There is limestone everywhere around here, that along with Basement Rocks form the building blocks of the nearby buildings. Though, like people , not all limestones are alike. This EarthCache gives an opportunity to learn about a different type of limestone. We are here to look at the large upstanding rock.
🚨 Here you are near where the Pennine Bridleway and the Dales Highway cross paths. This gives an opportunity to stop, have a look, and appreciate the beauty of Little Stainforth.
🚨 Please do not park on the grass. Please do not leave your cars here, or infront of any of the cottages. There is parking in Stainforth village.
🚨 This is a rural working environment, be aware of farm machinery going past.
🚨 Please be polite to locals.
The geology.
The geology of the area is made up of rocks from two different geological ages, the Silurian period, and the Carboniferous period.
In the Silurian period, this area was covered by a deep ocean known as the Iapteus Ocean. Sediment was deposited, and over time this formed sandstones and siltstones, these are the brown and black rocks you can see in nearby walls. These are what are known as Basement Rocks. Jump forward many millions of years, and there was a tropical sea here, lime mud and the shells of ancient sea creatures were deposited, and over time limestone was formed. Limestone is the pale grey rock you can see, which is what is known as a carbonate rock, as limestone is formed from calcium carbonate.
What is special about this rock?
Well, it's limestone, deposited in a marine environment many millions of years ago, but importantly it can help us understand the deposition conditions at the time. The limestone in this area, was deposited in the lower part of the Carboniferous period, which is known as the Dination. During the Dination shallow marine conditions were at first established, which formed a sedimentary platform known as the Askrigg Block, whilst to the south of this was deeper water conditions which are known as the Craven Basin. As time progressed, the marine conditions changed, with deeper sea water encroaching into the Askrigg Block. This led to the deposit of darker limestones, as a result of muddy sediments. As the environment settled, so the marine conditions settled, with less muddy sediment being deposited, as a result the sediment from these conditions now results in a uniform paler limestone.
It is possible to classify a type of limestone by the matrix it is made up of. A matrix is the material that makes up the rock, basically the grains of a material such as silt, or sand. Dunham (1962), devised a classification of limestone, looking at what makes up the rock, i.e its matrix, which can help to understand deposition conditions.
| Mudstone |
A mud-supported carbonate rock containing <10% mud grains.This would have been deposited in a low energy environment, such as a lagoon. |
| Wackestone |
A grain-supported fabric containing >10 % or more mud grains. This would gave been deposited in a moderate-energy, warm-water environments like semi-protected bays or lagoons. |
| Packstone |
A rock, which displays evident grains, and some fossils, whilst having > 1% mud. These would have been deposited in a moderate to high energy environment, where the current moved sand grains about, and enough of a current to prevent silt being deposited as mud. These conditions can include the sea side of coral reefs, and tidal channels. |
| Grainstone |
A grain-supported carbonate rock with <1% mud. These form in a high energy environment, where a current or tidal conditions prevents silt settling as mud. Coastlines and lagoons are amongst the conditions, similar to the Great Barrier Reef. There will be a lot of fossil fragments. |
References.
Dunham, R. J., 1962, Classification of carbonate Rocks according to depositional texture. In: Ham, W. E. (ed.), Classification of carbonate Rocks: American Association of Petroleum Geologists Memoir, p. 108-121.
This being an EarthCache, in order to log it, I ask that you complete the above tasks. Please send the answers to me, and do not include them in your log. You can send them to me by using the message facility or email, both of which can be found by looking at my profile.
1. Please examine the rock, and please describe what classification of limestone there is here, using the Dunham Classification.
2. What is the rationale for your answer, to question 1?
3. Please describe the environmental conditions at the time of deposition.
4. Please have your photograph taken, or that of your device in front of the large fir tree.