1. How they form, how they are classified, and why they are important.
Sedimentary Rocks
How they form, how they are classified, and why they are important.

2. Objectives Explain how sediments are produced
Describe and discuss siliciclastic rocks
Discuss how sedimentary rocks are classified
Describe and discuss sedimentary structures
Explain why sedimentary rocks are significant

3. Sedimentary Rocks Sediments produced by: Siliciclastic rocks
Weathering, erosion of other rocks
Crystals precipitated from seawater
Skeletal debris from organisms
Siliciclastic rocks
Sedimentary rocks composed of clasts of silicate minerals
Quartz is most resistant to weathering
Mafic minerals less stable at Earth’s surface

4. Sedimentary Rocks

5. Siliciclastic Rocks Classification based on grain size and shape:
Gravel
>2 mm diameter
Granules, pebbles, cobbles, boulders
Conglomerate
Rounded grains
Breccia
Angular grains

6. Siliciclastic Rocks (cont.)
Sand
1/16-2 mm diameter
Often quartz
Sandstone
Silt
1/256-1/16 mm
Clay
Smaller than 1/256 mm

7. Siliciclastic Rocks (cont.)
Muds form mudstones
Shale
Fissile mudstone
Fissile
breaks along bedding surface
Sediment aligned horizontally during deposition

8. Sorting Grains settle out of suspension
Coarse, dense material settles first

9. Sorting Measure of similarity in grain size Poorly sorted Well sorted
Mixed sizes
Well sorted
Similar sizes

10. Siliciclastic Rocks: Sandstone
Not always quartz
Arkose
Feldspar dominated rock
Pinkish color
Graywacke

11. Lithification Process by which siliciclastic sediments become rock
Primary process is compaction
Cementation
Chemical process in which minerals crystallize from solution that percolates through the grains of sediment
Iron oxide
Red beds

12. Evaporites Form from evaporation of seawater
Anhydrite
Gypsum
Halite
Readily formed, readily dissolved

13. Other Chemical Sedimentary Rocks
Chert
Flint
Extremely small quartz crystals precipitated from watery solutions
Brown, gray, or black
Impurities
Banded Iron Formations (BIF)

14. Carbonate Rocks Limestone Dolomite
Chemical and biogenic bodies of rock
Dolomite
Carbonate mineral
Uncommon in modern rocks
Common in ancient rocks
Dolostone

15. Carbonate Rocks (cont.)
Carbonate sediments
Often skeletal particles
Carbonate muds
Mainly aragonite needles
Direct precipitation
Collapse of carbonate algal skeletons

16. Carbonate Rocks (cont.)
Oolites
Nearly spherical sediment
Produced in shallow water
Formed by rolling and accumulating aragonite needles

17. Carbonate Rocks (cont.)
Cross-section of oolith
Concentric structure

18. Sedimentary Structures
Distinctive arrangements of grains in sedimentary rocks
Reflect modes of deposition
Useful tools for interpreting ancient environment of deposition
Graded Bed
Grain size increases from top to bottom
Normal

19. Sedimentary Structures
Ripples
Structures formed by wind or water
Sediments accumulate downslope (lee)
Symmetrical → Bidirectional current
Asymmetrical → Unidirectional current
Cross-bedding or cross-stratification
Mudcracks

20. Significance of Understanding Sediments and Sedimentary Rock
Sediment is a non-point source pollutant in California
Sedimentary rock contains oil and natural gas
Coal is a sedimentary rock and
Groundwater is found primarily in sedimentary rock

21. Sediment laden drainage, Betsiboka River, Madagascar

22. Sedimentary Rock and Oil Formation

23. Coal Formation Coal and Depth Peat Lignite Bituminous Coal
Anthracite Coal

24. Groundwater Resources

26. Summary Sediments form from detritus – broken down rocks
3 types of sedimentary rocks: 1) detrital; 2) chemical; and 3) biochemical or bioclastic
The environment in which sedimentary rocks form control the different types found
Sedimentary rocks are significant since they contain oil, natural gas, coal, and groundwater; sediments can also be considered pollutants