I have heard many a person saying that they live in a city, and will never see any fossils, or that they cannot physically get to fossil sites in the Dales as they are not able. Well, no need to worry, there is plenty to see in the city of Leeds itself. This EarthCache is suitable for the disabled, those with strollers and children. It is meant to be interesting and educational. Its is an easy walk from the railway station, and bus station.
So, what are we here to see. Well the coords should take you to the front of Leeds Civic Hall. The Hall, and the paving around it, is made from limestone. There are many other EarthCaches which describe limestone, but basically it is a sedimentary rock, which is formed from the accumulation of the shells of sea creatures in a shallow tropical sea. That sea had a variety of sea creatures and organisms with in, some of whcih can be seen in fossil form in other EarthCaches in the city. We are here to look at a specific feature of life in that shallow tropical sea - a patch reef, or rather the fossil evidence of part of a patch reef. I say part, as in reality patch reefs can be very large.
So what is a Patch Reef?
Patch reefs are located behind the main reef flat or barrier reef and are typically located in shallow waters of 10-20 feet in depth. They are small and isolated coral skeleton islands that form a circular or oval shape. The outer edge of each patch reef is completely surrounded by sand that extends to meet deeper sea grass meadows. This sandy area is formed by the distance that herbivorous fish feel is within safe foraging range from the patch reef. Patch reefs are highly variable in both size and development and contain species that are adapted to living on the open reef. There is evidence of small patch reefs formed by oysters, known as Oyster Patch Reefs, which occured at the location of what are known as hydrocarbon seeps. At these hydrocarbon seeps, gases such as methane and sulphur were realised, and a higher water temperature occured, which was conducive to marine organisms such as oysters living together, and thus forming a patch reef. Some patch reefs form when a boulder sticks out of the sea floor and it gets colonised with sea life such as oysters and corals.
So what are we looking for - what evidence on the ground?
The paving slaps are made of limestone slabs. The patch reefs would have originally been a 3 dimensional structure, but due to the work of the mason, we only get to see a one dimensional evidence of the patch reef on the paving slabs. Imagine a gathering of oyster shells and corals all together, in a mass. To help you see what you are looking for, there is a picture below.
So, you are looking for a mass like you can see in the above picture.
So its time to look at what is below your feet and do some learning.
This is the area of the EarthCache.
1. Please look for evidence of patch reefs on the flat area, not the steps, which shape of paving slab has them - the square or rectangular?
2. How many of the above identified slabs have specific areas of patch reefs.
3. Please tell which of the above slabs has the largest concentration of patch reef?
4. Pleae describe the part of the patch reef that is here, in terms of size, colour, feel and shape.
This is not meant to be a difficult EarthCache, the idea is to show you this element of geology, so you can learn from the experience, and hopefully if you spot another in the future, will know what it is. In order to show that that you have visited the EarthCache location and learnt from the experience, I ask that you answer the above questions. 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.