Sedimentary Rocks
Sedimentary rocks form when sediment is
compacted or cemented into solid rock
Fig. 3-2, p.46
The Rock Cycle
Weathering
• Sediment becomes
smaller, more
rounded and more
sorted
• silicate minerals
react with water to
form clay (a new
solid mineral) and
dissolved ions
(quartz is the
exception)
• Weathering agents:
water (most
important), wind,
gravity, glaciers
Rock Cycle Processes - Lithification
Lithification: Turning sediment into
sedimentary rock
• Compaction : wet,
buried sediment is
squeezed by overlying
sediments, causing it to
become more solid.
• Cementation minerals
dissolved during the
weathering process
precipitate and act as a
cement, e.g. calcite,
silica, and iron oxide.
Sedimentary Rock Classification
Based on sediment source
• Detrital Sedimentary Rocks
• Chemical Sedimentary Rocks
(which includes):
–Inorganic Sedimentary Rocks
–Biochemical Sedimentary Rocks
–Organic Chemical Sedimentary Rocks
Grain size
chart for
detrital
sedimentary
rocks
Arkose: sandstone
has significant
feldspar content
• Detrital Sedimentary
Rocks
– composed of solid
sediment from
weathered rocks
– conglomerate,
sandstone, shale
• Chemical
Sedimentary Rocks
– Composed of minerals
precipitated from
surface or ground
water (chemical
sediment)
– rock salt, rock
gypsum
– Includes biochemical
Sedimentary Rocks,
composed of sediment
of biological origin
(e.g. shell fragments)
– Most common example
is rock salt.
Coal
• Different from other rocks because it is
composed of organic, not mineral
material
• Stages in coal formation (in order)
1. Plant material
2. Peat
3. Lignite
4. Bituminous Coal
5. Anthracite (metamorphic)
Figure 6.13a,b
Figure 6.13b,c
Figure 6.13c,d
Sedimentary environments
• Sedimentary rocks
contain evidence of
past environments
• They provide
information about
climate (sediment
size, presence or
absence of water, sea
level)
• Often contain fossils,
which are indicators
of both past climates
and possible
presence of fossil
fuel.
Sedimentary environments
• Sedimentary environment
or environment of
deposition: A geographic
setting where sediment is
accumulating
• Determines the nature of
the sediments that
accumulate (grain size,
grain shape, and other
properties.)
• Today’s sedimentary rocks,
tell us about past
environments of deposition
Continental Sedimentary
Environments
Dominated by
erosion and
deposition
associated with
– Streams
– Wind (eolian
sandstones)
Continental Sedimentary
Environments
• Glacial (morainal
material)
• Alluvial fans
(arkosic, feldsparrich materials)
Shallow Marine Sedimentary
Environments
Deep Marine Sedimentary Environments
Transitional Sedimentary
Environments
• Tidal flats
• Lagoons
• Deltas
Sedimentary structures
• Provide information useful in the
interpretation of Earth’s history
• Types of sedimentary structures
• Strata, or beds (most characteristic of
sedimentary rocks)
• Cross-bedding
• Ripple marks
• Mud cracks
Strata or layers
Cross-bedding in sediment
Cross-bedding in rock
Ripple marks
Mudcracks
The Carbon Cycle
This is the process by which carbon moves throughout the
different “spheres” of the earth
Carbon Cycle – Hydrosphere and Biosphere
In the hydrosphere, CO2
– dissolves in seawater
– is released by organic matter and carbonate rocks
In the biosphere, CO2 accumulates from:
– photosynthesis of plant organisms
– uptake by land and marine organisms to make shells
or bones
Carbon Cycle – Atmosphere and Geosphere
In the atmosphere, CO2 accumulates from:
– burning of fossil fuels
– volcanic processes
– weathering of carbonate rock
– burning and decay of biomass
– respiration
In the geosphere, CO2 accumulates as
carbonate sediments and rocks.