Leeds, a city sitting astride the River Aire, and a place of many attractions. When you think of Leeds I bet that you don't think of fossils or traces of the past, but if you take your time to look, there is evidence of geology all around. What you need to do is look down, at the floor, or rather the pavement. So it is time to use your EarthCache skills to discover and learn.
The cache co-ordinates will take you to the pavement on Armouries Way, which is an urban area, so please remember to be polite and respect others when looking. If you are in a wheelchair, the site is very easily accessible.
The aim of this two stage EarthCache is to look for fossils.
A fossil is trace or remains of a plant, animal or other organisms. However, there is more to fossilization than just bones, or remains of a T Rex.
There are many EarthCaches which can teach you about the whole process of fossilization, what we are concerned with are ichnofossils. The simpler way to understand an ichnofossil are that there are traces of a biological activity, in the form of a geological record. They are also known as trace fossils, and thus show a trace of an impression made on the substrate, and can be root cavities, feeding marks, footprints, and remains of excretia, such as fossilized droppings. Geology can be difficult to understand, so below are some easy ways to describe types of trace fossils.
1. Cochlichnus. These are caused by locomotion (i.e movement), and can be a curving or a meandering smooth horizontal trace.
2. Scolicia. These are caused by the locomotion (i.e movement) or feeding traces made by animals on or under the seadbed. They appear as horizontal bilateral, symetrical meandering trails. Imagine the imprint a bike tyre makes, you have two symetrical borders.
3. Lockeia. These have the shape similar to an almond, and in technical terms could be described as ovoid. These are the trace of a bivalve resting place. A bivalve is a type of mollusc, such as a muscle.
At Stage One, please complete the following tasks:
(a) Looking at the pavement, which of the above ichnofossils can you see, there is only one type?
(b) Which direction (i.e north , south, east or west) is the paving slab point towards?
(c) Please explain your rationale for your answer to question (a).
Onwards to Stage Two.
The paving slabs that you are standing on are made of sandstone, which was laid down in the carboniferous era, which was a time when the north of England was covered by a vast river delta, similar to the Amazon or Mississipi deltas that we have today. Large amounts of sediment were carried downstream and deposited, which over time became sandstone. Included in the material that we washed downstream was plant remains.
Plant fossils you might find in Carboniferous rocks :
Calamites.
Calamites were a genus of extinct tree-like horsetails to which the modern horsetails are closely related. These plants were medium-sized trees, growing to heights of more than 30 meters (100 feet). The trunks of Calamites had a distinctive segmented, bamboo like appearance and vertical ribbing. The branches, leaves and cones were all borne in whorls. The leaves were needle-shaped, with up to 25 per whorl.
Lepidodendron
The Lepidodendron tree, also known as the scale tree, was an extinct primitive plant related to the club mosses which sometimes reached heights of over 30 metres. They thrived during the Carboniferous Period before going extinct. They had tall, thick trunks that rarely branched and were topped with a crown of branches bearing clusters of leaves . These leaves were long and narrow, similar to large blades of grass, and were spirally-arranged. The closely packed diamond-shaped leaf scars left on the trunk and stems as the plant grew provide some of the most interesting and common fossils in Carboniferous deposits.
Ferns
Ferns are still about today, and indeed you may see some about in summer.
Fossil branches
Sometimes, it is not possible to identify the plant remains, and commonly remains of branches can be found, these may be short, long, thick or wide, and tend to be striated (lined), a bit like a modern plank of wood
At Stage Two, please complete the following tasks:
(d) Using the above information, what type of plant fossil is there here?
(e) What is your rationale for this decision?
(f) How long and wide is the plant fossil?
This being an EarthCache, in order to log it, I ask that you answer the above tasks. Please send them 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. It is not meant to be difficult to do.