The Bristol Dinosaur EarthCache

The other day I thought I found a dinosaur bone in Clifton... but it was a fossil arm!

fig 1. Model of the Bristol Dinosaur, Thecodontosaurus, on display in the Bristol Museum & Art Gallery

Lesson:

This EarthCache aims to teach you about rock types and fossil formation

Tasks:

1. Estimate the overall size of the rock face and describe the colours seen in the rock
2. Observe the layers in the rock and describe their angle and width, from their presence do you think this rock is igneous, sedimentary or metamorphic?
3. What physical forces could have caused the angle of these rocks?
4. This rock is primarily made from carboniferous limestone, considering how limestone is formed what can you ascertain about the type of environment that this rock was formed in, give your reasons?
5. If you discovered a dinosaur here today, what would you name it?

Send your answers by email or via the Message Centre.

History:

This site formed part of the east end of the Durdham Down quarries that were worked during the 19th century. Fossil material was discovered in the quarry in the early 1830s, today most of the quarries have been built over but one section remains visible alongside the Quarry Steps street. The first fossils were uncovered by quarrymen working the area and the material was taken to the Bristol Institution where the curator, Samuel Stutchbury recognised the importance of the samples and encouraged the workers to gather as many fossils as they could.

The fossil remains attracted both local and national interest with the findings being presented at the Geological Society of London. They were identified as a type of early dinosaur and named the Thecodontosaurus, after its socket-toothed jaw, which set it aside from other known lizard species. The Thecodonotosaurus was only the fourth named dinosaur in the world and was named even before the term dinosaur was created. Remains of this species of dinosaur have only been found in the Bristol region, hence the nickname "The Bristol Dinosaur".

Today there is a display about the Bristol Dinosaur at the Bristol Museum & Art Gallery (WP1) which is free to visit and well worth doing after completing the EarthCache, but not required.

Geology:

fig 2. Diagram of the three main types of rock

There are three main types of rocks: igneous, sedimentary and metamorphic, each formed by physical changes such as melting, cooling, eroding, compacting or deforming.

Igneous - Formed when molten hot material cools and solidifies, igneous rocks either form within the earth's crust, where they are classed as intrusive or outside the earth's crust where they are extrusive.

Sedimentary - Formed from pieces of other existing rocks or organic material, layers of sand, silt, dead plants and animal skeletons. There are five stages to the formation of sedimentary rocks. Firstly is sediment transport, like small pebbles rolling along a river bed. Second, is deposition, where the carried sediment is laid down. Third is the sedimentation stage, where layers of sediment form on top of each other. Fourth is the compaction stage, as more layers build on top of each other they compress the layers below. Finally is the cementation stage, in this stage, the minerals contained in the lower compressed layers harden and form a cement that sticks the rock particles together.

Metamorphic - Metamorphic rocks are formed when other rock types undergo changes due to heat or pressure and become a different rock. There are three stages in the formation of metamorphic rocks, firstly movements within the earth cause rocks to become buried or compressed. Secondly, the rocks become heated and experience great pressure. Finally the rocks undergo chemical changes which turn them into metamorphic rocks. 

Folds and faults are both geological features that occur when the Earth's plates move and compress rocks:

Folds - Bends and twists in rocks that occur when compressional forces cause ductile or flexible rocks to bend.

Faults - Fractures in rocks that occur when tensional forces cause large rock masses to break and sometimes slide past each other.

fig 3. Diagram of the process of fossilization

Fossils are formed when the remains of a living organism are preserved, the most common method of fossilization is petrification, which is when an organism's remains are filled with minerals and replaced by stone. The process of fossilization is as follows:

1. Death of the organism
2. Decomposition, the soft parts of the organism rot away
3. Burial, the organism is buried by sediment
4. Sedimentation, more layers of sediment build up on top of the organism
5. Lithification, the layers of sediment harden into rock
6. Erosion, the rocks are worn away and washed away, revealing the fossil
7. Permineralization, the buried bones, teeth or shells are filled with minerals, like calcium carbonate or silica, which replace the organic material