Lithification/Diagenesis
• From pile of sand to solid rock
Loose sediment, like that shown in (A) may someday become a rock like the one
in (B) if compacted and cement fills the spaces
between clasts
Diagenesis: How Sediment Becomes Rock• Diagenesis:
collective term for all the chemical, physical, and biological changes that affect sediment as it goes from deposition through lithification
Sand or othersediment, grainsseparate
After compaction,grains crushedtogether andinterlocked
After cementation,mineral crystalscemented grainstogether
Diagenesis: Processes Involved
1. Compaction - packing together of sediment grains
When sediment has been deposited we start with a pile of fragments that enclose a great deal of pore space
As sediment continues to accumulate the sediment undergoes compaction: the geometric arrangement of grains changes so that pore space is reduced
In principle, compacted sediment can sit there foreverwithout becoming a rock - normally this doesn't happen
Diagenesis: Processes Involved
2. Desiccation – loss of water from sediment pore spaces
Desiccation cracks
ie. Desiccation and Compaction of Shale
Diagenesis: Processes Involved
3. Cementation – ions precipitate out in the pore spaces to form a cement that binds clasts together
ie. Compaction and Cementation of Sand
Clastic Sedimentary Rocks
Conglomerate
Sandstone
Breccia
Shale
Angular fragments
Breccia
Conglomerate
Rounded particles & dissimilar lithologies
Sandstone Sandstone
Quartz Sandstone - > 90% qtz
Mudstone
Shale –fissile (layered)
Claystone –not fissile (not layered)
Non-Clastic Sedimentary Rock
• Organic sediments• Sediment precipitates from solution in
water originating from chemical and organic processes– These chemical precipitants settle to the
bottom of a body of water. When first deposited, these sediments are loose and non-structured. In time, they are slowly hardened by compaction, cementation, and re-crystallization
Non-Clastic Sedimentary Rock
• Classified based on composition:– Siliceous Rocks– Carbonates– Evaporites
Non-Clastic Sediments: Siliceous rocks
Siliceous rocks - The siliceous rocks are those which are dominated by silica (SiO2)
Chert from Washademoak Lake, NB
Chert - Palaeoindian projectile points
Non-Clastic Sediments: Carbonates
Carbonates - The carbonate sedimentary rocks are formed through both chemical and biochemical processes
Example: Limestone
Chalk cliffs - Dover, England
Non-Clastic Sediments: EvaporitesEvaporites form from the evaporation of water
(usually sea water or lake water)
Example: Rock salt (halite)
Bonneville Salt Flats of the Great Salt Lake, Utah.
Rock salt forms as a result ofchanging physical conditions(increasing temperature), whereminerals dissolved in seawater areprecipitated when the waterevaporates
Non-Clastic Sedimentary Rocks
Dolostone
Oolitic Limestone Fossiliferous Limestone
Chalk
Non-Clastic Sedimentary Rocks Fossil Fuels Deposits• Found in areas of sedimentary rock
formation– Basically, plant and animal remains were deposited
in swamp and mud areas.
– Result: Poor oxygen quality, hence they did not decay.
– Overtime, they accumulated and then sands, silts and clay buried them
– As lithification of the sediments took place, the organic remains beneath turned to valuable fossil fuels
Fossil Fuel Deposits: Example
Coal – made of organic matter which is the end product of large amounts of plant material buried for millions of years
Coal bed,Trinidad
Fossil Fuel Deposits: Example
• Natural Gas and Oil Deposits– Drops of oil were scattered throughout source rocks– As source rock was squeezed, this oil becomes
trapped in reservoirs / traps• These reservoirs make this an economic goldmine
– Common characteristics for reservoir / trap• Source rock can be squeezed• Reservoir rock is porous and permeable• Cap rock is impermeable• Groundwater pushes the lighter gas and oil to the top• When a trap is tapped, an extreme amount of pressure is
released– Think oil well
Fossil Fuel Deposits: Common Trap Types• Structural traps hold oil and gas because the earth
has been bent and deformed in some way. The trap may be a simple dome (or big bump), just a "crease" in the rocks, or it may be a more complex.– Types: Anticline trap, Fault trap, Salt dome
• Stratigraphic traps are depositional in nature. This means they are formed in place, usually by a sandstone ending up enclosed in shale. The shale keeps the oil and gas from escaping the trap.– Types: Stratigraphic (pinch out) trap
Types of Traps
Sedimentary Rock: Non- Metallic Industrial Mineral Deposits
• Products of deposition, minerals in these rocks are non-metallic– Example:
• Thick salt beds are the result of the movement of ocean water into basins. As the water evaporates due to desert-like conditions, the salt is left behind
– These are Evaporites
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