Last week we looked at Ordovician Limestone, including some of the fossils that can be found in it. In fact, limestone in general is fantastic for fossils, and some absolutely amazing specimens have been found in it. This is often because of two reasons. The first is the limestone’s make up – calcium carbonate. It is a very fine mineral sediment, while also being very strong, which allows it to preserve creatures with a brilliant level of preservation. The second is the environment where the limestone formed. Most of the UK’s limestone is a marine deposit, having formed underwater where there is a large presence of very preservable creatures. And some limestone, such as chalk, is even entirely made up of fossils, as we learnt a few weeks back.
One of the best limestone formations to find fossils in is the Jurassic Lias. This is a banded rock formation, made up of alternating layers of limestone and mudstone shale. This formation is found all over the world and is particularly prevalent in the UK. Some of the good areas to see it include the North Devon Coast, South Wales, Yorkshire Coast, Scotland, and of course, the famous Jurassic Coast in Dorset.
Many of the best and most famous fossils ever found in the UK come from this Jurassic Lias. These include the Ichthyosaur and dinosaur fossils found by Mary Anning from Lyme Regis, basically sparking the science of Palaeontology (the study of fossils). Others such as ammonites, belemnites, bivalve shells, and crinoids are also very common.
The presence of fossils also means one very important thing as well. All the limestone formations had to form quickly, otherwise no fossils would be preserved in the rock. They would simply be destroyed long before they were able to become fossils, if the limestone had formed very slowly. Fossilisation has nothing to do with time, but everything to do with the right process!