Transcript Sedimentary Rocks

6.1/6.2 Guided Notes Hybrid
Weathering, Erosion and Deposition
• Produces Sediments: small pieces of rock
that are moved and deposited by water,
wind and gravity
Erosion: removal and transport of
sediment
Agents of erosion:
• Wind
• Moving water
• Gravity
• Glaciers
Deposition
• Sediment settles with the largest grains at
the bottom of the layering and the smallest
grains at the top
Lithification:
• Lithos = rock (Greek)
• Think “lithosphere” = earth’s crust
• Lithification Definition: The physical and
chemical processes that turn sediments
into rock
• Two parts of the process:
– Compaction
– Cementation
Lithification part 1 COMPACTION
• The weight forces the sediment grains to get
closer and closer together causing physical
changes to occur
• Mud can contain up to 60% water that gets
squeezed out
• Sand does not compact as much as mud does
because sand is mostly quartz
• Grain to grain contact in sand forms a supporting
framework that maintains open space between
the grains
Lithification part 2 CEMENTATION
• Minerals like calcite
CaCO3 and iron III oxide
Fe2O3 flow through the
open spaces left by
compaction
• The minerals linger and
cement the grains
together forming
sedimentary rock
Sedimentary Features:
• Sedimentary rock tells
geologists the history of
the area
• BEDDING: predominant
feature of sedimentary
rock is the horizontal
layering
– Feature results from the
way water or wind causes
the sediment to settle out
– Two types of bedding
Bedding Type #1: Graded Bedding
• Bedding in
which
heavier and
coarser
particles are
located near
the bottom
of the
sedimentary
rock
Bedding Type #2: Cross-Bedding
• Inclined layers of sediment deposited
along a horizontal surface
Ripple Marks
• Ripple Marks:
– Evidence that the sediment was
formerly moved by wave action
Fossils
• The best known feature
of sedimentary rock is
the propensity to find
fossils in it
• During cementation the
animal’s parts (like the
shell) can be replaced by
minerals and turned to
rock which make up a
fossil
Types of Sedimentary Rock
• Clastic / Detrital – made up of solid
particles (gravel, sand, silt and clay)
derived from preexisting rocks through
weathering
• Chemical – sedimentary rocks that result
from inorganic chemical processes or from
the chemical activities of organisms
Clastic / Detrital Sedimentary
Rocks
• Coarse-grained
– Gravel sized fragments
– Types of rock formed: conglomerate (rounded gravel), breccia
(angular gravel)
– Formed by high-energy flows of water
• Medium-grained
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Sand fragments
Type of rock formed: sandstone
Formed by stream & river channels, beaches, deserts
Importance: due to pore spacing, fluids can move through and
thus hold reservoirs of oil, natural gas, and groundwater
• Fine-grained
– Silt and mud fragments
– Type of rock formed: siltstone, shale, mudstone
– Importance: low porosity resulting in a barrier to movement of
groundwater & oil.
Chemical Sedimentary Rock
• Inorganic Sedimentary
Rock
– Evaporite – form as a
result of crystal grains
precipitating our of a
supersaturated body of
water
– Type of rock formed:
rock gypsum (made
up of the mineral
gypsum) & rock salt
(made up of the mineral
halite)
Chemical Sedimentary Rock
chert
coal
• Biochemical – form as a
result of the chemical
processes of organisms;
many types of remains
of once-living plants
and/or animals.
– Types of rock formed:
limestone, chert, and coal.
– Form in shallow-water,
swamp, and coastal
environments
Importance of Sedimentary Rock
• Provide historical timeline for area. Leaves a
‘footprint’ of all that’s come before us.
– Past plants and animals
– Bedrock
– Ancient rivers, lakes and shorelines
• Provides resources
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Oil, natural gas, and coal AKA: fossil fuels
Building materials
Uranium
Phosphate and iron