This concludes my attempt to "Set the Geological Scene" to what life was like in the Jurassic when the rocks that we see on the Dorset coast were deposited.
Well done to those, (quite possibly just an intrepid few of you), who have managed to read this far, and hopefully you might now have a bit of context to help understand the rocks that are described in Section B. I certainly enjoyed writing this, and would (I fear) be only too happy to discuss in more detail whilst we are out rowing together.
The key take-aways are that our area was : -
The diagram below is a highly stylised representation of how our part of Pangaea might have looked at the point where the North Atlantic had started to open up. The bit in red is the UK, and this is the area of Warm Seas in which the Jurassic rocks were formed. The bits in green are the mountains (formed from the collisions that occurred as the crustal plates pushed and jostled together to form the super-continent Pangaea) and which provided the source materials for the rocks as they are being eroded away.
- A shallow and expanding Warm Sea existing around 150 million years ago (pretty young in world terms)
- Being fed by sediment and nutrients from the eroding mountains of the super-continent Pangaea (which later split up to form the continents we know today)
- Different types of rocks were formed depending on the Rates of Sedimentation, Wave action and Water depth.
- These rocks were laid down over a period of 50 Million Years. This is a small percentage of the age of the earth but still and enormous length of time during which time mountains have been worn down, continents have moved and sea levels have risen and fallen multiple times.
- Subsequently these rocks have been Shifted around, Tilted and Fractured by movements in the crust leading to different rock units being assembled in different patterns against each other.
If all of this has left you confused, then you have my utmost sympathy! Most Geologists find themselves being confused much of the time, and scientific arguments between people are unfortunately quite common and often remain unresolved for long periods of time. But don't panic, Geology is a strange science where observable facts are in short supply. We only see a tiny percentage of the totality of rocks exposed and perhaps most crucially humans can't instinctively understand the passing of geological time. This last point means that the types of descriptions I have used above are definitely only a vague guide to the actual processes that might have been happening when the rocks were formed.
With Geology there has always been ample room for people to "Make things up for themselves" to cover the 99.9% of the facts that we just can't see as they are buried or have been eroded away. I might have been slightly guilty of a bit of this myself in the details in the sections above!
Alternatively, we can of course just enjoy the scenery without worrying too much over how it might have been created!
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