Lister Park Fossil Tree
Originally discovered in a sandstone quarry nearby in 1889, this fine example of a prehistoric fossil tree stump and roots (technically known as "stigmaria"). Was moved to Lister Park where it is on permanent display as an outdoor exhibit, currently residing near the entrance to the botanical gardens at the Frizinghall / Heaton end of the park.
Logging Requirements (Questions to Answer)
In order to log a find against this EarthCache, you will need to visit GZ and make some observations and then answer some questions and send answers to me via my Geocaching profile or through the Messenger Centre.
1) Compare the material forming the roots and trunk of the fossil tree to the material forming the mound that it is embedded in. Are they similar/different?
2) Look for crystals in the trunk/roots and evidence of the original tree structures such as bark or leaves. Can you see any? If so, where?
3) Based on your observations and answers to the above, would you say that any of the original wood of the tree remains, or has it all be replaced by permineralisation?
4) What are the roots technically known as?
5) From the information board nearby. Name the quarry where the fossil was found.
6) Compulsory task: Include in your log a photograph of you, your GPS or another identifiable item near GZ, taking care not to include anything in the photo that may give away your answers.
Tree Fossil.
Believed to be the stump and roots of a typical coal forest lycopsid tree such as sigillaria or lepidodendron, and having originally grown in the Carboniferous period is believed to be around 330 million years old. Yorkshire was a hot, steamy tropical swamp near the Equator. Can you see its huge spreading roots? During a flood the trunk was snapped off. The decaying hollow stump filled up with sand. The outer wood layers became coal. Over millions of years the sand hardened into sandstone rock, the tree stump became a fossil.
How tree fossils are formed.
Fossilisation only happens in the rarest of cases, when the tree dies in the right circumstances. The wood usually rots away before fossilisation can occur. To become a fossil the tree needs to die in a location where it is protected from the elements. This means getting buried in sand, soil or mud. The best place for that is on the seabed or a river bed. There it is preserved due to a lack of oxygen which inhibits aerobic decomposition. As time passes, the tree becomes buried deeper and deeper. What was mud or sand becomes compressed on its way to becoming rock.
Safely sealed away underground, chemicals and minerals percolate through the sediment and the original tree gradually recrystallizes. In extreme cases, the entire tree can dissolve away, leaving a hollow where it once was. The minerals from the enclosing rock can gradually fill the hollow to create a natural cast of the original. So sometimes a fossil doesn't contain anything of the original tree except its shape.
In other cases, minerals from the rocks gradually impregnate the wood, changing its chemical composition and making it capable of surviving for as long as, or longer than, the rock enclosing it. Eventually the rock enclosing the fossil is eroded away, and the fossil is revealed on the surface of the ground.
Permineralization is a process of fossilisation of bones and tissues in which mineral deposits form internal casts of organisms. Carried by water, these minerals fill the spaces within organic tissue. Because of the nature of the casts, permineralization is particularly useful in studies of the internal structures of organisms, usually of plants.
