Roche (Cabot Circus) EarthCache
Hidden : 12/24/2017
Difficulty:
1 out of 5
Terrain:
1 out of 5

Size: Size: other (other)

Join now to view geocache location details. It's free!

Watch

How Geocaching Works
Looking for a different adventure?

Please note Use of geocaching.com services is subject to the terms and conditions in our disclaimer.

Geocache Description:

A simple EarthCache that can act as a break from shopping!

Cabot Circus is a shopping centre in Bristol. Roche is the art installations that involve the fossils you see here; more info on that after the questions and earth science.

Questions first- as the description is quite sizeable and has many pictures:
To log this EarthCache, please send the answers to the following questions by email or message. Due to owning many EarthCaches I receive numerous emails per day so there is often a delay in replying, therefore feel free to log before awaiting a reply. Only answers that are drastically incorrect or photos that reveal answers will be deleted.

1) Describe the shape(s) and size(s) of the fossils here. Using the fossils picture below, tell me what fossil is most common in this wall?

2) Roughly what percentage of the entire Portland Stone wall is covered in fossils? What do you think this tells you about the conditions that the organisms lived in?

3) How does the presence of fossils PROVE that this Portland Stone is sedimentary, rather than igneous or metamorphic?

4) Post a photo of you/your GPSr at or near GZ, without showing the fossils. There is some nice decorated slate nearby which you could possibly pose at! As per the rules though, all photos are optional. Please note: I own many (15+) EarthCaches in many areas and therefore recieve a fair amount of email answers per day. I look through all answers sent and will reply, but it may take up to a few days depending on a backlog and general life.

The Earth Science:
Portland Stone
Portland Stone is a yellowish-sandy coloured sedimentary limestone that formed around what is now the Isle of Portland in Dorset. That particular location is famously known as the Jurassic coast, as the rocks there (including Portland Stone) formed during the Jurassic era (201 - 145 million years ago).

 Carbon dioxide (CO2) in seawater, when exposed to sunlight, is warmed up, and its ability to hold dissolved gases falls. As a result, the dissolved CO2 turns into a gas and enters the atmosphere. The loss of CO2 from the seawater allow calcium and bicarbonate ions within it to chemically bond into a calcium carbonate (CaCO3) precipitate, which is the the main mineral that makes up limestone. Portland Limestone is oolitic- in that it is made up of tiny rounded 'balls', called ooids/ooliths. They form from particles of sand and shell fragments being covered in layers of calcite and micrite and rolling around. Over time, ooliths lithified (became cemented together) to form Portland Limestone.
The fact that Portland Stone is made of many smaller fragments means it is a sedimentary rock type, rather than igneous or metamorphic. Fossils cannot exist in the other two rock types: igneous rocks are formed from molten volcanic rocks which solidify, and metamorphic rocks have been compressed under and pressure, heated/squashed/stretched, a process which fossils do not usually survive.

Fossil Formation:

A fossil is the preserved remains or trace of a dead organism. When an organism died millions of years ago, any soft material (skin, organs etc.) decayed, while hard material (teeth, bones, shells) did not and remained. Left untouched on the ground or sea bed, they were gradually covered over by sediment.
Portland Stone formed in marine conditions, so the fossils consist of hard shells which were covered up and compressed by the silt on the sea floor, leaving impressions in the newly formed sedimentary rock- fossils.
Below are some examples of the shells that created the fossils you will see in the stone.


These fossils are prevalent throughout the Portland Stone walls within Cabot Circus, not just limited to here. This GZ, however, is accessible from the pavement!

Use in Cabot Circus:

 The use of Portland Stone containing fossils is deliberate; Cabot Circus' architect wanted to create a shopping centre with a geological theme. Alongside the clever stone types used, Suzannah Herom designed many rooms of buildings noticeably jut out- these are meant to symbolise unpredictable tectonic plates passing each other.


More information about Roche and the materials used can be found at the waypointed plaque.

Additional Hints (Decrypt)

Dhrfgvba guerr fubhyq or rnfl vs lbh'ir ernq gur qrfpevcgvba!

Decryption Key

A|B|C|D|E|F|G|H|I|J|K|L|M
-------------------------
N|O|P|Q|R|S|T|U|V|W|X|Y|Z

(letter above equals below, and vice versa)


Advertising with Us