Notes 6.1 & 6.2 Sedimentary Rocks
Three Types of Sediment
Formation
Chemical processes
Rock names: Chemical sedimentary,
such as halite
Describe:
Rocks formed by crystals that come out of solution.
Plants and Animals
Rock names: Biogenic Sedimentary
Describe: Rocks formed from plants & animal remains, such as
shells.
Physical processes
Rock names: Clastic Sedimentary
Describe: Newer rocks created from breakdown of pre-existing,
older rocks that got eroded & transported through
water, wind, or ice.
Sediment Characteristics within
sedimentary rock
Source Rocks
Effect:
Source rocks erode into sediments. These
sediments can eventually form into new rocks or rock
layers.
Stratification
Describe:
Different layers seen within a rock or rock bed.
particle size
Measured using: Wentworth Scale.
Describe:
Particles undergo differ levels of erosion during transport.
The level & type of erosion determine grain sizes formed
from the particles.
Sediment Roundness
Describe: Rock edges are worn away differently by their transport
methods (water, wind,…)
Softer minerals wear away faster than harder minerals.
Sorting
Describe:
Well-sorted = rocks are separated into same-sized particles.
Not well sorted= rocks of all sizes are mixed together.
Method:
The transport method influences how well particles are sorted.
Wind- Sorts particles very well; can only pick up small sizes.
Water- Sorts fairly well; can’t pick up very large particles.
Ice- Does not sort well!! It can carry a wide range of sizes.
Formation of clastic rocks
Sediment transport
Main Points:
Wind, water, & ice can carry sediment.
Sediment Load- The number of particles a transporting agent can carry.
Physical load- refers to objects being carried
Chemical load- refers to ions in solution.
Increasing kinetic energy
Effect:
Increasing the kinetic energy (KE) of a transporting agent
increases the number & size of particles that can be
carried.
Sediment Deposition (decreasing kinetic energy)
As KE of a transporting agent decreases, sediment falls
Main Points:
out & gets deposited.
Sediment Lithification
Compaction
1. Sediment weight increases & pushes down w/ greater force.
2. Particles are pushed closer together; sediment gets less thick.
3. Pore spaces get smaller & water is squeezed out.
Cementation
1. Minerals precipitate out of solution while flowing through crushed
sediment.
2. This precipitate fills tiny pore spaces in the sediment .
3. This precipitate acts like cement; it binds small grains and hardens
them into rocks.
Mineralogic Constant compaction changes mineral composition of
Rocks.
changes:
Recrystallization New mineral grains can grow larger than the original
grains. Creates interlocking crystals that form
very hard rocks.
Continental Depositional Environments
Describe:
Where sediment are deposited on Earth’s continents.
Examples
Glaciers, glacial deposits, floodplains, lakes,
Alluvial fans, sand dunes, ….
Marine Depositional Environments
Describe:
Examples
Where sediments are deposited in seas or oceans.
Submarine fans, deep ocean floor, reefs
Transitional Depositional
Environments
Describe: Where sediment is deposited between Earth’s land &
ocean.
Examples Estuaries, barrier islands, deltas, beaches, tidal
lagoons, …
Fossils
Evidence Of:
Preserved remains or traces of organisms that lived in
the past are found in sedimentary rocks.
Ripple Marks
Evidence Of:
“Waves” in sandy material can indicate currents once
moved over the surface before being buried.
Structural Evidence of the Past
Found in Sedimentary Rock
Mud Cracks: Clay-rich sediment preserves cracks that form when
it dries.
Cross-beds
Evidence of:
Show that air or water carried the sediment load in mounds.
Clastic Rock Classification
Grain Texture Types:
Coarse:
Gravel, Cobble, Boulder
over 2mm & round
Medium:
SAND
1/16 -2mm & angular
Fine-grained:
SILT
1/256 -1/16 mm & gritty
Very Fine-grained:
CLAY
less than 1/256 & not gritty
Biogenic & Chemical Rock
Classification
Explain:
Mineral composition of a rock helps identify the rock’s name.