Stratigraphy at the Sand Tip EarthCache
Stratigraphy at the Sand Tip
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This EarthCache is placed on publically accessible land at the now closed Treskilling China Clay Pit. The route to, and area around GZ is on the Clay Trails and can be freely enjoyed on foot, horseback or by bicycle. There is also a picnic area in the sandpit.
Although it is fenced, if visiting with young cachers, please take care to keep them away from the edge.
Treskilling Sand Tip
Although the stratified (layered) sand tip at GZ is a man-made structure, created in living memory, it displays clear features that can help us to understand how ancient geological deposits were formed.
According to the doctrine known as Uniformitarianism, geological processes are essentially unchanged today from those of the past, therefore understanding the present is the key to understanding the past.
The British geologists James Hutton and Charles Lyell are considered to be the founding fathers of Uniformitarianism.
James Hutton
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Charles Lyell
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In geology, stratigraphy is the study of rock layers (strata) and layering (stratification).
The key principles in stratigraphy were first observed and described in detail in 1669 by a Danish scientist called Nicolas Steno in his snappily titled publication De solido intra solidum naturaliter contento dissertationis prodromus!
Nicolas Steno
The Principle of Superposition
Steno reasoned that in any flat-lying strata, the oldest layers are at the bottom and the youngest at the top (assuming of course that no later Earth movements have disturbed the layers).
Although seemingly simple, this idea still underpins how we think about the relative ages of sedimentary rock layers today.
A is the oldest layer and was then covered by layers B, C and D
The Principle of Original Horizontality
Sedimentary strata are broadly horizontal when originally deposited. Any strata later found not to be horizontal are likely to have been deformed by movements of the Earth’s crust, or in other words - "Strata either perpendicular to the horizon or inclined to the horizon were at one time parallel to the horizon!"
The strata were originally horizontal, but have been tilted by Earth movements
The Principle of Lateral Continuity
When originally deposited, strata would have been continuous over the surface of the Earth unless some other solid bodies stood in the way. After deposition, strata may get eroded, but they were still once present (or laterally continuous) prior to erosion.
The strata have been eroded by the river in the valley, but would originally have been present where the valley is now
In order to claim this EarthCache, please message or email me (through the link at the top of this page or via this link with the answers to the following questions:
1) At the headline coordinates, you are at the same level as the oldest deposited material. Estimate the height of the sandpit cliff from where you are up to the top of the cliff - where the youngest material is located
2) Assume that the strata were deposited at a rate of 1cm per day and the workers who created them worked Monday-Friday every week of the year. From your answer to question 1, calculate how many years it would have taken for the stratified sand here to have been deposited and therefore suggest how old the sand layer at the bottom is likely to be. For extra credit, suggest why simply using this sedimentation rate method to calculate the age of a deposit may give inaccurate results.
3) Observe and describe the sediment that the tip is formed from - It is the same as the material that forms the trackway where you are standing. I know that it is mainly sand and gravel, but say what it is like - colour, grain size, grain shape, what it feels like, how friable (crumbly) it is in your hand and see if you can identify any of the rock forming minerals present.
4) Describe evidence that you can observe in this sand tip that supports the Principle of Lateral Continuity. For instance, can you see anywhere where although the deposit has now been removed, it would have been present in the past? (Hint - Look up at the top of the cliff ).
If you’d like to post a photo of yourself or your GPSr at or around the sandpit, that would be great. Please just remember not to post any spoilers or give any of the answers away in your log.
Thanks for taking the time to visit this EarthCache and I hope you enjoy your visit.
If you'd like to find out more about Geological Time then check out the link below:
Additional Hints
(Decrypt)
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