Stratification
Stratification, in geological terms, describes the layering of rock strata and the processes involved in the formation of such layering. The process of stratification follows a few fundamental laws:
1. Sediments are originally laid down in horizontal beds.
2. In an undisturbed sedimentary sequence (series of layers) each layer is younger than the layer below.
3. Layered rocks are depositied in continuous contact.
The study of stratification is called stratigraphy - basically the study of rock layers and layering. It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy was essentially invented and first rigorously applied by William Smith in England in the 1790s and early 1800s.
Strike & Dip
Over time and due to massive forces, usually volcanic or tectonic in nature, layers can become disrupted and deformed. Where the strata has deformed but remains largely intact, these processes are usually gradual and not sudden in nature.
In order to measure the deformation of strata, there are two principal measurements: strike and dip.
Strike can be described as the line of intersection between the strata, or layer, and an imaginery horizontal plane that cuts through it.
This would be the same as the direction you would take if the layer was exposed and you were to traverse across it, remaining at the same elevation. The strike is usually represented in degrees from true north, expressed as the lower of the two bearings that would describe it.
Dip can be described as the angle of the slope of the strata where the dip direction is exactly perpendicular (90 degrees offset) to the strike direction. If the layer was a slope you were standing on, this would be the angle of the slope pointing directly downhill from you.
This Earthcache
The published coordinates will take you to a spot on Narroneck beach where there is an obvious display of deformed rock strata. You will be required to accurately measure the strike and dip of the rock strata at this location.
You must visit this site in order to complete this earthcache.
You will require the following equipment to complete the tasks for this earthcache:
- A spirit level, the bigger the better. A builder's level around a meter long would be ideal.
- An accurate compass (the compass on your GPS will NOT do).
- A ruler or tape measure.
You'll be using the above equipment to make an amateur version of a Brunton compass and clinometer. Obviously if you actually happen to have a Brunton compass and a clinometer and know how to use them, then use those instead!
To claim a find on this earthcache, please complete the tasks outlined below. Answers to the questions should be emailed to the cache owner and not mentioned in your online log.
1. Using the spirit level and the compass, determine the strike angle of the rock strata. To do this, lay the spirit level on the sloping rock surface and rotate it around until it is exactly level. Then use your compass to take a precise measurement of the bearing of the spirit level's orientation.
2. Based on the strike angle, estimate the dip angle. To do this, you must hold your spirit level at exactly 90 degrees (perpendicular) to the strike angle - you can use your compass to help. With one end of the spirit level touching the sloping rock, adjust the height of the other end so that it is perfectly level, then use your ruler to measure the height from the sloping rock strata to the end of the spirit level that you are holding (not the end sitting on the rock). If you measure also the length of the spirit level you now have a triangle and using basic trigonometry, you can work out the dip angle.
3. Describe the colouring you can see in the various layers. Is there a significant difference between the colouring of the younger layers vs the older layers? Are the layers cyclic, as in, you see repeating bands of the same kind of rock as you go through the layers from younger to older?
4. (Optional, but politely requested) Take a photo of your GPS, your equipment, and the beach, sea, or general view (but NOT the rock itself please).
You can log this cache straight away after you have emailed your answers to the cache owner, no need to wait for confirmation. Please include the name of this earthcache in the email - you'd be surprised how many people forget. Also, when contacting us with answers, if you want a reply, please include your email address. Any problems with your answers we'll be in touch.
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