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6.1/6.2 Guided Notes Hybrid. Weathering and Erosion. Sediments: small pieces of rock that are moved and deposited by water, wind and gravity. Lithification:. Sediment is deposited in low areas such as valleys and ocean basins Bottom layers are subjected to intense pressure and temperatures - PowerPoint PPT Presentation
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6.1/6.2 Guided Notes Hybrid
Weathering and Erosion
• Sediments: small pieces of rock that are moved and deposited by water, wind and
gravity
Lithification:
• Sediment is deposited in low areas such as valleys and ocean basins– Bottom layers are subjected to intense
pressure and temperatures– This process is called lithification: THE
PHYSICAL AND CHEMICAL PROCESSES THAT TRANSFORM SEDIMENT INTO SEDIMENTARY ROCK
Erosion: removal and transport of sediment
Agents of erosion:• Wind• Moving water• Gravity• Glaciers
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
Mud Cracks and Ripple Marks
• Mud (usually forms in hexagonal plates) cracks and sediments seep between the mud plates– The sediments build up over time forming
sedimentary rock• 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 lithification 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 times the 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– Building materials– Uranium– Phosphate and iron
Deposition
• Occurs when transported sediments are deposited on the ground or sink to the bottom of a body of water
• Settles with the largest grains at the bottom of the layering and the smallest grains at the top
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 oxide Fe2O3 flow through the open spaces left by compaction
• The minerals linger and cement the grains together forming sedimentary rock