PLEASE BE AWARE THIS CACHE IS UNDERWATER FOR ABOUT 2 HOURS EITHER SIDE OF HIGH TIDE SO DO NOT ATTMEPT TO ACCESS THE LOCATION AT THIS TIME.
Below is a link for tide times for Cresswell for your use
https://www.tideschart.com/United-Kingdom/England/Northumberland/Cresswell/
In order to claim a find for this EarthCache you are required to visit the location given, gather some information and send me the answers to the questions below.
Please be aware that this cache is on the beach and you will need to cross a small stream but will not need to get your feet wet.
No climbing is required but please only attempt to get to this cache with good footwear (possibly bare feet) and some determination.
You are welcome to log your find and send your answers at the same time. I will read your answer and respond quickly to email and within a few days if you used the message system.
At this location you will find you are about 200m from the sand dunes and having crossed the beach and a small stream flowing down the beach you should be standing on a sandbank with rocky outcrops. The outcrops consist of a black rough, soft sandstone a red hard fine grained sandstone and a yellow very soft sandstone. The focus of this EarthCache is the latter yellow sandstone.
Look around and find a flat section of the yellow sandstone which may only be a few inches to a foot above the sand surface, there are several sections which protrude and form a flat but broken surface which you can easily stand on. This rock surface iw what you need to look at, it is called a tessellated surface.
Tessellation is a mathematical term which you may remember from GCSE or GCE days, it means a series of shapes which fit together leaving no gaps, in maths they would be identical shapes but in nature the identical aspect doesn't happen.
Tessellation in rock structures
A rock that comprises a Tessellated Pavement is usually siltstone that formed in the Permian era which was about 300 million years ago, by sediments that accumulated on a relatively low-lying area such as a slow flowing river delta system. The sediments settled over time and eventually got compacted and lithified or concreted to form the solid siltstone.
After the rock has formed they were fractured essentially by the movement of the Earth crust due to tectonic movement and this fracturing resulted in something called jointing. The jointing process itself is not incredibly uncommon but it only occurs in rock structures which have small impurities in the rock. The fractures occur along these weaker lines giving a structure to the rock which looks like squares, rectangles, triangles and other shapes making the tessellated effect.
The most common type of tessellated pavement consists of relatively flat rock surfaces, typically the tops of beds of sandstones and other sedimentary rocks, that are subdivided into either more or less regular rectangles or blocks approaching rectangles by well-developed systematic joint systems.
Four types of tessellated pavements are recognized:
1)tessellated pavements formed by jointing;
2)tessellated pavements formed by cooling contraction;
3)tessellations formed by mud cracking and lithification;
4)tessellated sandstone pavements of uncertain origin.
1) The most common type of tessellated pavement consists of relatively flat rock surfaces, (like we have here) typically the top of beds of sandstones, mudstones and other sedimentary rocks. They are subdivided into either more or less regular rectangles or blocks approaching rectangles by well-developed systematic orthogonal joint systems.
The surface of individual beds, are exposed by erosion and typically divided into either squares, rectangles, and less commonly triangles or other shapes, depending on the number and orientation of the joint sets that comprise the joint system.
This relatively flat surface of individual beds of sedimentary rocks are frequently altered by weathering along joints as to cause the bedrock along the joints to be either raised or recessed as the result of differential erosion. Because of this process some of the blocks can sheer off leaving an uneven surface like a stack of dominoes on a table.
This type of tessellated pavement is commonly observed along shorelines and on beaches where wave action has created relatively flat and extensive wave-cut platforms on the surrounding sand surface that expose jointed bedrock and keeps the surfaces of these platforms relatively clear of debris.
2) The second type of tessellated pavement consists of a bedrock surface that exhibits joints that form polygons that are typically regular in size, spacing, and junctions. Typically, these polygons represent the cross-sections of polygonal, typically hexagonal joints, called columnar jointing, that formed as the result of the cooling of basaltic lava. This type of surface can be seen at the Giant's Causeway in Northern Ireland.
3) The third type of tessellation is associated with the shrinkage and cracking of fine-grained, either mudstone or calcareous, sediments. They consist of polygonal cracking, often associated with individual 'plates' that tend to be concave upward, that characterizes the formation of mud-cracks in fine-grained sediments. Often, the outlines of the polygons formed by this type of cracking are preserved and accentuated by the infilling of the cracks with material of a different composition from that of either the mudstone or calcareous sediments in which the cracks form. The infilling of the cracks by sediments of a different character often preserved the polygonal pattern of the cracking where it can be exhumed by erosion as a patterned pavement after the sediment becomes lithified into a sedimentary rock.
4) The final type recognised is simply not one of the ones above but how it has formed is undetermined.
So to some questions.
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Please describe the tessellated pattern in the yellow sandstone pavement, include the size of the pavement, the structure of the pavement and the shape and evenness of the tessellation.
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Please tell me how you think these tessellation occurred after the formation of the sandstone, choose from the three descriptions above and give reasons why you chose your answer or why you eliminated the other two.
You are welcome to log your find and send your answers at the same time. I will read your answer and respond quickly to email and within a few days if you used the message system.
PLEASE DO NOT ATTEMPT THIS CACHE WHEN THE SANDBANK IS UNDERWATER.
Thanks for attempting this cache, I hope you enjoyed the location and please stay safe.
treboR