URBAN EARTH - Ancient Seabeds Exposed EarthCache

Introduction

I love finding fossils and spotting and studying them has more than once resulted in a short walk taking much longer to complete than was originally planned .

Shopping on the other hand is one of my least favourite pastimes but the materials used to construct the various emporia frequently include stuff of geological interest in a higher concentration than one might see out on a regular walk - fossils included - as I discovered on a recent trip to Blackburn .

What I discovered there, you see, was yards and yards of different types of limestone, or at least I took it to be of different types because each was a different colour and each contained a different collection of fossils - hundreds of them! .

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The floor inside the bus terminus is made up entirely of one type of limestone, lets call that Type A. Outside the bus terminus, between the bus terminus and the shopping centre, the extensive paved concourse is made up of two types of limestone - one which is darker and one which is lighter. We'll refer to the darker one as Type B and the lighter one as Type C.

1. Which fossil types can you see in limestone Type A?
   
   
2. Which fossil types can you see in limestone Type B?
   
   
3. Which fossil types can you see in limestone Type C?
   
   
4. Which of the three types of limestone has the highest concentration of fossils?
   
   
5. Limestone Type A is at least how many million years old? How do you know this?
   
   
6. Optional task: feel free to add any photographs of your visit that do not show the specific features from the logging tasks - no spoilers please. In the interests of allowing everyone to experience the EarthCache fully for themselves obvious spoiler photographs will be deleted.
   
   

Background

At the given coordinates you will find lots of paving made from three different types of limestone.

Outside the newly constructed bus terminus the paving is made from two different types of limestone. Enter the bus terminus through the sliding glass doors and you will find that its floor is made entirely from a third type of limestone.

You can tell these three different types of limestone apart from each other quite easily because each of them has a different colouration and to some degree a different texture, and each of them contains a different collection of fossilised sea creatures which are plainly visible and easily recognisable.

Corals

Corals might look similar to forms of plant life but they are actually animals - specifically a type of marine invertebrate i.e. an animal which lives in the sea and does not have a skeleton made of bone. Other marine invertebrates include sponges, lobsters, octopus and crabs.

Each individual coral organism is known as a polyp. A polyp is typically a tube-like structure only a few millimetres in diameter and a few centimetres in length. At one end it has a mouth surrounded by tentacles which trap food particles floating in the sea water.

Although some coral species are solitary i.e. remain as a single polyp for life (and there are a few examples to be found around this site if you look hard), most live in large colonies. A single coral polyp attaches itself to the sea floor and then divides or buds into thousands of genetically identical clones. This group of clones is called a colony. Each clone removes calcium carbonate from the sea water to create a skeleton of calcite or aragonite which forms the hard parts of what, over many generations, becomes a coral reef.

Brachiopods

Brachiopods are marine invertebrates with soft bodies surrounded by a pair of hard shells made mostly of minerals containing calcium carbonate extracted from the sea water.

During the Paleozoic era, roughly 500-250 Mya (Million years ago), brachiopods ruled the sea. They were the most common and most diverse organisms around, each clinging to the seafloor with a muscular foot in such large numbers that, much like corals, they accumulated to form reefs. There are some 30,000 fossil brachiopod species known, but only around 385 are alive today.

If you're lucky, brachiopod fossils can be found largely intact so that the full shape of the shell can be appreciated but, when found in cut slabs as they are here, often the view of the shell that you'll see is a section sliced through the shell, a shape a bit like a letter O or a letter C.

Ammonites (Cephalopod)

Ammonites are extinct invertebrates... distant relatives of the nautilus, squid, cuttlefish and octopus. Ammonites first appeared during the Triassic Period around 240 Mya. They became especially abundant and widespread in the seas of the Jurassic and Cretaceous periods, 175 to 65 Mya.

Ammonites were soft bodied and lived inside their hard, calciferous shell and so it is the easily recognisable chambered shell that is found as an ammonite fossil.

Belemnites (Cephalopod)

Belemnitida (or belemnites) is an extinct order of cephalopods which existed during the Mesozoic era, from the Hettangian age of the Lower Jurassic to the Maastrichtian age of the Upper Cretaceous, so from around 200 Mya to 65 Mya.

Whereas ammonites were hard on the outside and soft on the inside, the hard, calciferous parts of the belemnite were contained inside the soft flesh of its body and thus, with very few exceptions, these smaller internal body parts are all that survive as fossils. All that typically survives of the belemnite in fossilised form is the the bullet-shaped rostrum or guard from its rear end.