Rocks from the Carboniferous, Permian and Triassic periods, underly the Merseyside area, these are primarily sandstones and mudstones. Though the area was later covered by glacial alluvenium during the Quartenary Period. There are many EarthCaches which cover these geological periods, and also sandstones and mudstones, what we are here to see are some fossils.
This is meant to be an EarthCache which is accesible to all, indeed the location is a car park, but you will need to get out of the car and look at the line of the large boulders at the given co-ordinates. You will be expected to use some of your senses here.
First the geology of the boulders
The boulders boulders are a type of rock known as limestone. Limestone is not local to the Wirral area, and most likely the boulders have come from North Wales, Lancashire or Yorkshire, where in places limestone is the predominant bedrock.
Limestone
Limestone is a sedimentary rock, these means it has been laid down in layers of sediment. In the case of limestone, the sediment is the remains of ancient sea creatures, such as shells and corals, that have broken down to form small grains. Most limestone in the United Kingdon was formed in a tropical environment when there were shallow seas, and the small grains gathered on the bottom of those shallow seas to forms layers of sediment, these then compacted over time to form rock. Limestone tends to be off white and grey in colour, though can be other colours such as black.
So what is a fossil?
Fossils are the preserved remains or traces of animals, plants, and other organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous (fossil-containing) rock formations and sedimentary layers (Strata) is known as the fossil record.
The process of fossilization varies according to tissue type and external conditions.
(1) Permineralization
This is a process of fossilization that occurs when an organism is buried. The empty spaces within an organism (spaces filled with liquid or gas during life) become filled with mineral-rich groundwater. Minerals precipitate from the groundwater, occupying the empty spaces. This process can occur in very small spaces, such as within the cell wall of a plant cell. Small scale permineralization can produce very detailed fossils. For permineralization to occur, the organism must become covered by sediment soon after death or soon after the initial decay process. The degree to which the remains are decayed when covered determines the later details of the fossil. Some fossils consist only of skeletal remains or teeth; other fossils contain traces of skin, feathers or even soft tissues.
(2) Casts and Molds
In some cases the original remains of the organism completely dissolve or are otherwise destroyed. The remaining organism-shaped hole in the rock is called an external mold. If this hole is later filled with other minerals, it is a cast. An endocast or internal mold is formed when sediments or minerals fill the internal cavity of an organism, such as the inside of a bivalve or snail or the hollow of a skull.
(3) Authigenic mineralisation
This is a special form of cast and mold formation. If the chemistry is right, the organism (or fragment of organism) can act as a nucleus for the precipitation of minerals such as siderite, resulting in a nodule forming around it. If this happens rapidly before significant decay to the organic tissue, very fine three-dimensional morphological detail can be preserved.
(4) Replacement and recrystallization
Replacement occurs when the shell, bone or other tissue is replaced with another mineral. In some cases mineral replacement of the original shell occurs so gradually and at such fine scales that microstructural features are preserved despite the total loss of original material. A shell is said to be recrystallized when the original skeletal compounds are still present but in a different crystal form.
(5) Adpression (compression-impression)
Compression fossils such as those of fossil ferns, are the result of chemical reduction of the complex organic molecules composing the organism's tissues. In this case the fossil consists of original material, albeit in a geochemically altered state. This chemical change is an expression of diagenesis. Often what remains is known as a phytoleim, in which case the fossil is known as a compression. Often, however, the phytoleim is lost and all that remains is an impression of the organism in the rock—an impression fossil.
Lets look at some fossils :
CRINOIDS
Crinoids live in the sea. Their name is derived from krinoeides (Greek) which means 'like a lily'. They are also called sea lilies or feather-stars.Crinoids have been around for a long time, about 480 million years ago. There are still crinoids alive today. A crinoid has three parts, a stem which it uses to stick to the sea floor, a calyx or body, and its arms which it uses to catch its food. Usually it's the stem which is found as a fossil.
CORALS
Corals are known as zooids, which when many combine together, reefs are formed. Many corals have a hard exoskeleton made of calcium carbonate. It is this exoskeleton that is usually fossilised. When the coral dies, the skeleton can be broken down to form limestone.
BIVAVLES
Clams, oysters and mussels are all examples of bivalves. The fossils here tend to be either bits of shells or whole shells.
This being an EarthCache, in order to log it, I ask that you complete the below tasks. Please send the answers 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) Walk along the line of limestone boulders, are they all the same? If not how do they differ?
(2) Please desribe the feel of the limestone.
(3) Closely looking at all the boulders, please tell me using the above information what type of fossils there are here.