This EarthCache takes you to Blua Crags, which sits high above Settle.
🚨 Always approach the EarthCache from the bottom of the crags. It involves some sterp and uneven terrain, be careful, and assess the risk for yourself. 🚨
So, what is the geology here?
Well, the rock is limestone. So, what you can see is limestone, lots of limestone. Limestone is a sedimentary rock, laid down in a marine environment, either as lime mud, or the accumulation of ancient sea creatures, which when compressed over time forms limestone. But, specifically, there is more to limestone, than just colour, and depositional environment, as otherwise every EarthCache would be like gound hog day....yet again another one, about the same subject. So, let's look at the specific and more in depth.
We are on the border here between two types of limestone, namely Gordale Formation Limestone and Kilnsey Formation Limestone. These place names relate to where the rock has first been identified in Upper Wharfedale.
We are here to look for, and at Stylolites. Now, there are a fair few EarthCaches about this subject, but they tend to be in limestone which forms part of a building, so in that cause they can be easy to see. Here, we will need to do a bit of examination and looking to get the best out of the experience. We will be exploring the length of the crags, so as to get the best of the EarthCache.
So, what is a stylolite? Well, basically it's a line in the limestone, but a line which can give a particular appearance.
The above shows a stylolite, it is the jagged line running across the rock. This was in a rock near Langcliffe Crags, so not too far away.
A stylolite in a rock in the scree slope at the south end of Blua Crags.
Stylolites form after lithification of sediments, which is a diagenetic process. Lithification is the process of sediment forming stone, this happens due to pressure, and during this process, fluid contained in the sediment is gradually expelled. A diagenetic process, is when physical and chemical changes in sediment occur. Pressure during the lithification process can cause stylolites to form.
Stylolites start to form when there is high porosity and stress present. High porosity basically means that a lot of fluids can run through it. They then stop forming when there is low porosity and low stress.
Tectonic action, affects stylolites. This is the movement of rocks by pressure due to tectonic plates and fault action. When there is just pressure stress from above, stylolites will be horizontal, though with tectonic action, they can be angled or perpendicular to the original way the rock was deposited.
There are different types of stylolites.
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.
THIS IS A THREE STAGE EARTHCACHE. THERE ARE PHOTOGRAPHS FOR EACH STAGE TO ASSIST YOU.
STAGE ONE.
1. At this location, find the stylolite. Please describe it it terms of type.
STAGE TWO
The view from STAGE TWO.
2. Please describe the stylolite here.
STAGE THREE
3. Please describe the stylolite here.
4. Please explain how stylolites form.