1. Chapter 6 Sediments and Sedimentary Rocks
GEOL 101
Introductory Geology
Chapter 6 Sediments and Sedimentary Rocks

2. Sediments
Collective name for loose, solid particles originated from weathering and erosion, thus Unconsolidated.
Classification of sediments based on sizes
Gravel > 2mm
Sand between 1/16 and 2 mm
Silt between 1/256 mm and 1/16 mm
Clay < 1/256 mm

3. Change from Sediments to Sed Rxs
Transportation
Roundness: round – distance from source
Sorting: well sorted - distance from source
Deposition: settle of particles
Preservation

4. Change from Sediments to Sed Rxs
Lithification
Compaction – reduction in pore space
Cementation – seal out the pores
Crystallization – growth of crystals from solution.

5. Sedimentation Process

6. What is Sedimentary Rock?
Sedimentary rocks are products of mechanical and chemical weathering
Account for about 5 % (by volume) of Earth’s upper crust
Contain evidence of past environments
Provide information about sediment transport
Often contain fossils
Economic importance
Coal
Petroleum and natural gas
Sources of iron, aluminum, and manganese

7. Sedimentary Rocks Rock types Classification Sedimentary Environments
Fossils

8. Sedimentary Rock Classification
Classified according to material type
Clastic
Chemical
Two major textures are used in the classification of sedimentary rocks
Discrete fragments and particles
All detrital rocks have a clastic texture
Nonclastic
Pattern of interlocking crystals
May resemble an igneous rock

9. Sedimentary Rocks Types
Sediment originates from mechanical and/or chemical weathering
Rock types are based on the source of the material
Clastic rocks – transported sediment as solid particles
Chemical rocks – sediment that was once in solution

10. Detrital Sedimentary Rocks
The chief constituents of detrital rocks include:
Clay minerals
Quartz
Feldspars
Micas
Particle size is used to distinguish among the various types of detrital rocks
Particle shape and sorting give indication of transport distance (maturity)

11. Particle Size Classification

12. Sorting, Shape, Setting Sorting Sphericity Roundness Depositional

13. Clastic Sedimentary Rocks
Common Clastic sedimentary rocks (in order of increasing particle size)
Shale
Mud-sized particles in thin layers that are commonly referred to as laminea
Most common sedimentary rock
Sandstone
Composed of sand-sized particles
Forms in a variety of environments
Sorting, shape, and composition of the grains can be used to interpret the rock’s history
Quartz is the predominant mineral

14. Detrital Sedimentary Rocks
Conglomerate and breccia
Both are composed of particles greater than 2mm in diameter
Conglomerate consists largely of rounded gravels
Breccia is composed mainly of large angular particles

15. Shale containing plant remains

16. Sandstone

17. Conglomerate

18. Breccia

19. Chemical Sedimentary Rocks
Consist of precipitated material that was once in solution
Precipitation of material occurs in two ways
Inorganic processes
Organic processes (biochemical origin)
Common chemical sedimentary rocks

20. Chemical Sedimentary Rocks Common Types
Limestone
Dolostone
Chert
Evaporites
Coal

21. Limestone Most abundant chemical rock
Composed of calcite carbonate CaCO3
Marine biochemical limestones form as coral reefs, coquina (broken shells), and chalk (microscopic organisms)
Inorganic limestones include travertine and oolitic limestone

22. Coquina

23. Fossiliferous Limestone

24. Chemical Sedimentary Rocks
Dolostone
Composed of calcite, magnesium carbonate CaMgCO3
Typically formed secondarily from limestone
Chert
Made of microcrystalline quartz
Varieties include flint , jasper and agate (banded form)
Evaporites
Evaporation triggers deposition of chemical precipitates
Examples include rock salt and rock gypsum

25. Chert
Agate – Banded Chert

26. Coal Common chemical sedimentary rocks
Different from other rocks because it is composed of organic material
Stages in coal formation (in order)
Plant material
Peat
Lignite
Bituminous

27. Coal

28. Coal Formation Stages

29. Sedimentary Environments
A geographic setting where sediment is accumulating
Determines the nature of the sediments that accumulate (grain size, grain shape, etc.)
Identified by sedimentary facies, fossils, and structures

30. Sedimentary Environments
Continental
Dominated by stream erosion and deposition
Glacial
Wind (eolian)
Marine
Shallow (< 200 meters)
Deep (seaward of continental shelves)
Transitional (shoreline)
Tidal flats
Lagoons
Deltas

31. Depositional Environments

32. Depositional Environments
Continental
Marine

33. Turbidity Currents

34. Turbidity Currents
Graded Bedding

35. Evaporite Formation

36. Sedimentary Facies
Different sediments often accumulate adjacent to one another at the same time
Facies: possesses a distinctive set of characteristics reflecting the conditions in a particular environment
Merging of adjacent facies tends to be a gradual transition

37. Sedimentary Facies

38. Sedimentary Structures
Useful for interpreting sedimentary environment
Strata: or beds, layers of similar sediment (most characteristic of sedimentary rocks)
Lamina: thin layers (< 1cm)
Bedding planes separate strata
Cross-bedding
Graded beds
Ripple marks
Mud cracks

39. Bedding

40. Bedding Structures
Graded bedding
Lamina

41. Cross Beds

42. Ripple Marks
unconsolidated sediment
lithified rock

43. Mud Cracks

44. Grand Canyon o

45. Fossils: Evidence of past life
By definition, fossils are the traces or remains of prehistoric life now preserved in rock
Fossils are generally found in sediment or sedimentary rock (rarely in metamorphic and never in igneous rock)

46. Dinosaur footprint in limestone

47. Fossils: Evidence of past life
Geologically fossils are important for several reasons
Aid in interpretation of the geologic past
Serve as important time indicators
Allow for correlation of rocks from different places
Studied in detail in Historical Geology (GEOL 102), offered in Spring 2004

48. Chalk Cliffs of Dover, England
Tiny planckon shells
Deposited on sea floor
Later uplifted