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)
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.
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.
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).
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).
21. Sedimentary or DepostionalSedimentary or Depostional
EnvironmentsEnvironments
• Each environment will have distinctive
physical, chemical, and biological
characteristics.
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.
33. Chemical Sedimentary RocksChemical Sedimentary Rocks
• Chemical sedimentary rocks result from
Lithification of organic or inorganic
chemical precipitates.
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.
