What is a sedimentary rock?

1. What is a sedimentary rock? • Sedimentary rocks result from mechanical and chemical weathering • Comprise ~ 5% of Earth’s upper crust • Contain evidence of past environments • Record how sediment is transported • Often contain fossils

2. Fossil Fish - 50 Million Year Old Lakes in southern Wyoming Sediment is fine-grained mudstone

3. Turning sediment into rock • Changes occur in sediment after it is deposited • Diagenesis – chemical and physical changes that take place after sediments are deposited

4. Turning sediment into rock • Diagenesis • Recrystallization – growth of stable minerals from less stable ones • Lithification – loose sediments is transformed into solid rock by compaction and cementation • Natural cements include calcite, silica, and iron oxide

5. Types of sedimentary rocks • Detrital rocks – transported sediment as solid particles • Chemical rocks – sediment that was once in solution

6. Detrital sedimentary rocks • Constituents of detrital rocks can include • Clay minerals • Quartz • Feldspars • Micas • Particle size is used to distinguish among the various types of detrital rocks

7. Detrital sedimentary rocks • Common detrital sedimentary rocks • Shale • Mud-sized particles deposited in thin layers called laminae

8. Detrital sedimentary rocks • Sandstone

9. Detrital sedimentary rocks • Conglomerate and breccia • Both composed of particles > 2mm in diameter • Conglomerate consists largely of rounded clasts • Breccia is composed of large angular particles

10. Chemical sedimentary rocks • Precipitated material once in solution • Precipitation of material occurs two ways: • Inorganic processes • Organic processes (biochemical origin)

11. Chemical sedimentary rocks • Common chemical sedimentary rocks • Limestone • Most abundant chemical rock • Made of the mineral calcite • Marine biochemical limestones form as coral reefs, coquina (broken shells), and chalk (microscopic organisms) • Inorganic limestones include travertine and oolitic limestone

12. Coquina

13. Fossiliferous limestone Note shells and lime matrix

14. Chalk Outcrops in SE USA Chalk Hand Specimen

15. Travertine forming in Hot Spring Travertine Hand Specimen

16. Chemical sedimentary rocks • Common chemical sedimentary rocks • Dolostone • Typically formed secondarily from limestone • Common in ancient rocks, rare today • Chert • Made of microcrystalline quartz • Usually deposited as siliceous ooze in deep oceans (can be diatomaceous) chert Diatomaceous chert

17. Chemical sedimentary rocks • Common chemical sedimentary rocks • Evaporites • Evaporation triggers deposition of chemical precipitates • Examples include rock salt and rock gypsum

18. Chemical sedimentary rocks • Common chemical sedimentary rocks • Coal • Different from other rocks because it is composed of organic material

19. Metamorphic Rocks • The transformation of rock by temperature and pressure • Metamorphic rocks are produced by transformation of: • Igneous, sedimentary and igneous rxs

20. Metamorphism • Metamorphism progresses from low to high grades • Rocks remain solid during metamorphism

21. Metamorphism • Three types of metamorphic settings: • Contact metamorphism – from a rise in temperature within host rock • Hydrothermal metamorphism – chemical alterations from hot, ion-rich water • Regional metamorphism -- Occurs in the cores of mountain belts and makes great volumes of metamorphic rock

22. Metamorphic Environments • Metamorphic grade • A group of minerals that form in a particular P-T environment Zeolite (really low T,P; <200C) Greenschist (low T, P; 200-450C, 10-15 km) Blueschist (low T, high P - subduction zones) Amphibolite (high T, P; 450-650C, 15-20 km) Granulite (super high T, P; >700C, >25km)

23. What are metamorphic textures? • Texture refers to the size, shape, and arrangement of mineral grains within a rock • Foliation – planar arrangement of mineral grains within a rock

24. Common metamorphic rocks • Nonfoliated rocks • Quartzite • Formed from a parent rock of quartz-rich sandstone • Forms in intermediate T, P conditions

25. Common metamorphic rocks • Nonfoliated rocks • Marble • Coarse, crystalline • Parent rock usually limestone • Composed of calcite crystals • Fabric can be random or oriented

26. Common metamorphic rocks • Foliated rocks • Slate • Very fine-grained • Made by low-grade metamorphism of shale

27. Common metamorphic rocks • Foliated rocks • Phyllite • Grade of metamorphism between slate and schist • Composed mainly of muscovite and/or chlorite

28. Common metamorphic rocks • Foliated rocks • Schist • Medium- to coarse-grained • Comprised of platy minerals (micas) • The term schist describes the texture

29. Common metamorphic rocks • Foliated rocks • Gneiss • Banded appearance • High-grade metamorphism • Composed of light-colored feldspar layers with bands of dark mafic minerals

30. Outcrop of foliated gneiss

31. The rock cycle

32. The rock cycle - Series of processes by which rocks changes into other types of rocks • Illustrates various processes and paths as earth materials change both on the surface and inside the Earth - What are the three main rocks ? 1- Igneous 2- Metamorphic 3- Sedimentary

33. The rock cycle

34. Fundamental Rock Types • Igneous Rocks: solidify from melt, e.g. lava (extrusive) or magma (intrusive) • Sedimentary Rocks: are made at the Earth’s surface from particle and chemical remnants of other rocks • Metamorphic rocks: form when other rocks are heated, squeezed, and deformed.