Lithification diagenesis
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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.

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Lithification/ Diagenesis

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Lithification diagenesis

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: 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 other

sediment, grains

separate

After compaction,

grains crushed

together and

interlocked

After cementation,

mineral crystals

cemented grains

together


Diagenesis processes involved

Diagenesis: Processes Involved

1. Compaction - packingtogether 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 forever

without becoming a rock - normally this doesn't happen


Diagenesis processes involved1

Diagenesis: Processes Involved

2. Desiccation – loss of water from sediment pore spaces

Desiccation cracks


Ie desiccation and compaction of shale

ie. Desiccation and Compaction of Shale


Diagenesis processes involved2

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

ie. Compaction and Cementation of Sand


Clastic sedimentary rocks

Clastic Sedimentary Rocks

Breccia

Conglomerate

Shale

Sandstone


Breccia

Breccia

Angular fragments


Conglomerate

Conglomerate

Rounded particles & dissimilar lithologies


Sandstone

Sandstone

Sandstone

Quartz Sandstone - > 90% qtz


Mudstone

Mudstone

Shale –

fissile (layered)

Claystone –

not fissile (not layered)


Non clastic sedimentary rock

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 rock1

Non-Clastic Sedimentary Rock

  • Classified based on composition:

    • Siliceous Rocks

    • Carbonates

    • Evaporites


Non clastic sediments siliceous rocks

Non-Clastic Sediments: Siliceous rocks

Siliceous rocks - The siliceous rocks are those which are dominated by silica (SiO2)

Chert - Palaeoindian projectile points

Chert from Washademoak Lake, NB


Non clastic sediments carbonates

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 evaporites

Non-Clastic Sediments: Evaporites

Evaporites form from the evaporation of water (usually sea water or lake water)

Example: Rock salt (halite)

Rock salt forms as a result of

changing physical conditions

(increasing temperature), where

minerals dissolved in seawater are

precipitated when the water

evaporates

Bonneville Salt Flats of the Great Salt Lake, Utah.


Non clastic sedimentary rocks

Non-Clastic Sedimentary Rocks

Oolitic Limestone

Fossiliferous Limestone

Dolostone

Chalk


Non clastic sedimentary rocks fossil fuels deposits

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

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 example1

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

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

Types of Traps


Sedimentary rock non metallic industrial mineral deposits

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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