Playing with your eyes
This image captures a road cut near the village of Mollina in southern Spain. Your eyes should immediately notice that something has happened to the rocks here – they’re broken and moved.
If you’ve had a bit of geology, you might recognize this pattern as caused by normal faults. The rocks to the right have slid downwards along the cracks, creating a pattern where the same layers seem to repeat themselves.
However, take a more careful look at the layers on top of the cracks. There’s something fishy here. The simple assumption would be that these faults completely cut all the rock layers, and at the crack on the right, if you study the above layers carefully you can recognize that they’re offset as well and the same pattern repeats on both sides of the fault.
But, near the top of this cut, the crack on the left peters out. If you stare carefully at the layers, it’s possible some of them are offset, but it’s possible some of them are just bent at that location or that they’re continuous and just change thickness.
This is a cool geologic problem and one I can’t solve easily from the image; are the layers at the top of the section on the left offset or is there a change in thickness across the fault, as might occur if the sediments on top were being deposited while the fault is moving?
Anyone want to fund a trip to Spain so we can give you the answer?
Lulworth Cove, Dorset, England.
Lulworth Cove is an Alpine fold structure in Lower Cretaceous rocks outcropping on the Dorset Coast in Southern England.
The cove itself whilst being very striking to look at, also shows several geological and palaeontological features important to our understanding of the geological evolution of the area.
The almost circular shape of the cove is the result of both rock type and folding, and there are “bands” of rock of alternating resistance running parallel to the coast Line. These alternating rock types have been eroded by wind and wave processes to form the cove.
The area is also important economically with petroleum exploration of Oil sands close by. The Oil Sands here form the largest British Oil Field outside of the North Sea, and is the highest quality Oil found anywhere in Europe.
The site is a designated UNESCO world heritage site, and is therefore afforded all of the protection that status allows.
The sea cliffs here are easily eroded, and because of this collectable fossils are not numerous. Please leave hammers at home, and do not prise any fossils out of the cliff face. Collect only loose material at the bottom of the cliffs and leave any well preserved fossils where you find them so that others may enjoy them also.
Links For more information;
Photograph Ian West
Distorted columnar basalt.
Many of these formations formed during the natural cooling of basaltic lava resemble organ pipes, but sometimes they come out all wavy. This is due to pressures within the Earth, either while the lava is cooling or as a result of subsequent tectonic movements that distort the normal shape. A dyke (vertical shaped intrusion of magma) has cut through the columns, possibly feeding a later eruption from a now eroded vent that once overlaid the older cooled basalt (the dark grey line running from the centre to bottom right of the photo), and the fact that is has also been distorted implies that the distorting pressures happened after the first magma cooled.
Image credit: Frequent Traveller
Previous posts in this series:
Part 1: Intro and Stromer
Part 2: Taking good photos
Part 3: Backdrops and lighting …