Sedimentary Rocks

1
Sedimentary Rocks

• PRESSURE!

2
If You Are Going to be a Sedimentary Rock
Four Things Happen to You

• You - the clast or particle will be
• Weathered
• Transported
• Deposited
• Lithified
• Perhaps several times

Unless you precipitate (which well get to
later..)
3
Weathered - Chemically or Physically Broken Away
4
Transported
By what agents of transportation? How do they
differ in what they carry? Gravity!

• http//www.geo.duke.edu/geo41/geo41.htm

5
Deposited
Low - basin accumulates sediment
(preserved) Go with gravity!
http//www.geo.duke.edu/geo41/geo41.htm
6
Buried and Lithified into Rock

• Uncompacted (loose) sediment slowly becomes rock
  through biological, chemical and physical
  changes.
• Diagenesis Changes from pressure, heat, chem.
• Physical - Compaction
• Chemical - Cementation
• lt300F (150C)
• 10-12 kilometers deep

7
Sediment Sedimentary Rocks

• Clastic Sedimentary Rocks
• Sediment particles (skeletal, rock fragment,
  mineral, plant particles) derived from erosion
  (breakdown / transport) of rock.

• Carbonate /
• Other Sedimentary Rocks

Press and Siever, 2000
8
Sediment Sedimentary Rocks

• Sediment - loose sedimentary particles
• Sedimentary Rock - lithified (cemented,
  compacted, crystallization)

Press and Siever, 2000
Clasts - particles Matrix - finer grained filler
- deposited at same time Cement - chemical
precip. crystalline - after deposition
9
ClasticSedimentary Rocks

• Rivers, wind, glaciers weather and transport
  sediment (erosion).
• When the transport agent can no longer carry the
  material, it is dropped or deposited.
• The sediment has the signature of the transport
  agent and the environment of deposition.
• Other sedimentary rocks are produced by organisms
  or precipitated by physical processes.

10
Clastic Sedimentary Rocks - Texture

• Size
• Sorting
• Shape
• Surface Texture

Provides clues to transportation and deposition
history
Press and Siever, 2000
11
Texture - Size
Conglomerate - Boulder to granule (gt 2 mm) sized
material - cemented by minerals or finer
particles. Rounded clasts (versus
breccia). Sandstone - Sand sized material
cemented by minerals or finer particles. 20 sed
rx. Siltstone - Silt-size material (1/256 -
1/16 mm) can barely see grains - looks like mud
/ clay slightly rough to touch, gritty to taste
commonly thin layers Claystone or Shale - Finest
mud-sized grains (lt1/256 mm) - can't see, feel,
or taste grains Claystones no layers Shales
split into layers (slate meta)
12
Texture - Size

• What was the energy of the transporting agent?

Parent material may determine what is available
to transport
Press and Siever, 2000
13
Texture - Sorting

• How much are all of the grains the same?
• How was it transported / deposited?
• How consistent was the energy?

Press and Siever, 2000
http//www.science.ubc.ca/geol202/sed/sili/sedstr
uctures.html
14
Texture - Shape
Roundness - how smooth are the edges? Sphericity
- how close is it to a sphere? How long was it
in transport?
15
Composition

• Clasts
• quartz (clear gray)
• feldspars (pink or white)
• olivine (green - igneous!)
• shell fragments (white - fizz)
• Rock fragments - PARENT!
• Matrix
• May be too fine to determine
• Cement
• Calcite - fizzes
• Silica - hard, clear-ish

16
Maturity

• With time in transport - becomes more texturally
  and compositionally mature
• Textural Maturity - Grains become more rounded,
  spherical, sorted SMALLER!
• Mineralogical Maturity - Less durable grains are
  broken down more durable grains remain

17
Sediment Sedimentary Rocks

• Clastic Sedimentary Rocks
• Sediment particles (skeletal, rock fragment,
  mineral, plant particles) derived from erosion
  (breakdown / transport) of rock.

• Carbonate /
• Other Sedimentary Rocks
• Chemical precipitates (halite) or biologically -
  produced (organic) material (shell fragments).
  In-situ.

Press and Siever, 2000
18

• Carbonate Rocks chemical or biological ppt
  clastic or crystalline - water
• Evaporites chemical, crystalline rocks formed
  by precipitation of dissolved salts during
  evaporation
• Miscellaneous biologic origin
• What you have tells you about the environment of
  deposition

19
Classification of Sediment Sedimentary Rocks

• Carbonate Rocks
• Calcium carbonate dominant constituent
• Limestone - calcite or aragonite (CaCO3) -
  usually from shell, skeleton, or algae inorganic
  precipitation rare
• Fizzes with HCl / Vinegar
• Name from material (bioclastic limestone,
  coquina, chalk, micrite, oolite)

http//www.uky.edu/KGS/coal/webrokmn/pages/limesto
ne.html
20
A Few Special Little Guys

• Chalk
• White Cliffs of Dover
• Coccoliths - carbonate
• Calcareous Ocean Deposits
• Foraminifers - single celled zooplankton

21
A Few Special Little Guys

• Diatomites / Cherts - silica

22
What Do Carbonate Rocks Tell You About the
Environment?
23
Evaporites

• Crystal precipitation during evaporation of salty
  water - halite, gypsum, anhydrite

http//www.dc.peachnet.edu/pgore/geology/geo101/s
edrx.htmSilica http//darkwing.uoregon.edu/mille
rm/evaporite.html http//www.emporia.edu/earthsci/
museum/salt.htm
24
What Do Evaporites Tell You About the Environment?
25
Coals

• Coal gt 50 plant-derived carbon and silt or
  clay.
• May see traces of plants (roots, leaves, etc)

What Do Coals Tell You About the Environment?
26

• Identify Away!

27
Weathering Transport Deposition Lithification What
sedimentary rocks are where