Sedimentary Rocks and Processes (A2)
Weathering and Erosion
Weathering – the in situ breakdown or decomposition of rocks and minerals through chemical, biological and
physical processes
Erosion – the weathering down of rocks by the mechanical action of transported debris
Types of Weathering
Physical Chemical Biological
• Freeze-thaw (frost • Carbonation • Root growth
shattering) • Oxidation
• Insolation • Hydration
• Hydrolysis
• Solution
Triangular Graphs
• 3 components
• All must add up to 100%
• Only need to plot two to get the third number
Pettijohn’s Sandstone Classification
Pettijohn developed a classification scheme for sandstone based upon their composition. The name allows the
rock to be described as fully as possible.
An arenite is a sandstone with less than 15% matrix
A lithic fragment is a rock fragment
A wacke is a sandstone with between 15 and 75% matrix
, Desert Environment
Facies – an area with a distinctive sediment type
(1) Scree
(2) Alluvial fan
(3) Aeolian sandstone 1
2 3
(4) Playa lake 4
Climatic Conditions – hot and
dry
Transportation Medium:
• More common – wind
• Less common – water
Landforms:
Mesa A portion of the plateau separated from the main plateau
Butte An isolated tower, remnant of the plateau
• Dry riverbed eroded by flash flooding
Wadi
• Forms where the wadi meets lower ground
Sabkha Evaporate deposits left behind after floodwater in coastal areas/lagoons is evaporated
Trend in Grain Size: Factors Controlling Size:
• Courser closer to the source and • The amount of water
fine further away • The velocity of the water
Alluvial
Fan
Mode of Transportation & Reason for Deposition:
• Carried as a bed load in water
• Grains are deposited when the water loses velocity
Mode of Transportation: Textural Evidence:
• Wind • Sand sized particles
• Very rounded
Sand
Sedimentary Structure Evidence: • Well sorted
Dunes
• Large scale cross bedding • Aeolian sandstone
- Sand accumulates on the • Red due to haematite
lee, erodes on the stoss
What is it? Reason for Order:
• Site of former or occasional lake • Different evaporation rates
Playa
Deposits: • Some go into solution before others
Lake
• Calcite, gypsum, halite and - Magnesium is most soluble so is last
magnesium to be deposited
Fluvial (River) Environment
Ripples:
A = Symmetrical currents e.g. sea
B = Asymmetrical currents e.g. river
Formation:
Weathering and Erosion
Weathering – the in situ breakdown or decomposition of rocks and minerals through chemical, biological and
physical processes
Erosion – the weathering down of rocks by the mechanical action of transported debris
Types of Weathering
Physical Chemical Biological
• Freeze-thaw (frost • Carbonation • Root growth
shattering) • Oxidation
• Insolation • Hydration
• Hydrolysis
• Solution
Triangular Graphs
• 3 components
• All must add up to 100%
• Only need to plot two to get the third number
Pettijohn’s Sandstone Classification
Pettijohn developed a classification scheme for sandstone based upon their composition. The name allows the
rock to be described as fully as possible.
An arenite is a sandstone with less than 15% matrix
A lithic fragment is a rock fragment
A wacke is a sandstone with between 15 and 75% matrix
, Desert Environment
Facies – an area with a distinctive sediment type
(1) Scree
(2) Alluvial fan
(3) Aeolian sandstone 1
2 3
(4) Playa lake 4
Climatic Conditions – hot and
dry
Transportation Medium:
• More common – wind
• Less common – water
Landforms:
Mesa A portion of the plateau separated from the main plateau
Butte An isolated tower, remnant of the plateau
• Dry riverbed eroded by flash flooding
Wadi
• Forms where the wadi meets lower ground
Sabkha Evaporate deposits left behind after floodwater in coastal areas/lagoons is evaporated
Trend in Grain Size: Factors Controlling Size:
• Courser closer to the source and • The amount of water
fine further away • The velocity of the water
Alluvial
Fan
Mode of Transportation & Reason for Deposition:
• Carried as a bed load in water
• Grains are deposited when the water loses velocity
Mode of Transportation: Textural Evidence:
• Wind • Sand sized particles
• Very rounded
Sand
Sedimentary Structure Evidence: • Well sorted
Dunes
• Large scale cross bedding • Aeolian sandstone
- Sand accumulates on the • Red due to haematite
lee, erodes on the stoss
What is it? Reason for Order:
• Site of former or occasional lake • Different evaporation rates
Playa
Deposits: • Some go into solution before others
Lake
• Calcite, gypsum, halite and - Magnesium is most soluble so is last
magnesium to be deposited
Fluvial (River) Environment
Ripples:
A = Symmetrical currents e.g. sea
B = Asymmetrical currents e.g. river
Formation:
