1. Rocks Formed by Surface Processes
Grotzinger • Jordan
Understanding Earth
Sixth Edition
Chapter 5:
SEDIMENTATION:
Rocks Formed by Surface Processes
© 2011 by W. H. Freeman and Company

2. Rocks Formed by Surface Processes
Chapter 5
Sedimentation:
Rocks Formed by Surface Processes

3. About Sedimentation
Sediments are produced on the Earth’s surface as a result of weathering.
Sediments are transported and become sedimentary rocks after they come to rest.
Sedimentary rocks give evidence of ancient sedimentary environments where they formed.

4. Lecture Outline Surface processes of the rock cycle
2. Sedimentary basins: the sinks for sediments
3. Sedimentary environments
4. Sedimentary structures
5. Burial and diagenesis: from sediment to rock

5. Lecture Outline
6. Classification of siliciclastic sediments and sedimentary rocks
7. Classification of chemical and biological sediments and sedimentary rocks

6. Surface Processes and the Rock Cycle
Weathering
Physical weathering
Chemical weathering

7. Surface Processes and the Rock Cycle
Processes forming sedimentary rock:
Weathering
Erosion
Transportation
Deposition (sedimentation)
Burial and compaction
Diagenesis

8. Surface Processes and the Rock Cycle

9. Surface Processes and the Rock Cycle
Classification of sediments
Siliciclastic sediments
Chemical sediments
Biological sediments

10. Surface Processes and the Rock Cycle
Current strength and distance of
transport affect:
Size of clastic particles
Sorting of clastic particles
Rounding of clastic particles

13. Surface Processes and the Rock Cycle
Chemical mixing vats:
Oceans
Lakes

14. Thought questions for this chapter
A geologist is heard to say that a particular sandstone was derived from a granite. What information could she have gleaned from the sandstone to support this?
Weathering of the continents has been much more widespread and intense in the past 10 million years than it was in earlier times. How might this be borne out in the sediments that now cover Earth’s surface?
Describe the beach sands that you would expect to be produced by the beating of waves on a coastal mountain range consisting largely of basalt.

15. Sediments tend to accumulate in depressions in the Earth’s crust.
2. Sedimentary Basins
Sediments tend to accumulate in depressions in the Earth’s crust.
Depressions are formed by subsidence.
Sedimentary basins are depressions filled with thick accumulations of sediment. They are sinks for sediment.

16. Types of sedimentary basins:
Rift basins and thermal subsidence basins
Flexural basins

17. Sedimentary basins
form on rifted
continental
margins

20. 3. Sedimentary Environments
Types of environments:
1. Continental
Lake
Alluvial
Desert
Glacier

21. 3. Sedimentary Environments
Types of environments:
2. Shoreline
Delta
Beach
Tidal flats

22. 3. Sedimentary Environments
Types of environments:
3. Marine
Deep sea
Continental shelf
Organic reef
Continental margin
Continental slope and slope

23. Sedimentary
Environments

24. 3. Sedimentary Environments

25. 3. Sedimentary Environments
Environments of siliciclastic sediments:
Continental (alluvial, desert, lake, and glacial)
Shoreline (deltas, beaches, and tidal flats)
Marine (shelf, margin, slope, and deep sea)

26. 3. Sedimentary Environments
Environments of chemical and biological sediments:
Carbonate deposits (organic reefs, beaches, shelves, and tidal flats)
Siliceous environments (deep sea)
Evaporite environments (lakes)

28. Thought questions for this chapter
From the base upward, a bedding sequence begins with a bioclastic limestone, passes upward into a dense carbonate rock made of carbonate-cementing organisms, and ends with beds of dolostone. Deduce the possible sedimentary environments represented by this sequence.
In what sedimentary environment are carbonate muds?
How can you use size and sorting of sediments to distinguish between sediments deposited in a glacial environment and those deposited in a desert?
Where are reefs likely to be found?

29. 4. Sedimentary Structures
Sedimentary structures – all kinds of features in sediments formed at the time of deposition.
Bedding (stratification)
Cross-bedding
Graded bedding
Ripples
Bioturbation structures

30. Cross-
bedding

33. Ripples – modern and ancient

34. Bioturbation Structures

35. 4. Sedimentary Structures
Bedding sequences – vertically stacked layers of sedimentary rock with different types of sedimentary structures in each layer.

36. Example of a Bedding Sequence

38. Thought questions for this chapter
You are looking at a cross section of rippled sandstone. What sedimentary structure would tell you the direction of current that deposited the sand?
You discover a bedding sequence that has a conglomerate at the base; grades upward into sandstone and then to a shale; and finally, at the top, grades to a limestone. What changes in the sediment source area would have been responsible for this sequence?

39. Burial is the preservation of sediments within a sedimentary basin.
5. Burial and Diagenesis
Burial is the preservation of sediments within a sedimentary basin.
Diagenesis is the physical and chemical change that converts sediments to sedimentary rocks.

40. Lithification includes: Compaction Cementation
5. Burial and Diagenesis
Lithification includes:
Compaction
Cementation

46. Thought questions for this chapter
If you drilled one oil well into the bottom of a sedimentary basin that is 1 km deep and another that is 5 km deep, which would have the higher pressures and temperatures? Oil turns into natural gas at high basin temperatures. In which well would you expect to find more natural gas?

47. 6. Classification of Siliciclastic Sediments
and Sedimentary Rocks
Classification of sediments by particle size
Classification of sedimentary rocks by texture and composition

48. 6. Classification of Siliciclastic Sediments
and Sedimentary Rocks

52. 6. Classification of Siliciclastic Sediments
and Sedimentary Rocks
Four major compositional groups of siliciclastic sediments:
Arkose
Lithic
Quartz arenite
Graywacke

54. 7. Classification of Chemical and Biological Sediments,
Sedimentary Rocks
Chemical sedimentary rocks
Limestone
Chert
Organics
Phosphorite

55. 7. Classification of Chemical and Biological Sediments,
Sedimentary rocks
Biological sedimentary rocks
Dolostone
Iron formation
Evaporite

61. Organic Reef Development

64. Organic Reef Rock

65. 7. Classification of Chemical and Biological Sediments,
Sedimentary Rocks
Carbonate sediments and rocks
Evaporite sediments and rocks
Other sediments and rocks

66. 7. Classification of Chemical and Biological Sediments,
Sedimentary Rocks
Carbonate sediments and rocks
Limestones
Dolostones

67. 7. Classification of Chemical and Biological Sediments,
Sedimentary Rocks
Evaporite sediments and rocks
Marine
Non-marine

69. 7. Classification of Chemical and Biological Sediments,
Sedimentary Rocks
Other sediments and rocks
Siliceous
Phosphorite
Iron oxide
Coal and peat

70. Thought questions for this chapter
What role do organisms play in the origin of some types of limestone?
A bay is separated from the open ocean by a narrow, shallow inlet. What kind of sediment would you expect to find on the floor of the bay if the climate were warm and arid? What kind of sediment would you find if the climate were cool and humid?
How are chert and limestone similar in origin? Discuss the roles of biological versus chemical processes.

71. Key terms and concepts Bedding sequence Bioclastic sediment
Arkose
Bedding sequence
Bioclastic sediment
Biological sediment
Bioturbation
Carbonate rock
Carbonate sediment
Cementation
Chemical sediment
Chemical weathering
Chert
Clay
Claystone
Coal
Compaction

72. Key terms and concepts Continental shelf Cross-bedding Crude oil
Conglomerate
Continental shelf
Cross-bedding
Crude oil
Diagenesis
Dolostone
Evaporite rock
Evaporite sediment
Flexural basin
Foraminifera
Graded bedding
Gravel
Graywacke
Iron formation
Limestone

73. Key terms and concepts Lithification Mud Mudstone Natural gas Oil
Lithic sandstone
Lithification
Mud
Mudstone
Natural gas
Oil
Organic sedimentary rock
Peat
Phosphorite
Physical weathering
Porosity
Quartz arenite
Reef
Rift basin
Ripple

74. Key terms and concepts Salinity Sand Sandstone Sedimentary basin
Sedimentary environment
Sedimentary structure
Shale
Siliciclastic sediments
Silt
Siltstone
Sorting
Subsidence
Terrigenous sediment
Thermal subsidence basin