In depth notes and diagrams about weathering and erosion, triangular graphs, desert and fluvial environments, deltaic systems, turbidity currents and turbidites, limestone formation, and diagenesis
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
• 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:
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