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