Ad1a Cretaceous Period – Smile Trail

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I have enjoyed visiting many places worldwide seeing incredible geographical landscapes and features. Whilst visiting these amazing places, I have developed my knowledge of the place whilst having the bonus of solving an EarthCache. This has inspired me to place my first EarthCache here, near home. Thanks to everyone who has spent their time researching and placing the EarthCaches around the world.

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As you walk north, along the footpath towards the EarthCache, (from Ad1) you should be able to see a cliff of Chalk slightly to your right.

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This chalk cliff is part of the Yorkshire Wolds Chalk Formation. This formation runs in a crescent shape from the Humber Estuary (near to the Humber Bridge) to the East Coast Cliffs between Bridlington and Scarborough.

The Yorkshire Wolds Chalk Formation continues south into the Lincolnshire Wolds. The Humber Estuary carved through the once single strip of high land, creating two areas of high, gently rolling landscapes: the Yorkshire Wolds and the Lincolnshire Wolds.

The Humber Bridge is built on the stable rock dividing both areas.

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When was Chalk formed?

Chalk formed during the Late Cretaceous Epoch, approximately 65-100 million years (Ma) ago.  During the Late Cretaceous, significant changes occurred as the land moved and the sea level rose (to their highest in the last 600 Ma). This resulted in the extinction of dinosaurs and many of the Chalk-forming calcareous nannoplankton towards the end of the Epoch. This is known as the Creaceous-Paleogene mass extinction or the K-T extinction event at approximately 65Ma.

How was Chalk formed?

The Chalk rock that you see today was formed by coccoliths (submicroscopic calcareous nannoplankton). The skeletal remains of the coccoliths sank deep down to the ocean floor at depths of about 100-500m. This is where the Chalk rock was formed over millions of years of build up of coccoliths through heat and pressure. Evidence of these coccoliths can be seen today embedded within the rock as fossils.

What is Chalk?

Organic Sedimentary rock:  Created by the deposition and the binding of organic particles on the ocean floor.

Limestone: Composed primarily of Calcium Carbonate CaCO³.

Soft & No Malleability: Chalk can crumble at a certain pressure hence why chalk has been used on blackboards for centuries. Chalk can also be eroded by the sea but is more resident to weathering in comparison to clay. For example, the boulder clay Holderness Coast is eroding on average 2m/year whereas the Chalk cliffs at Flamborough Head is eroding at about 2cm/year.

Porous & Permeable: Chalk can hold large volumes of water in the spaces in the rock creating ‘dry valleys’ in the Wolds.

White colour: Chalk is formed from colourless skeletons of the coccoliths. Due to the very high sea levels experienced at the time the Chalk was formed, very little of the chalk was exposed above sea level to other sediments and impurities (e.g. clays from the land) that would give them colouration.  

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Sedimentary Rocks

Sedimentary Rocks are Sediment grains from rocks or pieces of dead organisms, deposited from rivers, the sea, wind or ice. Over time they become cemented and compacted together to form rock. They build up in layers called ‘bands’ or ‘strata’ and can contain fossils

The chalk cliff is a sedimentary rock. Other examples of sedimentary rocks are:-

Is made largely of calcium carbonate, which is usually formed from remains of living organisms. When Limestone is exposed to extreme heat and pressure over many years, it forms the metamorphic rock marble. Chalk is a form of limestone.

Is one of the most common types of Sedimentary Rocks and is a rock which has sand or quartz grains, cemented together, usually red, yellow, or brown in colour. A medium grained rock which is rough

...... Greywacke :..... A type of Sandstone. A rock which is hard, durable and dull in colour with different sized grains of quartz, feldspar and small rock fragments in a clay rich matrix. A fine grained rock, which feels rough.

.......Mudstone: ..... Is a fine grained, flaky, dark sedimentary rock whose original constituent were clays and muds – When mudstone is exposed to extreme heat and pressure over many years forms the metamorphic rock shale and slate

Is a form of mineral quartz (chert). When looking at chalk you can often find flint in the nodules of the sedimentary rock. Flint is hard and tough

Logging requirements:

In accordance with the EarthCache guidelines this is how to log the cache: Send your answers to me via the "Message this owner" link under the cache name at the top of the page or via email. After the answers are sent you can log your find straight away, no need to wait for an answer. If there is something wrong with the answers or I think you haven't actually visited, I will contact you. Enjoy your visit.

Tasks:

1)  Estimate the height of the Chalk cliff as you walk north towards the EarthCache.

2)  When and why did the Chalk stop forming?

3)  What is the Chalk made of?

4) As you look at the Chalk cliff FROM THE FOOTPATH, you should be able to see layers (‘bands’ or ‘strata’) which were built up gradually over millions of years. How many layers can you see on the most exposed area?

5)  As you walk from Ad1 Big Beak GC81TMC ^* along the footpath to the EarthCache  you pass a large manmade rock next to the footpath :-

a) How long is this rock? Measure with your footsteps.

b) What shoe size did you use to measure the rock with? Dinosaurs feet where much longer (Tyrannosaurus rex foot length was approx. 1m).

c)  Can you describe the characteristics of the rock? E.g. Is there any chalk visible?  Is it smooth or bumpy?

d) Name a type of sedimentary rock found here which is not chalk, but could be found on the chalk cliff. Describe the texture and colour.

Name of Earthcache.     GC Code.     Your name(s).     Number of people in group

Answers 1, 2, 3, 4, 5a, 5b, 5c, 5d