Sedimentary Rocks

1. Sedimentary Rocks

2. Land sedimentary environments • Mountains – Formed on bedrock. Steep slopes allow sediment to travel far. • Desert – wind picks us fine particles • Glaciers – snow compacts to ice and the ice moves sediment below it. • Beach – stretches of coastline where sediments has accumulated.

3. Clasts and weathering • Clasts – pieces of rock • 2 types of weathering • Physical – breaking apart of rocks that are exposed to the environment. • 4 ways • Near-Surface Fracturing – Processes near the surface cause rocks to fracture

4. Physical weathering cont’d • Frost and Mineral Wedging – Rocks are pried apart when water freezes • Thermal Expansion – Heating during the day may cause rocks to break • Biological Activity – Roots can grow into fractures

5. Making Sediment: Physical Weathering Fracturing Roots and other biologic activity Frost and mineral wedging

6. Chemical Weathering • Minerals are broken down causing new minerals to form. • 4 processes • Dissolution – some minerals are dissolved in water • Oxidation – some minerals react with oxygen to form oxide minerals

7. Chemical Weathering • Hydrolysis – Silicate minerals react with water, the hydrogen ions in the water react with the minerals • Biological reactions – decaying plants produce acids, some bacteria consume rocks.

8. Making Sediment: Chemical Weathering Hydrolysis Oxidation Biological reactions

9. What are the characteristics of Clastic Sediments? • Clastic sediments are classified in 3 ways: • Size of clasts • Boulders, cobbles and pebbles • Sand • Fine particles

10. Observe the range of clast size (sorting) in each photograph Moderately sorted Poorly sorted 07.04.a Well sorted

11. Characteristics of Clastic Sediment cont’d • Shape of Clasts • Angular, rounded, partially rounded • Amount of Sorting • Size and range of clasts • Poorly to well sorted (poorly has wide range)

12. Observe the shape of these clasts Partially rounded Angular 07.04.a Rounded

13. Controls on Size, Shape, and Sorting Farther from source means rounder and smaller Steepness of slope Strength of current Agent of transport 07.04.b

14. Sedimentary Rock Formation • Clastic Sedimentary rocks form 2 ways • Compaction- increased pressure from being buried beneath sediment forces clasts together. • Compaction forces out excess water, sediments lose up to 40% of their volume.

15. Formation of Sedimentary Rocks • Cementation- after sediment is compacted open pores between sediment collects water containing dissolved minerals. • As water evaporates minerals left behind act as a cement holding the clasts together.

16. How Clastic Sediment Becomes Rock Compaction of sand grains Compaction of clay particles Cementation 07.05.a

17. Types of Cement • Rocks are held together by 3 types of “cement” • Calcite- CaCO3 • Moderate hold • Silica- SiO2 • Strong hold • Iron-oxide Minerals- ex. hematite • Come out of water and give mineral a reddish-color

18. Common Clastic Sedimentary Rocks Conglomerate Breccia 07.05.b Sandstone Shale

19. Nonclastic Rocks • Form when chemicals dissolved in water, precipitate. (when water evaporates) • Also, can be biochemical • Extracted by an organism and reformed into a sedimentary rock

20. Rocks Formed by Chemical Reactions Setting Rock Salt Setting Travertine (limestone) 07.06.a

21. Rocks Formed by Organisms 07.06.a Setting Limestone with fossils Setting Coal

22. Other Nonclastic Sedimentary Rocks Gypsum Chalk Dolostone Chert 07.06.b

23. Difference between Clastic and Nonclastic • Clastic rocks are made up of rocks and minerals • Nonclastic rocks are made by dissolved minerals left behind by evaporated water.

24. Why do sedimentary rocks have layers? • Most sediment is deposited in layers. • Classified by thickness and definition of layers. • Thinner, smaller layers referred to as beds.

25. How layers form • Discrete event – a one-time occurrence. Ex. Flood. • Change in current – Caused by change in strength or direction of current that deposited the sediment. • Sediment Supply – Change in type or amount of sediment being supplied.

26. How layers form • Sea-level change – global rise or fall in sea level causes sedimentary environments to move. • Climate Change – Boundaries between layers reflect regional or global changes in climate.

27. Types of Beds • Graded Beds- form when a current loses velocity and drops sediment. Larger sediment falls first followed by finer sediment.

28. Types of Beds • Cross Beds- form when sediment moves over a dune or underwater ripple. At an angle to other beds.

29. Types of Beds • Parallel Beds- form when one layer piling on another layer. Most common type.

30. Resources in Sedimentary Rocks • Groundwater – moves between pores in rocks • Petroleum – formed by organic-rich sedimentary rocks • Coal – consolidation of plant remains in wetland environments

31. Resources in Sedimentary Rocks • Cement from limestone – produced from limestone free of impurities • Salt – mined from ancient sedimentary salt layers • Uranium – Occur in sandstone and other sedimentary rocks but it is not formed there…brought by groundwater

32. Resources in Sedimentary Rocks Groundwater Petroleum Coal Uranium Cement from limestone Salt 07.14.a

33. Observe this sequence of sedimentary layers Sandstone, mudstone, coal Medium to dark gray shale with fossil marine organisms Sandstone with marine shells Sedimentary units with fossilized wood and dinosaur tracks 07.16.b