1. Chapter 7: Sediments andChapter 7: Sediments and
Sedimentary RocksSedimentary Rocks

3. Sedimentary RocksSedimentary Rocks
Two Categories:Two Categories:
Clastic(Detrital) and ChemicalClastic(Detrital) and Chemical

4. Sedimentary RocksSedimentary Rocks
• Clastic ( or detrital) sedimentary rocks reflect
several processes.
– Weathering – Generation of detritus via rock
disintegration.
– Erosion – Removal of sediment grains from rock.
– Transportation – Dispersal by wind, water and ice.
– Deposition – Accumulation after cessation of
transport.
– Lithification – Transformation into solid rock.
• Burial – Continued deposition buries sediments.
• Compaction – Squeezing by the weight overlying material.
• Cementation – Grains “glued” by pore-filling minerals.

5. Sediments In The Rock CycleSediments In The Rock Cycle
• Sediments are transported by:
– Water.
– Ice.
– Wind.
– Gravity.
• The transport and deposition of sediments
are initial phases of the rock cycle.
• The ultimate fate of most sediment is burial
and conversion to sedimentary rock.

6. Sediments Types AndSediments Types And
CharacteristicsCharacteristics
• Three broad classes:
– Clastic sediment is loose fragments of rock
debris produced by physical weathering.
– Chemical sediment precipitates from solution in
water.
– Biochemical/Biogenic/Bioclastic sediment is
composed of the fossilized remains of plants or
animals.

7. Characteristics of ClasticCharacteristics of Clastic
Sediment (1)Sediment (1)
• Clastic sediment is divided into four
main size classes:
– Gravel and larger ( 2mm and larger)
– Sand (0.0625 to 2 mm)
– Silt (0.0625 to 0.0039 mm)
– Clay (less than 0.0039 mm)

8. Characteristics of ClasticCharacteristics of Clastic
Sediment (2)Sediment (2)
• Gravel is subdivided into:
– Boulder gravel.
– Cobble gravel.
– Pebble gravel.

9. SortingSorting
• Sorting identifies sediment in terms of
the variability in the size of its particles.
– Poorly sorted (wide range of particle size),
– Well sorted (range is small).
• Changes of grain size typically result
from fluctuations in the velocity of the
transporting agent, such as water or
wind.

10. Figure 7.2 Sorting in Sediments

11. Figure 7.4 Sorting, rounding and sphericity

12. SortingSorting
• The greater the speed and energy
involved, the larger or heavier are the
particles that can be transported.

13. SortingSorting
• Nonsorted sediment is a mixture of
different sizes arranged chaotically.
– Till is a nonsorted sediment of glacial
origin.
• Smooth and rounded particles are
transported by water or air.

14. TransportTransport
• Sediments move by air, wind, rain, water,
organisms
- With increasing transport, average grain size
decreases.

15. Sedimentary RocksSedimentary Rocks
Chemical/BiochemicalChemical/Biochemical

16. Characteristics of ChemicalCharacteristics of Chemical
SedimentsSediments
• Chemical sediments are formed by precipitation of
minerals from solution in water.
• They form in two principal ways:
– Through biochemical reactions resulting from the
activity of plants and animals in the water.
– Inorganic reactions in the water.
• When water from a hot spring cools, it may
precipitate opal (a hydrated silicate) or calcite
(calcium carbonate).

17. Some Chemical SedimentarySome Chemical Sedimentary
RocksRocks

18. SaltsSalts
• Evaporation of sea water or lake water
forms salts.
• Lake waters precipitate sodium
carbonate (Na2CO3), sodium sulfate
Na2SO4), borax (Na2B4O7.10H2O),and trona
(Na2CO3.NaHCO3.2H2O).

19. Biochemical/BiogenicBiochemical/Biogenic
SedimentsSediments
• Biogenic sediments contain fossils.
• If the remains are broken and scattered it
is bioclastic sediment.

20. Depositional EnvironmentsDepositional Environments

21. Sedimentary or DepostionalSedimentary or Depostional
EnvironmentsEnvironments
• Each environment will have distinctive
physical, chemical, and biological
characteristics.

22. Figure 7.14

23. Sediments to RocksSediments to Rocks
How do we do this?How do we do this?

24. How Sediment Becomes RockHow Sediment Becomes Rock
• Lithification is the overall process of
creating sedimentary rock.

25. How Sediment Becomes RockHow Sediment Becomes Rock
• Processes involved include:
– Compaction.
• As the weight of an accumulating sediment forces the
grains together. The pore space is reduced.
– Cementation.
• Substances dissolved in water precipitate to form a
cement that binds the sediment grains together.

26. What do we call theseWhat do we call these
rocks?rocks?

27. Clastic Sedimentary RocksClastic Sedimentary Rocks
• The four basic classes of clastic
sedimentary rocks are:
– Conglomerate/Breccia, a lithified gravel.
– Sandstone, consisting mainly of sand grains.
– Siltstone, composed mainly of silt-size mineral
fragments, commonly quartz and feldspar.
– Mudstone, still-finer grain size.

28. Figure 7.24A

29. Figure 7.24B

30. Figure 7.24C

33. Chemical Sedimentary RocksChemical Sedimentary Rocks
• Chemical sedimentary rocks result from
Lithification of organic or inorganic
chemical precipitates.

35. Figure 7.27B

36. Figure 7.27C

37. Rock Salt
Rock Gypsum

38. Figure 7.27D
Chert

40. Sedimentary StructuresSedimentary Structures
Clues to the EarthClues to the Earth

41. Environmental clues inEnvironmental clues in
sedimentary rockssedimentary rocks
• Sedimentary rocks reflect the environment
in which they were formed.
• Clues from bedding planes.
– Ripples marks preserved in sandstones and
siltstones.
– Footprints, trails, and raindrop impressions.

42. Clues in the RocksClues in the Rocks
• Clues from fossils.
– Some animals and plants are restricted to
warm, moist climates, whereas others are
associated only with cold, dry climates.

43. Figure 7.30 Ripples

44. Figure 7.31 Mud cracks

45. Crossbedding

46. Layering and fining upward

47. Tilted Bedding or strata

48. Trace Fossil
Trace Fossil from Mt Cristo Rey

49. Where do we go next?Where do we go next?
• Metamorphic Rocks