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