Sedimentary Processes and Products (Lectures 36-41) Flashcards
Define sedimentology
Define sedimentary geology
Study of sediments
Study of sedimentary rock
Define lithification
The process of turning sediment into a sedimentary rock
What are the types of sediments?
Clastic
Carbonate
Organic
Chemogenic
What is clastic sediment formed from?
What is the most common type of clastic sediment?
Given that clastic sediment rocks are categorised by the dominant size of the individual grains, what are the group names?
What is a rarer type of clastic sediment?
Grains separated from a parent rock by erosion and moved by fluids
Siliciclastic
Mudstones, siltstones, sandstones and conglomerates
Volcaniclastic
What are the two most common ways carbonate sediment can form?
What can these carbonate sediments be converted to?
Shelly organisms in colonies, sedimentary accumulations of shelly material (reefs) OR shelly and skeletal material acts as grains
Limestones, oolites and chalk
What can form organic sediments?
What are these responsible for the creation of?
Mostly C-rich, photosynthetic organisms like plants and algae
Carbonaceous sediments, hydrocarbons (oil and gas) and peats (forms coal in burial)
How can chemical processes lead to chemogenic sediments? Give an example
How else can chemogenic sediments form?
Which chemogenic sediment can be inorganic or organic?
What are the two siliceous sediments?
Inorganic precipitation of different minerals
Ironstones
Interplay of chemical processes and biological products
Phosphorites
Chert and flint
How do evaporites form?
Salts which precipitate as masses of crystals out of natural bodies of water
Which processes cause early lithification?
Biological precipitation
Chemical precipitation
Cooling
What is cementation in the lithification process?
When does it occur?
Chemical processes solidifying sediment grains together
Water in the sediment precipitates out different minerals between sediment grains
How would a sediment lithify through compaction?
Enforced closer packing of grains under the weight of sediment deposited above
What is diagenesis?
Which two processes in lithification mark the first stages of diagenesis?
Processes that can result in mineralogical changes to a sediment after deposition
Cementation and compaction
What are the later diagenetic processes?
What induces them?
Recrystallisation, or dissolution and replacement
Increased p and T in burial
What is the primary technique for studying outcrops of sedimentary rock?
What are they?
Constructing sedimentary logs
Graphical representations of vertical rock sections
Define stratigraphy
The study of the relationships in time and space between different layers of rock
What is the most important aspect of stratigraphy?
The principle of superposition, read a succession of strata as a sequence of depositional events
What is the second important aspect of stratigraphy?
What does it recognise?
Give an example of this
Walther’s Law
If you see two sedimentary units superimposed on top of each other without an unconformity then the vertical transition reflects a lateral transition between two neighbouring environments
Modern sedimentary environments are diachronous - adjacent components of a sedimentary environment may be active at the same time
A river channel (sandy) and a nearby floodplain (muddy)
Sedimentary processes can be broadly grouped into what three categories?
Erosion - liberates new grains from previously deposited sediments or lithified rock
Transport - fluids or gravity move sedimentary grains around
Deposition - where fluids lose the capacity to keep moving the grains and deposit them in a temporary or final resting place
What does physical weathering involve?
The weakening and breaking up of rocks as cracks form and widen in the parent rock due to T changes, freeze-thaw action, salt growth or biological intrusion (roots)
What does chemical weathering involve?
Weakening the rock by altering the mechanical properties of original rock minerals - by solution in groundwater or brine, hydrolosis, or oxidation
What does weathered material produce?
What is it available for?
A loose regolith
Transport by fluids
Soil can form when what interacts with a regolith?
Biological processes
Erosion of weakened bedrock can occur by what means?
Through gravity alone - rockfall
Through gravity acting on water-saturated regolith - slumping
Incision from water
Abrasion by sedimentary grains already held in a fluid
Plucking by ice
Which fluids are mainly responsible for sediment erosion, transportation and deposition? (and what forms can they be in)
Water - rivers or marine currents
Air - wind
Ice - polar ice caps and glaciers
Sediment-water mixtures - debris flows and turbidites