Sedimentary Rocks

1
Sedimentary Rocks

• Chapter 6

2
What Are Sediments?

• Loose particulate material
• In order of decreasing size

3
Sources of Sediments

• 1. From weathering erosion
• 2. From chemical precipitation

4
What Happens to Sediments

• 1. transported by
• Water.
• Ice.
• Wind.
• Gravity.
• Most sediment is buried and converted to
  sedimentary rock.

5
What Happens to Sediments

• 2. Deposited by
• Rivers
• Wind
• Glaciers
• Other water
• When the transportation vector has run out of
  energy, the sediments are deposited (dropped).

6
River Sorting- Transporting Depositing
Headwaters
Mouth
Grade change in elevation/length
7
Principle of Original Horizontality
Most sedimentary layers of rock are deposited in
a horizontal position, with older rocks laid down
first
8
Lithification

• Sediment becomes sedimentary rock through
  lithification, which involves
• Compaction
• Cementation
• Recrystallization (of carbonate sediment)
• Ex sand

Remember that SiO2 is released into groundwater
from the chemical weathering of quartz and
feldspars.
9
3 Classes of Sedimentary Rock
Clastic - fragments of rock debris produced by
physical weathering. Ex. Sand clay. Chemical -
sediment precipitates from solution in water. Ex.
Calcium carbonate salt. Biogenic (organic) -
sediment composed of the fossilized remains. Ex.
Coal, oil, natural gas.
Chemical
10
Clastic Sedimentary Rock

• From the weathering of other rocks broken
  texture
• Clasts (larger pieces, such as sand or gravel)
• Matrix (mud or fine-grained sediment surrounding
  the clasts)
• Cement (the glue that holds it all together),
  such as
• calcite
• iron oxide
• silica

11
Gravel Clastic Rocks

• If rounded clasts conglomerate
• If angular clasts breccia

12
Sand Clastic Rocks

• Different Sandstones based on dominate grains
• quartz grains quartz sandstone
• feldspar grains arkose
• sand-sized rock fragment grains graywacke

13
Silt Clastic Rocks

• Siltstone - Grain size 1/256 to 1/16 mm (gritty)

14
Clay Clastic Rocks

• Grains less than 1/256 mm (smooth)
• Shale (if fissile splits)
• Kaolinite (if massive)also called Claystone
• Note Mud is technically a mixture of silt and
  clay. (Mudstone)

15
Chemical Sedimentary Rocks

• Chemicals removed from seawater and made into
  rocks by chemical processes, or with help of
  biological processes (such as shell growth).
• 3 types
• Evaporites
• Carbonates
• Siliceous

16
Chemical Evaporites

• From the evaporation of water (usually seawater).
  
• Rock salt - composed of halite (NaCl).
• Rock gypsum - composed of gypsum (CaSO4.2H20)
• Travertine - composed of calcium carbonate
  (CaCO3), and therefore, also technically a
  carbonate rock

17
Chemical Carbonates

• Formed through both chemical biochemical
  processes.
• Include the limestones (many types)
• Two minerals are dominant
• Calcite (CaCO3)
• Dolomite (CaMg(CO3)2)

18
Chemical Siliceous

• Dominated by silica (SiO2).
• From diatoms, radiolarians, or sponges.
• Diatomite - looks like chalk, but doesnt fizz in
  acid. Made of diatoms. Also referred to as
  Diatomaceous Earth.
• Chert - Massive and hard, microcrystalline
  quartz. May be dark or light in color. Often
  replaces limestone. Does not fizz in acid.

19
Biogenic (Organic) Sedimentary Rocks

• Coals
• organic matter (plants).
• Increasing depth of burial (temperature and
  pressure)
• Peat (porous, brownish plant fragments)
• Lignite (crumbly and black)
• Bituminous (dull to shiny and black sooty
  layers may be visible)
• Anthracite (extremely shiny and black low
  density not sooty

20
Formations from Sediments

• Large enough to be recognized.
• Ex.- haystack rock, sand dunes, delicate arch,
  balanced rock

21
Sedimentary Environments (Sinks)

• Places where sediments accumulate and sedimentary
  rocks form
• 3 Major Groups
• Continental
• Marine
• Transitional

22
Terrestrial Environments

• Aluvial Fan
• Braided stream
• Lakes
• Rivers
• Levees
• Swamps
• Deserts
• Glacial

23
Marine Environments

• Seas oceans
• Continental shelf
• Continental slope and rise (deep sea fans)
• Abyssal plain
• Reefs

24
Transitional Environments

• between the land and the sea.