Sedimentary Rocks

  • All fossils and fossil fuels found are from sedimentary rocks

  • Least common type of the 3 kinds of rocks 


  • Sedimentary rocks are products of mechanical (physically breaking something into smaller and smaller pieces- expansion and contractions) and chemical weathering (when things chemically dissolve - rain)

  • They account for about 5% (by volume) of Earth’s outer 10 miles

  • They contain evidence of past environments - info about sediment transport and often contain fossils 


Sedimentary rocks are important for economic considerations because they contain : coal, petroleum and natural gas, (sources of iron, aluminum and manganese


  • Many changes occur to sediment after it is deposited

Diagenesis - all of the chemical, physical, and biological changes that take place after sediments are deposited (occurs within the upper few kilometers of Earth’s crusts



Diagenesis

Includes…

Recrystallization - development of more stable minerals from less stable ones

Lithification - unconsolidated sediments are transformed into solid sedimentary rock by…

  1. Compaction

  2. cementation - by calcite, silica, and iron oxide


  • Sediment originates from mechanical and/ or chemical weathering

  • Rock types are based on the source of the material

  1. Detriatal rocks - transported sediment as solid particles (if you can lightly scratch the rocks, small bits should break off if it is a detriatal rock)

  2. Chemical rocks - sediment that was once in solution


Two major textures are used in the classification of sedimentary rocks

  1. Clastic - discrete fragments and particles; all detrital rocks have a clastic textures

  2. Nonclastic - pattern of interlocking crystals; may resemble an igneous rock


  • The chief constituents of detrital rocks include: clay minerals, quartz, feldspars, micas (rare to find sedimentary rocks with dark colored minerals like amphibole and pyroxene because they are more sensitive to Earth’s surface - they dissolve quicker)

  • Particle size is used to distinguish what type of rock it is




Smallest sed. Particles are clay (particles less 1/256 of a millimeter) and silt (any particle 1/256 of a millimeter to 1/16 of a millimeter)

referred to as mud 


Sand (1/16 of a millimeter to 2 millimeters) - feels “griddy”


Granule (2 to 4 millimeters)

Pebble (4 to 64 millimeters)

Cobble (64 to 256 millimeters)

Boulder (larger than 256 millimeters)

all referred to as gravel 



Common detrital sedimentary Rocks (in order of increasing particle size) 

  • Shale - mud-sized particles in thin layers that are commonly referred to as laminea; most common sedimentary rock

  • Sandstone - composed of sand-sized particles; forms in a variety of environments; sorting, shape, and composition of the grains can be used to interpret the rock’s history; quartz is the predominant mineral


Conglomerate and breccia

  • Both are composed of particles greater than 2 millimeters in diameter

  • Conglomerate consists largely of rounded gravels (rounded from continuously moving after they got cemented together)

  • Breccia is composed mainly of large, sharp, angular particles (they haven’t moved much since they got cemented together because their sharp edges haven’t been worn down)


Chemical Sedimentary Rocks

  • Consists of precipitated material that was once in solutions

  • Precipitation of material occurs in two ways 

  1. Inorganic processes

  2. Organic process (biochemical process - coral, clams, shellfish, snails)


Limestone

  • Most abundant chemical rock

  • Composed chiefly of the mineral calcite (use acid - if it fizzes, it is limestone)

  • Marine biochemical limestone form as coral reefs, coquina (broken shells), and chalk (microscopic organisms)

  • Inorganic limestones include travertine and oolitic limestone

  • Not going to scratch glass (?)


Dolostone

  • Typically formed secondarily from limestone

  • Mostly magnesium carbonate

  • Looks almost identical to limestone

  • Usually a little bit darker than limestone

  • Also is reactive to acid but not as much as limestone (should scratch it before pouring acid)

basalt does not react with acid 


Chert

  • Made of microcrystalline quartz that have grown and locked together

  • Depending on the color, there are different names

  • If it is a light color, it is chert

  • Varieties include flint (dark, black) and jasper (red or purple) (banded form is called agate - when it is a mix/swirl of colors)

  • Can scratch glass


Evaporites

  • Evaporation triggers deposition of chemical precipitates

  • Examples include rock salt and rock gypsum



COAL

  • Different from other rocks because it is composed of organic material

  • Always associated with igneous rocks 

  • Forms from plants (in hot, humid environments


Stages in coal formation (in order)

  1. Plant material

  2. Compacts into a material called peat (can also be burned but doesn’t produce a lot of heat/energy

  3. More compacting creates lignite

  4. More compaction and more time creates Bituminous (most common and most widely used for energy)

  5. If the temperature and pressure is increased, anthracite (rich in_) is made (metamorphic rock) only creates a small amount of pollution 



  • Formed mostly from plant material 

  • Along with oil and natural gas, coal is commonly called a fossil fuel

  • The major fuel used in power plants to generate electricity

  • Potential environmental problems from mining and air pollution



Oil and Natural gas

  • Derived from the remains of marine plants and animals 

  • Both are composed of various hydrocarbon compounds and found in similar environments

Oil trap - geologic environment that allows significant amounts of oil and gas to accumulate


Two basic conditions for an oil trap 

  1. Porous, permeable reservoir rock

  2. Impermeable cap rock, such as shale


  • Cap rock keeps the mobile oil and gas from escaping at the surface



Sedimentary environments 

(EOD)Environment of Deposition: a geographic setting where sediment is accumulating

Determines the nature of the sediments that accumulate (grain size, grain shape, etc.)



Continental

  • Dominated by erosion and deposition associated with streams

  • Glacial 

  • Wind (colian)


Marine

Shallow (to abt 200 meters)

Deep (seaward and onwards)


Transitional (shoreline)

  • Tidal flats 

  • Lagoons

  • deltas















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  1. Determine if the rock is chemical or sedimentary

  2. Use the top (clastic) or bottom (chemical) charts




Silica- no fizz

Calcite- fizz

Iron oxide- pinkish color