Ripples preserved in rock:
When a wind or water current flows across loose sand, the sand is dragged along the bottom and frequently is piled up to form ripples. On a large scale this action also forms sand dunes. The main difference between a ripple and dune is size, with dunes being taller than about 10 cm. You have no doubt seen ripples and dunes at the beach (lake or ocean), along a sandy river bank, or in the desert. Sometimes tiny ripples form on silty sediment, and larger dunes form where very fast water currents flow over gravel.
Ripples are useful because they are often preserved in the sedimentary record of solid rock. Preserved ripples provide clues as to whether a given sandstone was influenced by waves or unidirectional currents, and in the latter case they indicate which way the water flowed.
* Asymetrical (uneven shape) ripples form when current flows in a single direction, such as along a river bottom. The shape on one face of the ripple is different to the opposite face.
* Symmetrical (even or mirror-image shape) ripples form where currents flow in two directions, such as waves washing back and forth at the beach. The shape on one face of the ripple is the same or very-similar to the opposite face.
Sometimes, layers or rock are twisted or tilted because of the movement of the Earth’s tectonic plates. Rocks on a fault line may snap or break. Scientists study these layers to learn more about the Earth’s history. The amount and direction of tilting in a given area can help scientists learn how old the rock and surrounding area is.
You task is to observe the rock and preserved ripples at and near GZ and answer the following questions:
1. Are the ripples symmetrical or asymetrical?
2. What colours can you observe in the layers of the ripples?
3. What angle is the rock tilted to?
4. Is the tilt facing to the North-east or South-east?
Send your answers to me via Geocache email messaging. You can log your find straight away, but please understand logs will be removed if no answers are received, answers are incorrect, or appear guessed.