Wensley war memorial, sits watching over the road to Leyburn. Many drive past it, though take a moment to stop, read the names and look at the geology of this memorial. It records men of the village who served, but also those who died.
So, let's look at the geology of the war memorial. The war memorial is constructed from a type of rock known as limestone. Limestone is a sedimentary rock, formed by the accumulation of sediment in a shallow tropical sea, which over time formed layers of sediment, which then compacted and eventually limestone was formed. Now different sedimentary rocks have different sediment beginnings, and example of this is that sandstone is made from the accumulation of sand grains, whilst limestone is formed by the deposition of lime mud and the remains of ancient sea creatures.
The Yorkshire Dales are known for their limestone scenery, and some may argue that all limestone is alike, but look a bit closer, and it soon becomes apparent that it isn't. Different depositional conditions in the tropical sea, led to different limestones. Just look at the marine environment around the UK, the sea changes its currents which means different amounts of sediment can be deposited.
So, when we look at this war memorial closely, we can learn about how to classify different types of 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.
This being an EarthCache, in order to log it, I ask that you complete the below 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 war memorial.
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.
If anybody would like to expand to this series please do, I would just ask that you could let Just-Us-Two know first at justustwo1013@gmail.com so they can keep track of the memorial numbers and names to avoid any duplication.