WEATHERING AND FOSSILS-I

1. WEATHERING AND FOSSILS-I BY: MS. SAWERA FARRUKH

2. Contents • Rocks • Sedimentary, Igneous, Metamorphic • Rock Cycle • Transportation, Deposition, Sedimentation • Weathering • Physical, Chemical, Biological • Fossil formation and Quarrying

3. What are rocks? • Rocks are made ofgrainsof amineral(which is a chemical compound). • The grains that fit together in a rock can be of different colours,shapes andsizes. Granite has interlocking grains Sandstone has rounded grains

4. Rocks are of different textures • Crystalline Texture Some types of rock have interlocking grainsthat fit tightly together. • Fragmental Texture Other types of rock have rounded grains that do not fit together neatly. • Crystalline Texture • Fragmental Texture

5. Types of rocks There are three main types of rock: • Sedimentary • Igneous • Metamorphic • Sandstone has layers Granite has large crystals • Marble has wavy patterns

6. Sedimentary rocks

7. Sedimentary rocks • A river carries, or transports, pieces of broken rock as it flows along. • When the river reaches a lake or the sea, its load of transported rocks settles to the bottom. We say that the rocks are deposited. • The deposited rocks build up in layers, called sediments. This process is called sedimentation.

8. Sedimentary rocks • The weight of the sediments on top squashes the sediments at the bottom. This is called compaction. • The water is squeezed out from between the pieces of rock and crystals of different salts form. • The crystals form a sort of glue that sticks or cements the pieces of rock together. This process is called cementation.

9. Sedimentary rocks • Thedifferent processes occurring in order to eventually make a sedimentary rock are: sedimentation → compaction → cementation • Sedimentary rocks contain rounded grains in layers which may take millions of years to form. • Sedimentary rocks may contain fossils of animals and plants trapped in the sediments as the rock was formed.

10. Examples of Sedimentary rocks chalk limestone sandstone sandstone shale

11. Igneous rocks • The inside of the Earth is hot enough to melt rocks. The molten rock is called magma. When the magma cools and solidifies, igneous rock forms. • They contain randomly arranged interlocking crystals,whose size depends on how quickly the molten magma solidified. The more slowly the magma cools, the bigger the crystals.

12. Igneous rocks • These rocks do not contain any fossils, because any fossils in the original rock will have melted when the magma formed. basalt

13. Igneous rocks • Magma above the Earth’s surface cools quickly, so only small crystals are formed as the magma solidifies. Extrusive igneous rocks like pumice, obsidian and basalt are formed from eruptions of magma from a volcano. • Magma below the Earth’s surface cools slowly, so there is time for large crystals to grow as the magma solidifies. Intrusive igneous rockslike granite and gabbro are formed from magma underground.

14. Examples of Igneous rocks granite pumice obsidian gabbro

15. Metamorphic rocks

16. Metamorphic rocks • Earth movements can cause rocks to be deeplyburiedorsqueezed. As a result, the rocks areheatedand put under greatpressure. • They do not melt, but the mineralsthey contain are changed chemically, forming metamorphic rocks. • These rocks can be formed from any other type of rock - sedimentary or igneous.

17. Metamorphic rocks • They are usually denser and harder than sedimentary rocks. • Sometimes, they are formed when rocks are close to molten magma, and so get heated up. • When a metamorphic rock is formed under pressure, its crystals become arranged in layers. Slate, which is formed from shale, is like this.

18. Metamorphic rocks • They sometimes show distortions caused by the movements that led to their formation. This may give rise to wavyorzig-zagpatterns within the rock.Marble, which is formed from limestone, has these patterns in it. • Metamorphic rocks sometimes contain fossils if they were formed from a sedimentary rock, but the fossils are usually squashed out of shape.

19. Examples of Metamorphic rocks marble slate

20. The Rock Cycle Weathering breaks down rocks. extrusive igneous rocks:basalt Rocks rise to the surface by uplift and erosion. transportation and deposition Rocks rise to the surface by uplift and erosion. sea Magma rises to the surface where it cools rapidly. Magma rises to the surface where it cools rapidly. intrusive igneous rocks:granite sedimentary rocks mudstone high pressure and temperature slow solidification metamorphic rocks slate and marble magma melt

21. The Rock Cycle • The Earth's rocks do not stay the same forever. They are continually changing because of weatheringand large earth movements. • The rocks are gradually recycled over millions of years. For example sedimentary rocks can be changed into metamorphic rocks, and these can be weathered and the pieces transportedaway. These pieces could be deposited in lakes or seas and eventually form new sedimentary rock. • Many routesthrough the rock cycle are possible.

22. From Weathering to Sedimentation

23. From Weathering to Sedimentation • Transportation • It is the movement of rock fragments one place to another. • The rock fragments can be transported in different ways: by rivers by strong winds by glaciers

24. From Weathering to Sedimentation • Deposition • It occurs when pieces of weathered rock sink to the bottom of the river bed or sea forming sediment. • Dead creatures can get trapped in the sediment and form fossils. • Sedimentation • It creates layers of rock particles by compaction and cementation.

25. From Weathering to Sedimentation • Rock Formation and Uplift • It is the forming of all the three types of rocks. • Sometimes areas of rock can move slowly upwards, pushed up by pressure of the rocks forming underneath. This is calleduplift. • Weathering • It is the wearing away of rocks. • Erosion • It is the movement of the broken pieces away from the site of weathering by wind and water.