🚨You are best walking to the EarthCache location. The road from Helwith Bridge, is often busy with quarry waggons🚨.
In geology people tend to look for the larger features, as they are easier to see, though sometimes smaller things can catch the eye, and then lead to interest and understanding. In some locations, looking at the rocks which make up the anatomy of a wall can give interest, and also learning about geology. The below photograph shows a wall in nearby Little Stainforth, which demonstrates the geology of the local area.
(Photograph: Hillgorillas' wall).
We are here to look at an aspect of geology on a macro level. You would benefit from having a camera📷 or mobile phone🤳 that can take an image on a macro level, or a magnifying glass🔎. The below photograph shows where to look. DO NOT MOVE ANY STONES.
The geology of the area.
The wall is made up of greywacke, which was deposited during the Silurian period, which was 445 to 420 millions of years ago. Geologically, its story starts in an ancient ocean known as the Iapteus Ocean. Sediment in the form of sand and silt was laid down on the ocean floor, then turbulent movement of the sea bed occured. Over time sediment built up , and eventually rock was formed. However this is not the end of the story. The Iapteus Ocean dissapeared eventually, and the sedimentary layers were uplifted and folded due to massive tectonic forces. The rock was also subjected to metamorphism, which is where pressure and heat alter the structure of the rock.
So, what are we here to see?
We are here to look at an example of soft sediment deformation. Soft sediment deformation, is the distortion of sediments, which happens rapidly during or shortly after deposition, and before significant transformation into rock, which is known as diagenesis.
Lets first look at sedimentation.
Sedimentary rocks are types of rock that are formed by the deposition and subsequent cementation of that material at the earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles to settle in place. The particles that form a sedimentary rock by accumulating are called sediment. Before being deposited, the sediment was formed by weathering and erosion from the source area, and then transported to the place of deposition by water, wind, ice, mass movement or glaciers. Sedimentation may also occur as minerals precipitate from water solution or shells of aquatic creatures settle out of suspension.
The proess of the sediment becoming rock is known as lithification. This happens as the sediment compacts and cements together , either at the time of deposition or at a later date. The process can happen due to pressure, and the expulsion of fluids in the sediment.
So where does soft sediment deformation structures fit in this process?
Well, these develop either at the deposition of the sediment or soon after. For these to develop, the sediment will have been almost like a fluid, before consolidation occured, and thus solidification of the sediment. They tend to occur in marine environments, such as deep water basins, rivers, river deltas and shallow marine locations, which are affected by storm conditions. In this locations, there is a high rate if sediment deposition, which means that initiatilly the sediment is loosely packed.
Soft sediment deformation and Greywacke.
Soft sedimentation deformation can occur in greywacke due to the original environment it originates from. A deep water environment can produce a number of events which can lead to soft sediment deformation.
Turbidity Currents.
This is when an amount of sediment is rapidly moved down a slope on the sea bed, often dislodging and impacting into the sediment below it.
Seismic Activity.
Earthquakes can cause sediment to become liquefied, basically more like fluid, which can cause features like soft sediment deformation to occur.
Slope Failure.
There can be unstable slopes in a marine environment, if that slope fails, then sediment will move downwards. In the process, the sedimentary layers willl become deformed.
Fluidization.
Changes of the deep sea pressure, and also sudden rushes of a water current, can cause sediment to basically become fluid. Imagine a cake, changing to jelly, then to fluid. Sedimentary layers become deformed as a result.
Reverse Density.
This occurs when heavier sediment settles on top of a lighter sediment. It can push into it, and also through it.
Types of soft sediment deformation.
Clastic Dykes.
Clastic dykes occur when there is a rapid injection of fluid material into the sediment, these can be seen at times to have sediment and clastic material in them, such as gravel. They can present as vertical bodies cutting through sediment.
Disturbed Laminitis.
If you look at the lower aspect of this picture, you will see that the sedimentary beds, are disturbed, this is Disturbed Laminitis.
Convolute Bedding.
Convolute bedding tends to have peaks and troughs in its appearance.
Dish Structures.
These are dish shaped structures, which are causes by the removal of water (dewatering) from the sediment.
Flame Structures.
These are projections, which look like waves or flames (hence the name). In this case, the weight of the overlying sediment, forces the underlying to push upwards, so that one gets projections into the layer above it.
At times, though the flames can present as above.
Fluid-Escape Features.
This occurs when a fluid filled sediment is placed under pressure, and basically the fluid is squeezed out through sediment.
Load Structures.
These occur when heavier sediment scours the sediment filled sea floor, causing gauge marks, and also when heavier sediment settles onto softer sediment below it.
Slumps.
This occurs when heavier sediment slumps into softer sediment below it.
This being an EarthCache, in order to log it, I ask that you answer some questions. Please send them 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. Using the above information, what type of soft sediment deformation structure is here.
2. Please explain in your own words, what type of environment that this rock originates from, and why soft sediment deformation structures can form in thus environment.