Weathering and Sedimentary Rocks


Weathering is the process of breaking down large rocks into smaller pieces. There are three main types of weathering we will look at:

Biological Weathering

This is a form of weathering that is caused by plants and animals, where they break rocks into smaller pieces.

An example of this is when you see weeds growing in a pavement. The weed roots grow into the cracks of the rock, making the cracks deeper and breaking away smaller pieces of rock.

Weeds are able to grow out of pavements and the roots will find cracks, making them larger.

Chemical Weathering

Chemical weathering is the breakdown of rocks caused by chemical reactions, breaking down rocks into smaller pieces

The most common example of chemical weathering is rainwater eroding certain types of rocks. For example, rainwater can be slightly acidic, as it contains dissolved carbon dioxide (CO2). Minerals in certain rocks can react with the acidic rainwater, causing the rock to be weathered.

For example, the limestone statue below:

The small pieces of rock dissolved in the water are carried away.

Erosion is the process of carrying away weathered rock or other materials. Which can be carried by gravity water or wind.

Mechanical Weathering

Mechanical weathering is the breaking down of rocks through physical force. In this process, there is no change to the chemical nature of the rock when weathered mechanically.

Extreme hot and cold temperature are typically the cause by mechanical weathering. Another example is freeze thawing, which is when water seeps into cracks and freezes, it expands. This puts pressure on the cracks, causing breakdown of rocks into smaller pieces.

Another example is when water bashes into rocks and causes weathering.

Sedimentary Rocks

The three main types of rock are: sedimentary, igneous and metamorphic.

Sedimentary rocks are formed by joining many broken remains of other rocks together.

Some examples of sedimentary rocks are conglomerate, mudstone and limestone.

As bits of minerals settle into layers over thousands of years, the weight of water and the layers of sediment above press down and cement the minerals into sedimentary rock

How Sedimentary Rocks Form

Process of Erosion – Step 1 and 2

1. Large rocks breaking up into smaller pieces (sediment) – This process is weathering

2. The pieces of broken rock get transported when by wind, water, etc. – This process is transportation

3. The pieces then settle in layers at the bottom of the ocean – This is called deposition.

4. The weights sediments above and the water squashes the sediment together – This process is known as compaction.

5. Sedimentary rock is formed as the sediment layers stick together – This process is called cementation.

Here is the order of the whole process to form sedimentary rocks:

1) Weathering 2) Transportation 3) Deposition 4) Compaction 5) Cementation

This is what Sedimentary Rock might look like:

You can clearly see the layers of sediment, compacted and built up over time.

As the layers of sediment build up, fossils can be found in sedimentary rock. This is because dead organisms settle between the layers

Ammonite fossil