Sediments and DiagenesisThe Rock Cycle is a group
of changes. It is an ongoing process.
Igneous rock can change into sedimentary rock or into metamorphic rock.
Sedimentary rock can change into metamorphic rock or into igneous rock.
Metamorphic rock can change into igneous or sedimentary rock.
Sediments and DiagenesisSediment & Diagenesis
75% of all the rocks exposed at the Earth’s land surface (only 5% of Earth’s outer 10 miles - so mostly at the surface)
I. Sediment
Rock fragments created by weathering and erosion
Accumulates everywhere—oceans, beaches, lakes, rivers, deserts, swamps, caves, base of glaciers
A. Classified based on its origin.
1. Detrital: composed of transported solid fragments (detritus) of preexisting rocks
2. Chemical: forms when previously dissolved minerals either precipitate from solution or are extracted from water by living organisms and converted to shells/skeletons
Sediments and Diagenesis
B. Sediment Transport and Deposition
1. DetritalGenerally move from high
ground to low ground by the pull of gravity (assisted by water, wind, or glacial ice)
Deposited when the carrying material loses it’s capacity to carry the sediment
2. ChemicalIons remain in solution until
there’s a change in the water’s temperature, pressure, or chemical composition and then the ions precipitate
Sediments
C. Sediment Texture: Detrital sediment and chemical sediment are classified based on composition.
1. Grain sizeGrain composition - some
minerals are stronger than others.
a. Distance - smaller grains travel longer distances.
b. Energy of the transportation medium - high energy environment moves larger grains.
Sediments
2. Grain shapea. Distance transported - over far
distances, grained become more rounded.
b. Transportation medium
High energy river, wind produce rounded grains
Middle of glacier, mudflow, debris flow preserve angular grains – not enough distance to round grains
Sediments
C. Sediment Texture: detrital sediment and chemical sediment are classified based on composition.
3. SortingRelated to the carrying
capacity of the transport medium
Well sorted = windMedium - well sorting =
wavesMedium - poor sorting =
streamsPoorly sorted = glaciers,
debris flows
Sediments
II. Turning sediments into rock
Eventually accumulated sediment turns into rock
A. Diagenesis: All the chemical, physical, and biological changes that take place after sediments are deposited.
Burial
Alteration by groundwater Recrystallization: regrowth of less
stable minerals into more stable ones.
Lithification: occurs within the upper few kilometers of the crust at temperatures < 200C (400F)
Sediments and Diagenesis
II. Turning sediments into rock
B. Lithification: the process by which unconsolidated sediments are transformed into solid sedimentary rocks (part of diagensis)
1. Compaction: pressure (from overlying sediment) reduces the volume of sediment—
Compaction forces out air and water and packs grains together.
Sediments and Diagenesis
II. Turning sediments into rock
B. Lithification
2. Cementation
Cements grains together - ions dissolved in water by chemical weathering may be deposited by groundwater circulating through the sediment.
Calcium carbonate = CaCO3
Calcium ions plus CO2 and H2O
Silica = SiO2 is produced by chemical weathering of silicate igneous rocks
Iron oxide = Fe2O3
Sediments and Diagenesis
III. Types of Sedimentary rocks
A. Detrital Sedimentary rocks: made of sediment that is transported as solid particles
Particle size is the primary basis for distinguishing various detrital sedimentary rocks.
Particle size indicates environment of deposition
Water and air currents sort by size.
Stronger current = larger grain sizes
Sediments and Diagenesis
III. Types of Sedimentary rocks
A. Detrital Sedimentary rocks: made of sediment that is transported as solid particles
1. Shale (mudstone, siltstone)
>50% of all sedimentary rocks:
Silt and clay Small grain size = settling from
quiet, non-turbulent water
Silt and class form in lakes, lagoons, swamps, deep ocean.
Need quiet water depositional setting
Sediments and Diagenesis
III. Types of Sedimentary rocks
A. Detrital Sedimentary rocks
2. Sandstone: sand sized particles (1/16 – 2 millimeters)
~25% of all sedimentary rocks
Windblown dunes, some rivers, and beaches
Shape and sorting important for determining depositional environment.
Sorting: well sorted = wind & wavespoorly sorted = streams
Shape: well rounded = water or wind transported over long distances
Angular = glacier or debris flow
Transported over short distances
Sediments and Diagenesis
III. Types of Sedimentary rocks
A.Detrital Sedimentary rocks
2. Sandstone: sand sized particles (1/16 – 2 millimeters) (
~25% of all sedimentary rocks
Windblown dunes, some rivers, and beaches
Shape and sorting important for determining depositional environment.
Sorting: well sorted = wind & wavespoorly sorted = streams
Shape: well rounded = water or wind transported over long distances
Angular = glacier
Transported over short distances
Sediments and Diagenesis
III. Types of Sedimentary rocks
A. Detrital Sedimentary rocks
2. Sandstone: sand sized particles (1/16 – 2 millimeters) (
~25% of all sedimentary rocks
Windblown dunes, some rivers, and beaches
Shape and sorting important for determining depositional environment.
Sorting: well sorted = wind & waves; poorly sorted = streams
Shape: well rounded = transported over long distances (water)
Angular = transported over short distances (glacier)
Sediments and Diagenesis
III. Types of Sedimentary rocks
A.Detrital Sedimentary rocks
3. Conglomerate and Breccia—
Composed of gravels (pea to large boulders, >2 mm)
Conglomerate: composed of rounded grains of difference sizes.
Formed in energetic mountain streams or coasts (storm deposits)
Breccia: composed of angular pieces.
Did not travel far: glaciers, landslides
Sediments and Diagenesis
III. Types of Sedimentary rocks
A. Detrital Sedimentary rocks
3. Conglomerate and Breccia
Composed of gravels (pea to large boulders, >2 mm)
Conglomerate: composed of rounded grains of difference sizes.
Formed in energetic mountain streams or coasts (storm deposits)
Breccia: composed of angular pieces.
Did not travel far: glaciers, landslides, (close to source)
Sediments and Diagenesis
Top Related