Transcript Sedimentary Rock

CHAPTER 8:
SEDIMENTARY
ROCK
Sedimentary rock is formed from the
weathered and eroded remains of
other rocks
Many of the rock
layers in this
photograph are
composed of
sediments that
accumulated on
the seafloor.
What evidence
would reveal to a
geologist that a
rock formed in a
marine
environment?
Sedimentary Rock
• Most of Earth’s surface is
covered with layers of
loose sediment
• >75% of the land surface is
Sedimentary Rock
• They reflect physical and
chemical characteristics of their
source environments and
depositional processes
Steven Earle
Why study sedimentary rocks?
Fossiliferous Cambrian
Planetary nebula
Burgess Shale at Mt.
remaining
Stephen,
BC mineral
particles and gas
after a star explodes
• They can be interpreted to
understand geological history
• The are the source of important
resources, including metals,
building materials and energy
Steven Earle
• They contain direct and indirect
evidence of life and its evolution
Triassic limestone being quarried for
cement at Texada Island, BC
There are three common types of sediment:
Clastic, Chemical, and Biogenic
• CLASTIC SEDIMENTS are broken and eroded pieces of rocks and
minerals
• deposited by water, wind, ice, or some other physical process
What is the main mineral in this sandy sediment?
What else might be present?
Chemical and Biogenic Sediments
CHEMICAL SEDIMENTS are produced
by inorganic (nonbiological)
precipitation of dissolved compounds
(e.g., through evaporation)
BIOGENIC SEDIMENTS are
produced by organic (biological)
precipitation of the remains of
Comet exhibiting coma (tail)
living organisms
Change in Sediments
• Sediments change as they are
transported across Earth’s surface…
en route to their depositional
environment
What are the likely
depositional environments of
these three types of sediment?
Particle Size Reflects
Depositional Energy
Sorting
Particles
separated
based on
grain size
Decreasing grain
size with increased
transport distance
and decreased
energy level
?
What does multigenerational mean in
this context? Why are
these grains so well
rounded and so
dominated by quartz?
Steven Earle
Coral Pink Sand Dunes, southern Utah
0.1 mm
Close-up view of the multigenerational fine-grained sand at
the Coral Pink Sand Dunes
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Clastic Grains
• Clastic grains
combine with
chemical and
biogenic sediments
through either
organic or inorganic
precipitation.
• The black material in
these thin
sections
photographs is
organic matter.
Sedimentary Basins
• Dissolved compounds are transported from weathering sites into Sedimentary
Basins
Sediments evolve during transportation and
deposition
.
• Unstable grains (olivine, pyroxene, feldspar, amphibole, and others) become
less abundant
• Stable grains (quartz, clays, muscovite) become more abundant
• Biogenic sediments accumulate
• Chemical sediments may become more abundant
The Sedimentary Cycle
• Sediment becomes
sedimentary rock during
the sedimentary cycle
Sediments typically
accumulate at rates of
less than 1 mm per
year. How long would
it take to accumulate
1000 m of sediment at
a rate of 0.2 mm/year?
Lithification
• Lithification is caused by compaction and
cementation
The important types of clastic sedimentary
rock
• Distinguished by:
– grain size and shape
– grain type (mineralogy)
– texture of the grains,
matrix and cements
Why are they called clastic sedimentary rocks? What is a clast?
Types of Sediment
• Specific combinations of texture and composition for each type.
• Determined by sediment’s history: transport energy and distance, weathering
intensity, and composition of source rock.
Important clastic sedimentary rocks
conglomerate
breccia
quartz sandstone
arkose
What is the textural difference between conglomerate and breccia?
What are the compositional differences between quartz sandstone,
arkose and lithic sandstone?
lithic sandstone
siltstone
claystone
shale
Chemical sedimentary rocks
Rock salt
Gyspum
Chert
Travertine
Biogenic Sedimentary Rock
Skeletal
limestone
Chalk
What do skeletal
limestone, chalk and
coquina have in
common?
Coquina
Coal
Sedimentary rocks preserve evidence of past
environments and ecology
Continental depositional environments
Wetland, alluvial fan, stream, desert, lake, glacier – which is which?
Do all of these environments exist in Canada?
Coastal depositional environments
Barrier island, carbonate lagoon, beach, tidal wetland, delta – which is
which? Do all of these environments exist in Canada?
Marine Environments of deposition
Primary sedimentary structures record
modern and ancient sedimentary processes
Ripples
Mud Cracks
Steven Earle
Cross-bedding
in eolian
sandstones,
Zion Canyon,
Utah
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Graded bedding
in submarine fan
rocks, Gabriola
Island ,BC
Bedding in
fluvial and
lacustrine
deposits,
Horseshoe
Canyon, Alberta
Choose four depositional
environments in this figure. For
each, describe the texture of the
sediments likely to form there.
Consider the beach and glacier. If the
Haiti, 2010
sediment source for each was granitic
mountains, predict the composition of
sediments in each case.
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