Introduction
I always thought that stress and strain were pretty much the same thing but it turns out that, within the scientific context of geology at least, their meaning differs.
Stress is the application of force to a material. Strain is the amount of deformation (change in shape) in that material arising from the applied stress. So it follows that more stress = more strain ๐ง.
The way a body of rock responds to stress depends on lots of things including the rock type, the surrounding temperature and pressure conditions, the length of time the stress is applied, and the type of stress.
The rocks exposed at the cache location - Hetton Beck Limestone - have been subjected to considerable stress in the geological past. The effects of that stress are clear to see in the exposed rocks today.
Logging Tasks
IN ORDER TO COMPLETE THESE LOGGING TASKS PLEASE SEND US YOUR ANSWERS USING THE Message this owner LINK AT THE TOP OF THIS PAGE OR USING THE MESSAGE CENTRE OR EMAIL VIA OUR GEOCACHING PROFILE BEFORE SUBMITTING YOUR LOG. PLEASE DO NOT INCLUDE ANSWERS OR SPOILERS IN YOUR ONLINE LOG. YOU CAN GO AHEAD AND LOG YOUR FIND AS SOON AS YOU HAVE SENT YOUR ANSWERS IN ACCORDANCE WITH GROUNDSPEAK GUIDELINES. LOGS WITHOUT ADEQUATE LOGGING TASK EVIDENCE MAY SUBSEQUENTLY BE DELETED.
Thanks to United Utilities for permission to stage this EarthCache here. The quarry face closest to the published coordinates is on public access land as specified under the Countryside and Rights of Way Act 2000 - so you may enter through the nearby gate to get a closer view of the rock. Please make sure you close the gate behind you. This permission does not extend to the quarry face on the opposite side of the road - you'll need to make your observations from the published coordinates but there's a clear view so this should pose no problems.
Please remember and respect the fact that this site falls within the Bowland Fells Site of Special Scientific Interest (SSSI)and adhere to Leave No Trace principles and guidelines.
Based on your observations at the cache location and the information on the cache page, please tell me:
- The same Hetton Beck limestone is exposed due to quarrying on both sides of the road but there are some differences between the two examples and also some similarities - please describe some. Do you see any folds?
- Using the access gate provided you may get close to the exposed face nearest to the published coordinates - although I advise you to stay to the lower sections as the face is steep and quite slippery - especially when wet. Describe / identify any fossils you can see here.
- Please provide a photograph of yourself - or a personal item - next to the old lime kiln at the roadside as proof of your visit.
- Optional task: feel free to add any photographs of your visit that do not show the specific features from the logging tasks - no spoilers please. In the interests of allowing everyone to experience the EarthCache fully for themselves obvious spoiler photographs will be deleted.
Plate Tectonics
The Earthโs crust is made up of fifteen or so enormous tectonic plates, which shuffle around on the surface and their movement causes stresses to be set up in the rocks they are made of.
Close to the surface the rocks in the crust are cooler and more brittle and tend to crack when subjected to stress. These cracks are called joints and faults.
Deep down though where the Earth is hotter (below 16km, roughly), the rocks are softer and bend rather than break, resulting in folds which may be angular or more curvaceous.
Earth's crust is divided into two types - continental crust, which mostly sticks up above the sea and so is commonly depicted on maps and globes and oceanic crust which, as you may guess, is found beneath the waves 
.
Oceanic crust is only 5km to 10km thick. Continental crust on the other hand is between 30km and 50km thick so, as you can imagine, those fifteen large plates are pretty hefty beasts and their movement, however slow, goes hand-in-hand with enormous stress levels, especially when, say, they collide with one another.
A Tale of Ups and Downs and Squeezing and Stretching...
Our story begins around 490 million years ago in the Ordovician Period.
The British Isles, as we know them today, didn't exist. At least they didn't exist as a single landmass. The northern and southern parts were on completely different continents - Laurentia and Avalonia - separated by thousands of miles of sea in the form of the Iapetus ocean.
Later tectonic movements saw Laurentia and Avalonia gradually moving closer together until, around the middle of the Devonian Period, around 375 million years ago, they collided with one another, uniting the British Isles in a form we would recognise today. This collision is known as the Caledonian Orogeny.
An orogeny is also known as a mountain building episode. When plates collide the rock they are made of is subjected to enormous compressive stress (it gets squeezed) and the resulting strain is the uprising of mountain ranges.
The late Devonian / early Carboniferous periods saw a change from compressive stress to tensile stress (the jury is still out on specifically why this happened) and saw the crustal rocks, which had been squeezed and bunched up into mountains, being stretched, broken and pulled apart, eroding the roots of the Caledonian mountains.
Differences in density of the now separate blocks of crust saw some of them sink downward, producing troughs and basins, while other blocks remained upstanding.
As the Carboniferous Period progressed these basins were filled with many hundreds of metres of new sedimentary deposits, which then became lithified into new sedimentary rocks such as mudstones, sandstones and shales and a significant amount of limestone. In the Tournaisian and early Visean stages of the Carboniferous Period (around 360 to 330 million years ago) England was located close to the equator where conditions - warm, clear seas - favoured deposition of the sediments which later became limestone.
There followed more tectonic plate collisions and thus more compressive stress and thus more faulting and folding of rocks and uprising of mountains.
In the late Carboniferous, the collision of Laurussia (present-day Europe and North America) into Gondwanaland (present-day Africa and South America) produced the Appalachian mountain belt of eastern North America and the Hercynian Mountains in the United Kingdom. These events are known as the Hercynian or Varsican orogeny and took place over a period of around 100 million years.
Although the compressive stresses arising from this orogeny and the strains resulting from them were greater in the south of England, they were still sufficient to produce faulting and folding of rocks in the north of England too - including the Ribblesdale Fold Belt - an exposure of which forms the basis of this EarthCache.
By the late Palaeozoic (250 million years ago), the continents had converged to form a supercontinent, called Pangea.
Obviously we can tell from the way the Earth's surface looks today, Pangea didn't last - it broke up between 175 and 140 million years ago - and nor was it the first supercontinent - between 620 million and 1 billion years ago Britain formed part of another supercontinent called Rodinia - but that's a story for another time .
Fossils In Limestone
-
Colonial Coral - Corals still inhabit our oceans today and at first glance, you may think that coral reefs are made up of rocks, but they are actually made up of tiny living organisms called polyps.
Some coral polyps build hard carbonate skeletons and also reproduce by making lots of copies of themselves, so that what starts off as a single coral polyp gradually grows into a whole community, with each polyp adding to the growing mass of carbonate material.
If you see a coral fossil in carboniferous limestone you're seeing the hard carbonate material left behind by the many polyps which built it millions of years ago.
-
Solitary Coral - In some species of coral the polyps do not form colonies and instead remain as solitary organisms.
Coral polyps are essentially tube-like structures which can range in length from a few mm to as much as 30cm. The tube has a mouth at one end with poisonous tentacles which trap food from the water. There's no anus though - any waste products from the food consumed have to be regurgitated back out through the animal's mouth ๐คฎ.
Fossils of solitary corals tend to be obvious due to being at the larger end of the spectrum and might be described as sausage-shaped.
-
Brachiopod - a modern Latin word derived originally from the Greek brakhion meaning arm and podรฒs meaning foot. So if we think of gastropods as stomachfoots we might think of brachiopods as armfoots
.
Brachiopods get their name because they have two muscular arms which they use to collect food.
Brachiopods have two valves or shells, just like bivalves but where bivalves have a left valve and a right valve which tend to be a mirror image of each other, brachiopods have an upper valve (which covers the upper side of the body) and a lower valve (which covers the lower side of the body) - which are not symmetrical.
In brachiopods one shell is larger than the other which has led to them being commonly known as lamp shells because they resemble early Roman oil lamps.
Brachiopods have existed for around 550 million years and at one time were one of the most abundant forms of life in the sea. The fossil record includes around 12,000 individual species but most of them became extinct a long time ago.
It isn't too difficult to identify brachiopod fossils in cut stone but they can be different shapes depending on the direction of the cut made when the rock was quarried - which is why there are two images to the right showing the most common shapes to help you recognise them.
-
Crinoid - also known as sea lilies because some species look more than a little like the flowers of the same name (as shown in the image to the right of a rare fossilised crinoid in which the soft parts were preserved as well as the hard parts). The ancient Greeks must have thought so anyway because crinoid is from the Greek words krinon and eidos which together translate roughly as lily form or lily shaped if you prefer.
Crinoids are very much animals though and definitely not plants. Though crinoids appeared in the Ordovician (488 mya), they survived the Permian mass extinction and diversified into hundreds of species which survive, today.
Crinoids can very basically be described as upside-down starfish with a stem. The stem of a crinoid extends down from what would be the top of a starfish, leaving the mouth of the organism opening skyward, with the feathery arms splayed out to catch any passing food particles. At the bottom of a crinoid stem there's a part called a holdfast which helps to anchor the crinoid to the sea bed.
-
Typical crinoid fossil appearance - so the only parts of crinoids that are fossilised most of the time are the hard parts - the ossicles of carbonate material which, in life, are stacked one on top of the other in the long stem. Because they are little tube-like structures with a hole through the middle, some people think that they look like polo mints when viewed end-on - the ossicle in the top-left corner of the image on the right is a good example of this.
If you're lucky enough to see a cylindrical stack of articulated ossicles that haven't been cut through, the narrow grooves around the cylinder make the stack look a bit like a bolt or a screw - which is why people sometimes call these fossils screws.
If you've carefully read and digested the information from this cache page your tasks at the cache location should prove relatively straight forward, although you may wish to take a printed copy of the page with you so that you can check your answers while there .
Please submit your logging task responses before posting your log.