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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– 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
• 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
chert
coal
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– Oil, natural gas, and coal AKA: fossil fuels– Building materials– Uranium– Phosphate and iron