Ecca Group - Shale EarthCache
Hidden : 10/6/2015
Difficulty:
2 out of 5
Terrain:
2 out of 5

Size: Size: other (other)

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Geocache Description:


There is enough space to park off the road. Please be careful of moving vehicles while exploring the area.



Logging requirements:

To be able to log this earthcache as a find please answer the following questions via our profile. Feel free to log the cache at the date of your visit with the answers following within 7 days.

The information needed to answer the following questions can be found in the listing.

1. Would you classify shale as Igneous, Metamorphic or Sedimentary?
2. Name two uses of shale.

To answer these questions you will need to combine information from the listing with some observations made on site.

3. Describe the shale in relation to the colour you see.
4. Take a piece of shale and try to break it with your hands. Describe your experience.
5. Estimate the angle of the formation at this point. What has caused this?


The following table will give us an idea of the time in history we are looking at.

Geological timescale
Eon Era Period Millions of Years
Phanerozoic Cenozoic Quarternary 0 - 2.58
Neogene 2.58 - 23.03
Paleogene 23.03 - 66
Mesozoic Cretaceous 66 - 145
Jurassic 145 - 201.3
Triassic 201.3 - 252.17
Paleozoic Permian 252.17 - 298.9
Carboniferous 298.9 - 358.9
Devonian 358.9 - 419.2
Silurian 419.2 - 443.8
Ordovician 443.8 - 485.4
Cambrian 485.4 - 541
Proterozoic
Neoproterozoic Ediacaran 541 - 635
Cryogenian 635 - 720
Tonian 720 - 1000
Mesoproterozoic Stenian 1000 - 1200
Ectasian 1200 - 1400
Calymmian 1400 - 1600
Paleoproterozoic Statherian 1600 - 1800
Orosirian 1800 - 2050
Rhyacian 2050 - 2300
Siderian 2300 - 2500
Archean Neoarchean 2500 - 2800
Mesoarchean 2800 - 3200
Paleoarchean 3200 - 3600
Eoarchean 3600 - 4000
Hadean Early Imbrian 4000 - 4100
Nectarian 4100 - 4300
Basin Groups 4300 - 4500
Cryptic 4500 - 4567

The following table show the place of the Ecca group within the Karoo Supergroup. It also link it to the period in the geological timescale that the group was formed.

Formations of the Karoo Supergroup in the Eastern Cape
Period Group Formation
Jurassic Drakensberg Drakensberg
Stormberg Clarens
Triassic Elliot
Molteno
Beaufort Burgersdorp
Katberg
Balfour
Permian
Balfour
Koonap
Ecca Waterford
Fort Brown
Ripon
Collingham
White Hill
Prince Albert
Carboniferous Dwyka Elandsvlei


Permian

By now the supercontinent Pangea had moved out of the polar region north into more temperate climates. The Karoo Sea was covering most of modern day Southern Africa. To the south it was flanked by the Cape Fold Mountains and to the south of that was the Falklands Platueau towering over it. To the north lay the Cargonian Highlands. The Falklands Plateau eroded, covering the Cape Fold Mountains on its way to the Karoo Sea. Although the rivers from the south did form deltas, there was not as much vegetation as on the northern side. To the north swampy area had formed, that was ideal for plant material to grow. These eventually lead to the coal deposits in the northern part of the country.

Rivers from both the north and the south emptied into the sea. The faster flowing rivers from the south deposited larger particles and the slower flowing rivers from the north deposited smaller particles. Over time the water changed from marine to fresh water.

The Permian ended with the Permian–Triassic extinction event. This is the largest extinction event recorded. About 90% of marine species and about 70% of land organisms became extinct.

Ecca

The Ecca group was created during this sedimentation process into the Karoo Sea. The rocks of this group predominantly consist of shale and sandstone. The Ecca Group have a total thickness of 1300 m, but the largest vertical exposure is 900 m at Skoorsteenberg.

Sedimentary rocks are typically laid down in horizontal layers. Over time this can be distorted by things like tectonic plates that move or volcanic outbursts. The most well know occurrence in this area is the Cape Fold Mountains, although that occurred long before the Ecca formations was laid down.

Shale

Shale is the most common sedimentary rock and found all over the world. The process to form shale start with the erosion of material from higher ground. This material is then carried via rivers downstream to a sea or lake. As the water slows down on entering the large water body, the material that have been suspended start to sink to the bottom. Larger heavier material will settle first, but finer lighter material will be carried deeper into the sea/lake before it settles down. Over time, layer upon layer will be deposited, and the weight will compact it to form shale.

Shale is made up of fine grained material like silt and clay. We refer to it as "mud". This places shale in a category of sedimentary rocks known as "mudstones." Shale is made up of many thin layers "Laminated". It is also "Fissile", meaning it is easy to break along these laminations. Like many rocks, shale can be found in a variety of colours. The colour is as a result of a tiny amount of mineral, or other material present. Some of the more common colours can include red, brown, yellow, green, grey and black.

Shale is often associated with land slides. When shale gets weathered it forms a clay rich soil. This soil does not have a high shear strength, especially when wet. Man made structures on these slopes will often be the reason for such slides.

Natural clay only occur in small quantities around the world, and most of these have been depleted. It has been found that if shale is ground into a fine powder and mixed with water you get clay. This can then be used for everything clay has been used in the past. Pottery and bricks are some of the common uses.

Reference: Wikipedia
Norman, N. (2013) Geology off the beaten track. Cape Town: Struik Nature
Norman, N. & Whitfield, G (2006) Geological Journeys. Cape Town: Struik Nature
McCarthy, T. & Rubidge, B. (2005) The Story of Earth and Life. Cape Town: Struik Nature

Additional Hints (Decrypt)

Erzrzore gb znvy lbh nafjref.

Decryption Key

A|B|C|D|E|F|G|H|I|J|K|L|M
-------------------------
N|O|P|Q|R|S|T|U|V|W|X|Y|Z

(letter above equals below, and vice versa)


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