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Sedimentary Rock
Formation
Formation
Pre-existing rocks must be broken down
Sediments: bits & pieces of pre-existing
rock
2 general ways for this to happen
1. Weathering: break down of rocks in place
2. Erosion: break down and transport of rocks
Weathering
Rocks must be exposed to the surface
2 forms
1. Chemical: rocks are chemically altered
2. Physical: rocks simply broken into smaller
pieces
Clasts: rock fragments produced from
physical weathering
Chemical weathering
Physical Weathering
Erosion
After rocks are broken down they must be
transported
4 general agents of transport
1.
2.
3.
4.
Wind
Moving water
Glaciers
Gravity
Sediment is almost always carried downhill
Deposition
When the agent of erosion loses
energy (slows down/stops)
sediment is dropped or
deposited
Sediment Transport & Settling
Sediment is transported farther distances
due to 2 factors
1.
2.


Clast size
How much power the agent of transport has
As particles settle out the larger ones are
dropped first
Therefore sediments are usually sorted by size
(exception: glaciers)
Stream Deposition & Sorting
Lithification Process
Lithos: Stone in Greek
Lithify: rock making process
3 Steps
1.
2.
3.
Deposition: Sediment is deposited in basins or
natural bowls
Compaction: Weight of overlying layers pile up
increasing pressure & temp.
Cementation: Dissolved minerals act as glue
when they solidify, cementing grains together
 Ex/ calcite, iron oxide, & silica
Sedimentary Features
Bedding: sediments are deposited in
horizontal layers
Graded Bedding: clast size gets bigger
towards the bottom
Cross-bedding: inclined layers of
sediment (ex/ sand dunes)
Bedding
Bedding
Cross-bedding & Ripple Marks
Fossils
Remains of once living organisms

Can be parts of the organism, imprints, or
actual remains

Preservation of bones (other hard parts) is
called mineralization
– Process where organic material replaced by
dissolved minerals
Classifying sedimentary rocks
Two groups based on source material
1. Clastic rocks
•
Solid particles classified by size
•
•
•
•
•
Gravel (>2mm in size)
Sand (1/16th – 2mm in size)
Silt (1/256th – 1/16th mm in size)
Clay(less than 1/256th mm in size)
Common rocks include
•
•
•
•
Conglomerate
Sandstone
Siltstone
Shale (most abundant clastic)
Classification of
sedimentary rocks
Shale with plant fossils
Conglomerate
Breccia
Sandstone
Classifying sedimentary rocks
2. Chemical rocks
•
Formed from material once dissolved in
solution
•
2 types based on formation:
1.
Evaporite: liquid evaporates & solid deposited
on the bottom
2.
Organic: Through life processes (biochemical
origin)
Sedimentary rocks
Common chemical sedimentary rocks
• Limestone – the most abundant chemical rock
• Microcrystalline quartz (precipitated quartz)
known as chert, flint, jasper, or agate
• Evaporites such as rock salt or gypsum
• Coal
Fossiliferous limestone
Rock salt