Fossils as naturally-preserved physical traces of long-dead organisms. Usually, these traces consist of an organism's hard parts, such as bones, teeth, shells, or wood. Occasionally, when conditions are optimal, soft parts of organisms can also fossilize, such as impressions of skin, body outlines, and, more commonly, leaves. Other traces of objects made by organisms, such as footprints, burrows, and nests, also qualify to be called fossils. Most definitions of fossils require that the organism's body part or other physical trace be more than 10,000 years old in order to truly be called a fossil. In this one location you will be able to observe two types of fossils in the stone used as building blocks for this facility; Petrified wood and fosillized fragments of long ago shell creatures.
Fossilized Wood
Petrified wood is a special type of fossil that forms when plant material is buried under sediment and avoids decaying because of a lack of oxygen. Once the tree or plant material has been buried, water rich in minerals such as silicate, quartz, calcite, pyrite, and opal, begins to flow through it, slowly replacing the organic remains with stone in a process known as permineralization.
The minerals - over millions of years - eventually crystallize in the tree but help to retain the original structure of the stem tissue and preserve details of the bark and wood. The organic materials will eventually decompose and the remaining fossil will essentially become a stone.
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. Depending on the level of preservation, some fossils of petrified wood will look exactly like the original piece of wood but weigh much more. Many, however, will begin to take on a distinctive look featuring exotic colors that can include copper, cobalt, pink, and on rare occasions, red and green hues.
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 (240-65 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 Cenozoic in age and were discovered on private land in adjoining counties southeast of where you are standing.
Fossilized Limestone
Take a close look at a piece of Texas limestone on many buildings in the State and you often will see what appear to be tiny seashells. How did these sea creatures get into the rock from the Texas Hill Country? The answer might surprise you, and you may also find it interesting how easy it is to find these fossils.
Texas limestone comes from the calcium carbonate in sea organisms from millions of years ago. Though many types of limestone exist, the type seen at this building contains visible fossils, and as such, is known as fossiliferous limestone. The majority of limestone comes from shallow seas, which covered central Texas during the Cretaceous Period more than 100 million years ago when dinosaurs ruled. Bodies of sea creatures would sink to the floor when they died, and over time, only their calcium-rich skeletons or shells remained. These formed the calcium carbonate that accounts for at least 50 percent of all limestone.
When you see fossiliferous limestone around the Texas, look carefully for fossils of sea life. Bivalves, such as clams (Trigonia), often left behind imprints rather than their actual shells, which broke down over time. Another frequently seen fossil comes from gastropods, better known as snails (Turritella). Like clams, their shells demineralized, but left their impression in the rock. Less commonly seen are other sea animals such as crabs, corals, and sea urchins. Many of the building stones in the wall of this building contain both of the above varieties as well as mash-ups of shell fragments.
In order to log this geocache, please answer the following questions:
1. Inspect at least 5 randomly pieces of petrified wood in various locations on the building at ground zero and a) describe the textures and colors of the fossilized wood, b) based upon those colors, what chemical elements likely existed in the ground water to have yielded these colors, and c) do the sections of wood appear to have come from a forest of similar species of trees or from a forest of multiple species? Explain why you have arived at this conclusion.
2. Find several blocks of the fossilized limestone. Describe the types of fossils you find, tell which of the two species (shown above) predominates, and finally tell if you see more intact fossils or more shell fragments. Based on these findings, what do you think was the environment in which these shells were deposited (quiet water or a high energy flow) and tell why?
3. Finally, please post a photo of yourself (or of a unique personal item) taken at the site.
For extra credit,: Describe the colorations crystals found in the blocks of igneous pink granite that also can be found in the wall of the building, a rock also used in the Texas State Capitol.
Please Note: Please respect the rules of Fireman's Park and only visit during daylight hours, dawn to dusk.